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(a) The FSF’s Back-Cover Text is: “You have the freedom to copy and modify this GNU manual. Buying copies from the FSF supports it in developing GNU and promoting software freedom.” Table of ContentsIntroductionBison is a general-purpose parser generator that converts an annotated context-free grammar into a deterministic LR or generalized LR (GLR) parser employing LALR(1), IELR(1) or canonical LR(1) parser tables. Once you are proficient with Bison, you can use it to develop a wide range of language parsers, from those used in simple desk calculators to complex programming languages. Bison is upward compatible with Yacc: all properly-written Yacc grammars ought to work with Bison with no change. Anyone familiar with Yacc should be able to use Bison with little trouble. You need to be fluent in C, C++, D or Java programming in order to use Bison or to understand this manual. We begin with tutorial chapters that explain the basic concepts of using Bison and show three explained examples, each building on the last. If you don’t know Bison or Yacc, start by reading these chapters. Reference chapters follow, which describe specific aspects of Bison in detail. Bison was written originally by Robert Corbett. Richard Stallman made it Yacc-compatible. Wilfred Hansen of Carnegie Mellon University added multi-character string literals and other features. Since then, Bison has grown more robust and evolved many other new features thanks to the hard work of a long list of volunteers. For details, see the THANKS and ChangeLog files included in the Bison distribution. This edition corresponds to version 3.8.1 of Bison. Conditions for Using BisonThe distribution terms for Bison-generated parsers permit using the parsers in nonfree programs. Before Bison version 2.2, these extra permissions applied only when Bison was generating LALR(1) parsers in C. And before Bison version 1.24, Bison-generated parsers could be used only in programs that were free software. The other GNU programming tools, such as the GNU C compiler, have never had such a requirement. They could always be used for nonfree software. The reason Bison was different was not due to a special policy decision; it resulted from applying the usual General Public License to all of the Bison source code. The main output of the Bison utility—the Bison parser implementation file—contains a verbatim copy of a sizable piece of Bison, which is the code for the parser’s implementation. (The actions from your grammar are inserted into this implementation at one point, but most of the rest of the implementation is not changed.) When we applied the GPL terms to the skeleton code for the parser’s implementation, the effect was to restrict the use of Bison output to free software. We didn’t change the terms because of sympathy for people who want to make software proprietary. Software should be free. But we concluded that limiting Bison’s use to free software was doing little to encourage people to make other software free. So we decided to make the practical conditions for using Bison match the practical conditions for using the other GNU tools. This exception applies when Bison is generating code for a parser. You can tell whether the exception applies to a Bison output file by inspecting the file for text beginning with “As a special exception…”. The text spells out the exact terms of the exception. GNU GENERAL PUBLIC LICENSEVersion 3, 29 June 2007 Copyright © 2007 Free Software Foundation, Inc. <https://fsf.org/> Everyone is permitted to copy and distribute verbatim copies of this license document, but changing it is not allowed. PreambleThe GNU General Public License is a free, copyleft license for software and other kinds of works. The licenses for most software and other practical works are designed to take away your freedom to share and change the works. By contrast, the GNU General Public License is intended to guarantee your freedom to share and change all versions of a program—to make sure it remains free software for all its users. We, the Free Software Foundation, use the GNU General Public License for most of our software; it applies also to any other work released this way by its authors. You can apply it to your programs, too. When we speak of free software, we are referring to freedom, not price. Our General Public Licenses are designed to make sure that you have the freedom to distribute copies of free software (and charge for them if you wish), that you receive source code or can get it if you want it, that you can change the software or use pieces of it in new free programs, and that you know you can do these things. To protect your rights, we need to prevent others from denying you these rights or asking you to surrender the rights. Therefore, you have certain responsibilities if you distribute copies of the software, or if you modify it: responsibilities to respect the freedom of others. For example, if you distribute copies of such a program, whether gratis or for a fee, you must pass on to the recipients the same freedoms that you received. You must make sure that they, too, receive or can get the source code. And you must show them these terms so they know their rights. Developers that use the GNU GPL protect your rights with two steps: (1) assert copyright on the software, and (2) offer you this License giving you legal permission to copy, distribute and/or modify it. For the developers’ and authors’ protection, the GPL clearly explains that there is no warranty for this free software. For both users’ and authors’ sake, the GPL requires that modified versions be marked as changed, so that their problems will not be attributed erroneously to authors of previous versions. Some devices are designed to deny users access to install or run modified versions of the software inside them, although the manufacturer can do so. This is fundamentally incompatible with the aim of protecting users’ freedom to change the software. The systematic pattern of such abuse occurs in the area of products for individuals to use, which is precisely where it is most unacceptable. Therefore, we have designed this version of the GPL to prohibit the practice for those products. If such problems arise substantially in other domains, we stand ready to extend this provision to those domains in future versions of the GPL, as needed to protect the freedom of users. Finally, every program is threatened constantly by software patents. States should not allow patents to restrict development and use of software on general-purpose computers, but in those that do, we wish to avoid the special danger that patents applied to a free program could make it effectively proprietary. To prevent this, the GPL assures that patents cannot be used to render the program non-free. The precise terms and conditions for copying, distribution and modification follow. TERMS AND CONDITIONS
END OF TERMS AND CONDITIONSHow to Apply These Terms to Your New ProgramsIf you develop a new program, and you want it to be of the greatest possible use to the public, the best way to achieve this is to make it free software which everyone can redistribute and change under these terms. To do so, attach the following notices to the program. It is safest to attach them to the start of each source file to most effectively state the exclusion of warranty; and each file should have at least the “copyright” line and a pointer to where the full notice is found. one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. Also add information on how to contact you by electronic and paper mail. If the program does terminal interaction, make it output a short notice like this when it starts in an interactive mode: program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. The hypothetical commands ‘show w’ and ‘show c’ should show the appropriate parts of the General Public License. Of course, your program’s commands might be different; for a GUI interface, you would use an “about box”. You should also get your employer (if you work as a programmer) or school, if any, to sign a “copyright disclaimer” for the program, if necessary. For more information on this, and how to apply and follow the GNU GPL, see https://www.gnu.org/licenses/. The GNU General Public License does not permit incorporating your program into proprietary programs. If your program is a subroutine library, you may consider it more useful to permit linking proprietary applications with the library. If this is what you want to do, use the GNU Lesser General Public License instead of this License. But first, please read https://www.gnu.org/licenses/why-not-lgpl.html. 1 The Concepts of BisonThis chapter introduces many of the basic concepts without which the details of Bison will not make sense. If you do not already know how to use Bison or Yacc, we suggest you start by reading this chapter carefully. 1.1 Languages and Context-Free GrammarsIn order for Bison to parse a language, it must be described by a context-free grammar. This means that you specify one or more syntactic groupings and give rules for constructing them from their parts. For example, in the C language, one kind of grouping is called an ‘expression’. One rule for making an expression might be, “An expression can be made of a minus sign and another expression”. Another would be, “An expression can be an integer”. As you can see, rules are often recursive, but there must be at least one rule which leads out of the recursion. The most common formal system for presenting such rules for humans to read is Backus-Naur Form or “BNF”, which was developed in order to specify the language Algol 60. Any grammar expressed in BNF is a context-free grammar. The input to Bison is essentially machine-readable BNF. There are various important subclasses of context-free grammars. Although it can handle almost all context-free grammars, Bison is optimized for what are called LR(1) grammars. In brief, in these grammars, it must be possible to tell how to parse any portion of an input string with just a single token of lookahead. For historical reasons, Bison by default is limited by the additional restrictions of LALR(1), which is hard to explain simply. See , for more information on this. You can escape these additional restrictions by requesting IELR(1) or canonical LR(1) parser tables. See , to learn how. Parsers for LR(1) grammars are deterministic, meaning roughly that the next grammar rule to apply at any point in the input is uniquely determined by the preceding input and a fixed, finite portion (called a lookahead) of the remaining input. A context-free grammar can be ambiguous, meaning that there are multiple ways to apply the grammar rules to get the same inputs. Even unambiguous grammars can be nondeterministic, meaning that no fixed lookahead always suffices to determine the next grammar rule to apply. With the proper declarations, Bison is also able to parse these more general context-free grammars, using a technique known as GLR parsing (for Generalized LR). Bison’s GLR parsers are able to handle any context-free grammar for which the number of possible parses of any given string is finite. In the formal grammatical rules for a language, each kind of syntactic unit or grouping is named by a symbol. Those which are built by grouping smaller constructs according to grammatical rules are called nonterminal symbols; those which can’t be subdivided are called terminal symbols or token kinds. We call a piece of input corresponding to a single terminal symbol a token, and a piece corresponding to a single nonterminal symbol a grouping. We can use the C language as an example of what symbols, terminal and nonterminal, mean. The tokens of C are identifiers, constants (numeric and string), and the various keywords, arithmetic operators and punctuation marks. So the terminal symbols of a grammar for C include ‘identifier’, ‘number’, ‘string’, plus one symbol for each keyword, operator or punctuation mark: ‘if’, ‘return’, ‘const’, ‘static’, ‘int’, ‘char’, ‘plus-sign’, ‘open-brace’, ‘close-brace’, ‘comma’ and many more. (These tokens can be subdivided into characters, but that is a matter of lexicography, not grammar.) Here is a simple C function subdivided into tokens: int / keyword ‘int’ /
square (int x) / identifier, open-paren, keyword ‘int’, The syntactic groupings of C include the expression, the statement, the declaration, and the function definition. These are represented in the grammar of C by nonterminal symbols ‘expression’, ‘statement’, ‘declaration’ and ‘function definition’. The full grammar uses dozens of additional language constructs, each with its own nonterminal symbol, in order to express the meanings of these four. The example above is a function definition; it contains one declaration, and one statement. In the statement, each ‘x’ is an expression and so is ‘x * x’. Each nonterminal symbol must have grammatical rules showing how it is made out of simpler constructs. For example, one kind of C statement is the type subrange = lo .. hi; type enum = (a, b, c); 76 statement; this would be described with a grammar rule which reads informally as follows: A ‘statement’ can be made of a ‘return’ keyword, an ‘expression’ and a ‘semicolon’. There would be many other rules for ‘statement’, one for each kind of statement in C. One nonterminal symbol must be distinguished as the special one which defines a complete utterance in the language. It is called the start symbol. In a compiler, this means a complete input program. In the C language, the nonterminal symbol ‘sequence of definitions and declarations’ plays this role. For example, ‘1 + 2’ is a valid C expression—a valid part of a C program—but it is not valid as an entire C program. In the context-free grammar of C, this follows from the fact that ‘expression’ is not the start symbol. The Bison parser reads a sequence of tokens as its input, and groups the tokens using the grammar rules. If the input is valid, the end result is that the entire token sequence reduces to a single grouping whose symbol is the grammar’s start symbol. If we use a grammar for C, the entire input must be a ‘sequence of definitions and declarations’. If not, the parser reports a syntax error. 1.2 From Formal Rules to Bison InputA formal grammar is a mathematical construct. To define the language for Bison, you must write a file expressing the grammar in Bison syntax: a Bison grammar file. See . A nonterminal symbol in the formal grammar is represented in Bison input as an identifier, like an identifier in C. By convention, it should be in lower case, such as type subrange = lo .. hi; type enum = (a, b, c); 77, type subrange = lo .. hi; type enum = (a, b, c); 78 or type subrange = lo .. hi; type enum = (a, b, c); 79. The Bison representation for a terminal symbol is also called a token kind. Token kinds as well can be represented as C-like identifiers. By convention, these identifiers should be upper case to distinguish them from nonterminals: for example, type subrange = lo .. hi; type enum = (a, b, c); 80, type subrange = lo .. hi; type enum = (a, b, c); 81, type subrange = lo .. hi; type enum = (a, b, c); 82 or type subrange = lo .. hi; type enum = (a, b, c); 83. A terminal symbol that stands for a particular keyword in the language should be named after that keyword converted to upper case. The terminal symbol type subrange = lo .. hi; type enum = (a, b, c); 84 is reserved for error recovery. See . A terminal symbol can also be represented as a character literal, just like a C character constant. You should do this whenever a token is just a single character (parenthesis, plus-sign, etc.): use that same character in a literal as the terminal symbol for that token. A third way to represent a terminal symbol is with a C string constant containing several characters. See , for more information. The grammar rules also have an expression in Bison syntax. For example, here is the Bison rule for a C type subrange = lo .. hi; type enum = (a, b, c); 76 statement. The semicolon in quotes is a literal character token, representing part of the C syntax for the statement; the naked semicolon, and the colon, are Bison punctuation used in every rule. See . 1.3 Semantic ValuesA formal grammar selects tokens only by their classifications: for example, if a rule mentions the terminal symbol ‘integer constant’, it means that any integer constant is grammatically valid in that position. The precise value of the constant is irrelevant to how to parse the input: if ‘x+4’ is grammatical then ‘x+1’ or ‘x+3989’ is equally grammatical. But the precise value is very important for what the input means once it is parsed. A compiler is useless if it fails to distinguish between 4, 1 and 3989 as constants in the program! Therefore, each token in a Bison grammar has both a token kind and a semantic value. See , for details. The token kind is a terminal symbol defined in the grammar, such as type subrange = lo .. hi; type enum = (a, b, c); 80, type subrange = lo .. hi; type enum = (a, b, c); 81 or type subrange = lo .. hi; type enum = (a, b, c); 88. It tells everything you need to know to decide where the token may validly appear and how to group it with other tokens. The grammar rules know nothing about tokens except their kinds. The semantic value has all the rest of the information about the meaning of the token, such as the value of an integer, or the name of an identifier. (A token such as type subrange = lo .. hi; type enum = (a, b, c); 88 which is just punctuation doesn’t need to have any semantic value.) For example, an input token might be classified as token kind type subrange = lo .. hi; type enum = (a, b, c); 80 and have the semantic value 4. Another input token might have the same token kind type subrange = lo .. hi; type enum = (a, b, c); 80 but value 3989. When a grammar rule says that type subrange = lo .. hi; type enum = (a, b, c); 80 is allowed, either of these tokens is acceptable because each is an type subrange = lo .. hi; type enum = (a, b, c); 80. When the parser accepts the token, it keeps track of the token’s semantic value. Each grouping can also have a semantic value as well as its nonterminal symbol. For example, in a calculator, an expression typically has a semantic value that is a number. In a compiler for a programming language, an expression typically has a semantic value that is a tree structure describing the meaning of the expression. 1.4 Semantic ActionsIn order to be useful, a program must do more than parse input; it must also produce some output based on the input. In a Bison grammar, a grammar rule can have an action made up of C statements. Each time the parser recognizes a match for that rule, the action is executed. See . Most of the time, the purpose of an action is to compute the semantic value of the whole construct from the semantic values of its parts. For example, suppose we have a rule which says an expression can be the sum of two expressions. When the parser recognizes such a sum, each of the subexpressions has a semantic value which describes how it was built up. The action for this rule should create a similar sort of value for the newly recognized larger expression. For example, here is a rule that says an expression can be the sum of two subexpressions: expr: expr '+' expr { $$ = $1 + $3; } ; The action says how to produce the semantic value of the sum expression from the values of the two subexpressions. 1.5 Writing GLR ParsersIn some grammars, Bison’s deterministic LR(1) parsing algorithm cannot decide whether to apply a certain grammar rule at a given point. That is, it may not be able to decide (on the basis of the input read so far) which of two possible reductions (applications of a grammar rule) applies, or whether to apply a reduction or read more of the input and apply a reduction later in the input. These are known respectively as reduce/reduce conflicts (see ), and shift/reduce conflicts (see ). To use a grammar that is not easily modified to be LR(1), a more general parsing algorithm is sometimes necessary. If you include type subrange = lo .. hi; type enum = (a, b, c); 94 among the Bison declarations in your file (see ), the result is a Generalized LR (GLR) parser. These parsers handle Bison grammars that contain no unresolved conflicts (i.e., after applying precedence declarations) identically to deterministic parsers. However, when faced with unresolved shift/reduce and reduce/reduce conflicts, GLR parsers use the simple expedient of doing both, effectively cloning the parser to follow both possibilities. Each of the resulting parsers can again split, so that at any given time, there can be any number of possible parses being explored. The parsers proceed in lockstep; that is, all of them consume (shift) a given input symbol before any of them proceed to the next. Each of the cloned parsers eventually meets one of two possible fates: either it runs into a parsing error, in which case it simply vanishes, or it merges with another parser, because the two of them have reduced the input to an identical set of symbols. During the time that there are multiple parsers, semantic actions are recorded, but not performed. When a parser disappears, its recorded semantic actions disappear as well, and are never performed. When a reduction makes two parsers identical, causing them to merge, Bison records both sets of semantic actions. Whenever the last two parsers merge, reverting to the single-parser case, Bison resolves all the outstanding actions either by precedences given to the grammar rules involved, or by performing both actions, and then calling a designated user-defined function on the resulting values to produce an arbitrary merged result. 1.5.1 Using GLR on Unambiguous GrammarsIn the simplest cases, you can use the GLR algorithm to parse grammars that are unambiguous but fail to be LR(1). Such grammars typically require more than one symbol of lookahead. Consider a problem that arises in the declaration of enumerated and subrange types in the programming language Pascal. Here are some examples: type subrange = lo .. hi; type enum = (a, b, c); The original language standard allows only numeric literals and constant identifiers for the subrange bounds (‘lo’ and ‘hi’), but Extended Pascal (ISO/IEC 10206) and many other Pascal implementations allow arbitrary expressions there. This gives rise to the following situation, containing a superfluous pair of parentheses: type subrange = (a) .. b; Compare this to the following declaration of an enumerated type with only one value: (These declarations are contrived, but they are syntactically valid, and more-complicated cases can come up in practical programs.) These two declarations look identical until the ‘..’ token. With normal LR(1) one-token lookahead it is not possible to decide between the two forms when the identifier ‘a’ is parsed. It is, however, desirable for a parser to decide this, since in the latter case ‘a’ must become a new identifier to represent the enumeration value, while in the former case ‘a’ must be evaluated with its current meaning, which may be a constant or even a function call. You could parse ‘(a)’ as an “unspecified identifier in parentheses”, to be resolved later, but this typically requires substantial contortions in both semantic actions and large parts of the grammar, where the parentheses are nested in the recursive rules for expressions. You might think of using the lexer to distinguish between the two forms by returning different tokens for currently defined and undefined identifiers. But if these declarations occur in a local scope, and ‘a’ is defined in an outer scope, then both forms are possible—either locally redefining ‘a’, or using the value of ‘a’ from the outer scope. So this approach cannot work. A simple solution to this problem is to declare the parser to use the GLR algorithm. When the GLR parser reaches the critical state, it merely splits into two branches and pursues both syntax rules simultaneously. Sooner or later, one of them runs into a parsing error. If there is a ‘..’ token before the next ‘;’, the rule for enumerated types fails since it cannot accept ‘..’ anywhere; otherwise, the subrange type rule fails since it requires a ‘..’ token. So one of the branches fails silently, and the other one continues normally, performing all the intermediate actions that were postponed during the split. If the input is syntactically incorrect, both branches fail and the parser reports a syntax error as usual. The effect of all this is that the parser seems to “guess” the correct branch to take, or in other words, it seems to use more lookahead than the underlying LR(1) algorithm actually allows for. In this example, LR(2) would suffice, but also some cases that are not LR(k) for any k can be handled this way. In general, a GLR parser can take quadratic or cubic worst-case time, and the current Bison parser even takes exponential time and space for some grammars. In practice, this rarely happens, and for many grammars it is possible to prove that it cannot happen. The present example contains only one conflict between two rules, and the type-declaration context containing the conflict cannot be nested. So the number of branches that can exist at any time is limited by the constant 2, and the parsing time is still linear. Here is a Bison grammar corresponding to the example above. It parses a vastly simplified form of Pascal type declarations. %token TYPE DOTDOT ID %left '+' '-' %left '*' '/' %% type_decl: TYPE ID '=' type ';' ; one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 0 one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 1 one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 2 one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 1 one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 4 When used as a normal LR(1) grammar, Bison correctly complains about one reduce/reduce conflict. In the conflicting situation the parser chooses one of the alternatives, arbitrarily the one declared first. Therefore the following correct input is not recognized: The parser can be turned into a GLR parser, while also telling Bison to be silent about the one known reduce/reduce conflict, by adding these two declarations to the Bison grammar file (before the first ‘%%’): No change in the grammar itself is required. Now the parser recognizes all valid declarations, according to the limited syntax above, transparently. In fact, the user does not even notice when the parser splits. So here we have a case where we can use the benefits of GLR, almost without disadvantages. Even in simple cases like this, however, there are at least two potential problems to beware. First, always analyze the conflicts reported by Bison to make sure that GLR splitting is only done where it is intended. A GLR parser splitting inadvertently may cause problems less obvious than an LR parser statically choosing the wrong alternative in a conflict. Second, consider interactions with the lexer (see ) with great care. Since a split parser consumes tokens without performing any actions during the split, the lexer cannot obtain information via parser actions. Some cases of lexer interactions can be eliminated by using GLR to shift the complications from the lexer to the parser. You must check the remaining cases for correctness. In our example, it would be safe for the lexer to return tokens based on their current meanings in some symbol table, because no new symbols are defined in the middle of a type declaration. Though it is possible for a parser to define the enumeration constants as they are parsed, before the type declaration is completed, it actually makes no difference since they cannot be used within the same enumerated type declaration. 1.5.2 Using GLR to Resolve AmbiguitiesLet’s consider an example, vastly simplified from a C++ grammar. one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 5 This models a problematic part of the C++ grammar—the ambiguity between certain declarations and statements. For example, parses as either an type subrange = lo .. hi; type enum = (a, b, c); 77 or a type subrange = lo .. hi; type enum = (a, b, c); 78 (assuming that ‘T’ is recognized as a type subrange = lo .. hi; type enum = (a, b, c); 97 and ‘x’ as an type subrange = lo .. hi; type enum = (a, b, c); 98). Bison detects this as a reduce/reduce conflict between the rules type subrange = lo .. hi; type enum = (a, b, c); 99 and type subrange = (a) .. b; 00, which it cannot resolve at the time it encounters type subrange = (a) .. b; 01 in the example above. Since this is a GLR parser, it therefore splits the problem into two parses, one for each choice of resolving the reduce/reduce conflict. Unlike the example from the previous section (see ), however, neither of these parses “dies,” because the grammar as it stands is ambiguous. One of the parsers eventually reduces type subrange = (a) .. b; 02 and the other reduces type subrange = (a) .. b; 03, after which both parsers are in an identical state: they’ve seen ‘prog stmt’ and have the same unprocessed input remaining. We say that these parses have merged. At this point, the GLR parser requires a specification in the grammar of how to choose between the competing parses. In the example above, the two type subrange = (a) .. b; 04 declarations specify that Bison is to give precedence to the parse that interprets the example as a type subrange = (a) .. b; 05, which implies that type subrange = (a) .. b; 01 is a declarator. The parser therefore prints one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 6 The type subrange = (a) .. b; 04 declarations only come into play when more than one parse survives. Consider a different input string for this parser: This is another example of using GLR to parse an unambiguous construct, as shown in the previous section (see ). Here, there is no ambiguity (this cannot be parsed as a declaration). However, at the time the Bison parser encounters type subrange = (a) .. b; 01, it does not have enough information to resolve the reduce/reduce conflict (again, between type subrange = (a) .. b; 01 as an type subrange = lo .. hi; type enum = (a, b, c); 77 or a type subrange = (a) .. b; 11). In this case, no precedence declaration is used. Again, the parser splits into two, one assuming that type subrange = (a) .. b; 01 is an type subrange = lo .. hi; type enum = (a, b, c); 77, and the other assuming type subrange = (a) .. b; 01 is a type subrange = (a) .. b; 11. The second of these parsers then vanishes when it sees type subrange = (a) .. b; 16, and the parser prints Suppose that instead of resolving the ambiguity, you wanted to see all the possibilities. For this purpose, you must merge the semantic actions of the two possible parsers, rather than choosing one over the other. To do so, you could change the declaration of type subrange = lo .. hi; type enum = (a, b, c); 78 as follows: one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 7 and define the type subrange = (a) .. b; 18 function as: one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 8 with an accompanying forward declaration in the C declarations at the beginning of the file: one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 9 With these declarations, the resulting parser parses the first example as both an type subrange = lo .. hi; type enum = (a, b, c); 77 and a type subrange = (a) .. b; 05, and prints program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 0 Bison requires that all of the productions that participate in any particular merge have identical ‘%merge’ clauses. Otherwise, the ambiguity would be unresolvable, and the parser will report an error during any parse that results in the offending merge. The signature of the merger depends on the type of the symbol. In the previous example, the merged-to symbol ( type subrange = lo .. hi; type enum = (a, b, c);
program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 1 However, if type subrange = lo .. hi; type enum = (a, b, c); 78 had a declared type, e.g., or program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 2 program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 3 then the prototype of the merger must be: program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 4 (This signature might be a mistake originally, and maybe it should have been ‘Node *stmt_merge (Node *x0, Node *x1)’. If you have an opinion about it, please let us know.) 1.5.3 GLR Semantic ActionsThe nature of GLR parsing and the structure of the generated parsers give rise to certain restrictions on semantic values and actions. 1.5.3.1 Deferred semantic actionsBy definition, a deferred semantic action is not performed at the same time as the associated reduction. This raises caveats for several Bison features you might use in a semantic action in a GLR parser. In any semantic action, you can examine type subrange = (a) .. b; 23 to determine the kind of the lookahead token present at the time of the associated reduction. After checking that type subrange = (a) .. b; 23 is not set to type subrange = (a) .. b; 25 or type subrange = (a) .. b; 26, you can then examine type subrange = (a) .. b; 27 and type subrange = (a) .. b; 28 to determine the lookahead token’s semantic value and location, if any. In a nondeferred semantic action, you can also modify any of these variables to influence syntax analysis. See . In a deferred semantic action, it’s too late to influence syntax analysis. In this case, type subrange = (a) .. b; 23, type subrange = (a) .. b; 27, and type subrange = (a) .. b; 28 are set to shallow copies of the values they had at the time of the associated reduction. For this reason alone, modifying them is dangerous. Moreover, the result of modifying them is undefined and subject to change with future versions of Bison. For example, if a semantic action might be deferred, you should never write it to invoke type subrange = (a) .. b; 32 (see ) or to attempt to free memory referenced by type subrange = (a) .. b; 27. 1.5.3.2 YYERRORAnother Bison feature requiring special consideration is type subrange = (a) .. b; 34 (see ), which you can invoke in a semantic action to initiate error recovery. During deterministic GLR operation, the effect of type subrange = (a) .. b; 34 is the same as its effect in a deterministic parser. The effect in a deferred action is similar, but the precise point of the error is undefined; instead, the parser reverts to deterministic operation, selecting an unspecified stack on which to continue with a syntax error. In a semantic predicate (see ) during nondeterministic parsing, type subrange = (a) .. b; 34 silently prunes the parse that invoked the test. 1.5.3.3 Restrictions on semantic values and locationsGLR parsers require that you use POD (Plain Old Data) types for semantic values and location types when using the generated parsers as C++ code. 1.5.4 Controlling a Parse with Arbitrary PredicatesIn addition to the type subrange = (a) .. b; 04 and type subrange = (a) .. b; 38 directives, GLR parsers allow you to reject parses on the basis of arbitrary computations executed in user code, without having Bison treat this rejection as an error if there are alternative parses. For example, program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 5 is one way to allow the same parser to handle two different syntaxes for widgets. The clause preceded by type subrange = (a) .. b; 39 is treated like an ordinary midrule action, except that its text is handled as an expression and is always evaluated immediately (even when in nondeterministic mode). If the expression yields 0 (false), the clause is treated as a syntax error, which, in a nondeterministic parser, causes the stack in which it is reduced to die. In a deterministic parser, it acts like type subrange = (a) .. b; 34. As the example shows, predicates otherwise look like semantic actions, and therefore you must take them into account when determining the numbers to use for denoting the semantic values of right-hand side symbols. Predicate actions, however, have no defined value, and may not be given labels. There is a subtle difference between semantic predicates and ordinary actions in nondeterministic mode, since the latter are deferred. For example, we could try to rewrite the previous example as program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 6 (reversing the sense of the predicate tests to cause an error when they are false). However, this does not have the same effect if type subrange = (a) .. b; 41 and type subrange = (a) .. b; 42 have overlapping syntax. Since the midrule actions testing type subrange = (a) .. b; 43 are deferred, a GLR parser first encounters the unresolved ambiguous reduction for cases where type subrange = (a) .. b; 41 and type subrange = (a) .. b; 42 recognize the same string before performing the tests of type subrange = (a) .. b; 43. It therefore reports an error. Finally, be careful in writing predicates: deferred actions have not been evaluated, so that using them in a predicate will have undefined effects. 1.6 LocationsMany applications, like interpreters or compilers, have to produce verbose and useful error messages. To achieve this, one must be able to keep track of the textual location, or location, of each syntactic construct. Bison provides a mechanism for handling these locations. Each token has a semantic value. In a similar fashion, each token has an associated location, but the type of locations is the same for all tokens and groupings. Moreover, the output parser is equipped with a default data structure for storing locations (see , for more details). Like semantic values, locations can be reached in actions using a dedicated set of constructs. In the example above, the location of the whole grouping is type subrange = (a) .. b; 47, while the locations of the subexpressions are type subrange = (a) .. b; 48 and type subrange = (a) .. b; 49. When a rule is matched, a default action is used to compute the semantic value of its left hand side (see ). In the same way, another default action is used for locations. However, the action for locations is general enough for most cases, meaning there is usually no need to describe for each rule how type subrange = (a) .. b; 47 should be formed. When building a new location for a given grouping, the default behavior of the output parser is to take the beginning of the first symbol, and the end of the last symbol. 1.7 Bison Output: the Parser Implementation FileWhen you run Bison, you give it a Bison grammar file as input. The most important output is a C source file that implements a parser for the language described by the grammar. This parser is called a Bison parser, and this file is called a Bison parser implementation file. Keep in mind that the Bison utility and the Bison parser are two distinct programs: the Bison utility is a program whose output is the Bison parser implementation file that becomes part of your program. The job of the Bison parser is to group tokens into groupings according to the grammar rules—for example, to build identifiers and operators into expressions. As it does this, it runs the actions for the grammar rules it uses. The tokens come from a function called the lexical analyzer that you must supply in some fashion (such as by writing it in C). The Bison parser calls the lexical analyzer each time it wants a new token. It doesn’t know what is “inside” the tokens (though their semantic values may reflect this). Typically the lexical analyzer makes the tokens by parsing characters of text, but Bison does not depend on this. See . The Bison parser implementation file is C code which defines a function named type subrange = (a) .. b; 52 which implements that grammar. This function does not make a complete C program: you must supply some additional functions. One is the lexical analyzer. Another is an error-reporting function which the parser calls to report an error. In addition, a complete C program must start with a function called type subrange = (a) .. b; 53; you have to provide this, and arrange for it to call type subrange = (a) .. b; 52 or the parser will never run. See . Aside from the token kind names and the symbols in the actions you write, all symbols defined in the Bison parser implementation file itself begin with ‘yy’ or ‘YY’. This includes interface functions such as the lexical analyzer function type subrange = (a) .. b; 51, the error reporting function type subrange = (a) .. b; 56 and the parser function type subrange = (a) .. b; 52 itself. This also includes numerous identifiers used for internal purposes. Therefore, you should avoid using C identifiers starting with ‘yy’ or ‘YY’ in the Bison grammar file except for the ones defined in this manual. Also, you should avoid using the C identifiers ‘malloc’ and ‘free’ for anything other than their usual meanings. In some cases the Bison parser implementation file includes system headers, and in those cases your code should respect the identifiers reserved by those headers. On some non-GNU hosts, type subrange = (a) .. b; 58, type subrange = (a) .. b; 59, type subrange = (a) .. b; 60 (if available), and type subrange = (a) .. b; 61 are included to declare memory allocators and integer types and constants. type subrange = (a) .. b; 62 is included if message translation is in use (see ). Other system headers may be included if you define type subrange = (a) .. b; 63 (see ) or type subrange = (a) .. b; 64 (see ) to a nonzero value. 1.8 Stages in Using BisonThe actual language-design process using Bison, from grammar specification to a working compiler or interpreter, has these parts:
To turn this source code as written into a runnable program, you must follow these steps:
1.9 The Overall Layout of a Bison GrammarThe input file for the Bison utility is a Bison grammar file. The general form of a Bison grammar file is as follows: program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 7 The ‘%%’, ‘%{’ and ‘%}’ are punctuation that appears in every Bison grammar file to separate the sections. The prologue may define types and variables used in the actions. You can also use preprocessor commands to define macros used there, and use type subrange = (a) .. b; 66 to include header files that do any of these things. You need to declare the lexical analyzer type subrange = (a) .. b; 51 and the error printer type subrange = (a) .. b; 56 here, along with any other global identifiers used by the actions in the grammar rules. The Bison declarations declare the names of the terminal and nonterminal symbols, and may also describe operator precedence and the data types of semantic values of various symbols. The grammar rules define how to construct each nonterminal symbol from its parts. The epilogue can contain any code you want to use. Often the definitions of functions declared in the prologue go here. In a simple program, all the rest of the program can go here. 2 ExamplesNow we show and explain several sample programs written using Bison: a Reverse Polish Notation calculator, an algebraic (infix) notation calculator — later extended to track “locations” — and a multi-function calculator. All produce usable, though limited, interactive desk-top calculators. These examples are simple, but Bison grammars for real programming languages are written the same way. You can copy these examples into a source file to try them. Bison comes with several examples (including for the different target languages). If this package is properly installed, you shall find them in prefix/share/doc/bison/examples, where prefix is the root of the installation, probably something like /usr/local or /usr. 2.1 Reverse Polish Notation CalculatorThe first example is that of a simple double-precision Reverse Polish Notation calculator (a calculator using postfix operators). This example provides a good starting point, since operator precedence is not an issue. The second example will illustrate how operator precedence is handled. The source code for this calculator is named rpcalc.y. The ‘.y’ extension is a convention used for Bison grammar files. 2.1.1 Declarations fortype subrange = (a) .. b; 72 Here are the C and Bison declarations for the Reverse Polish Notation calculator. As in C, comments are placed between ‘/*…*/’ or after ‘//’. program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 8 program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 9 int / keyword ‘int’ /
square (int x) / identifier, open-paren, keyword ‘int’, 0 The declarations section (see ) contains two preprocessor directives and two forward declarations. The type subrange = (a) .. b; 66 directive is used to declare the exponentiation function type subrange = (a) .. b; 77. The forward declarations for type subrange = (a) .. b; 51 and type subrange = (a) .. b; 56 are needed because the C language requires that functions be declared before they are used. These functions will be defined in the epilogue, but the parser calls them so they must be declared in the prologue. The second section, Bison declarations, provides information to Bison about the tokens and their types (see ). The type subrange = (a) .. b; 80 directive defines the variable type subrange = (a) .. b; 81, thus specifying the C data type for semantic values of both tokens and groupings (see ). The Bison parser will use whatever type type subrange = (a) .. b; 81 is defined as; if you don’t define it, type subrange = (a) .. b; 83 is the default. Because we specify ‘{double}’, each token and each expression has an associated value, which is a floating point number. C code can use type subrange = (a) .. b; 84 to refer to the value type subrange = (a) .. b; 81. Each terminal symbol that is not a single-character literal must be declared. (Single-character literals normally don’t need to be declared.) In this example, all the arithmetic operators are designated by single-character literals, so the only terminal symbol that needs to be declared is type subrange = (a) .. b; 86, the token kind for numeric constants. 2.1.2 Grammar Rules fortype subrange = (a) .. b; 72 Here are the grammar rules for the Reverse Polish Notation calculator. int / keyword ‘int’ /
square (int x) / identifier, open-paren, keyword ‘int’, 1 one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 1 int / keyword ‘int’ /
square (int x) / identifier, open-paren, keyword ‘int’, 3 one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 1 int / keyword ‘int’ /
square (int x) / identifier, open-paren, keyword ‘int’, 5 int / keyword ‘int’ /
square (int x) / identifier, open-paren, keyword ‘int’, 6 The groupings of the rpcalc “language” defined here are the expression (given the name type subrange = (a) .. b; 88), the line of input ( type subrange = (a) .. b; 89), and the complete input transcript ( type subrange = (a) .. b; 90). Each of these nonterminal symbols has several alternate rules, joined by the vertical bar ‘|’ which is read as “or”. The following sections explain what these rules mean. The semantics of the language is determined by the actions taken when a grouping is recognized. The actions are the C code that appears inside braces. See . You must specify these actions in C, but Bison provides the means for passing semantic values between the rules. In each action, the pseudo-variable type subrange = (a) .. b; 91 stands for the semantic value for the grouping that the rule is going to construct. Assigning a value to type subrange = (a) .. b; 91 is the main job of most actions. The semantic values of the components of the rule are referred to as type subrange = (a) .. b; 93, type subrange = (a) .. b; 94, and so on. 2.1.2.1 Explanation oftype subrange = (a) .. b; 90 Consider the definition of type subrange = (a) .. b; 90: int / keyword ‘int’ /
square (int x) / identifier, open-paren, keyword ‘int’, 1 This definition reads as follows: “A complete input is either an empty string, or a complete input followed by an input line”. Notice that “complete input” is defined in terms of itself. This definition is said to be left recursive since type subrange = (a) .. b; 90 appears always as the leftmost symbol in the sequence. See . The first alternative is empty because there are no symbols between the colon and the first ‘|’; this means that type subrange = (a) .. b; 90 can match an empty string of input (no tokens). We write the rules this way because it is legitimate to type Ctrl-d right after you start the calculator. It’s conventional to put an empty alternative first and to use the (optional) %token TYPE DOTDOT ID 02 directive, or to write the comment ‘/* empty */’ in it (see ). The second alternate rule ( %token TYPE DOTDOT ID
The parser function type subrange = (a) .. b; 52 continues to process input until a grammatical error is seen or the lexical analyzer says there are no more input tokens; we will arrange for the latter to happen at end-of-input. 2.1.2.2 Explanation oftype subrange = (a) .. b; 89 Now consider the definition of type subrange = (a) .. b; 89: int / keyword ‘int’ /
square (int x) / identifier, open-paren, keyword ‘int’, 8 The first alternative is a token which is a newline character; this means that rpcalc accepts a blank line (and ignores it, since there is no action). The second alternative is an expression followed by a newline. This is the alternative that makes rpcalc useful. The semantic value of the type subrange = (a) .. b; 88 grouping is the value of type subrange = (a) .. b; 93 because the type subrange = (a) .. b; 88 in question is the first symbol in the alternative. The action prints this value, which is the result of the computation the user asked for. This action is unusual because it does not assign a value to type subrange = (a) .. b; 91. As a consequence, the semantic value associated with the type subrange = (a) .. b; 89 is uninitialized (its value will be unpredictable). This would be a bug if that value were ever used, but we don’t use it: once rpcalc has printed the value of the user’s input line, that value is no longer needed. 2.1.2.3 Explanation oftype subrange = (a) .. b; 88 The type subrange = (a) .. b; 88 grouping has several rules, one for each kind of expression. The first rule handles the simplest expressions: those that are just numbers. The second handles an addition-expression, which looks like two expressions followed by a plus-sign. The third handles subtraction, and so on. int / keyword ‘int’ /
square (int x) / identifier, open-paren, keyword ‘int’, 9 We have used ‘|’ to join all the rules for type subrange = (a) .. b; 88, but we could equally well have written them separately: expr: expr '+' expr { $$ = $1 + $3; } ; 0 Most of the rules have actions that compute the value of the expression in terms of the value of its parts. For example, in the rule for addition, type subrange = (a) .. b; 93 refers to the first component type subrange = (a) .. b; 88 and type subrange = (a) .. b; 94 refers to the second one. The third component, %token TYPE DOTDOT ID 18, has no meaningful associated semantic value, but if it had one you could refer to it as %token TYPE DOTDOT ID 19. The first rule relies on the implicit default action: ‘{ $$ = $1; }’. When type subrange = (a) .. b; 52 recognizes a sum expression using this rule, the sum of the two subexpressions’ values is produced as the value of the entire expression. See . You don’t have to give an action for every rule. When a rule has no action, Bison by default copies the value of type subrange = (a) .. b; 93 into type subrange = (a) .. b; 91. This is what happens in the first rule (the one that uses type subrange = (a) .. b; 86). The formatting shown here is the recommended convention, but Bison does not require it. You can add or change white space as much as you wish. For example, this: expr: expr '+' expr { $$ = $1 + $3; } ; 1 means the same thing as this: expr: expr '+' expr { $$ = $1 + $3; } ; 2 The latter, however, is much more readable. 2.1.3 Thetype subrange = (a) .. b; 72 Lexical Analyzer The lexical analyzer’s job is low-level parsing: converting characters or sequences of characters into tokens. The Bison parser gets its tokens by calling the lexical analyzer. See . Only a simple lexical analyzer is needed for the RPN calculator. This lexical analyzer skips blanks and tabs, then reads in numbers as %token TYPE DOTDOT ID 26 and returns them as type subrange = (a) .. b; 86 tokens. Any other character that isn’t part of a number is a separate token. Note that the token-code for such a single-character token is the character itself. The return value of the lexical analyzer function is a numeric code which represents a token kind. The same text used in Bison rules to stand for this token kind is also a C expression for the numeric code of the kind. This works in two ways. If the token kind is a character literal, then its numeric code is that of the character; you can use the same character literal in the lexical analyzer to express the number. If the token kind is an identifier, that identifier is defined by Bison as a C enum whose definition is the appropriate code. In this example, therefore, type subrange = (a) .. b; 86 becomes an enum for type subrange = (a) .. b; 51 to use. The semantic value of the token (if it has one) is stored into the global variable type subrange = (a) .. b; 27, which is where the Bison parser will look for it. (The C data type of type subrange = (a) .. b; 27 is type subrange = (a) .. b; 84, whose value was defined at the beginning of the grammar via ‘%define api.value.type {double}’; see .) A token kind code of zero is returned if the end-of-input is encountered. (Bison recognizes any nonpositive value as indicating end-of-input.) Here is the code for the lexical analyzer: expr: expr '+' expr { $$ = $1 + $3; } ; 3 one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 1 expr: expr '+' expr { $$ = $1 + $3; } ; 5 expr: expr '+' expr { $$ = $1 + $3; } ; 6 expr: expr '+' expr { $$ = $1 + $3; } ; 7 2.1.4 The Controlling FunctionIn keeping with the spirit of this example, the controlling function is kept to the bare minimum. The only requirement is that it call type subrange = (a) .. b; 52 to start the process of parsing. expr: expr '+' expr { $$ = $1 + $3; } ; 8 2.1.5 The Error Reporting RoutineWhen type subrange = (a) .. b; 52 detects a syntax error, it calls the error reporting function type subrange = (a) .. b; 56 to print an error message (usually but not always %token TYPE DOTDOT ID 37). It is up to the programmer to supply type subrange = (a) .. b; 56 (see ), so here is the definition we will use: expr: expr '+' expr { $$ = $1 + $3; } ; 9 type subrange = lo .. hi; type enum = (a, b, c); 0 After type subrange = (a) .. b; 56 returns, the Bison parser may recover from the error and continue parsing if the grammar contains a suitable error rule (see ). Otherwise, type subrange = (a) .. b; 52 returns nonzero. We have not written any error rules in this example, so any invalid input will cause the calculator program to exit. This is not clean behavior for a real calculator, but it is adequate for the first example. 2.1.6 Running Bison to Make the ParserBefore running Bison to produce a parser, we need to decide how to arrange all the source code in one or more source files. For such a simple example, the easiest thing is to put everything in one file, the grammar file. The definitions of type subrange = (a) .. b; 51, type subrange = (a) .. b; 56 and type subrange = (a) .. b; 53 go at the end, in the epilogue of the grammar file (see ). For a large project, you would probably have several source files, and use %token TYPE DOTDOT ID 44 to arrange to recompile them. With all the source in the grammar file, you use the following command to convert it into a parser implementation file: In this example, the grammar file is called rpcalc.y (for “Reverse Polish CALCulator”). Bison produces a parser implementation file named file.tab.c, removing the ‘.y’ from the grammar file name. The parser implementation file contains the source code for type subrange = (a) .. b; 52. The additional functions in the grammar file ( type subrange = (a) .. b; 51, type subrange = (a) .. b; 56 and type subrange = (a) .. b;
2.1.7 Compiling the Parser Implementation FileHere is how to compile and run the parser implementation file: type subrange = lo .. hi; type enum = (a, b, c); 1 one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 1 type subrange = lo .. hi; type enum = (a, b, c); 3 one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 1 type subrange = lo .. hi; type enum = (a, b, c); 5 The file rpcalc now contains the executable code. Here is an example session using type subrange = (a) .. b; 72. type subrange = lo .. hi; type enum = (a, b, c); 6 2.2 Infix Notation Calculator:type subrange = (a) .. b; 69 We now modify rpcalc to handle infix operators instead of postfix. Infix notation involves the concept of operator precedence and the need for parentheses nested to arbitrary depth. Here is the Bison code for calc.y, an infix desk-top calculator. type subrange = lo .. hi; type enum = (a, b, c); 7 type subrange = lo .. hi; type enum = (a, b, c); 8 one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 1 type subrange = (a) .. b; 0 type subrange = (a) .. b; 1 int / keyword ‘int’ /
square (int x) / identifier, open-paren, keyword ‘int’, 1 one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 1 type subrange = (a) .. b; 4 one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 1 type subrange = (a) .. b; 6 int / keyword ‘int’ /
square (int x) / identifier, open-paren, keyword ‘int’, 6 The functions type subrange = (a) .. b; 51, type subrange = (a) .. b; 56 and type subrange = (a) .. b; 53 can be the same as before. There are two important new features shown in this code. In the second section (Bison declarations), %token TYPE DOTDOT ID 54 declares token kinds and says they are left-associative operators. The declarations %token TYPE DOTDOT ID 54 and %token TYPE DOTDOT ID 56 (right associativity) take the place of %token TYPE DOTDOT ID 57 which is used to declare a token kind name without associativity/precedence. (These tokens are single-character literals, which ordinarily don’t need to be declared. We declare them here to specify the associativity/precedence.) Operator precedence is determined by the line ordering of the declarations; the higher the line number of the declaration (lower on the page or screen), the higher the precedence. Hence, exponentiation has the highest precedence, unary minus ( %token TYPE DOTDOT ID
%token TYPE DOTDOT ID 59. See . The other important new feature is the %token TYPE DOTDOT ID 60 in the grammar section for the unary minus operator. The %token TYPE DOTDOT ID 60 simply instructs Bison that the rule ‘| '-' exp’ has the same precedence as %token TYPE DOTDOT ID 58—in this case the next-to-highest. See . Here is a sample run of calc.y: type subrange = (a) .. b; 8 2.3 Simple Error RecoveryUp to this point, this manual has not addressed the issue of error recovery—how to continue parsing after the parser detects a syntax error. All we have handled is error reporting with type subrange = (a) .. b; 56. Recall that by default type subrange = (a) .. b; 52 returns after calling type subrange = (a) .. b; 56. This means that an erroneous input line causes the calculator program to exit. Now we show how to rectify this deficiency. The Bison language itself includes the reserved word type subrange = lo .. hi; type enum = (a, b, c); 84, which may be included in the grammar rules. In the example below it has been added to one of the alternatives for type subrange = (a) .. b; 89: type subrange = (a) .. b; 9 This addition to the grammar allows for simple error recovery in the event of a syntax error. If an expression that cannot be evaluated is read, the error will be recognized by the third rule for type subrange = (a) .. b; 89, and parsing will continue. (The type subrange = (a) .. b; 56 function is still called upon to print its message as well.) The action executes the statement %token TYPE DOTDOT ID 70, a macro defined automatically by Bison; its meaning is that error recovery is complete (see ). Note the difference between %token TYPE DOTDOT ID 70 and type subrange = (a) .. b; 56; neither one is a misprint. This form of error recovery deals with syntax errors. There are other kinds of errors; for example, division by zero, which raises an exception signal that is normally fatal. A real calculator program must handle this signal and use %token TYPE DOTDOT ID 73 to return to type subrange = (a) .. b; 53 and resume parsing input lines; it would also have to discard the rest of the current line of input. We won’t discuss this issue further because it is not specific to Bison programs. 2.4 Location Tracking Calculator:type subrange = (a) .. b; 70 This example extends the infix notation calculator with location tracking. This feature will be used to improve the error messages. For the sake of clarity, this example is a simple integer calculator, since most of the work needed to use locations will be done in the lexical analyzer. 2.4.1 Declarations fortype subrange = (a) .. b; 70 The C and Bison declarations for the location tracking calculator are the same as the declarations for the infix notation calculator. %token TYPE DOTDOT ID 0 Note there are no declarations specific to locations. Defining a data type for storing locations is not needed: we will use the type provided by default (see ), which is a four member structure with the following integer fields: %token TYPE DOTDOT ID 80, %token TYPE DOTDOT ID 81, %token TYPE DOTDOT ID 82 and %token TYPE DOTDOT ID 83. By conventions, and in accordance with the GNU Coding Standards and common practice, the line and column count both start at 1. 2.4.2 Grammar Rules fortype subrange = (a) .. b; 70 Whether handling locations or not has no effect on the syntax of your language. Therefore, grammar rules for this example will be very close to those of the previous example: we will only modify them to benefit from the new information. Here, we will use locations to report divisions by zero, and locate the wrong expressions or subexpressions. int / keyword ‘int’ /
square (int x) / identifier, open-paren, keyword ‘int’, 1 one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 1 %token TYPE DOTDOT ID 3 one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 1 %token TYPE DOTDOT ID 5 %token TYPE DOTDOT ID 6 %token TYPE DOTDOT ID 7 This code shows how to reach locations inside of semantic actions, by using the pseudo-variables %token TYPE DOTDOT ID 85 for rule components, and the pseudo-variable type subrange = (a) .. b; 47 for groupings. We don’t need to assign a value to type subrange = (a) .. b; 47: the output parser does it automatically. By default, before executing the C code of each action, type subrange = (a) .. b; 47 is set to range from the beginning of type subrange = (a) .. b; 48 to the end of %token TYPE DOTDOT ID 85, for a rule with n components. This behavior can be redefined (see ), and for very specific rules, type subrange = (a) .. b; 47 can be computed by hand. 2.4.3 Thetype subrange = (a) .. b; 70 Lexical Analyzer. Until now, we relied on Bison’s defaults to enable location tracking. The next step is to rewrite the lexical analyzer, and make it able to feed the parser with the token locations, as it already does for semantic values. To this end, we must take into account every single character of the input text, to avoid the computed locations of being fuzzy or wrong: %token TYPE DOTDOT ID 8 one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 1 %left '+' '-' %left '*' '/' 0 one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 1 %left '+' '-' %left '*' '/' 2 one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 1 %left '+' '-' %left '*' '/' 4 %left '+' '-' %left '*' '/' 5 %left '+' '-' %left '*' '/' 6 Basically, the lexical analyzer performs the same processing as before: it skips blanks and tabs, and reads numbers or single-character tokens. In addition, it updates type subrange = (a) .. b; 28, the global variable (of type %token TYPE DOTDOT ID
Now, each time this function returns a token, the parser has its kind as well as its semantic value, and its location in the text. The last needed change is to initialize type subrange = (a) .. b; 28, for example in the controlling function: %left '+' '-' %left '*' '/' 7 Remember that computing locations is not a matter of syntax. Every character must be associated to a location update, whether it is in valid input, in comments, in literal strings, and so on. 2.5 Multi-Function Calculator:type subrange = (a) .. b; 71 Now that the basics of Bison have been discussed, it is time to move on to a more advanced problem. The above calculators provided only five functions, ‘+’, ‘-’, ‘*’, ‘/’ and ‘^’. It would be nice to have a calculator that provides other mathematical functions such as %token TYPE DOTDOT ID 97, %token TYPE DOTDOT ID 98, etc. It is easy to add new operators to the infix calculator as long as they are only single-character literals. The lexical analyzer type subrange = (a) .. b; 51 passes back all nonnumeric characters as tokens, so new grammar rules suffice for adding a new operator. But we want something more flexible: built-in functions whose syntax has this form: At the same time, we will add memory to the calculator, by allowing you to create named variables, store values in them, and use them later. Here is a sample session with the multi-function calculator: %left '+' '-' %left '*' '/' 8 %left '+' '-' %left '*' '/' 9 %% type_decl: TYPE ID '=' type ';' ; 0 Note that multiple assignment and nested function calls are permitted. 2.5.1 Declarations fortype subrange = (a) .. b; 71 Here are the C and Bison declarations for the multi-function calculator. %% type_decl: TYPE ID '=' type ';' ; 1 %% type_decl: TYPE ID '=' type ';' ; 2 %% type_decl: TYPE ID '=' type ';' ; 3 The above grammar introduces only two new features of the Bison language. These features allow semantic values to have various data types (see ). The special %left '+' '-' %left '*' '/' 06 value assigned to the type subrange = (a) .. b; 80 variable type subrange = (a) .. b; 81 specifies that the symbols are defined with their data types. Bison will generate an appropriate definition of type subrange = (a) .. b; 84 to store these values. Since values can now have various types, it is necessary to associate a type with each grammar symbol whose semantic value is used. These symbols are type subrange = (a) .. b; 86, %left '+' '-' %left '*' '/' 11, %left '+' '-' %left '*' '/' 12, and type subrange = (a) .. b; 88. Their declarations are augmented with their data type (placed between angle brackets). For instance, values of type subrange = (a) .. b; 86 are stored in %token TYPE DOTDOT ID 26. The Bison construct %left '+' '-' %left '*' '/' 16 is used for declaring nonterminal symbols, just as %token TYPE DOTDOT ID 57 is used for declaring token kinds. Previously we did not use %left '+' '-' %left '*' '/' 16 before because nonterminal symbols are normally declared implicitly by the rules that define them. But type subrange = (a) .. b; 88 must be declared explicitly so we can specify its value type. See . 2.5.2 Grammar Rules fortype subrange = (a) .. b; 71 Here are the grammar rules for the multi-function calculator. Most of them are copied directly from type subrange = (a) .. b; 69; three rules, those which mention %left '+' '-' %left '*' '/' 11 or %left '+' '-' %left '*' '/' 12, are new. %% type_decl: TYPE ID '=' type ';' ; 4 int / keyword ‘int’ /
square (int x) / identifier, open-paren, keyword ‘int’, 1 one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 1 %% type_decl: TYPE ID '=' type ';' ; 7 one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 1 %% type_decl: TYPE ID '=' type ';' ; 9 one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 00 2.5.3 Thetype subrange = (a) .. b; 71 Symbol Table The multi-function calculator requires a symbol table to keep track of the names and meanings of variables and functions. This doesn’t affect the grammar rules (except for the actions) or the Bison declarations, but it requires some additional C functions for support. The symbol table itself consists of a linked list of records. Its definition, which is kept in the header calc.h, is as follows. It provides for either functions or variables to be placed in the table. one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 01 one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 1 one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 03 one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 1 one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 05 The new version of type subrange = (a) .. b; 53 will call %left '+' '-' %left '*' '/' 26 to initialize the symbol table: one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 06 one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 1 one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 08 one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 1 one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 10 one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 1 one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 12 one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 13 By simply editing the initialization list and adding the necessary include files, you can add additional functions to the calculator. Two important functions allow look-up and installation of symbols in the symbol table. The function %left '+' '-' %left '*' '/' 27 is passed a name and the kind ( %left '+' '-' %left '*' '/' 11 or %left '+' '-' %left '*' '/'
%left '+' '-' %left '*' '/' 30 is passed the name of the symbol to look up. If found, a pointer to that symbol is returned; otherwise zero is returned. one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 14 one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 1 one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 16 one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 1 one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 18 2.5.4 Thetype subrange = (a) .. b; 71 Lexer The function type subrange = (a) .. b; 51 must now recognize variables, numeric values, and the single-character arithmetic operators. Strings of alphanumeric characters with a leading letter are recognized as either variables or functions depending on what the symbol table says about them. The string is passed to %left '+' '-' %left '*' '/' 30 for look up in the symbol table. If the name appears in the table, a pointer to its location and its type ( %left '+' '-' %left '*' '/' 11 or %left '+' '-' %left '*' '/'
type subrange = (a) .. b; 52. If it is not already in the table, then it is installed as a %left '+' '-' %left '*' '/' 11 using %left '+' '-' %left '*' '/' 27. Again, a pointer and its type (which must be %left '+' '-' %left '*' '/'
type subrange = (a) .. b; 52. No change is needed in the handling of numeric values and arithmetic operators in type subrange = (a) .. b; 51. one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 19 one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 20 one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 1 one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 22 Bison generated a definition of type subrange = (a) .. b; 84 with a member named type subrange = (a) .. b; 86 to store value of type subrange = (a) .. b; 86 symbols. one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 23 one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 24 one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 25 one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 26 one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 1 one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 28 2.5.5 Thetype subrange = (a) .. b; 71 Main The error reporting function is unchanged, and the new version of type subrange = (a) .. b; 53 includes a call to %left '+' '-' %left '*' '/' 26 and sets the %left '+' '-' %left '*' '/' 48 on user demand (See , for details): one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 29 one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 1 one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 31 one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 32 one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 33 This program is both powerful and flexible. You may easily add new functions, and it is a simple job to modify this code to install predefined variables such as %left '+' '-' %left '*' '/' 49 or %left '+' '-' %left '*' '/' 50 as well. 2.6 Exercises
3 Bison Grammar FilesBison takes as input a context-free grammar specification and produces a C-language function that recognizes correct instances of the grammar. The Bison grammar file conventionally has a name ending in ‘.y’. See . 3.1 Outline of a Bison GrammarA Bison grammar file has four main sections, shown here with the appropriate delimiters: one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 34 Comments enclosed in ‘/* … */’ may appear in any of the sections. As a GNU extension, ‘//’ introduces a comment that continues until end of line. 3.1.1 The prologueThe Prologue section contains macro definitions and declarations of functions and variables that are used in the actions in the grammar rules. These are copied to the beginning of the parser implementation file so that they precede the definition of type subrange = (a) .. b; 52. You can use ‘ include’ to get the declarations from a header file. If you don’t need any C declarations, you may omit the ‘%{’ and ‘%}’ delimiters that bracket this section.The Prologue section is terminated by the first occurrence of ‘%}’ that is outside a comment, a string literal, or a character constant. You may have more than one Prologue section, intermixed with the Bison declarations. This allows you to have C and Bison declarations that refer to each other. For example, the %left '+' '-' %left '*' '/' 54 declaration may use types defined in a header file, and you may wish to prototype functions that take arguments of type type subrange = (a) .. b; 84. This can be done with two Prologue blocks, one before and one after the %left '+' '-' %left '*' '/' 54 declaration. one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 35 one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 1 one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 37 one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 1 one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 39 one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 40 When in doubt, it is usually safer to put prologue code before all Bison declarations, rather than after. For example, any definitions of feature test macros like %left '+' '-' %left '*' '/' 57 or %left '+' '-' %left '*' '/' 58 should appear before all Bison declarations, as feature test macros can affect the behavior of Bison-generated type subrange = (a) .. b; 66 directives. 3.1.2 Prologue AlternativesThe functionality of Prologue sections can often be subtle and inflexible. As an alternative, Bison provides a %left '+' '-' %left '*' '/' 60 directive with an explicit qualifier field, which identifies the purpose of the code and thus the location(s) where Bison should generate it. For C/C++, the qualifier can be omitted for the default location, or it can be one of %left '+' '-' %left '*' '/' 61, %left '+' '-' %left '*' '/' 62, %left '+' '-' %left '*' '/' 63. See . Look again at the example of the previous section: one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 35 one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 1 one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 37 one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 1 one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 39 one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 40 Notice that there are two Prologue sections here, but there’s a subtle distinction between their functionality. For example, if you decide to override Bison’s default definition for %token TYPE DOTDOT ID 94, in which Prologue section should you write your new definition? You should write it in the first since Bison will insert that code into the parser implementation file before the default %token TYPE DOTDOT ID 94 definition. In which Prologue section should you prototype an internal function, %left '+' '-' %left '*' '/' 66, that accepts %token TYPE DOTDOT ID 94 and %left '+' '-' %left '*' '/' 68 as arguments? You should prototype it in the second since Bison will insert that code after the %token TYPE DOTDOT ID 94 and %left '+' '-' %left '*' '/' 68 definitions. This distinction in functionality between the two Prologue sections is established by the appearance of the %left '+' '-' %left '*' '/' 54 between them. This behavior raises a few questions. First, why should the position of a %left '+' '-' %left '*' '/' 54 affect definitions related to %token TYPE DOTDOT ID 94 and %left '+' '-' %left '*' '/' 68? Second, what if there is no %left '+' '-' %left '*' '/' 54? In that case, the second kind of Prologue section is not available. This behavior is not intuitive. To avoid this subtle %left '+' '-' %left '*' '/' 54 dependency, rewrite the example using a %left '+' '-' %left '*' '/' 77 and an unqualified %left '+' '-' %left '*' '/' 60. Let’s go ahead and add the new %token TYPE DOTDOT ID 94 definition and the %left '+' '-' %left '*' '/' 66 prototype at the same time: one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 47 one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 37 one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 1 one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 50 one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 40 In this way, %left '+' '-' %left '*' '/' 77 and the unqualified %left '+' '-' %left '*' '/' 60 achieve the same functionality as the two kinds of Prologue sections, but it’s always explicit which kind you intend. Moreover, both kinds are always available even in the absence of %left '+' '-' %left '*' '/' 54. The %left '+' '-' %left '*' '/' 77 block above logically contains two parts. The first two lines before the warning need to appear near the top of the parser implementation file. The first line after the warning is required by type subrange = (a) .. b; 84 and thus also needs to appear in the parser implementation file. However, if you’ve instructed Bison to generate a parser header file (see ), you probably want that line to appear before the type subrange = (a) .. b; 84 definition in that header file as well. The %token TYPE DOTDOT ID 94 definition should also appear in the parser header file to override the default %token TYPE DOTDOT ID 94 definition there. In other words, in the %left '+' '-' %left '*' '/' 77 block above, all but the first two lines are dependency code required by the type subrange = (a) .. b; 84 and %token TYPE DOTDOT ID 94 definitions. Thus, they belong in one or more %left '+' '-' %left '*' '/' 92: one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 52 one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 1 one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 54 one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 37 one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 1 one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 57 one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 1 one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 50 one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 40 Now Bison will insert %left '+' '-' %left '*' '/' 93 and the new %token TYPE DOTDOT ID 94 definition before the Bison-generated type subrange = (a) .. b; 84 and %token TYPE DOTDOT ID 94 definitions in both the parser implementation file and the parser header file. (By the same reasoning, %left '+' '-' %left '*' '/' 92 would also be the appropriate place to write your own definition for type subrange = (a) .. b; 84.) When you are writing dependency code for type subrange = (a) .. b; 84 and %token TYPE DOTDOT ID 94, you should prefer %left '+' '-' %left '*' '/' 92 over %left '+' '-' %left '*' '/' 77 regardless of whether you instruct Bison to generate a parser header file. When you are writing code that you need Bison to insert only into the parser implementation file and that has no special need to appear at the top of that file, you should prefer the unqualified %left '+' '-' %left '*' '/' 60 over %% type_decl: TYPE ID '=' type ';' ; 04. These practices will make the purpose of each block of your code explicit to Bison and to other developers reading your grammar file. Following these practices, we expect the unqualified %left '+' '-' %left '*' '/' 60 and %left '+' '-' %left '*' '/' 92 to be the most important of the four Prologue alternatives. At some point while developing your parser, you might decide to provide %left '+' '-' %left '*' '/' 66 to modules that are external to your parser. Thus, you might wish for Bison to insert the prototype into both the parser header file and the parser implementation file. Since this function is not a dependency required by type subrange = (a) .. b; 84 or %token TYPE DOTDOT ID 94, it doesn’t make sense to move its prototype to a %left '+' '-' %left '*' '/' 92. More importantly, since it depends upon %token TYPE DOTDOT ID 94 and %left '+' '-' %left '*' '/' 68, %% type_decl: TYPE ID '=' type ';' ; 13 is not sufficient. Instead, move its prototype from the unqualified %left '+' '-' %left '*' '/' 60 to a %% type_decl: TYPE ID '=' type ';' ; 15: one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 52 one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 1 one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 54 one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 37 one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 1 one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 57 one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 1 one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 68 one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 1 one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 70 one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 40 Bison will insert the %left '+' '-' %left '*' '/' 66 prototype into both the parser header file and the parser implementation file after the definitions for %left '+' '-' %left '*' '/' 68, %token TYPE DOTDOT ID 94, and type subrange = (a) .. b; 84. The above examples are careful to write directives in an order that reflects the layout of the generated parser implementation and header files: %left '+' '-' %left '*' '/' 77, %left '+' '-' %left '*' '/' 92, %% type_decl: TYPE ID '=' type ';' ; 15, and then %left '+' '-' %left '*' '/' 60. While your grammar files may generally be easier to read if you also follow this order, Bison does not require it. Instead, Bison lets you choose an organization that makes sense to you. You may declare any of these directives multiple times in the grammar file. In that case, Bison concatenates the contained code in declaration order. This is the only way in which the position of one of these directives within the grammar file affects its functionality. The result of the previous two properties is greater flexibility in how you may organize your grammar file. For example, you may organize semantic-type-related directives by semantic type: one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 72 one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 1 one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 74 You could even place each of the above directive groups in the rules section of the grammar file next to the set of rules that uses the associated semantic type. (In the rules section, you must terminate each of those directives with a semicolon.) And you don’t have to worry that some directive (like a %left '+' '-' %left '*' '/'
This section has been concerned with explaining the advantages of the four Prologue alternatives over the original Yacc Prologue. However, in most cases when using these directives, you shouldn’t need to think about all the low-level ordering issues discussed here. Instead, you should simply use these directives to label each block of your code according to its purpose and let Bison handle the ordering. %left '+' '-' %left '*' '/' 60 is the most generic label. Move code to %left '+' '-' %left '*' '/' 92, %% type_decl: TYPE ID '=' type ';' ; 15, or %left '+' '-' %left '*' '/' 77 as needed. 3.1.3 The Bison Declarations SectionThe Bison declarations section contains declarations that define terminal and nonterminal symbols, specify precedence, and so on. In some simple grammars you may not need any declarations. See . 3.1.4 The Grammar Rules SectionThe grammar rules section contains one or more Bison grammar rules, and nothing else. See . There must always be at least one grammar rule, and the first ‘%%’ (which precedes the grammar rules) may never be omitted even if it is the first thing in the file. 3.1.5 The epilogueThe Epilogue is copied verbatim to the end of the parser implementation file, just as the Prologue is copied to the beginning. This is the most convenient place to put anything that you want to have in the parser implementation file but which need not come before the definition of type subrange = (a) .. b; 52. For example, the definitions of type subrange = (a) .. b; 51 and type subrange = (a) .. b; 56 often go here. Because C requires functions to be declared before being used, you often need to declare functions like type subrange = (a) .. b; 51 and type subrange = (a) .. b; 56 in the Prologue, even if you define them in the Epilogue. See . If the last section is empty, you may omit the ‘%%’ that separates it from the grammar rules. The Bison parser itself contains many macros and identifiers whose names start with ‘yy’ or ‘YY’, so it is a good idea to avoid using any such names (except those documented in this manual) in the epilogue of the grammar file. 3.2 Symbols, Terminal and NonterminalSymbols in Bison grammars represent the grammatical classifications of the language. A terminal symbol (also known as a token kind) represents a class of syntactically equivalent tokens. You use the symbol in grammar rules to mean that a token in that class is allowed. The symbol is represented in the Bison parser by a numeric code, and the type subrange = (a) .. b; 51 function returns a token kind code to indicate what kind of token has been read. You don’t need to know what the code value is; you can use the symbol to stand for it. A nonterminal symbol stands for a class of syntactically equivalent groupings. The symbol name is used in writing grammar rules. By convention, it should be all lower case. Symbol names can contain letters, underscores, periods, and non-initial digits and dashes. Dashes in symbol names are a GNU extension, incompatible with POSIX Yacc. Periods and dashes make symbol names less convenient to use with named references, which require brackets around such names (see ). Terminal symbols that contain periods or dashes make little sense: since they are not valid symbols (in most programming languages) they are not exported as token names. There are three ways of writing terminal symbols in the grammar:
How you choose to write a terminal symbol has no effect on its grammatical meaning. That depends only on where it appears in rules and on when the parser function returns that symbol. The value returned by type subrange = (a) .. b; 51 is always one of the terminal symbols, except that a zero or negative value signifies end-of-input. Whichever way you write the token kind in the grammar rules, you write it the same way in the definition of type subrange = (a) .. b; 51. The numeric code for a character token kind is simply the positive numeric code of the character, so type subrange = (a) .. b; 51 can use the identical value to generate the requisite code, though you may need to convert it to %% type_decl: TYPE ID '=' type ';' ; 47 to avoid sign-extension on hosts where %% type_decl: TYPE ID '=' type ';' ; 48 is signed. Each named token kind becomes a C macro in the parser implementation file, so type subrange = (a) .. b; 51 can use the name to stand for the code. (This is why periods don’t make sense in terminal symbols.) See . If type subrange = (a) .. b; 51 is defined in a separate file, you need to arrange for the token-kind definitions to be available there. Use the -d option when you run Bison, so that it will write these definitions into a separate header file name.tab.h which you can include in the other source files that need it. See . If you want to write a grammar that is portable to any Standard C host, you must use only nonnull character tokens taken from the basic execution character set of Standard C. This set consists of the ten digits, the 52 lower- and upper-case English letters, and the characters in the following C-language string: one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 75 The type subrange = (a) .. b; 51 function and Bison must use a consistent character set and encoding for character tokens. For example, if you run Bison in an ASCII environment, but then compile and run the resulting program in an environment that uses an incompatible character set like EBCDIC, the resulting program may not work because the tables generated by Bison will assume ASCII numeric values for character tokens. It is standard practice for software distributions to contain C source files that were generated by Bison in an ASCII environment, so installers on platforms that are incompatible with ASCII must rebuild those files before compiling them. The symbol type subrange = lo .. hi; type enum = (a, b, c); 84 is a terminal symbol reserved for error recovery (see ); you shouldn’t use it for any other purpose. In particular, type subrange = (a) .. b; 51 should never return this value. The default value of the error token is 256, unless you explicitly assigned 256 to one of your tokens with a %token TYPE DOTDOT ID 57 declaration. 3.3 Grammar RulesA Bison grammar is a list of rules. 3.3.1 Syntax of Grammar RulesA Bison grammar rule has the following general form: where result is the nonterminal symbol that this rule describes, and components are various terminal and nonterminal symbols that are put together by this rule (see ). For example, says that two groupings of type type subrange = (a) .. b; 88, with a ‘+’ token in between, can be combined into a larger grouping of type type subrange = (a) .. b; 88. White space in rules is significant only to separate symbols. You can add extra white space as you wish. Scattered among the components can be actions that determine the semantics of the rule. An action looks like this: This is an example of braced code, that is, C code surrounded by braces, much like a compound statement in C. Braced code can contain any sequence of C tokens, so long as its braces are balanced. Bison does not check the braced code for correctness directly; it merely copies the code to the parser implementation file, where the C compiler can check it. Within braced code, the balanced-brace count is not affected by braces within comments, string literals, or character constants, but it is affected by the C digraphs ‘<%’ and ‘%>’ that represent braces. At the top level braced code must be terminated by ‘}’ and not by a digraph. Bison does not look for trigraphs, so if braced code uses trigraphs you should ensure that they do not affect the nesting of braces or the boundaries of comments, string literals, or character constants. Usually there is only one action and it follows the components. See . Multiple rules for the same result can be written separately or can be joined with the vertical-bar character ‘|’ as follows: one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 76 They are still considered distinct rules even when joined in this way. 3.3.2 Empty RulesA rule is said to be empty if its right-hand side (components) is empty. It means that result in the previous example can match the empty string. As another example, here is how to define an optional semicolon: It is easy not to see an empty rule, especially when %% type_decl: TYPE ID '=' type ';' ; 58 is used. The %token TYPE DOTDOT ID 02 directive allows to make explicit that a rule is empty on purpose: one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 77 Flagging a non-empty rule with %token TYPE DOTDOT ID 02 is an error. If run with -Wempty-rule, %% type_decl: TYPE ID '=' type ';' ; 61 will report empty rules without %token TYPE DOTDOT ID 02. Using %token TYPE DOTDOT ID 02 enables this warning, unless -Wno-empty-rule was specified. The %token TYPE DOTDOT ID 02 directive is a Bison extension, it does not work with Yacc. To remain compatible with POSIX Yacc, it is customary to write a comment ‘/* empty */’ in each rule with no components: one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 78 3.3.3 Recursive RulesA rule is called recursive when its result nonterminal appears also on its right hand side. Nearly all Bison grammars need to use recursion, because that is the only way to define a sequence of any number of a particular thing. Consider this recursive definition of a comma-separated sequence of one or more expressions: one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 79 Since the recursive use of %% type_decl: TYPE ID '=' type ';' ; 65 is the leftmost symbol in the right hand side, we call this left recursion. By contrast, here the same construct is defined using right recursion: one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 80 Any kind of sequence can be defined using either left recursion or right recursion, but you should always use left recursion, because it can parse a sequence of any number of elements with bounded stack space. Right recursion uses up space on the Bison stack in proportion to the number of elements in the sequence, because all the elements must be shifted onto the stack before the rule can be applied even once. See , for further explanation of this. Indirect or mutual recursion occurs when the result of the rule does not appear directly on its right hand side, but does appear in rules for other nonterminals which do appear on its right hand side. For example: one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 81 one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 1 one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 83 defines two mutually-recursive nonterminals, since each refers to the other. 3.4 Defining Language SemanticsThe grammar rules for a language determine only the syntax. The semantics are determined by the semantic values associated with various tokens and groupings, and by the actions taken when various groupings are recognized. For example, the calculator calculates properly because the value associated with each expression is the proper number; it adds properly because the action for the grouping ‘x + y’ is to add the numbers associated with x and y. 3.4.1 Data Types of Semantic ValuesIn a simple program it may be sufficient to use the same data type for the semantic values of all language constructs. This was true in the RPN and infix calculator examples (see ). Bison normally uses the type type subrange = (a) .. b; 83 for semantic values if your program uses the same data type for all language constructs. To specify some other type, define the type subrange = (a) .. b; 80 variable type subrange = (a) .. b; 81 like this: one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 84 or one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 85 The value of type subrange = (a) .. b; 81 should be a type name that does not contain parentheses or square brackets. Alternatively in C, instead of relying of Bison’s type subrange = (a) .. b; 80 support, you may rely on the C preprocessor and define type subrange = (a) .. b; 84 as a macro: This macro definition must go in the prologue of the grammar file (see ). If compatibility with POSIX Yacc matters to you, use this. Note however that Bison cannot know type subrange = (a) .. b; 84’s value, not even whether it is defined, so there are services it cannot provide. Besides this works only for C. 3.4.2 More Than One Value TypeIn most programs, you will need different data types for different kinds of tokens and groupings. For example, a numeric constant may need type type subrange = (a) .. b; 83 or %% type_decl: TYPE ID '=' type ';' ; 74, while a string constant needs type %% type_decl: TYPE ID '=' type ';' ; 75, and an identifier might need a pointer to an entry in the symbol table. To use more than one data type for semantic values in one parser, Bison requires you to do two things:
3.4.3 Generating the Semantic Value TypeThe special value %left '+' '-' %left '*' '/' 06 of the type subrange = (a) .. b; 80 variable type subrange = (a) .. b; 81 instructs Bison that the type tags (used with the %token TYPE DOTDOT ID 57, %left '+' '-' %left '*' '/' 16 and %% type_decl: TYPE ID '=' type ';' ; 84 directives) are genuine types, not names of members of type subrange = (a) .. b; 84. For example: one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 86 generates an appropriate value of type subrange = (a) .. b; 84 to support each symbol type. The name of the member of type subrange = (a) .. b; 84 for tokens than have a declared identifier id (such as %% type_decl: TYPE ID '=' type ';' ; 94 and type subrange = lo .. hi; type enum = (a, b, c); 98 above, but not %% type_decl: TYPE ID '=' type ';' ;
%% type_decl: TYPE ID '=' type ';' ; 97. The other symbols have unspecified names on which you should not depend; instead, relying on C casts to access the semantic value with the appropriate type: one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 87 If the type subrange = (a) .. b; 80 variable %% type_decl: TYPE ID '=' type ';' ; 99 is defined (see ), then it is also used to prefix the union member names. For instance, with ‘%define api.token.prefix {TOK_}’: one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 88 This Bison extension cannot work if one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 000 (or -y/--yacc) is enabled, as POSIX mandates that Yacc generate tokens as macros (e.g., ‘ define INT 258’, or ‘define TOK_INT 258’).A similar feature is provided for C++ that in addition overcomes C++ limitations (that forbid non-trivial objects to be part of a %left '+' '-' %left '*' '/' 06): ‘%define api.value.type variant’, see . 3.4.4 The Union DeclarationThe %left '+' '-' %left '*' '/' 54 declaration specifies the entire collection of possible data types for semantic values. The keyword %left '+' '-' %left '*' '/' 54 is followed by braced code containing the same thing that goes inside a %left '+' '-' %left '*' '/' 06 in C. For example: one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 89 This says that the two alternative types are %token TYPE DOTDOT ID 26 and one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 006. They are given names one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 007 and one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 008; these names are used in the %token TYPE DOTDOT ID 57, %left '+' '-' %left '*' '/' 16 and %% type_decl: TYPE ID '=' type ';' ; 84 declarations to pick one of the types for a terminal or nonterminal symbol (see ). As an extension to POSIX, a tag is allowed after the %left '+' '-' %left '*' '/' 54. For example: one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 90 specifies the union tag one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 013, so the corresponding C type is one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 014. If you do not specify a tag, it defaults to type subrange = (a) .. b; 84 (see ). As another extension to POSIX, you may specify multiple %left '+' '-' %left '*' '/' 54 declarations; their contents are concatenated. However, only the first %left '+' '-' %left '*' '/' 54 declaration can specify a tag. Note that, unlike making a %left '+' '-' %left '*' '/' 06 declaration in C, you need not write a semicolon after the closing brace. 3.4.5 Providing a Structured Semantic Value TypeInstead of %left '+' '-' %left '*' '/' 54, you can define and use your own union type type subrange = (a) .. b; 84 if your grammar contains at least one ‘<type>’ tag. For example, you can put the following into a header file parser.h: one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 91 and then your grammar can use the following instead of %left '+' '-' %left '*' '/' 54: one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 92 Actually, you may also provide a one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 022 rather that a %left '+' '-' %left '*' '/' 06, which may be handy if you want to track information for every symbol (such as preceding comments). The type you provide may even be structured and include pointers, in which case the type tags you provide may be composite, with ‘.’ and ‘->’ operators. 3.4.6 ActionsAn action accompanies a syntactic rule and contains C code to be executed each time an instance of that rule is recognized. The task of most actions is to compute a semantic value for the grouping built by the rule from the semantic values associated with tokens or smaller groupings. An action consists of braced code containing C statements, and can be placed at any position in the rule; it is executed at that position. Most rules have just one action at the end of the rule, following all the components. Actions in the middle of a rule are tricky and used only for special purposes (see ). The C code in an action can refer to the semantic values of the components matched by the rule with the construct one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 024, which stands for the value of the nth component. The semantic value for the grouping being constructed is type subrange = (a) .. b; 91. In addition, the semantic values of symbols can be accessed with the named references construct one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 026 or one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 027. Bison translates both of these constructs into expressions of the appropriate type when it copies the actions into the parser implementation file. type subrange = (a) .. b; 91 (or one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 026, when it stands for the current grouping) is translated to a modifiable lvalue, so it can be assigned to. Here is a typical example: one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 93 Or, in terms of named references: one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 94 This rule constructs an type subrange = (a) .. b; 88 from two smaller type subrange = (a) .. b; 88 groupings connected by a plus-sign token. In the action, type subrange = (a) .. b; 93 and %token TYPE DOTDOT ID 19 ( one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 034 and one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>.
type subrange = (a) .. b; 88 groupings, which are the first and third symbols on the right hand side of the rule. The sum is stored into type subrange = (a) .. b; 91 ( one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>.
type subrange = (a) .. b; 94. See , for more information about using the named references construct. Note that the vertical-bar character ‘|’ is really a rule separator, and actions are attached to a single rule. This is a difference with tools like Flex, for which ‘|’ stands for either “or”, or “the same action as that of the next rule”. In the following example, the action is triggered only when ‘b’ is found: one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 95 If you don’t specify an action for a rule, Bison supplies a default: one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 040. Thus, the value of the first symbol in the rule becomes the value of the whole rule. Of course, the default action is valid only if the two data types match. There is no meaningful default action for an empty rule; every empty rule must have an explicit action unless the rule’s value does not matter. one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 024 with n zero or negative is allowed for reference to tokens and groupings on the stack before those that match the current rule. This is a very risky practice, and to use it reliably you must be certain of the context in which the rule is applied. Here is a case in which you can use this reliably: one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 96 one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 1 one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 98 As long as one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 042 is used only in the fashion shown here, one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 043 always refers to the type subrange = lo .. hi; type enum = (a, b, c); 77 which precedes one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 042 in the definition of one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 046. It is also possible to access the semantic value of the lookahead token, if any, from a semantic action. This semantic value is stored in type subrange = (a) .. b; 27. See . 3.4.7 Data Types of Values in ActionsIf you have chosen a single data type for semantic values, the type subrange = (a) .. b; 91 and one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 024 constructs always have that data type. If you have used %left '+' '-' %left '*' '/' 54 to specify a variety of data types, then you must declare a choice among these types for each terminal or nonterminal symbol that can have a semantic value. Then each time you use type subrange = (a) .. b; 91 or one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 024, its data type is determined by which symbol it refers to in the rule. In this example, one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 99 type subrange = (a) .. b; 93 and %token TYPE DOTDOT ID 19 refer to instances of type subrange = (a) .. b; 88, so they all have the data type declared for the nonterminal symbol type subrange = (a) .. b; 88. If type subrange = (a) .. b; 94 were used, it would have the data type declared for the terminal symbol %token TYPE DOTDOT ID 18, whatever that might be. Alternatively, you can specify the data type when you refer to the value, by inserting ‘<type>’ after the ‘$’ at the beginning of the reference. For example, if you have defined types as shown here: program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 00 then you can write one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 059 to refer to the first subunit of the rule as an integer, or one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 060 to refer to it as a double. 3.4.8 Actions in MidruleOccasionally it is useful to put an action in the middle of a rule. These actions are written just like usual end-of-rule actions, but they are executed before the parser even recognizes the following components. 3.4.8.1 Using Midrule ActionsA midrule action may refer to the components preceding it using one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 024, but it may not refer to subsequent components because it is run before they are parsed. The midrule action itself counts as one of the components of the rule. This makes a difference when there is another action later in the same rule (and usually there is another at the end): you have to count the actions along with the symbols when working out which number n to use in one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 024. The midrule action can also have a semantic value. The action can set its value with an assignment to type subrange = (a) .. b; 91, and actions later in the rule can refer to the value using one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 024. Since there is no symbol to name the action, there is no way to declare a data type for the value in advance, so you must use the ‘$<…>n’ construct to specify a data type each time you refer to this value. There is no way to set the value of the entire rule with a midrule action, because assignments to type subrange = (a) .. b; 91 do not have that effect. The only way to set the value for the entire rule is with an ordinary action at the end of the rule. Here is an example from a hypothetical compiler, handling a one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 066 statement that looks like ‘let (variable) statement’ and serves to create a variable named variable temporarily for the duration of statement. To parse this construct, we must put variable into the symbol table while statement is parsed, then remove it afterward. Here is how it is done: program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 01 As soon as ‘let (variable)’ has been recognized, the first action is run. It saves a copy of the current semantic context (the list of accessible variables) as its semantic value, using alternative one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 067 in the data-type union. Then it calls one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 068 to add the new variable to that list. Once the first action is finished, the embedded statement type subrange = lo .. hi; type enum = (a, b, c); 78 can be parsed. Note that the midrule action is component number 5, so the ‘stmt’ is component number 6. Named references can be used to improve the readability and maintainability (see ): program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 02 After the embedded statement is parsed, its semantic value becomes the value of the entire one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 066-statement. Then the semantic value from the earlier action is used to restore the prior list of variables. This removes the temporary one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 066-variable from the list so that it won’t appear to exist while the rest of the program is parsed. Because the types of the semantic values of midrule actions are unknown to Bison, type-based features (e.g., ‘%printer’, ‘%destructor’) do not work, which could result in memory leaks. They also forbid the use of the one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 072 implementation of the type subrange = (a) .. b; 81 in C++ (see ). See , for one way to address this issue, and , for another: turning mid-action actions into regular actions. 3.4.8.2 Typed Midrule ActionsIn the above example, if the parser initiates error recovery (see ) while parsing the tokens in the embedded statement type subrange = lo .. hi; type enum = (a, b, c); 78, it might discard the previous semantic context one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 075 without restoring it. Thus, one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 075 needs a destructor (see ), and Bison needs the type of the semantic value ( one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>.
As an extension to Yacc’s midrule actions, Bison offers a means to type their semantic value: specify its type tag (‘<...>’ before the midrule action. Consider the previous example, with an untyped midrule action: program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 03 If instead you write: program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 04 then one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 078 and one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 079 work properly (no more leaks!), C++ one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 072s can be used, and redundancy is reduced ( one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 081 is specified once). 3.4.8.3 Midrule Action TranslationMidrule actions are actually transformed into regular rules and actions. The various reports generated by Bison (textual, graphical, etc., see ) reveal this translation, best explained by means of an example. The following rule: program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 05 is translated into: program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 06 with new nonterminal symbols one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 082, where n is a number. A midrule action is expected to generate a value if it uses type subrange = (a) .. b; 91, or the (final) action uses one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 024 where n denote the midrule action. In that case its nonterminal is rather named %token TYPE DOTDOT ID 85: program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 07 is translated into program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 08 There are probably two errors in the above example: the first midrule action does not generate a value (it does not use type subrange = (a) .. b; 91 although the final action uses it), and the value of the second one is not used (the final action does not use %token TYPE DOTDOT ID 19). Bison reports these errors when the one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 088 warnings are enabled (see ): program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 09 program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 10 program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 11 It is sometimes useful to turn midrule actions into regular actions, e.g., to factor them, or to escape from their limitations. For instance, as an alternative to typed midrule action, you may bury the midrule action inside a nonterminal symbol and to declare a printer and a destructor for that symbol: program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 12 program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 13 program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 14 one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 1 program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 16 3.4.8.4 Conflicts due to Midrule ActionsTaking action before a rule is completely recognized often leads to conflicts since the parser must commit to a parse in order to execute the action. For example, the following two rules, without midrule actions, can coexist in a working parser because the parser can shift the open-brace token and look at what follows before deciding whether there is a declaration or not: program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 17 But when we add a midrule action as follows, the rules become nonfunctional: program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 18 program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 19 Now the parser is forced to decide whether to run the midrule action when it has read no farther than the open-brace. In other words, it must commit to using one rule or the other, without sufficient information to do it correctly. (The open-brace token is what is called the lookahead token at this time, since the parser is still deciding what to do about it. See .) You might think that you could correct the problem by putting identical actions into the two rules, like this: program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 20 But this does not help, because Bison does not realize that the two actions are identical. (Bison never tries to understand the C code in an action.) If the grammar is such that a declaration can be distinguished from a statement by the first token (which is true in C), then one solution which does work is to put the action after the open-brace, like this: program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 21 Now the first token of the following declaration or statement, which would in any case tell Bison which rule to use, can still do so. Another solution is to bury the action inside a nonterminal symbol which serves as a subroutine: program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 22 one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 1 program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 24 Now Bison can execute the action in the rule for one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 089 without deciding which rule for one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 090 it will eventually use. 3.5 Tracking LocationsThough grammar rules and semantic actions are enough to write a fully functional parser, it can be useful to process some additional information, especially symbol locations. The way locations are handled is defined by providing a data type, and actions to take when rules are matched. 3.5.1 Data Type of LocationsDefining a data type for locations is much simpler than for semantic values, since all tokens and groupings always use the same type. The location type is specified using ‘%define api.location.type’: program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 25 This defines, in the C generated code, the %token TYPE DOTDOT ID 94 type name. When %token TYPE DOTDOT ID 94 is not defined, Bison uses a default structure type with four members: program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 26 In C, you may also specify the type of locations by defining a macro called %token TYPE DOTDOT ID 94, just as you can specify the semantic value type by defining a type subrange = (a) .. b; 84 macro (see ). However, rather than using macros, we recommend the type subrange = (a) .. b; 81 and one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 096 type subrange = (a) .. b; 80 variables. Default locations represent a range in the source file(s), but this is not a requirement. It could be a single point or just a line number, or even more complex structures. When the default location type is used, Bison initializes all these fields to 1 for type subrange = (a) .. b; 28 at the beginning of the parsing. To initialize type subrange = (a) .. b; 28 with a custom location type (or to chose a different initialization), use the one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 100 directive. See . 3.5.2 Actions and LocationsActions are not only useful for defining language semantics, but also for describing the behavior of the output parser with locations. The most obvious way for building locations of syntactic groupings is very similar to the way semantic values are computed. In a given rule, several constructs can be used to access the locations of the elements being matched. The location of the nth component of the right hand side is %token TYPE DOTDOT ID 85, while the location of the left hand side grouping is type subrange = (a) .. b; 47. In addition, the named references construct one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 103 and one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 104 may also be used to address the symbol locations. See , for more information about using the named references construct. Here is a basic example using the default data type for locations: program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 27 As for semantic values, there is a default action for locations that is run each time a rule is matched. It sets the beginning of type subrange = (a) .. b; 47 to the beginning of the first symbol, and the end of type subrange = (a) .. b; 47 to the end of the last symbol. With this default action, the location tracking can be fully automatic. The example above simply rewrites this way: program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 28 It is also possible to access the location of the lookahead token, if any, from a semantic action. This location is stored in type subrange = (a) .. b; 28. See . 3.5.3 Printing LocationsWhen using the default location type, the debug traces report the symbols’ location. The generated parser does so using the one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 108 macro. Macro: YYLOCATION_PRINT (file, loc) one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 109 When traces are enabled, print loc (of type ‘YYLTYPE const *’) on file (of type ‘FILE *’). Do nothing when traces are disabled, or if the location type is user defined. To get locations in the debug traces with your user-defined location types, define the one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 108 macro. For instance: program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 29 3.5.4 Default Action for LocationsActually, actions are not the best place to compute locations. Since locations are much more general than semantic values, there is room in the output parser to redefine the default action to take for each rule. The one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 111 macro is invoked each time a rule is matched, before the associated action is run. It is also invoked while processing a syntax error, to compute the error’s location. Before reporting an unresolvable syntactic ambiguity, a GLR parser invokes one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 111 recursively to compute the location of that ambiguity. Most of the time, this macro is general enough to suppress location dedicated code from semantic actions. The one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 111 macro takes three parameters. The first one is the location of the grouping (the result of the computation). When a rule is matched, the second parameter identifies locations of all right hand side elements of the rule being matched, and the third parameter is the size of the rule’s right hand side. When a GLR parser reports an ambiguity, which of multiple candidate right hand sides it passes to one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 111 is undefined. When processing a syntax error, the second parameter identifies locations of the symbols that were discarded during error processing, and the third parameter is the number of discarded symbols. By default, one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 111 is defined this way: program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 30 where one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 116 is the location of the kth symbol in rhs when k is positive, and the location of the symbol just before the reduction when k and n are both zero. When defining one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 111, you should consider that:
3.6 Named ReferencesAs described in the preceding sections, the traditional way to refer to any semantic value or location is a positional reference, which takes the form one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 024, type subrange = (a) .. b; 91, %token TYPE DOTDOT ID 85, and type subrange = (a) .. b; 47. However, such a reference is not very descriptive. Moreover, if you later decide to insert or remove symbols in the right-hand side of a grammar rule, the need to renumber such references can be tedious and error-prone. To avoid these issues, you can also refer to a semantic value or location using a named reference. First of all, original symbol names may be used as named references. For example: program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 31 Positional and named references can be mixed arbitrarily. For example: program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 32 However, sometimes regular symbol names are not sufficient due to ambiguities: program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 33 When ambiguity occurs, explicitly declared names may be used for values and locations. Explicit names are declared as a bracketed name after a symbol appearance in rule definitions. For example: program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 34 In order to access a semantic value generated by a midrule action, an explicit name may also be declared by putting a bracketed name after the closing brace of the midrule action code: program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 35 In references, in order to specify names containing dots and dashes, an explicit bracketed syntax one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 027 and one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 104 must be used: program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 36 It often happens that named references are followed by a dot, dash or other C punctuation marks and operators. By default, Bison will read ‘$name.suffix’ as a reference to symbol value one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 026 followed by ‘.suffix’, i.e., an access to the one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 126 field of the semantic value. In order to force Bison to recognize ‘name.suffix’ in its entirety as the name of a semantic value, the bracketed syntax ‘$[name.suffix]’ must be used. 3.7 Bison DeclarationsThe Bison declarations section of a Bison grammar defines the symbols used in formulating the grammar and the data types of semantic values. See . All token kind names (but not single-character literal tokens such as %token TYPE DOTDOT ID 18 and one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>.
The first rule in the grammar file also specifies the start symbol, by default. If you want some other symbol to be the start symbol, you must declare it explicitly (see ). 3.7.1 Require a Version of BisonYou may require the minimum version of Bison to process the grammar. If the requirement is not met, %% type_decl: TYPE ID '=' type ';' ; 61 exits with an error (exit status 63). Some deprecated behaviors are disabled for some required version: one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 130 (or better) The C++ deprecated files position.hh and stack.hh are no longer generated. 3.7.2 Token Kind NamesThe basic way to declare a token kind name (terminal symbol) is as follows: Bison will convert this into a definition in the parser, so that the function type subrange = (a) .. b; 51 (if it is in this file) can use the name name to stand for this token kind’s code. Alternatively, you can use %token TYPE DOTDOT ID 54, %token TYPE DOTDOT ID 56, %token TYPE DOTDOT ID 59, or one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 135 instead of %token TYPE DOTDOT ID 57, if you wish to specify associativity and precedence. See . However, for clarity, we recommend to use these directives only to declare associativity and precedence, and not to add string aliases, semantic types, etc. You can explicitly specify the numeric code for a token kind by appending a nonnegative decimal or hexadecimal integer value in the field immediately following the token name: program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 37 It is generally best, however, to let Bison choose the numeric codes for all token kinds. Bison will automatically select codes that don’t conflict with each other or with normal characters. In the event that the stack type is a union, you must augment the %token TYPE DOTDOT ID 57 or other token declaration to include the data type alternative delimited by angle-brackets (see ). For example: program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 38 You can associate a literal string token with a token kind name by writing the literal string at the end of a %token TYPE DOTDOT ID 57 declaration which declares the name. For example: For example, a grammar for the C language might specify these names with equivalent literal string tokens: program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 39 Once you equate the literal string and the token kind name, you can use them interchangeably in further declarations or the grammar rules. The type subrange = (a) .. b; 51 function can use the token name or the literal string to obtain the token kind code (see ). String aliases allow for better error messages using the literal strings instead of the token names, such as ‘syntax error, unexpected ||, expecting number or (’ rather than ‘syntax error, unexpected OR, expecting NUM or LPAREN’. String aliases may also be marked for internationalization (see ): program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 40 would produce in French ‘erreur de syntaxe, || inattendu, attendait nombre ou (’ rather than ‘erreur de syntaxe, || inattendu, attendait number ou (’. 3.7.3 Operator PrecedenceUse the %token TYPE DOTDOT ID 54, %token TYPE DOTDOT ID 56, one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 135, or %token TYPE DOTDOT ID 59 declaration to declare a token and specify its precedence and associativity, all at once. These are called precedence declarations. See , for general information on operator precedence. The syntax of a precedence declaration is nearly the same as that of %token TYPE DOTDOT ID 57: either or And indeed any of these declarations serves the purposes of %token TYPE DOTDOT ID 57. But in addition, they specify the associativity and relative precedence for all the symbols:
For backward compatibility, there is a confusing difference between the argument lists of %token TYPE DOTDOT ID 57 and precedence declarations. Only a %token TYPE DOTDOT ID 57 can associate a literal string with a token kind name. A precedence declaration always interprets a literal string as a reference to a separate token. For example: program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 41 3.7.4 Nonterminal SymbolsWhen you use %left '+' '-' %left '*' '/' 54 to specify multiple value types, you must declare the value type of each nonterminal symbol for which values are used. This is done with a %% type_decl: TYPE ID '=' type ';' ; 84 declaration, like this: program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 42 Here nonterminal is the name of a nonterminal symbol, and type is the name given in the %left '+' '-' %left '*' '/' 54 to the alternative that you want (see ). You can give any number of nonterminal symbols in the same %% type_decl: TYPE ID '=' type ';' ; 84 declaration, if they have the same value type. Use spaces to separate the symbol names. While POSIX Yacc allows %% type_decl: TYPE ID '=' type ';' ; 84 only for nonterminals, Bison accepts that this directive be also applied to terminal symbols. To declare exclusively nonterminal symbols, use the safer %left '+' '-' %left '*' '/' 16: program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 43 3.7.5 Syntax of Symbol DeclarationsThe syntax of the various directives to declare symbols is as follows. program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 44 where tag denotes a type tag such as ‘<ival>’, id denotes an identifier such as ‘NUM’, number a decimal or hexadecimal integer such as ‘300’ or ‘0x12d’, char a character literal such as ‘'+'’, and string a string literal such as ‘"number"’. The postfix quantifiers are ‘?’ (zero or one), ‘*’ (zero or more) and ‘+’ (one or more). The directives %token TYPE DOTDOT ID 59, %token TYPE DOTDOT ID 56 and one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 135 behave like %token TYPE DOTDOT ID 54. 3.7.6 Performing Actions before ParsingSometimes your parser needs to perform some initializations before parsing. The one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 100 directive allows for such arbitrary code. Directive: %initial-action { code } Declare that the braced code must be invoked before parsing each time type subrange = (a) .. b; 52 is called. The code may use type subrange = (a) .. b; 91 (or one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>.
type subrange = (a) .. b; 47 — initial value and location of the lookahead — and the one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 168. For instance, if your locations use a file name, you may use program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 45 3.7.7 Freeing Discarded SymbolsDuring error recovery (see ), symbols already pushed on the stack and tokens coming from the rest of the file are discarded until the parser falls on its feet. If the parser runs out of memory, or if it returns via one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 169, one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 170 or one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 171, all the symbols on the stack must be discarded. Even if the parser succeeds, it must discard the start symbol. When discarded symbols convey heap based information, this memory is lost. While this behavior can be tolerable for batch parsers, such as in traditional compilers, it is unacceptable for programs like shells or protocol implementations that may parse and execute indefinitely. The one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 079 directive defines code that is called when a symbol is automatically discarded. Directive: %destructor { code } symbols Invoke the braced code whenever the parser discards one of the symbols. Within code, type subrange = (a) .. b; 91 (or one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>.
type subrange = (a) .. b; 47 designates its location. The additional parser parameters are also available (see ). When a symbol is listed among symbols, its one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 079 is called a per-symbol one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 079. You may also define a per-type one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 079 by listing a semantic type tag among symbols. In that case, the parser will invoke this code whenever it discards any grammar symbol that has that semantic type tag unless that symbol has its own per-symbol one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 079. Finally, you can define two different kinds of default one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 079s. You can place each of one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 182 and one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 183 in the symbols list of exactly one one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 079 declaration in your grammar file. The parser will invoke the code associated with one of these whenever it discards any user-defined grammar symbol that has no per-symbol and no per-type one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 079. The parser uses the code for one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 182 in the case of such a grammar symbol for which you have formally declared a semantic type tag ( %token TYPE DOTDOT ID 57, %left '+' '-' %left '*' '/' 16, and %% type_decl: TYPE ID '=' type ';' ; 84 count as such a declaration, but one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 166 does not). The parser uses the code for one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 183 in the case of such a grammar symbol that has no declared semantic type tag. For example: program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 46 guarantees that, when the parser discards any user-defined symbol that has a semantic type tag other than one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 192, it passes its semantic value to one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 193 by default. However, when the parser discards a one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 194 or a one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 195, it uses the third one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 079, which frees it and prints its line number to one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 197 ( one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 193 is invoked only once). Finally, the parser merely prints a message whenever it discards any symbol, such as one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 199, that has no semantic type tag. A Bison-generated parser invokes the default one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 079s only for user-defined as opposed to Bison-defined symbols. For example, the parser will not invoke either kind of default one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 079 for the special Bison-defined symbols one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 202, one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 203, or one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 204 (see ), none of which you can reference in your grammar. It also will not invoke either for the type subrange = lo .. hi; type enum = (a, b, c); 84 token (see ), which is always defined by Bison regardless of whether you reference it in your grammar. However, it may invoke one of them for the end token (token 0) if you redefine it from one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 204 to, for example, one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 207: Finally, Bison will never invoke a one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 079 for an unreferenced midrule semantic value (see ). That is, Bison does not consider a midrule to have a semantic value if you do not reference type subrange = (a) .. b; 91 in the midrule’s action or one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 024 (where n is the right-hand side symbol position of the midrule) in any later action in that rule. However, if you do reference either, the Bison-generated parser will invoke the one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 183 one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 079 whenever it discards the midrule symbol. Discarded symbols are the following:
The parser can return immediately because of an explicit call to one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 169, one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 170 or one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 171, or failed error recovery, or memory exhaustion. Right-hand side symbols of a rule that explicitly triggers a syntax error via type subrange = (a) .. b; 34 are not discarded automatically. As a rule of thumb, destructors are invoked only when user actions cannot manage the memory. 3.7.8 Printing Semantic ValuesWhen run-time traces are enabled (see ), the parser reports its actions, such as reductions. When a symbol involved in an action is reported, only its kind is displayed, as the parser cannot know how semantic values should be formatted. The one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 078 directive defines code that is called when a symbol is reported. Its syntax is the same as one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 079 (see ). Directive: %printer { code } symbols Invoke the braced code whenever the parser displays one of the symbols. Within code, one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 220 denotes the output stream (a one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 221 in C, an one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 222 in C++, and one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 197 in D), type subrange = (a) .. b; 91 (or one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>.
type subrange = (a) .. b; 47 its location. The additional parser parameters are also available (see ). The symbols are defined as for one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 079 (see .): they can be per-type (e.g., ‘<ival>’), per-symbol (e.g., ‘exp’, ‘NUM’, ‘"float"’), typed per-default (i.e., ‘<*>’, or untyped per-default (i.e., ‘<>’). For example: program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 47 guarantees that, when the parser print any symbol that has a semantic type tag other than one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 192, it display the address of the semantic value by default. However, when the parser displays a one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 194 or a one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 195, it formats it as a string in double quotes. It performs only the second one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 078 in this case, so it prints only once. Finally, the parser print ‘<>’ for any symbol, such as one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 199, that has no semantic type tag. See , for a complete example. 3.7.9 Suppressing Conflict WarningsBison normally warns if there are any conflicts in the grammar (see ), but most real grammars have harmless shift/reduce conflicts which are resolved in a predictable way and would be difficult to eliminate. It is desirable to suppress the warning about these conflicts unless the number of conflicts changes. You can do this with the one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 235 declaration. The declaration looks like this: Here n is a decimal integer. The declaration says there should be n shift/reduce conflicts and no reduce/reduce conflicts. Bison reports an error if the number of shift/reduce conflicts differs from n, or if there are any reduce/reduce conflicts. For deterministic parsers, reduce/reduce conflicts are more serious, and should be eliminated entirely. Bison will always report reduce/reduce conflicts for these parsers. With GLR parsers, however, both kinds of conflicts are routine; otherwise, there would be no need to use GLR parsing. Therefore, it is also possible to specify an expected number of reduce/reduce conflicts in GLR parsers, using the declaration: You may wish to be more specific in your specification of expected conflicts. To this end, you can also attach one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 235 and one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 237 modifiers to individual rules. The interpretation of these modifiers differs from their use as declarations. When attached to rules, they indicate the number of states in which the rule is involved in a conflict. You will need to consult the output resulting from -v to determine appropriate numbers to use. For example, for the following grammar fragment, the first rule for one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 238 appears in two states in which the ‘[’ token is a lookahead. Having determined that, you can document this fact with an one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 235 modifier as follows: program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 48 Mid-rule actions generate implicit rules that are also subject to conflicts (see ). To attach an one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 235 or one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 237 annotation to an implicit mid-rule action’s rule, put it before the action. For example, program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 49 Here, the appropriate mid-rule action will not be determined until after the ‘(’ token is shifted. Thus, the two actions will clash with each other, and we should expect one reduce/reduce conflict for each. In general, using one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 235 involves these steps:
Now Bison will report an error if you introduce an unexpected conflict, but will keep silent otherwise. 3.7.10 The Start-SymbolBison assumes by default that the start symbol for the grammar is the first nonterminal specified in the grammar specification section. The programmer may override this restriction with the one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 248 declaration as follows: 3.7.11 A Pure (Reentrant) ParserA reentrant program is one which does not alter in the course of execution; in other words, it consists entirely of pure (read-only) code. Reentrancy is important whenever asynchronous execution is possible; for example, a nonreentrant program may not be safe to call from a signal handler. In systems with multiple threads of control, a nonreentrant program must be called only within interlocks. Normally, Bison generates a parser which is not reentrant. This is suitable for most uses, and it permits compatibility with Yacc. (The standard Yacc interfaces are inherently nonreentrant, because they use statically allocated variables for communication with type subrange = (a) .. b; 51, including type subrange = (a) .. b; 27 and type subrange = (a) .. b; 28.) Alternatively, you can generate a pure, reentrant parser. The Bison declaration ‘%define api.pure’ says that you want the parser to be reentrant. It looks like this: The result is that the communication variables type subrange = (a) .. b; 27 and type subrange = (a) .. b; 28 become local variables in type subrange = (a) .. b; 52, and a different calling convention is used for the lexical analyzer function type subrange = (a) .. b; 51. See , for the details of this. The variable one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 256 becomes local in type subrange = (a) .. b; 52 in pull mode but it becomes a member of one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 258 in push mode. (see ). The convention for calling type subrange = (a) .. b; 52 itself is unchanged. Whether the parser is pure has nothing to do with the grammar rules. You can generate either a pure parser or a nonreentrant parser from any valid grammar. 3.7.12 A Push ParserA pull parser is called once and it takes control until all its input is completely parsed. A push parser, on the other hand, is called each time a new token is made available. A push parser is typically useful when the parser is part of a main event loop in the client’s application. This is typically a requirement of a GUI, when the main event loop needs to be triggered within a certain time period. Normally, Bison generates a pull parser. The following Bison declaration says that you want the parser to be a push parser (see ): program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 50 In almost all cases, you want to ensure that your push parser is also a pure parser (see ). The only time you should create an impure push parser is to have backwards compatibility with the impure Yacc pull mode interface. Unless you know what you are doing, your declarations should look like this: program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 51 There is a major notable functional difference between the pure push parser and the impure push parser. It is acceptable for a pure push parser to have many parser instances, of the same type of parser, in memory at the same time. An impure push parser should only use one parser at a time. When a push parser is selected, Bison will generate some new symbols in the generated parser. one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 258 is a structure that the generated parser uses to store the parser’s state. one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 262 is the function that will create a new parser instance. one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 263 will free the resources associated with the corresponding parser instance. Finally, one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 264 is the function that should be called whenever a token is available to provide the parser. A trivial example of using a pure push parser would look like this: program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 52 If the user decided to use an impure push parser, a few things about the generated parser will change. The type subrange = (a) .. b; 23 variable becomes a global variable instead of a local one in the one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 264 function. For this reason, the signature of the one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 264 function is changed to remove the token as a parameter. A nonreentrant push parser example would thus look like this: program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 53 That’s it. Notice the next token is put into the global variable type subrange = (a) .. b; 23 for use by the next invocation of the one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 264 function. Bison also supports both the push parser interface along with the pull parser interface in the same generated parser. In order to get this functionality, you should replace the ‘%define api.push-pull push’ declaration with the ‘%define api.push-pull both’ declaration. Doing this will create all of the symbols mentioned earlier along with the two extra symbols, type subrange = (a) .. b; 52 and one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 271. type subrange = (a) .. b; 52 can be used exactly as it normally would be used. However, the user should note that it is implemented in the generated parser by calling one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 271. This makes the type subrange = (a) .. b; 52 function that is generated with the ‘%define api.push-pull both’ declaration slower than the normal type subrange = (a) .. b; 52 function. If the user calls the one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 271 function it will parse the rest of the input stream. It is possible to one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 264 tokens to select a subgrammar and then one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 271 the rest of the input stream. If you would like to switch back and forth between between parsing styles, you would have to write your own one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 271 function that knows when to quit looking for input. An example of using the one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 271 function would look like this: program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 54 Adding the ‘%define api.pure’ declaration does exactly the same thing to the generated parser with ‘%define api.push-pull both’ as it did for ‘%define api.push-pull push’. 3.7.13 Bison Declaration SummaryHere is a summary of the declarations used to define a grammar: Directive: %union Declare the collection of data types that semantic values may have (see ). Directive: %token Declare a terminal symbol (token kind name) with no precedence or associativity specified (see ). Directive: %right Declare a terminal symbol (token kind name) that is right-associative (see ). Directive: %left Declare a terminal symbol (token kind name) that is left-associative (see ). Directive: %nonassoc Declare a terminal symbol (token kind name) that is nonassociative (see ). Using it in a way that would be associative is a syntax error. Directive: %nterm Declare the type of semantic values for a nonterminal symbol (see ). Directive: %type Declare the type of semantic values for a symbol (see ). Directive: %start Specify the grammar’s start symbol (see ). Directive: %expect Declare the expected number of shift/reduce conflicts, either overall or for a given rule (see ). Directive: %expect-rr Declare the expected number of reduce/reduce conflicts, either overall or for a given rule (see ). In order to change the behavior of %% type_decl: TYPE ID '=' type ';' ; 61, use the following directives: Directive: %code {code} Directive: %code qualifier {code} Insert code verbatim into the output parser source at the default location or at the location specified by qualifier. See . Directive: %debug Instrument the parser for traces. Obsoleted by ‘%define parse.trace’. See . Directive: %define variable Directive: %define variable value Directive: %define variable {value} Directive: %define variable "value" Define a variable to adjust Bison’s behavior. See . Directive: %defines Directive: %defines defines-file Historical name for one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 282. See . Directive: %destructor Specify how the parser should reclaim the memory associated to discarded symbols. See . Directive: %file-prefix "prefix" Specify a prefix to use for all Bison output file names. The names are chosen as if the grammar file were named prefix.y. Write a parser header file containing definitions for the token kind names defined in the grammar as well as a few other declarations. If the parser implementation file is named name.c then the parser header file is named name.h. For C parsers, the parser header file declares type subrange = (a) .. b; 84 unless type subrange = (a) .. b; 84 is already defined as a macro or you have used a one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 286 tag without using %left '+' '-' %left '*' '/' 54. Therefore, if you are using a %left '+' '-' %left '*' '/' 54 (see ) with components that require other definitions, or if you have defined a type subrange = (a) .. b; 84 macro or type definition (see ), you need to arrange for these definitions to be propagated to all modules, e.g., by putting them in a prerequisite header that is included both by your parser and by any other module that needs type subrange = (a) .. b; 84. Unless your parser is pure, the parser header file declares type subrange = (a) .. b; 27 as an external variable. See . If you have also used locations, the parser header file declares %token TYPE DOTDOT ID 94 and type subrange = (a) .. b; 28 using a protocol similar to that of the type subrange = (a) .. b; 84 macro and type subrange = (a) .. b; 27. See . This parser header file is normally essential if you wish to put the definition of type subrange = (a) .. b; 51 in a separate source file, because type subrange = (a) .. b; 51 typically needs to be able to refer to the above-mentioned declarations and to the token kind codes. See . If you have declared %left '+' '-' %left '*' '/' 92 or %% type_decl: TYPE ID '=' type ';' ; 15, the output header also contains their code. See . The generated header is protected against multiple inclusions with a C preprocessor guard: ‘YY_PREFIX_FILE_INCLUDED’, where PREFIX and FILE are the prefix (see ) and generated file name turned uppercase, with each series of non alphanumerical characters converted to a single underscore. For instance with ‘%define api.prefix {calc}’ and ‘%header "lib/parse.h"’, the header will be guarded as follows. program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 55 Introduced in Bison 3.8. Same as above, but save in the file header-file. Directive: %language "language" Specify the programming language for the generated parser. Currently supported languages include C, C++, D and Java. language is case-insensitive. Directive: %locations Generate the code processing the locations (see ). This mode is enabled as soon as the grammar uses the special ‘@n’ tokens, but if your grammar does not use it, using ‘%locations’ allows for more accurate syntax error messages. Directive: %name-prefix "prefix" Obsoleted by ‘%define api.prefix {prefix}’. See . For C++ parsers, see the ‘%define api.namespace’ documentation in this section. Rename the external symbols used in the parser so that they start with prefix instead of ‘yy’. The precise list of symbols renamed in C parsers is type subrange = (a) .. b; 52, type subrange = (a) .. b; 51, type subrange = (a) .. b; 56, one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 256, type subrange = (a) .. b; 27, type subrange = (a) .. b; 23, %left '+' '-' %left '*' '/' 48, and (if locations are used) type subrange = (a) .. b; 28. If you use a push parser, one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 264, one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 271, one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 258, one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 262 and one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 263 will also be renamed. For example, if you use ‘%name-prefix "c_"’, the names become one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 313, one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 314, and so on. Contrary to defining one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 315, some symbols are not renamed by one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 316, for instance type subrange = (a) .. b; 63, one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 318, %left '+' '-' %left '*' '/' 68, type subrange = (a) .. b; 84, %token TYPE DOTDOT ID 94. Directive: %no-lines Don’t generate any one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 322 preprocessor commands in the parser implementation file. Ordinarily Bison writes these commands in the parser implementation file so that the C compiler and debuggers will associate errors and object code with your source file (the grammar file). This directive causes them to associate errors with the parser implementation file, treating it as an independent source file in its own right. Directive: %output "file" Generate the parser implementation in file. Directive: %pure-parser Deprecated version of ‘%define api.pure’ (see ), for which Bison is more careful to warn about unreasonable usage. Directive: %require "version" Require version version or higher of Bison. See . Directive: %skeleton "file" Specify the skeleton to use. If file does not contain a one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 323, file is the name of a skeleton file in the Bison installation directory. If it does, file is an absolute file name or a file name relative to the directory of the grammar file. This is similar to how most shells resolve commands. Directive: %token-table This feature is obsolescent, avoid it in new projects. Generate an array of token names in the parser implementation file. The name of the array is %% type_decl: TYPE ID '=' type ';' ; 41; one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 325 is the name of the token whose internal Bison token code is i. The first three elements of %% type_decl: TYPE ID '=' type ';' ; 41 correspond to the predefined tokens one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 327, one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 328, and one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 329; after these come the symbols defined in the grammar file. The name in the table includes all the characters needed to represent the token in Bison. For single-character literals and literal strings, this includes the surrounding quoting characters and any escape sequences. For example, the Bison single-character literal %token TYPE DOTDOT ID 18 corresponds to a three-character name, represented in C as one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 331; and the Bison two-character literal string one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 332 corresponds to a five-character name, represented in C as one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 333. When you specify one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 334, Bison also generates macro definitions for macros one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 335, one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 336, and one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 337, and one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 338: one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 335 The number of terminal symbols, i.e., the highest token code, plus one. one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 336 The number of nonterminal symbols. one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 337 The number of grammar rules, one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 338 The number of parser states (see ). Here’s code for looking up a multicharacter token in %% type_decl: TYPE ID '=' type ';' ; 41, assuming that the characters of the token are stored in one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 344, and assuming that the token does not contain any characters like ‘"’ that require escaping. program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 56 This method is discouraged: the primary purpose of string aliases is forging good error messages, not describing the spelling of keywords. In addition, looking for the token kind at runtime incurs a (small but noticeable) cost. Finally, one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 334 is incompatible with the one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 346 and one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 347 values of the one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 348 type subrange = (a) .. b; 80 variable. Directive: %verbose Write an extra output file containing verbose descriptions of the parser states and what is done for each type of lookahead token in that state. See , for more information. Directive: %yacc Pretend the option --yacc was given (see ), i.e., imitate Yacc, including its naming conventions. Only makes sense with the yacc.c skeleton. See , for more. Of course, being a Bison extension, one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 000 is somewhat self-contradictory… 3.7.14 %define SummaryThere are many features of Bison’s behavior that can be controlled by assigning the feature a single value. For historical reasons, some such features are assigned values by dedicated directives, such as one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 248, which assigns the start symbol. However, newer such features are associated with variables, which are assigned by the type subrange = (a) .. b; 80 directive: Directive: %define variable Directive: %define variable value Directive: %define variable {value} Directive: %define variable "value" Define variable to value. The type of the values depend on the syntax. Braces denote value in the target language (e.g., a namespace, a type, etc.). Keyword values (no delimiters) denote finite choice (e.g., a variation of a feature). String values denote remaining cases (e.g., a file name). It is an error if a variable is defined by type subrange = (a) .. b; 80 multiple times, but see . The rest of this section summarizes variables and values that type subrange = (a) .. b; 80 accepts. Some variables take Boolean values. In this case, Bison will complain if the variable definition does not meet one of the following four conditions:
What variables are accepted, as well as their meanings and default values, depend on the selected target language and/or the parser skeleton (see , see ). Unaccepted variables produce an error. Some of the accepted variables are described below. Directive: %define api.filename.type {type}
one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 379
Obsoleted by one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 471 Directive: %define parse.assert
Obsoleted by one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 493 3.7.15 %code SummaryThe %left '+' '-' %left '*' '/' 60 directive inserts code verbatim into the output parser source at any of a predefined set of locations. It thus serves as a flexible and user-friendly alternative to the traditional Yacc prologue, one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 495. This section summarizes the functionality of %left '+' '-' %left '*' '/' 60 for the various target languages supported by Bison. For a detailed discussion of how to use %left '+' '-' %left '*' '/' 60 in place of one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 495 for C/C++ and why it is advantageous to do so, see . Directive: %code {code} This is the unqualified form of the %left '+' '-' %left '*' '/' 60 directive. It inserts code verbatim at a language-dependent default location in the parser implementation. For C/C++, the default location is the parser implementation file after the usual contents of the parser header file. Thus, the unqualified form replaces one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 495 for most purposes. For D and Java, the default location is inside the parser class. Directive: %code qualifier {code} This is the qualified form of the %left '+' '-' %left '*' '/' 60 directive. qualifier identifies the purpose of code and thus the location(s) where Bison should insert it. That is, if you need to specify location-sensitive code that does not belong at the default location selected by the unqualified %left '+' '-' %left '*' '/' 60 form, use this form instead. For any particular qualifier or for the unqualified form, if there are multiple occurrences of the %left '+' '-' %left '*' '/' 60 directive, Bison concatenates the specified code in the order in which it appears in the grammar file. Not all qualifiers are accepted for all target languages. Unaccepted qualifiers produce an error. Some of the accepted qualifiers are: %left '+' '-' %left '*' '/' 61
%left '+' '-' %left '*' '/' 62
%left '+' '-' %left '*' '/' 63
one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 523
Though we say the insertion locations are language-dependent, they are technically skeleton-dependent. Writers of non-standard skeletons however should choose their locations consistently with the behavior of the standard Bison skeletons. 3.8 Multiple Parsers in the Same ProgramMost programs that use Bison parse only one language and therefore contain only one Bison parser. But what if you want to parse more than one language with the same program? Then you need to avoid name conflicts between different definitions of functions and variables such as type subrange = (a) .. b; 52, type subrange = (a) .. b; 27. To use different parsers from the same compilation unit, you also need to avoid conflicts on types and macros (e.g., type subrange = (a) .. b;
The easy way to do this is to define the type subrange = (a) .. b; 80 variable one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 315. With different one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 315s it is guaranteed that headers do not conflict when included together, and that compiled objects can be linked together too. Specifying ‘%define api.prefix {prefix}’ (or passing the option -Dapi.prefix={prefix}, see ) renames the interface functions and variables of the Bison parser to start with prefix instead of ‘yy’, and all the macros to start by PREFIX (i.e., prefix upper-cased) instead of ‘YY’. The renamed symbols include type subrange = (a) .. b; 52, type subrange = (a) .. b; 51, type subrange = (a) .. b; 56, one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 256, type subrange = (a) .. b; 27, type subrange = (a) .. b; 28, type subrange = (a) .. b; 23 and %left '+' '-' %left '*' '/' 48. If you use a push parser, one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 264, one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 271, one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 258, one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 262 and one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 263 will also be renamed. The renamed macros include type subrange = (a) .. b; 84, %token TYPE DOTDOT ID 94, and type subrange = (a) .. b; 63, which is treated specifically — more about this below. For example, if you use ‘%define api.prefix {c}’, the names become one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 546, one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 547, …, one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 548, one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 549, and so on. Users of Flex must update the signature of the generated type subrange = (a) .. b; 51 function. Since the Flex scanner usually includes the generated header of the parser (to get the definitions of the tokens, etc.), the most convenient way is to insert the declaration of type subrange = (a) .. b; 51 in the %left '+' '-' %left '*' '/' 62 section: program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 76 The type subrange = (a) .. b; 80 variable one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 315 works in two different ways. In the implementation file, it works by adding macro definitions to the beginning of the parser implementation file, defining type subrange = (a) .. b; 52 as one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 556, and so on: program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 77 This effectively substitutes one name for the other in the entire parser implementation file, thus the “original” names ( type subrange = (a) .. b; 51, type subrange = (a) .. b; 84, …) are also usable in the parser implementation file. However, in the parser header file, the symbols are defined renamed, for instance: program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 78 The macro type subrange = (a) .. b; 63 is commonly used to enable the tracing support in parsers. To comply with this tradition, when one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 315 is used, type subrange = (a) .. b; 63 (not renamed) is used as a default value: program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 79 Prior to Bison 2.6, a feature similar to one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 315 was provided by the obsolete directive one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 316 (see ) and the option --name-prefix (see ). 4 Parser C-Language InterfaceThe Bison parser is actually a C function named type subrange = (a) .. b; 52. Here we describe the interface conventions of type subrange = (a) .. b; 52 and the other functions that it needs to use. Keep in mind that the parser uses many C identifiers starting with ‘yy’ and ‘YY’ for internal purposes. If you use such an identifier (aside from those in this manual) in an action or in epilogue in the grammar file, you are likely to run into trouble. 4.1 The Parser Functiontype subrange = (a) .. b; 52 You call the function type subrange = (a) .. b; 52 to cause parsing to occur. This function reads tokens, executes actions, and ultimately returns when it encounters end-of-input or an unrecoverable syntax error. You can also write an action which directs type subrange = (a) .. b; 52 to return immediately without reading further. Function: int yyparse ( one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. The value returned by type subrange = (a) .. b; 52 is 0 if parsing was successful (return is due to end-of-input). The value is 1 if parsing failed because of invalid input, i.e., input that contains a syntax error or that causes one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 169 to be invoked. The value is 2 if parsing failed due to memory exhaustion. In an action, you can cause immediate return from type subrange = (a) .. b; 52 by using these macros: Macro: YYACCEPT Return immediately with value 0 (to report success). Macro: YYABORT Return immediately with value 1 (to report failure). Macro: YYNOMEM Return immediately with value 2 (to report memory exhaustion). If you use a reentrant parser, you can optionally pass additional parameter information to it in a reentrant way. To do so, use the declaration one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 168: Directive: %parse-param {argument-declaration} … Declare that one or more argument-declaration are additional type subrange = (a) .. b; 52 arguments. The argument-declaration is used when declaring functions or prototypes. The last identifier in argument-declaration must be the argument name. Here’s an example. Write this in the parser: program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 80 Then call the parser like this: program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 81 In the grammar actions, use expressions like this to refer to the data: program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 82 Using the following: program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 83 Results in these signatures: program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 84 Or, if both one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 410 (or just one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>.
one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 579 are used: program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 85 4.2 Push Parser InterfaceYou call the function one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 262 to create a new parser instance. This function is available if either the ‘%define api.push-pull push’ or ‘%define api.push-pull both’ declaration is used. See . Function: yypstate* yypstate_new ( one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. Return a valid parser instance if there is memory available, 0 otherwise. In impure mode, it will also return 0 if a parser instance is currently allocated. You call the function one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 263 to delete a parser instance. function is available if either the ‘%define api.push-pull push’ or ‘%define api.push-pull both’ declaration is used. See . Function: void yypstate_delete ( one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 583yyps) Reclaim the memory associated with a parser instance. After this call, you should no longer attempt to use the parser instance. You call the function one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 264 to parse a single token. This function is available if either the ‘%define api.push-pull push’ or ‘%define api.push-pull both’ declaration is used. See . Function: int yypush_parse ( one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 583yyps) The value returned by one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 264 is the same as for type subrange = (a) .. b; 52 with the following exception: it returns one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 588 if more input is required to finish parsing the grammar. After one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 264 returned, the instance may be consulted. For instance check one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 256 to see whether there were (possibly recovered) syntax errors. After one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 264 returns a status other than one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 588, the parser instance one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 593 may be reused for a new parse. The fact that the parser state is reusable even after an error simplifies reuse. For example, a calculator application which parses each input line as an expression can just keep reusing the same one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 593 even if an input was invalid. You call the function one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 271 to parse the rest of the input stream. This function is available if the ‘%define api.push-pull both’ declaration is used. See . Function: int yypull_parse ( one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 583yyps) The value returned by one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 271 is the same as for type subrange = (a) .. b; 52. The parser instance one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 593 may be reused for new parses. Function: int yypstate_expected_tokens ( one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 600yyps, one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 601 argv one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 602, type subrange = (a) .. b; 83 argc) Fill argv with the expected tokens, which never includes one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 604, one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 605, or one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 606. Never put more than argc elements into argv, and on success return the number of tokens stored in argv. If there are more expected tokens than argc, fill argv up to argc and return 0. If there are no expected tokens, also return 0, but set one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 607 to one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 604. When LAC is enabled, may return a negative number on errors, such as one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 609 on memory exhaustion. If argv is null, return the size needed to store all the possible values, which is always less than one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 335. 4.3 The Lexical Analyzer Functiontype subrange = (a) .. b; 51 The lexical analyzer function, type subrange = (a) .. b; 51, recognizes tokens from the input stream and returns them to the parser. Bison does not create this function automatically; you must write it so that type subrange = (a) .. b; 52 can call it. The function is sometimes referred to as a lexical scanner. In simple programs, type subrange = (a) .. b; 51 is often defined at the end of the Bison grammar file. If type subrange = (a) .. b; 51 is defined in a separate source file, you need to arrange for the token-kind definitions to be available there. To do this, use the -d option when you run Bison, so that it will write these definitions into the separate parser header file, name.tab.h, which you can include in the other source files that need it. See . 4.3.1 Calling Convention fortype subrange = (a) .. b; 51 The value that type subrange = (a) .. b; 51 returns must be the positive numeric code for the kind of token it has just found; a zero or negative value signifies end-of-input. When a token kind is referred to in the grammar rules by a name, that name in the parser implementation file becomes an enumerator of the enum %left '+' '-' %left '*' '/' 68 whose definition is the proper numeric code for that token kind. So type subrange = (a) .. b; 51 should use the name to indicate that type. See . When a token is referred to in the grammar rules by a character literal, the numeric code for that character is also the code for the token kind. So type subrange = (a) .. b; 51 can simply return that character code, possibly converted to one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 622 to avoid sign-extension. The null character must not be used this way, because its code is zero and that signifies end-of-input. Here is an example showing these things: program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 86 This interface has been designed so that the output from the one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 623 utility can be used without change as the definition of type subrange = (a) .. b; 51. 4.3.2 Special TokensIn addition to the user defined tokens, Bison generates a few special tokens that type subrange = (a) .. b; 51 may return. The type subrange = (a) .. b; 26 token denotes the end of file, and signals to the parser that there is nothing left afterwards. See , for an example. Returning one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 628 tells the parser that some lexical error was found. It will emit an error message about an “invalid token”, and enter error-recovery (see ). Returning an unknown token kind results in the exact same behavior. Returning one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 629 requires the parser to enter error-recovery without emitting an error message. This way the lexical analyzer can produce an accurate error messages about the invalid input (something the parser cannot do), and yet benefit from the error-recovery features of the parser. program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 87 4.3.3 Finding Tokens by String LiteralsIf the grammar uses literal string tokens, there are two ways that type subrange = (a) .. b; 51 can determine the token kind codes for them:
4.3.4 Semantic Values of TokensIn an ordinary (nonreentrant) parser, the semantic value of the token must be stored into the global variable type subrange = (a) .. b; 27. When you are using just one data type for semantic values, type subrange = (a) .. b; 27 has that type. Thus, if the type is type subrange = (a) .. b; 83 (the default), you might write this in type subrange = (a) .. b; 51: program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 88 When you are using multiple data types, type subrange = (a) .. b; 27’s type is a union made from the %left '+' '-' %left '*' '/' 54 declaration (see ). So when you store a token’s value, you must use the proper member of the union. If the %left '+' '-' %left '*' '/' 54 declaration looks like this: program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 89 then the code in type subrange = (a) .. b; 51 might look like this: program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 90 4.3.5 Textual Locations of TokensIf you are using the ‘@n’-feature (see ) in actions to keep track of the textual locations of tokens and groupings, then you must provide this information in type subrange = (a) .. b; 51. The function type subrange = (a) .. b; 52 expects to find the textual location of a token just parsed in the global variable type subrange = (a) .. b; 28. So type subrange = (a) .. b; 51 must store the proper data in that variable. By default, the value of type subrange = (a) .. b; 28 is a structure and you need only initialize the members that are going to be used by the actions. The four members are called %token TYPE DOTDOT ID 80, %token TYPE DOTDOT ID 81, %token TYPE DOTDOT ID 82 and %token TYPE DOTDOT ID 83. Note that the use of this feature makes the parser noticeably slower. The data type of type subrange = (a) .. b; 28 has the name %token TYPE DOTDOT ID 94. 4.3.6 Calling Conventions for Pure ParsersWhen you use the Bison declaration one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 410 to request a pure, reentrant parser, the global communication variables type subrange = (a) .. b; 27 and type subrange = (a) .. b; 28 cannot be used. (See .) In such parsers the two global variables are replaced by pointers passed as arguments to type subrange = (a) .. b; 51. You must declare them as shown here, and pass the information back by storing it through those pointers. program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 91 If the grammar file does not use the ‘@’ constructs to refer to textual locations, then the type %token TYPE DOTDOT ID 94 will not be defined. In this case, omit the second argument; type subrange = (a) .. b; 51 will be called with only one argument. If you wish to pass additional arguments to type subrange = (a) .. b; 51, use one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 663 just like one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 168 (see ). To pass additional arguments to both type subrange = (a) .. b; 51 and type subrange = (a) .. b; 52, use one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 668. Directive: %lex-param {argument-declaration} … Specify that argument-declaration are additional type subrange = (a) .. b; 51 argument declarations. You may pass one or more such declarations, which is equivalent to repeating one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 663. Directive: %param {argument-declaration} … Specify that argument-declaration are additional type subrange = (a) .. b; 51/ type subrange = (a) .. b; 52 argument declaration. This is equivalent to ‘%lex-param {argument-declaration} … %parse-param {argument-declaration} …’. You may pass one or more declarations, which is equivalent to repeating one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 668. For instance: program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 92 results in the following signatures: program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 93 If ‘%define api.pure full’ is added: program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 94 and finally, if both ‘%define api.pure full’ and one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 579 are used: program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 95 4.4 Error ReportingDuring its execution the parser may have error messages to pass to the user, such as syntax error, or memory exhaustion. How this message is delivered to the user must be specified by the developer. 4.4.1 The Error Reporting Functiontype subrange = (a) .. b; 56 The Bison parser detects a syntax error (or parse error) whenever it reads a token which cannot satisfy any syntax rule. An action in the grammar can also explicitly proclaim an error, using the macro type subrange = (a) .. b; 34 (see ). The Bison parser expects to report the error by calling an error reporting function named type subrange = (a) .. b; 56, which you must supply. It is called by type subrange = (a) .. b; 52 whenever a syntax error is found, and it receives one argument. For a syntax error, the string is normally one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 475. If you invoke ‘%define parse.error detailed’ (or ‘custom’) in the Bison declarations section (see ), then Bison provides a more verbose and specific error message string instead of just plain one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 475. However, that message sometimes contains incorrect information if LAC is not enabled (see ). The parser can detect one other kind of error: memory exhaustion. This can happen when the input contains constructions that are very deeply nested. It isn’t likely you will encounter this, since the Bison parser normally extends its stack automatically up to a very large limit. But if memory is exhausted, type subrange = (a) .. b; 52 calls type subrange = (a) .. b; 56 in the usual fashion, except that the argument string is one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 685. In some cases diagnostics like one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 475 are translated automatically from English to some other language before they are passed to type subrange = (a) .. b; 56. See . The following definition suffices in simple programs: program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 96 program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 97 After type subrange = (a) .. b; 56 returns to type subrange = (a) .. b; 52, the latter will attempt error recovery if you have written suitable error recovery grammar rules (see ). If recovery is impossible, type subrange = (a) .. b; 52 will immediately return 1. Obviously, in location tracking pure parsers, type subrange = (a) .. b; 56 should have an access to the current location. With one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 578, this is indeed the case for the GLR parsers, but not for the Yacc parser, for historical reasons, and this is the why one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 410 should be preferred over one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 578. When one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 695 is used, type subrange = (a) .. b; 56 has the following signature: program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 98 The prototypes are only indications of how the code produced by Bison uses type subrange = (a) .. b; 56. Bison-generated code always ignores the returned value, so type subrange = (a) .. b; 56 can return any type, including one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 571. Also, type subrange = (a) .. b; 56 can be a variadic function; that is why the message is always passed last. Traditionally type subrange = (a) .. b; 56 returns an type subrange = (a) .. b; 83 that is always ignored, but this is purely for historical reasons, and one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 571 is preferable since it more accurately describes the return type for type subrange = (a) .. b; 56. The variable one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 256 contains the number of syntax errors reported so far. Normally this variable is global; but if you request a pure parser (see ) then it is a local variable which only the actions can access. 4.4.2 The Syntax Error Reporting Functionone line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 480 If you invoke ‘%define parse.error custom’ (see ), then the parser no longer passes syntax error messages to type subrange = (a) .. b; 56, rather it delegates that task to the user by calling the one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 480 function. The following functions and types are “ one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 709”: they are defined in the implementation file (*.c) and available only from there. They are meant to be used from the grammar’s epilogue. Function: static int yyreport_syntax_error ( one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 710ctx) Report a syntax error to the user. Return 0 on success, one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 609 on memory exhaustion. Whether it uses type subrange = (a) .. b; 56 is up to the user. Use the following types and functions to build the error message. Type: yypcontext_t An opaque type that captures the circumstances of the syntax error. Type: yysymbol_kind_t An enum of all the grammar symbols, tokens and nonterminals. Its enumerators are forged from the symbol names: program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 99 Function: static yysymbol_kind_t yypcontext_token ( one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 710ctx) The “unexpected” token: the symbol kind of the lookahead token that caused the syntax error. Returns one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 604 if there is no lookahead. Function: static YYLTYPE * yypcontext_location ( one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 710ctx) The location of the syntax error (that of the unexpected token). Function: static int yypcontext_expected_tokens ( one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 710ctx, one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 601 argv one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 602, type subrange = (a) .. b; 83 argc) Fill argv with the expected tokens, which never includes one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 604, one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 605, or one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 606. Never put more than argc elements into argv, and on success return the number of tokens stored in argv. If there are more expected tokens than argc, fill argv up to argc and return 0. If there are no expected tokens, also return 0, but set one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 607 to one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 604. When LAC is enabled, may return a negative number on errors, such as one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 609 on memory exhaustion. If argv is null, return the size needed to store all the possible values, which is always less than one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 335. Function: static const char * yysymbol_name ( one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 727 symbol) The name of the symbol whose kind is symbol, possibly translated. A custom syntax error function looks as follows. This implementation is inappropriate for internationalization, see the c/bistromathic example for a better alternative. int / keyword ‘int’ /
square (int x) / identifier, open-paren, keyword ‘int’, 00 You still must provide a type subrange = (a) .. b; 56 function, used for instance to report memory exhaustion. 4.5 Special Features for Use in ActionsHere is a table of Bison constructs, variables and macros that are useful in actions. Variable: $$ Acts like a variable that contains the semantic value for the grouping made by the current rule. See . Variable: $n Acts like a variable that contains the semantic value for the nth component of the current rule. See . Variable: $<typealt>$ Like type subrange = (a) .. b; 91 but specifies alternative typealt in the union specified by the %left '+' '-' %left '*' '/' 54 declaration. See . Variable: $<typealt>n Like one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 024 but specifies alternative typealt in the union specified by the %left '+' '-' %left '*' '/' 54 declaration. See . Macro: YYABORT one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 109 Return immediately from type subrange = (a) .. b; 52, indicating failure. See . Macro: YYACCEPT one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 109 Return immediately from type subrange = (a) .. b; 52, indicating success. See . Macro: YYBACKUP (token, value) one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 109 Unshift a token. This macro is allowed only for rules that reduce a single value, and only when there is no lookahead token. It is also disallowed in GLR parsers. It installs a lookahead token with token kind token and semantic value value; then it discards the value that was going to be reduced by this rule. If the macro is used when it is not valid, such as when there is a lookahead token already, then it reports a syntax error with a message ‘cannot back up’ and performs ordinary error recovery. In either case, the rest of the action is not executed. Value: YYEMPTY Value stored in type subrange = (a) .. b; 23 when there is no lookahead token. Value: YYEOF Value stored in type subrange = (a) .. b; 23 when the lookahead is the end of the input stream. Macro: YYERROR one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 109 Cause an immediate syntax error. This statement initiates error recovery just as if the parser itself had detected an error; however, it does not call type subrange = (a) .. b; 56, and does not print any message. If you want to print an error message, call type subrange = (a) .. b; 56 explicitly before the ‘YYERROR;’ statement. See . Macro: YYNOMEM one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 109 Return immediately from type subrange = (a) .. b; 52, indicating memory exhaustion. See . Macro: YYRECOVERING The expression one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 748 yields 1 when the parser is recovering from a syntax error, and 0 otherwise. See . Variable: yychar Variable containing either the lookahead token, or type subrange = (a) .. b; 26 when the lookahead is the end of the input stream, or type subrange = (a) .. b; 25 when no lookahead has been performed so the next token is not yet known. Do not modify type subrange = (a) .. b; 23 in a deferred semantic action (see ). See . Macro: yyclearin one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 109 Discard the current lookahead token. This is useful primarily in error rules. Do not invoke type subrange = (a) .. b; 32 in a deferred semantic action (see ). See . Macro: yyerrok one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 109 Resume generating error messages immediately for subsequent syntax errors. This is useful primarily in error rules. See . Variable: yylloc Variable containing the lookahead token location when type subrange = (a) .. b; 23 is not set to type subrange = (a) .. b; 25 or type subrange = (a) .. b; 26. Do not modify type subrange = (a) .. b; 28 in a deferred semantic action (see ). See . Variable: yylval Variable containing the lookahead token semantic value when type subrange = (a) .. b; 23 is not set to type subrange = (a) .. b; 25 or type subrange = (a) .. b; 26. Do not modify type subrange = (a) .. b; 27 in a deferred semantic action (see ). See . Value: @$ Acts like a structure variable containing information on the textual location of the grouping made by the current rule. See . Value: @n Acts like a structure variable containing information on the textual location of the nth component of the current rule. See . 4.6 Parser InternationalizationA Bison-generated parser can print diagnostics, including error and tracing messages. By default, they appear in English. However, Bison also supports outputting diagnostics in the user’s native language. To make this work, the user should set the usual environment variables. See in GNU one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 763 utilities. For example, the shell command ‘export LC_ALL=fr_CA.UTF-8’ might set the user’s locale to French Canadian using the UTF-8 encoding. The exact set of available locales depends on the user’s installation. 4.6.1 Enabling InternationalizationThe maintainer of a package that uses a Bison-generated parser enables the internationalization of the parser’s output through the following steps. Here we assume a package that uses GNU Autoconf and GNU Automake.
4.6.2 Token InternationalizationWhen the type subrange = (a) .. b; 80 variable one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 348 is set to one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 346 or one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 347, token aliases can be internationalized: int / keyword ‘int’ /
square (int x) / identifier, open-paren, keyword ‘int’, 05 The remainder of the grammar may freely use either the token symbol ( %left '+' '-' %left '*' '/'
one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 778), but not with the internationalization marker ( one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 779). If at least one token alias is internationalized, then the generated parser will use both one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 780 and one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 781, that must be defined (see in GNU one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 763 utilities). They are used only on string aliases marked for translation. In other words, even if your catalog features a translation for “function”, then with int / keyword ‘int’ /
square (int x) / identifier, open-paren, keyword ‘int’, 06 “function” will appear untranslated in debug traces and error messages. Unless defined by the user, the end-of-file token, type subrange = (a) .. b; 26, is provided “end of file” as an alias. It is also internationalized if the user internationalized tokens. To map it to another string, use: int / keyword ‘int’ /
square (int x) / identifier, open-paren, keyword ‘int’, 07 5 The Bison Parser AlgorithmAs Bison reads tokens, it pushes them onto a stack along with their semantic values. The stack is called the parser stack. Pushing a token is traditionally called shifting. For example, suppose the infix calculator has read ‘1 + 5 *’, with a ‘3’ to come. The stack will have four elements, one for each token that was shifted. But the stack does not always have an element for each token read. When the last n tokens and groupings shifted match the components of a grammar rule, they can be combined according to that rule. This is called reduction. Those tokens and groupings are replaced on the stack by a single grouping whose symbol is the result (left hand side) of that rule. Running the rule’s action is part of the process of reduction, because this is what computes the semantic value of the resulting grouping. For example, if the infix calculator’s parser stack contains this: and the next input token is a newline character, then the last three elements can be reduced to 15 via the rule: Then the stack contains just these three elements: At this point, another reduction can be made, resulting in the single value 16. Then the newline token can be shifted. The parser tries, by shifts and reductions, to reduce the entire input down to a single grouping whose symbol is the grammar’s start-symbol (see ). This kind of parser is known in the literature as a bottom-up parser. 5.1 Lookahead TokensThe Bison parser does not always reduce immediately as soon as the last n tokens and groupings match a rule. This is because such a simple strategy is inadequate to handle most languages. Instead, when a reduction is possible, the parser sometimes “looks ahead” at the next token in order to decide what to do. When a token is read, it is not immediately shifted; first it becomes the lookahead token, which is not on the stack. Now the parser can perform one or more reductions of tokens and groupings on the stack, while the lookahead token remains off to the side. When no more reductions should take place, the lookahead token is shifted onto the stack. This does not mean that all possible reductions have been done; depending on the token kind of the lookahead token, some rules may choose to delay their application. Here is a simple case where lookahead is needed. These three rules define expressions which contain binary addition operators and postfix unary factorial operators (‘!’), and allow parentheses for grouping. int / keyword ‘int’ /
square (int x) / identifier, open-paren, keyword ‘int’, 08 one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 1 int / keyword ‘int’ /
square (int x) / identifier, open-paren, keyword ‘int’, 10 Suppose that the tokens ‘1 + 2’ have been read and shifted; what should be done? If the following token is ‘)’, then the first three tokens must be reduced to form an type subrange = lo .. hi; type enum = (a, b, c); 77. This is the only valid course, because shifting the ‘)’ would produce a sequence of symbols one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 785, and no rule allows this. If the following token is ‘!’, then it must be shifted immediately so that ‘2 !’ can be reduced to make a one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 786. If instead the parser were to reduce before shifting, ‘1 + 2’ would become an type subrange = lo .. hi; type enum = (a, b, c); 77. It would then be impossible to shift the ‘!’ because doing so would produce on the stack the sequence of symbols one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 788. No rule allows that sequence. The lookahead token is stored in the variable type subrange = (a) .. b; 23. Its semantic value and location, if any, are stored in the variables type subrange = (a) .. b; 27 and type subrange = (a) .. b; 28. See . 5.2 Shift/Reduce ConflictsSuppose we are parsing a language which has if-then and if-then-else statements, with a pair of rules like this: int / keyword ‘int’ /
square (int x) / identifier, open-paren, keyword ‘int’, 11 Here one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 792, one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 793 and one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 794 are terminal symbols for specific keyword tokens. When the one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 794 token is read and becomes the lookahead token, the contents of the stack (assuming the input is valid) are just right for reduction by the first rule. But it is also legitimate to shift the one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 794, because that would lead to eventual reduction by the second rule. This situation, where either a shift or a reduction would be valid, is called a shift/reduce conflict. Bison is designed to resolve these conflicts by choosing to shift, unless otherwise directed by operator precedence declarations. To see the reason for this, let’s contrast it with the other alternative. Since the parser prefers to shift the one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 794, the result is to attach the else-clause to the innermost if-statement, making these two inputs equivalent: int / keyword ‘int’ /
square (int x) / identifier, open-paren, keyword ‘int’, 12 But if the parser chose to reduce when possible rather than shift, the result would be to attach the else-clause to the outermost if-statement, making these two inputs equivalent: int / keyword ‘int’ /
square (int x) / identifier, open-paren, keyword ‘int’, 13 The conflict exists because the grammar as written is ambiguous: either parsing of the simple nested if-statement is legitimate. The established convention is that these ambiguities are resolved by attaching the else-clause to the innermost if-statement; this is what Bison accomplishes by choosing to shift rather than reduce. (It would ideally be cleaner to write an unambiguous grammar, but that is very hard to do in this case.) This particular ambiguity was first encountered in the specifications of Algol 60 and is called the “dangling one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 798” ambiguity. To assist the grammar author in understanding the nature of each conflict, Bison can be asked to generate “counterexamples”. In the present case it actually even proves that the grammar is ambiguous by exhibiting a string with two different parses: int / keyword ‘int’ /
square (int x) / identifier, open-paren, keyword ‘int’, 14 See , for more details. To avoid warnings from Bison about predictable, legitimate shift/reduce conflicts, you can use the one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 799 declaration. There will be no warning as long as the number of shift/reduce conflicts is exactly n, and Bison will report an error if there is a different number. See . However, we don’t recommend the use of one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 235 (except ‘%expect 0’!), as an equal number of conflicts does not mean that they are the same. When possible, you should rather use precedence directives to fix the conflicts explicitly (see ). The definition of one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 801 above is solely to blame for the conflict, but the conflict does not actually appear without additional rules. Here is a complete Bison grammar file that actually manifests the conflict: int / keyword ‘int’ /
square (int x) / identifier, open-paren, keyword ‘int’, 6 int / keyword ‘int’ /
square (int x) / identifier, open-paren, keyword ‘int’, 16 one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 1 int / keyword ‘int’ /
square (int x) / identifier, open-paren, keyword ‘int’, 11 int / keyword ‘int’ /
square (int x) / identifier, open-paren, keyword ‘int’, 19 5.3 Operator PrecedenceAnother situation where shift/reduce conflicts appear is in arithmetic expressions. Here shifting is not always the preferred resolution; the Bison declarations for operator precedence allow you to specify when to shift and when to reduce. 5.3.1 When Precedence is NeededConsider the following ambiguous grammar fragment (ambiguous because the input ‘1 - 2 * 3’ can be parsed in two different ways): int / keyword ‘int’ /
square (int x) / identifier, open-paren, keyword ‘int’, 20 Suppose the parser has seen the tokens ‘1’, ‘-’ and ‘2’; should it reduce them via the rule for the subtraction operator? It depends on the next token. Of course, if the next token is ‘)’, we must reduce; shifting is invalid because no single rule can reduce the token sequence ‘- 2 )’ or anything starting with that. But if the next token is ‘*’ or ‘<’, we have a choice: either shifting or reduction would allow the parse to complete, but with different results. To decide which one Bison should do, we must consider the results. If the next operator token op is shifted, then it must be reduced first in order to permit another opportunity to reduce the difference. The result is (in effect) ‘1 - (2 op 3)’. On the other hand, if the subtraction is reduced before shifting op, the result is ‘(1 - 2) op 3’. Clearly, then, the choice of shift or reduce should depend on the relative precedence of the operators ‘-’ and op: ‘*’ should be shifted first, but not ‘<’. What about input such as ‘1 - 2 - 5’; should this be ‘(1 - 2) - 5’ or should it be ‘1 - (2 - 5)’? For most operators we prefer the former, which is called left association. The latter alternative, right association, is desirable for assignment operators. The choice of left or right association is a matter of whether the parser chooses to shift or reduce when the stack contains ‘1 - 2’ and the lookahead token is ‘-’: shifting makes right-associativity. 5.3.2 Specifying Operator PrecedenceBison allows you to specify these choices with the operator precedence declarations %token TYPE DOTDOT ID 54 and %token TYPE DOTDOT ID 56. Each such declaration contains a list of tokens, which are operators whose precedence and associativity is being declared. The %token TYPE DOTDOT ID 54 declaration makes all those operators left-associative and the %token TYPE DOTDOT ID 56 declaration makes them right-associative. A third alternative is one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 135, which declares that it is a syntax error to find the same operator twice “in a row”. The last alternative, %token TYPE DOTDOT ID 59, allows to define only precedence and no associativity at all. As a result, any associativity-related conflict that remains will be reported as an compile-time error. The directive one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 135 creates run-time error: using the operator in a associative way is a syntax error. The directive %token TYPE DOTDOT ID 59 creates compile-time errors: an operator can be involved in an associativity-related conflict, contrary to what expected the grammar author. The relative precedence of different operators is controlled by the order in which they are declared. The first precedence/associativity declaration in the file declares the operators whose precedence is lowest, the next such declaration declares the operators whose precedence is a little higher, and so on. 5.3.3 Specifying Precedence OnlySince POSIX Yacc defines only %token TYPE DOTDOT ID 54, %token TYPE DOTDOT ID 56, and one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 135, which all defines precedence and associativity, little attention is paid to the fact that precedence cannot be defined without defining associativity. Yet, sometimes, when trying to solve a conflict, precedence suffices. In such a case, using %token TYPE DOTDOT ID 54, %token TYPE DOTDOT ID 56, or one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 135 might hide future (associativity related) conflicts that would remain hidden. The dangling one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 798 ambiguity (see ) can be solved explicitly. This shift/reduce conflicts occurs in the following situation, where the period denotes the current parsing state: int / keyword ‘int’ /
square (int x) / identifier, open-paren, keyword ‘int’, 21 The conflict involves the reduction of the rule ‘IF expr THEN stmt’, which precedence is by default that of its last token ( one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 817), and the shifting of the token one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 818. The usual disambiguation (attach the one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 798 to the closest one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 820), shifting must be preferred, i.e., the precedence of one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 818 must be higher than that of one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 817. But neither is expected to be involved in an associativity related conflict, which can be specified as follows. int / keyword ‘int’ /
square (int x) / identifier, open-paren, keyword ‘int’, 22 The unary-minus is another typical example where associativity is usually over-specified, see . The %token TYPE DOTDOT ID 54 directive is traditionally used to declare the precedence of %token TYPE DOTDOT ID 58, which is more than needed since it also defines its associativity. While this is harmless in the traditional example, who knows how %token TYPE DOTDOT ID 58 might be used in future evolutions of the grammar… 5.3.4 Precedence ExamplesIn our example, we would want the following declarations: int / keyword ‘int’ /
square (int x) / identifier, open-paren, keyword ‘int’, 23 In a more complete example, which supports other operators as well, we would declare them in groups of equal precedence. For example, %token TYPE DOTDOT ID 18 is declared with one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 828: int / keyword ‘int’ /
square (int x) / identifier, open-paren, keyword ‘int’, 24 5.3.5 How Precedence WorksThe first effect of the precedence declarations is to assign precedence levels to the terminal symbols declared. The second effect is to assign precedence levels to certain rules: each rule gets its precedence from the last terminal symbol mentioned in the components. (You can also specify explicitly the precedence of a rule. See .) Finally, the resolution of conflicts works by comparing the precedence of the rule being considered with that of the lookahead token. If the token’s precedence is higher, the choice is to shift. If the rule’s precedence is higher, the choice is to reduce. If they have equal precedence, the choice is made based on the associativity of that precedence level. The verbose output file made by -v (see ) says how each conflict was resolved. Not all rules and not all tokens have precedence. If either the rule or the lookahead token has no precedence, then the default is to shift. 5.3.6 Using Precedence For Non OperatorsUsing properly precedence and associativity directives can help fixing shift/reduce conflicts that do not involve arithmetic-like operators. For instance, the “dangling one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 798” problem (see ) can be solved elegantly in two different ways. In the present case, the conflict is between the token one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 794 willing to be shifted, and the rule ‘if_stmt: "if" expr "then" stmt’, asking for reduction. By default, the precedence of a rule is that of its last token, here one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 793, so the conflict will be solved appropriately by giving one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 794 a precedence higher than that of one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 793, for instance as follows: int / keyword ‘int’ /
square (int x) / identifier, open-paren, keyword ‘int’, 25 Alternatively, you may give both tokens the same precedence, in which case associativity is used to solve the conflict. To preserve the shift action, use right associativity: Neither solution is perfect however. Since Bison does not provide, so far, “scoped” precedence, both force you to declare the precedence of these keywords with respect to the other operators your grammar. Therefore, instead of being warned about new conflicts you would be unaware of (e.g., a shift/reduce conflict due to ‘if test then 1 else 2 + 3’ being ambiguous: ‘if test then 1 else (2 + 3)’ or ‘(if test then 1 else 2) + 3’?), the conflict will be already “fixed”. 5.4 Context-Dependent PrecedenceOften the precedence of an operator depends on the context. This sounds outlandish at first, but it is really very common. For example, a minus sign typically has a very high precedence as a unary operator, and a somewhat lower precedence (lower than multiplication) as a binary operator. The Bison precedence declarations can only be used once for a given token; so a token has only one precedence declared in this way. For context-dependent precedence, you need to use an additional mechanism: the %token TYPE DOTDOT ID 60 modifier for rules. The %token TYPE DOTDOT ID 60 modifier declares the precedence of a particular rule by specifying a terminal symbol whose precedence should be used for that rule. It’s not necessary for that symbol to appear otherwise in the rule. The modifier’s syntax is: and it is written after the components of the rule. Its effect is to assign the rule the precedence of terminal-symbol, overriding the precedence that would be deduced for it in the ordinary way. The altered rule precedence then affects how conflicts involving that rule are resolved (see ). Here is how %token TYPE DOTDOT ID 60 solves the problem of unary minus. First, declare a precedence for a fictitious terminal symbol named one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 837. There are no tokens of this type, but the symbol serves to stand for its precedence: int / keyword ‘int’ /
square (int x) / identifier, open-paren, keyword ‘int’, 26 Now the precedence of one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 837 can be used in specific rules: int / keyword ‘int’ /
square (int x) / identifier, open-paren, keyword ‘int’, 27 5.5 Parser StatesThe function type subrange = (a) .. b; 52 is implemented using a finite-state machine. The values pushed on the parser stack are not simply token kind codes; they represent the entire sequence of terminal and nonterminal symbols at or near the top of the stack. The current state collects all the information about previous input which is relevant to deciding what to do next. Each time a lookahead token is read, the current parser state together with the kind of lookahead token are looked up in a table. This table entry can say, “Shift the lookahead token.” In this case, it also specifies the new parser state, which is pushed onto the top of the parser stack. Or it can say, “Reduce using rule number n.” This means that a certain number of tokens or groupings are taken off the top of the stack, and replaced by one grouping. In other words, that number of states are popped from the stack, and one new state is pushed. There is one other alternative: the table can say that the lookahead token is erroneous in the current state. This causes error processing to begin (see ). 5.6 Reduce/Reduce ConflictsA reduce/reduce conflict occurs if there are two or more rules that apply to the same sequence of input. This usually indicates a serious error in the grammar. For example, here is an erroneous attempt to define a sequence of zero or more one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 840 groupings. int / keyword ‘int’ /
square (int x) / identifier, open-paren, keyword ‘int’, 28 one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 1 int / keyword ‘int’ /
square (int x) / identifier, open-paren, keyword ‘int’, 30 The error is an ambiguity: as counterexample generation would demonstrate (see ), there is more than one way to parse a single one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 840 into a one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 842. It could be reduced to a one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 843 and then into a one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 842 via the second rule. Alternatively, nothing-at-all could be reduced into a one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 842 via the first rule, and this could be combined with the one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 840 using the third rule for one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 842. There is also more than one way to reduce nothing-at-all into a one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 842. This can be done directly via the first rule, or indirectly via one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 843 and then the second rule. You might think that this is a distinction without a difference, because it does not change whether any particular input is valid or not. But it does affect which actions are run. One parsing order runs the second rule’s action; the other runs the first rule’s action and the third rule’s action. In this example, the output of the program changes. Bison resolves a reduce/reduce conflict by choosing to use the rule that appears first in the grammar, but it is very risky to rely on this. Every reduce/reduce conflict must be studied and usually eliminated. Here is the proper way to define one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 842: int / keyword ‘int’ /
square (int x) / identifier, open-paren, keyword ‘int’, 31 Here is another common error that yields a reduce/reduce conflict: int / keyword ‘int’ /
square (int x) / identifier, open-paren, keyword ‘int’, 32 one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 1 int / keyword ‘int’ /
square (int x) / identifier, open-paren, keyword ‘int’, 34 one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 1 int / keyword ‘int’ /
square (int x) / identifier, open-paren, keyword ‘int’, 36 The intention here is to define a sequence which can contain either one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 840 or one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 852 groupings. The individual definitions of one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 842, one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 854 and one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 855 are error-free, but the three together make a subtle ambiguity: even an empty input can be parsed in infinitely many ways! Consider: nothing-at-all could be a one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 854. Or it could be two one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 854 in a row, or three, or any number. It could equally well be a one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 855, or two, or any number. Or it could be a one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 854 followed by three one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 855 and another one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 854. And so on. Here are two ways to correct these rules. First, to make it a single level of sequence: int / keyword ‘int’ /
square (int x) / identifier, open-paren, keyword ‘int’, 37 Second, to prevent either a one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 854 or a one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 855 from being empty: int / keyword ‘int’ /
square (int x) / identifier, open-paren, keyword ‘int’, 32 one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 1 int / keyword ‘int’ /
square (int x) / identifier, open-paren, keyword ‘int’, 40 one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 1 int / keyword ‘int’ /
square (int x) / identifier, open-paren, keyword ‘int’, 42 Yet this proposal introduces another kind of ambiguity! The input ‘word word’ can be parsed as a single one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 854 composed of two ‘word’s, or as two one- one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 840 one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 854 (and likewise for one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 852/ one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 855). However this ambiguity is now a shift/reduce conflict, and therefore it can now be addressed with precedence directives. To simplify the matter, we will proceed with one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 840 and one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 852 being tokens: one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 871 and one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 872. To prefer the longest one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 854, the conflict between the token one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 871 and the rule ‘sequence: sequence words’ must be resolved as a shift. To this end, we use the same techniques as exposed above, see . One solution relies on precedences: use %token TYPE DOTDOT ID 60 to give a lower precedence to the rule: int / keyword ‘int’ /
square (int x) / identifier, open-paren, keyword ‘int’, 43 int / keyword ‘int’ /
square (int x) / identifier, open-paren, keyword ‘int’, 44 one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 1 int / keyword ‘int’ /
square (int x) / identifier, open-paren, keyword ‘int’, 46 Another solution relies on associativity: provide both the token and the rule with the same precedence, but make them right-associative: int / keyword ‘int’ /
square (int x) / identifier, open-paren, keyword ‘int’, 47 int / keyword ‘int’ /
square (int x) / identifier, open-paren, keyword ‘int’, 48 5.7 Mysterious ConflictsSometimes reduce/reduce conflicts can occur that don’t look warranted. Here is an example: int / keyword ‘int’ /
square (int x) / identifier, open-paren, keyword ‘int’, 49 one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 1 int / keyword ‘int’ /
square (int x) / identifier, open-paren, keyword ‘int’, 51 int / keyword ‘int’ /
square (int x) / identifier, open-paren, keyword ‘int’, 52 int / keyword ‘int’ /
square (int x) / identifier, open-paren, keyword ‘int’, 53 It would seem that this grammar can be parsed with only a single token of lookahead: when a one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 876 is being read, an one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 877 is a one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 878 if a comma or colon follows, or a one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 879 if another one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 877 follows. In other words, this grammar is LR(1). Yet Bison finds one reduce/reduce conflict, for which counterexample generation (see ) would find a nonunifying example. This is because Bison does not handle all LR(1) grammars by default, for historical reasons. In this grammar, two contexts, that after an one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 877 at the beginning of a one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 876 and likewise at the beginning of a one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 883, are similar enough that Bison assumes they are the same. They appear similar because the same set of rules would be active—the rule for reducing to a one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 878 and that for reducing to a one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 879. Bison is unable to determine at that stage of processing that the rules would require different lookahead tokens in the two contexts, so it makes a single parser state for them both. Combining the two contexts causes a conflict later. In parser terminology, this occurrence means that the grammar is not LALR(1). For many practical grammars (specifically those that fall into the non-LR(1) class), the limitations of LALR(1) result in difficulties beyond just mysterious reduce/reduce conflicts. The best way to fix all these problems is to select a different parser table construction algorithm. Either IELR(1) or canonical LR(1) would suffice, but the former is more efficient and easier to debug during development. See , for details. If you instead wish to work around LALR(1)’s limitations, you can often fix a mysterious conflict by identifying the two parser states that are being confused, and adding something to make them look distinct. In the above example, adding one rule to one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 883 as follows makes the problem go away: int / keyword ‘int’ /
square (int x) / identifier, open-paren, keyword ‘int’, 54 This corrects the problem because it introduces the possibility of an additional active rule in the context after the one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 877 at the beginning of one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 883. This rule is not active in the corresponding context in a one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 876, so the two contexts receive distinct parser states. As long as the token one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 890 is never generated by type subrange = (a) .. b; 51, the added rule cannot alter the way actual input is parsed. In this particular example, there is another way to solve the problem: rewrite the rule for one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 883 to use one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 877 directly instead of via one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 878. This also causes the two confusing contexts to have different sets of active rules, because the one for one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 883 activates the altered rule for one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 883 rather than the one for one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 878. int / keyword ‘int’ /
square (int x) / identifier, open-paren, keyword ‘int’, 55 one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 1 int / keyword ‘int’ /
square (int x) / identifier, open-paren, keyword ‘int’, 57 For a more detailed exposition of LALR(1) parsers and parser generators, see . 5.8 Tuning LRThe default behavior of Bison’s LR-based parsers is chosen mostly for historical reasons, but that behavior is often not robust. For example, in the previous section, we discussed the mysterious conflicts that can be produced by LALR(1), Bison’s default parser table construction algorithm. Another example is Bison’s one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 898 directive, which instructs the generated parser to produce verbose syntax error messages, which can sometimes contain incorrect information. In this section, we explore several modern features of Bison that allow you to tune fundamental aspects of the generated LR-based parsers. Some of these features easily eliminate shortcomings like those mentioned above. Others can be helpful purely for understanding your parser. 5.8.1 LR Table ConstructionFor historical reasons, Bison constructs LALR(1) parser tables by default. However, LALR does not possess the full language-recognition power of LR. As a result, the behavior of parsers employing LALR parser tables is often mysterious. We presented a simple example of this effect in . As we also demonstrated in that example, the traditional approach to eliminating such mysterious behavior is to restructure the grammar. Unfortunately, doing so correctly is often difficult. Moreover, merely discovering that LALR causes mysterious behavior in your parser can be difficult as well. Fortunately, Bison provides an easy way to eliminate the possibility of such mysterious behavior altogether. You simply need to activate a more powerful parser table construction algorithm by using the one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 899 directive. Directive: %define lr.type type Specify the type of parser tables within the LR(1) family. The accepted values for type are:
For example, to activate IELR, you might add the following directive to you grammar file: For the example in , the mysterious conflict is then eliminated, so there is no need to invest time in comprehending the conflict or restructuring the grammar to fix it. If, during future development, the grammar evolves such that all mysterious behavior would have disappeared using just LALR, you need not fear that continuing to use IELR will result in unnecessarily large parser tables. That is, IELR generates LALR tables when LALR (using a deterministic parsing algorithm) is sufficient to support the full language-recognition power of LR. Thus, by enabling IELR at the start of grammar development, you can safely and completely eliminate the need to consider LALR’s shortcomings. While IELR is almost always preferable, there are circumstances where LALR or the canonical LR parser tables described by Knuth (see ) can be useful. Here we summarize the relative advantages of each parser table construction algorithm within Bison:
For a more detailed exposition of the mysterious behavior in LALR parsers and the benefits of IELR, see , and . 5.8.2 Default ReductionsAfter parser table construction, Bison identifies the reduction with the largest lookahead set in each parser state. To reduce the size of the parser state, traditional Bison behavior is to remove that lookahead set and to assign that reduction to be the default parser action. Such a reduction is known as a default reduction. Default reductions affect more than the size of the parser tables. They also affect the behavior of the parser:
For canonical LR, the only default reduction that Bison enables by default is the accept action, which appears only in the accepting state, which has no other action and is thus a defaulted state. However, the default accept action does not delay any type subrange = (a) .. b; 51 invocation or syntax error detection because the accept action ends the parse. For LALR and IELR, Bison enables default reductions in nearly all states by default. There are only two exceptions. First, states that have a shift action on the type subrange = lo .. hi; type enum = (a, b, c); 84 token do not have default reductions because delayed syntax error detection could then prevent the type subrange = lo .. hi; type enum = (a, b, c); 84 token from ever being shifted in that state. However, parser state merging can cause the same effect anyway, and LAC fixes it in both cases, so future versions of Bison might drop this exception when LAC is activated. Second, GLR parsers do not record the default reduction as the action on a lookahead token for which there is a conflict. The correct action in this case is to split the parse instead. To adjust which states have default reductions enabled, use the one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 921 directive. Directive: %define lr.default-reduction where Specify the kind of states that are permitted to contain default reductions. The accepted values of where are:
5.8.3 LACCanonical LR, IELR, and LALR can suffer from a couple of problems upon encountering a syntax error. First, the parser might perform additional parser stack reductions before discovering the syntax error. Such reductions can perform user semantic actions that are unexpected because they are based on an invalid token, and they cause error recovery to begin in a different syntactic context than the one in which the invalid token was encountered. Second, when verbose error messages are enabled (see ), the expected token list in the syntax error message can both contain invalid tokens and omit valid tokens. The culprits for the above problems are one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 135, default reductions in inconsistent states (see ), and parser state merging. Because IELR and LALR merge parser states, they suffer the most. Canonical LR can suffer only if one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 135 is used or if default reductions are enabled for inconsistent states. LAC (Lookahead Correction) is a new mechanism within the parsing algorithm that solves these problems for canonical LR, IELR, and LALR without sacrificing one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 135, default reductions, or state merging. You can enable LAC with the one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 928 directive. Directive: %define parse.lac value Enable LAC to improve syntax error handling.
This feature is currently only available for deterministic parsers in C and C++. Conceptually, the LAC mechanism is straight-forward. Whenever the parser fetches a new token from the scanner so that it can determine the next parser action, it immediately suspends normal parsing and performs an exploratory parse using a temporary copy of the normal parser state stack. During this exploratory parse, the parser does not perform user semantic actions. If the exploratory parse reaches a shift action, normal parsing then resumes on the normal parser stacks. If the exploratory parse reaches an error instead, the parser reports a syntax error. If verbose syntax error messages are enabled, the parser must then discover the list of expected tokens, so it performs a separate exploratory parse for each token in the grammar. There is one subtlety about the use of LAC. That is, when in a consistent parser state with a default reduction, the parser will not attempt to fetch a token from the scanner because no lookahead is needed to determine the next parser action. Thus, whether default reductions are enabled in consistent states (see ) affects how soon the parser detects a syntax error: immediately when it reaches an erroneous token or when it eventually needs that token as a lookahead to determine the next parser action. The latter behavior is probably more intuitive, so Bison currently provides no way to achieve the former behavior while default reductions are enabled in consistent states. Thus, when LAC is in use, for some fixed decision of whether to enable default reductions in consistent states, canonical LR and IELR behave almost exactly the same for both syntactically acceptable and syntactically unacceptable input. While LALR still does not support the full language-recognition power of canonical LR and IELR, LAC at least enables LALR’s syntax error handling to correctly reflect LALR’s language-recognition power. There are a few caveats to consider when using LAC:
While the LAC algorithm shares techniques that have been recognized in the parser community for years, for the publication that introduces LAC, see . 5.8.4 Unreachable StatesIf there exists no sequence of transitions from the parser’s start state to some state s, then Bison considers s to be an unreachable state. A state can become unreachable during conflict resolution if Bison disables a shift action leading to it from a predecessor state. By default, Bison removes unreachable states from the parser after conflict resolution because they are useless in the generated parser. However, keeping unreachable states is sometimes useful when trying to understand the relationship between the parser and the grammar. Directive: %define lr.keep-unreachable-state value Request that Bison allow unreachable states to remain in the parser tables. value must be a Boolean. The default is one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 361. There are a few caveats to consider:
5.9 Generalized LR (GLR) ParsingBison produces deterministic parsers that choose uniquely when to reduce and which reduction to apply based on a summary of the preceding input and on one extra token of lookahead. As a result, normal Bison handles a proper subset of the family of context-free languages. Ambiguous grammars, since they have strings with more than one possible sequence of reductions cannot have deterministic parsers in this sense. The same is true of languages that require more than one symbol of lookahead, since the parser lacks the information necessary to make a decision at the point it must be made in a shift/reduce parser. Finally, as previously mentioned (see ), there are languages where Bison’s default choice of how to summarize the input seen so far loses necessary information. When you use the ‘%glr-parser’ declaration in your grammar file, Bison generates a parser that uses a different algorithm, called Generalized LR (or GLR). A Bison GLR parser uses the same basic algorithm for parsing as an ordinary Bison parser, but behaves differently in cases where there is a shift/reduce conflict that has not been resolved by precedence rules (see ) or a reduce/reduce conflict. When a GLR parser encounters such a situation, it effectively splits into a several parsers, one for each possible shift or reduction. These parsers then proceed as usual, consuming tokens in lock-step. Some of the stacks may encounter other conflicts and split further, with the result that instead of a sequence of states, a Bison GLR parsing stack is what is in effect a tree of states. In effect, each stack represents a guess as to what the proper parse is. Additional input may indicate that a guess was wrong, in which case the appropriate stack silently disappears. Otherwise, the semantics actions generated in each stack are saved, rather than being executed immediately. When a stack disappears, its saved semantic actions never get executed. When a reduction causes two stacks to become equivalent, their sets of semantic actions are both saved with the state that results from the reduction. We say that two stacks are equivalent when they both represent the same sequence of states, and each pair of corresponding states represents a grammar symbol that produces the same segment of the input token stream. Whenever the parser makes a transition from having multiple states to having one, it reverts to the normal deterministic parsing algorithm, after resolving and executing the saved-up actions. At this transition, some of the states on the stack will have semantic values that are sets (actually multisets) of possible actions. The parser tries to pick one of the actions by first finding one whose rule has the highest dynamic precedence, as set by the ‘%dprec’ declaration. Otherwise, if the alternative actions are not ordered by precedence, but there the same merging function is declared for both rules by the ‘%merge’ declaration, Bison resolves and evaluates both and then calls the merge function on the result. Otherwise, it reports an ambiguity. It is possible to use a data structure for the GLR parsing tree that permits the processing of any LR(1) grammar in linear time (in the size of the input), any unambiguous (not necessarily LR(1)) grammar in quadratic worst-case time, and any general (possibly ambiguous) context-free grammar in cubic worst-case time. However, Bison currently uses a simpler data structure that requires time proportional to the length of the input times the maximum number of stacks required for any prefix of the input. Thus, really ambiguous or nondeterministic grammars can require exponential time and space to process. Such badly behaving examples, however, are not generally of practical interest. Usually, nondeterminism in a grammar is local—the parser is “in doubt” only for a few tokens at a time. Therefore, the current data structure should generally be adequate. On LR(1) portions of a grammar, in particular, it is only slightly slower than with the deterministic LR(1) Bison parser. For a more detailed exposition of GLR parsers, see . 5.10 Memory Management, and How to Avoid Memory ExhaustionThe Bison parser stack can run out of memory if too many tokens are shifted and not reduced. When this happens, the parser function type subrange = (a) .. b; 52 calls type subrange = (a) .. b; 56 and then returns 2. Because Bison parsers have growing stacks, hitting the upper limit usually results from using a right recursion instead of a left recursion, see . By defining the macro one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 934, you can control how deep the parser stack can become before memory is exhausted. Define the macro with a value that is an integer. This value is the maximum number of tokens that can be shifted (and not reduced) before overflow. The stack space allowed is not necessarily allocated. If you specify a large value for one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 934, the parser normally allocates a small stack at first, and then makes it bigger by stages as needed. This increasing allocation happens automatically and silently. Therefore, you do not need to make one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 934 painfully small merely to save space for ordinary inputs that do not need much stack. However, do not allow one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 934 to be a value so large that arithmetic overflow could occur when calculating the size of the stack space. Also, do not allow one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 934 to be less than one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 939. The default value of one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 934, if you do not define it, is 10000. You can control how much stack is allocated initially by defining the macro one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 939 to a positive integer. For the deterministic parser in C, this value must be a compile-time constant unless you are assuming C99 or some other target language or compiler that allows variable-length arrays. The default is 200. Do not allow one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 939 to be greater than one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 934. You can generate a deterministic parser containing C++ user code from the default (C) skeleton, as well as from the C++ skeleton (see ). However, if you do use the default skeleton and want to allow the parsing stack to grow, be careful not to use semantic types or location types that require non-trivial copy constructors. The C skeleton bypasses these constructors when copying data to new, larger stacks. 6 Error RecoveryIt is not usually acceptable to have a program terminate on a syntax error. For example, a compiler should recover sufficiently to parse the rest of the input file and check it for errors; a calculator should accept another expression. In a simple interactive command parser where each input is one line, it may be sufficient to allow type subrange = (a) .. b; 52 to return 1 on error and have the caller ignore the rest of the input line when that happens (and then call type subrange = (a) .. b; 52 again). But this is inadequate for a compiler, because it forgets all the syntactic context leading up to the error. A syntax error deep within a function in the compiler input should not cause the compiler to treat the following line like the beginning of a source file. You can define how to recover from a syntax error by writing rules to recognize the special token type subrange = lo .. hi; type enum = (a, b, c); 84. This is a terminal symbol that is always defined (you need not declare it) and reserved for error handling. The Bison parser generates an type subrange = lo .. hi; type enum = (a, b, c); 84 token whenever a syntax error happens; if you have provided a rule to recognize this token in the current context, the parse can continue. For example: int / keyword ‘int’ /
square (int x) / identifier, open-paren, keyword ‘int’, 58 The fourth rule in this example says that an error followed by a newline makes a valid addition to any one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 948. What happens if a syntax error occurs in the middle of an type subrange = (a) .. b; 88? The error recovery rule, interpreted strictly, applies to the precise sequence of a one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 948, an type subrange = lo .. hi; type enum = (a, b, c); 84 and a newline. If an error occurs in the middle of an type subrange = (a) .. b; 88, there will probably be some additional tokens and subexpressions on the stack after the last one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 948, and there will be tokens to read before the next newline. So the rule is not applicable in the ordinary way. But Bison can force the situation to fit the rule, by discarding part of the semantic context and part of the input. First it discards states and objects from the stack until it gets back to a state in which the type subrange = lo .. hi; type enum = (a, b, c); 84 token is acceptable. (This means that the subexpressions already parsed are discarded, back to the last complete one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 948.) At this point the type subrange = lo .. hi; type enum = (a, b, c); 84 token can be shifted. Then, if the old lookahead token is not acceptable to be shifted next, the parser reads tokens and discards them until it finds a token which is acceptable. In this example, Bison reads and discards input until the next newline so that the fourth rule can apply. Note that discarded symbols are possible sources of memory leaks, see , for a means to reclaim this memory. The choice of error rules in the grammar is a choice of strategies for error recovery. A simple and useful strategy is simply to skip the rest of the current input line or current statement if an error is detected: int / keyword ‘int’ /
square (int x) / identifier, open-paren, keyword ‘int’, 59 It is also useful to recover to the matching close-delimiter of an opening-delimiter that has already been parsed. Otherwise the close-delimiter will probably appear to be unmatched, and generate another, spurious error message: int / keyword ‘int’ /
square (int x) / identifier, open-paren, keyword ‘int’, 60 Error recovery strategies are necessarily guesses. When they guess wrong, one syntax error often leads to another. In the above example, the error recovery rule guesses that an error is due to bad input within one type subrange = lo .. hi; type enum = (a, b, c); 78. Suppose that instead a spurious semicolon is inserted in the middle of a valid type subrange = lo .. hi; type enum = (a, b, c); 78. After the error recovery rule recovers from the first error, another syntax error will be found straight away, since the text following the spurious semicolon is also an invalid type subrange = lo .. hi; type enum = (a, b, c); 78. To prevent an outpouring of error messages, the parser will output no error message for another syntax error that happens shortly after the first; only after three consecutive input tokens have been successfully shifted will error messages resume. Note that rules which accept the type subrange = lo .. hi; type enum = (a, b, c); 84 token may have actions, just as any other rules can. You can make error messages resume immediately by using the macro %token TYPE DOTDOT ID 70 in an action. If you do this in the error rule’s action, no error messages will be suppressed. This macro requires no arguments; ‘yyerrok;’ is a valid C statement. The previous lookahead token is reanalyzed immediately after an error. If this is unacceptable, then the macro type subrange = (a) .. b; 32 may be used to clear this token. Write the statement ‘yyclearin;’ in the error rule’s action. See . For example, suppose that on a syntax error, an error handling routine is called that advances the input stream to some point where parsing should once again commence. The next symbol returned by the lexical scanner is probably correct. The previous lookahead token ought to be discarded with ‘yyclearin;’. The expression one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 748 yields 1 when the parser is recovering from a syntax error, and 0 otherwise. Syntax error diagnostics are suppressed while recovering from a syntax error. 7 Handling Context DependenciesThe Bison paradigm is to parse tokens first, then group them into larger syntactic units. In many languages, the meaning of a token is affected by its context. Although this violates the Bison paradigm, certain techniques (known as kludges) may enable you to write Bison parsers for such languages. (Actually, “kludge” means any technique that gets its job done but is neither clean nor robust.) 7.1 Semantic Info in Token KindsThe C language has a context dependency: the way an identifier is used depends on what its current meaning is. For example, consider this: This looks like a function call statement, but if one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 046 is a typedef name, then this is actually a declaration of type subrange = (a) .. b; 01. How can a Bison parser for C decide how to parse this input? The method used in GNU C is to have two different token kinds, type subrange = lo .. hi; type enum = (a, b, c); 81 and type subrange = lo .. hi; type enum = (a, b, c); 97. When type subrange = (a) .. b; 51 finds an identifier, it looks up the current declaration of the identifier in order to decide which token kind to return: type subrange = lo .. hi; type enum = (a, b, c); 97 if the identifier is declared as a typedef, type subrange = lo .. hi; type enum = (a, b, c); 81 otherwise. The grammar rules can then express the context dependency by the choice of token kind to recognize. type subrange = lo .. hi; type enum = (a, b, c); 81 is accepted as an expression, but type subrange = lo .. hi; type enum = (a, b, c); 97 is not. type subrange = lo .. hi; type enum = (a, b, c); 97 can start a declaration, but type subrange = lo .. hi; type enum = (a, b, c); 81 cannot. In contexts where the meaning of the identifier is not significant, such as in declarations that can shadow a typedef name, either type subrange = lo .. hi; type enum = (a, b, c); 97 or type subrange = lo .. hi; type enum = (a, b, c); 81 is accepted—there is one rule for each of the two token kinds. This technique is simple to use if the decision of which kinds of identifiers to allow is made at a place close to where the identifier is parsed. But in C this is not always so: C allows a declaration to redeclare a typedef name provided an explicit type has been specified earlier: int / keyword ‘int’ /
square (int x) / identifier, open-paren, keyword ‘int’, 61 int / keyword ‘int’ /
square (int x) / identifier, open-paren, keyword ‘int’, 62 Unfortunately, the name being declared is separated from the declaration construct itself by a complicated syntactic structure—the “declarator”. As a result, part of the Bison parser for C needs to be duplicated, with all the nonterminal names changed: once for parsing a declaration in which a typedef name can be redefined, and once for parsing a declaration in which that can’t be done. Here is a part of the duplication, with actions omitted for brevity: int / keyword ‘int’ /
square (int x) / identifier, open-paren, keyword ‘int’, 63 one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 1 int / keyword ‘int’ /
square (int x) / identifier, open-paren, keyword ‘int’, 65 Here one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 977 can redeclare a typedef name, but one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 978 cannot. The distinction between type subrange = (a) .. b; 11 and one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 980 is the same sort of thing. There is some similarity between this technique and a lexical tie-in (described next), in that information which alters the lexical analysis is changed during parsing by other parts of the program. The difference is here the information is global, and is used for other purposes in the program. A true lexical tie-in has a special-purpose flag controlled by the syntactic context. 7.2 Lexical Tie-insOne way to handle context-dependency is the lexical tie-in: a flag which is set by Bison actions, whose purpose is to alter the way tokens are parsed. For example, suppose we have a language vaguely like C, but with a special construct ‘hex (hex-expr)’. After the keyword one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 981 comes an expression in parentheses in which all integers are hexadecimal. In particular, the token ‘a1b’ must be treated as an integer rather than as an identifier if it appears in that context. Here is how you can do it: int / keyword ‘int’ /
square (int x) / identifier, open-paren, keyword ‘int’, 66 int / keyword ‘int’ /
square (int x) / identifier, open-paren, keyword ‘int’, 67 one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 1 int / keyword ‘int’ /
square (int x) / identifier, open-paren, keyword ‘int’, 69 Here we assume that type subrange = (a) .. b; 51 looks at the value of one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 983; when it is nonzero, all integers are parsed in hexadecimal, and tokens starting with letters are parsed as integers if possible. The declaration of one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 983 shown in the prologue of the grammar file is needed to make it accessible to the actions (see ). You must also write the code in type subrange = (a) .. b; 51 to obey the flag. 7.3 Lexical Tie-ins and Error RecoveryLexical tie-ins make strict demands on any error recovery rules you have. See . The reason for this is that the purpose of an error recovery rule is to abort the parsing of one construct and resume in some larger construct. For example, in C-like languages, a typical error recovery rule is to skip tokens until the next semicolon, and then start a new statement, like this: int / keyword ‘int’ /
square (int x) / identifier, open-paren, keyword ‘int’, 70 If there is a syntax error in the middle of a ‘hex (expr)’ construct, this error rule will apply, and then the action for the completed ‘hex (expr)’ will never run. So one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 983 would remain set for the entire rest of the input, or until the next one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 981 keyword, causing identifiers to be misinterpreted as integers. To avoid this problem the error recovery rule itself clears one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 983. There may also be an error recovery rule that works within expressions. For example, there could be a rule which applies within parentheses and skips to the close-parenthesis: int / keyword ‘int’ /
square (int x) / identifier, open-paren, keyword ‘int’, 71 If this rule acts within the one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 981 construct, it is not going to abort that construct (since it applies to an inner level of parentheses within the construct). Therefore, it should not clear the flag: the rest of the one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 981 construct should be parsed with the flag still in effect. What if there is an error recovery rule which might abort out of the one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 981 construct or might not, depending on circumstances? There is no way you can write the action to determine whether a one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 981 construct is being aborted or not. So if you are using a lexical tie-in, you had better make sure your error recovery rules are not of this kind. Each rule must be such that you can be sure that it always will, or always won’t, have to clear the flag. 8 Debugging Your ParserDeveloping a parser can be a challenge, especially if you don’t understand the algorithm (see ). This chapter explains how to understand and debug a parser. The most frequent issue users face is solving their conflicts. To fix them, the first step is understanding how they arise in a given grammar. This is made much easier by automated generation of counterexamples, cover in the first section (see ). In most cases though, looking at the structure of the automaton is still needed. The following sections explain how to generate and read the detailed structural description of the automaton. There are several formats available:
The last section focuses on the dynamic part of the parser: how to enable and understand the parser run-time traces (see ). 8.1 Generation of CounterexamplesSolving conflicts is probably the most delicate part of the design of an LR parser, as demonstrated by the number of sections devoted to them in this very documentation. To solve a conflict, one must understand it: when does it occur? Is it because of a flaw in the grammar? Is it rather because LR(1) cannot cope with this grammar? One difficulty is that conflicts occur in the automaton, and it can be tricky to relate them to issues in the grammar itself. With experience and patience, analysis of the detailed description of the automaton (see ) allows one to find example strings that reach these conflicts. That task is made much easier thanks to the generation of counterexamples, initially developed by Chinawat Isradisaikul and Andrew Myers (see ). As a first example, see the grammar of , which features one shift/reduce conflict: int / keyword ‘int’ /
square (int x) / identifier, open-paren, keyword ‘int’, 72 Let’s rerun %% type_decl: TYPE ID '=' type ';' ; 61 with the option -Wcex/-Wcounterexamples: int / keyword ‘int’ /
square (int x) / identifier, open-paren, keyword ‘int’, 73 int / keyword ‘int’ /
square (int x) / identifier, open-paren, keyword ‘int’, 14 This shows two different derivations for one single expression, which proves that the grammar is ambiguous. As a more delicate example, consider the example grammar of , which features a reduce/reduce conflict: int / keyword ‘int’ /
square (int x) / identifier, open-paren, keyword ‘int’, 75 Bison generates the following counterexamples: int / keyword ‘int’ /
square (int x) / identifier, open-paren, keyword ‘int’, 76 int / keyword ‘int’ /
square (int x) / identifier, open-paren, keyword ‘int’, 77 int / keyword ‘int’ /
square (int x) / identifier, open-paren, keyword ‘int’, 78 int / keyword ‘int’ /
square (int x) / identifier, open-paren, keyword ‘int’, 79 int / keyword ‘int’ /
square (int x) / identifier, open-paren, keyword ‘int’, 80 Each of these three conflicts, again, prove that the grammar is ambiguous. For instance, the second conflict (the reduce/reduce one) shows that the grammar accepts the empty input in two different ways. Sometimes, the search will not find an example that can be derived in two ways. In these cases, counterexample generation will provide two examples that are the same up until the dot. Most notably, this will happen when your grammar requires a stronger parser (more lookahead, LR instead of LALR). The following example isn’t LR(1): int / keyword ‘int’ /
square (int x) / identifier, open-paren, keyword ‘int’, 81 %% type_decl: TYPE ID '=' type ';' ; 61 reports: int / keyword ‘int’ /
square (int x) / identifier, open-paren, keyword ‘int’, 82 int / keyword ‘int’ /
square (int x) / identifier, open-paren, keyword ‘int’, 83 int / keyword ‘int’ /
square (int x) / identifier, open-paren, keyword ‘int’, 84 This conflict is caused by the parser not having enough information to know the difference between these two examples. The parser would need an additional lookahead token to know whether or not a comma follows the type subrange = lo .. hi; type enum = (a, b, c); 98 after type subrange = lo .. hi; type enum = (a, b, c); 77. These types of conflicts tend to be more difficult to fix, and usually need a rework of the grammar. In this case, it can be fixed by changing around the recursion: one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 997. Alternatively, you might also want to consider using a GLR parser (see ). On occasions, it is useful to look at counterexamples in situ: with the automaton report (See , in particular ). 8.2 Understanding Your ParserBison parsers are shift/reduce automata (see ). In some cases (much more frequent than one would hope), looking at this automaton is required to tune or simply fix a parser. The textual file is generated when the options --report or --verbose are specified, see . Its name is made by removing ‘.tab.c’ or ‘.c’ from the parser implementation file name, and adding ‘.output’ instead. Therefore, if the grammar file is foo.y, then the parser implementation file is called foo.tab.c by default. As a consequence, the verbose output file is called foo.output. The following grammar file, calc.y, will be used in the sequel: int / keyword ‘int’ /
square (int x) / identifier, open-paren, keyword ‘int’, 85 int / keyword ‘int’ /
square (int x) / identifier, open-paren, keyword ‘int’, 86 int / keyword ‘int’ /
square (int x) / identifier, open-paren, keyword ‘int’, 87 int / keyword ‘int’ /
square (int x) / identifier, open-paren, keyword ‘int’, 88 int / keyword ‘int’ /
square (int x) / identifier, open-paren, keyword ‘int’, 6 int / keyword ‘int’ /
square (int x) / identifier, open-paren, keyword ‘int’, 90 int / keyword ‘int’ /
square (int x) / identifier, open-paren, keyword ‘int’, 91 %% type_decl: TYPE ID '=' type ';' ; 61 reports: int / keyword ‘int’ /
square (int x) / identifier, open-paren, keyword ‘int’, 92 Going back to the calc example, when given --report=state, in addition to calc.tab.c, it creates a file calc.output with contents detailed below. The order of the output and the exact presentation might vary, but the interpretation is the same. The first section reports useless tokens, nonterminals and rules. Useless nonterminals and rules are removed in order to produce a smaller parser, but useless tokens are preserved, since they might be used by the scanner (note the difference between “useless” and “unused” below): int / keyword ‘int’ /
square (int x) / identifier, open-paren, keyword ‘int’, 93 The next section lists states that still have conflicts. int / keyword ‘int’ /
square (int x) / identifier, open-paren, keyword ‘int’, 94 Then Bison reproduces the exact grammar it used: int / keyword ‘int’ /
square (int x) / identifier, open-paren, keyword ‘int’, 95 and reports the uses of the symbols: int / keyword ‘int’ /
square (int x) / identifier, open-paren, keyword ‘int’, 96 one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 1 int / keyword ‘int’ /
square (int x) / identifier, open-paren, keyword ‘int’, 98 Bison then proceeds onto the automaton itself, describing each state with its set of items, also known as dotted rules. Each item is a production rule together with a point (‘.’) marking the location of the input cursor. int / keyword ‘int’ /
square (int x) / identifier, open-paren, keyword ‘int’, 99 This reads as follows: “state 0 corresponds to being at the very beginning of the parsing, in the initial rule, right before the start symbol (here, type subrange = (a) .. b; 88). When the parser returns to this state right after having reduced a rule that produced an type subrange = (a) .. b; 88, the control flow jumps to state 2. If there is no such transition on a nonterminal symbol, and the lookahead is a type subrange = (a) .. b; 86, then this token is shifted onto the parse stack, and the control flow jumps to state 1. Any other lookahead triggers a syntax error.” Even though the only active rule in state 0 seems to be rule 0, the report lists type subrange = (a) .. b; 86 as a lookahead token because type subrange = (a) .. b; 86 can be at the beginning of any rule deriving an type subrange = (a) .. b; 88. By default Bison reports the so-called core or kernel of the item set, but if you want to see more detail you can invoke %% type_decl: TYPE ID '=' type ';' ; 61 with --report=itemset to list the derived items as well: expr: expr '+' expr { $$ = $1 + $3; } ; 00 In the state 1… expr: expr '+' expr { $$ = $1 + $3; } ; 01 the rule 5, ‘exp: NUM;’, is completed. Whatever the lookahead token (‘$default’), the parser will reduce it. If it was coming from State 0, then, after this reduction it will return to state 0, and will jump to state 2 (‘exp: go to state 2’). expr: expr '+' expr { $$ = $1 + $3; } ; 02 In state 2, the automaton can only shift a symbol. For instance, because of the item ‘exp: exp • '+' exp’, if the lookahead is ‘+’ it is shifted onto the parse stack, and the automaton jumps to state 4, corresponding to the item ‘exp: exp '+' • exp’. Since there is no default action, any lookahead not listed triggers a syntax error. The state 3 is named the final state, or the accepting state: expr: expr '+' expr { $$ = $1 + $3; } ; 03 the initial rule is completed (the start symbol and the end-of-input were read), the parsing exits successfully. The interpretation of states 4 to 7 is straightforward, and is left to the reader. expr: expr '+' expr { $$ = $1 + $3; } ; 04 As was announced in beginning of the report, ‘State 8 conflicts: 1 shift/reduce’: expr: expr '+' expr { $$ = $1 + $3; } ; 05 Indeed, there are two actions associated to the lookahead ‘/’: either shifting (and going to state 7), or reducing rule 1. The conflict means that either the grammar is ambiguous, or the parser lacks information to make the right decision. Indeed the grammar is ambiguous, as, since we did not specify the precedence of ‘/’, the sentence ‘NUM + NUM / NUM’ can be parsed as ‘NUM + (NUM / NUM)’, which corresponds to shifting ‘/’, or as ‘(NUM + NUM) / NUM’, which corresponds to reducing rule 1. Because in deterministic parsing a single decision can be made, Bison arbitrarily chose to disable the reduction, see . Discarded actions are reported between square brackets. Note that all the previous states had a single possible action: either shifting the next token and going to the corresponding state, or reducing a single rule. In the other cases, i.e., when shifting and reducing is possible or when several reductions are possible, the lookahead is required to select the action. State 8 is one such state: if the lookahead is ‘*’ or ‘/’ then the action is shifting, otherwise the action is reducing rule 1. In other words, the first two items, corresponding to rule 1, are not eligible when the lookahead token is ‘*’, since we specified that ‘*’ has higher precedence than ‘+’. More generally, some items are eligible only with some set of possible lookahead tokens. When run with --report=lookahead, Bison specifies these lookahead tokens: expr: expr '+' expr { $$ = $1 + $3; } ; 06 Note however that while ‘NUM + NUM / NUM’ is ambiguous (which results in the conflicts on ‘/’), ‘NUM + NUM * NUM’ is not: the conflict was solved thanks to associativity and precedence directives. If invoked with --report=solved, Bison includes information about the solved conflicts in the report: expr: expr '+' expr { $$ = $1 + $3; } ; 07 When given --report=counterexamples, %% type_decl: TYPE ID '=' type ';' ; 61 will generate counterexamples within the report, augmented with the corresponding items (see ). expr: expr '+' expr { $$ = $1 + $3; } ; 08 expr: expr '+' expr { $$ = $1 + $3; } ; 09 This shows two separate derivations in the grammar for the same type subrange = (a) .. b; 88: ‘e1 + e2 / e3’. The derivations show how your rules would parse the given example. Here, the first derivation completes a reduction when seeing ‘/’, causing ‘e1 + e2’ to be grouped as an type subrange = (a) .. b; 88. The second derivation shifts on ‘/’, resulting in ‘e2 / e3’ being grouped as an type subrange = (a) .. b; 88. Therefore, it is easy to see that adding precedence/associativity directives would fix this conflict. The remaining states are similar: expr: expr '+' expr { $$ = $1 + $3; } ; 10 one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 1 expr: expr '+' expr { $$ = $1 + $3; } ; 12 one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 1 expr: expr '+' expr { $$ = $1 + $3; } ; 14 Observe that state 11 contains conflicts not only due to the lack of precedence of ‘/’ with respect to ‘+’, ‘-’, and ‘*’, but also because the associativity of ‘/’ is not specified. Bison may also produce an HTML version of this output, via an XML file and XSLT processing (see ). 8.3 Visualizing Your ParserAs another means to gain better understanding of the shift/reduce automaton corresponding to the Bison parser, a DOT file can be generated. Note that debugging a real grammar with this is tedious at best, and impractical most of the times, because the generated files are huge (the generation of a PDF or PNG file from it will take very long, and more often than not it will fail due to memory exhaustion). This option was rather designed for beginners, to help them understand LR parsers. This file is generated when the --graph option is specified (see ). Its name is made by removing ‘.tab.c’ or ‘.c’ from the parser implementation file name, and adding ‘.gv’ instead. If the grammar file is foo.y, the Graphviz output file is called foo.gv. A DOT file may also be produced via an XML file and XSLT processing (see ). The following grammar file, rr.y, will be used in the sequel: int / keyword ‘int’ /
square (int x) / identifier, open-paren, keyword ‘int’, 6 expr: expr '+' expr { $$ = $1 + $3; } ; 16 The graphical output (see ) is very similar to the textual one, and as such it is easier understood by making direct comparisons between them. See , for a detailed analysis of the textual report.
Figure 8.1: A graphical rendering of the parser. Graphical Representation of StatesThe items (dotted rules) for each state are grouped together in graph nodes. Their numbering is the same as in the verbose file. See the following points, about transitions, for examples When invoked with --report=lookaheads, the lookahead tokens, when needed, are shown next to the relevant rule between square brackets as a comma separated list. This is the case in the figure for the representation of reductions, below. The transitions are represented as directed edges between the current and the target states. Graphical Representation of ShiftsShifts are shown as solid arrows, labeled with the lookahead token for that shift. The following describes a reduction in the rr.output file: expr: expr '+' expr { $$ = $1 + $3; } ; 17 A Graphviz rendering of this portion of the graph could be:
Graphical Representation of ReductionsReductions are shown as solid arrows, leading to a diamond-shaped node bearing the number of the reduction rule. The arrow is labeled with the appropriate comma separated lookahead tokens. If the reduction is the default action for the given state, there is no such label. This is how reductions are represented in the verbose file rr.output: expr: expr '+' expr { $$ = $1 + $3; } ; 18 A Graphviz rendering of this portion of the graph could be:
When unresolved conflicts are present, because in deterministic parsing a single decision can be made, Bison can arbitrarily choose to disable a reduction, see . Discarded actions are distinguished by a red filling color on these nodes, just like how they are reported between square brackets in the verbose file. The reduction corresponding to the rule number 0 is the acceptation state. It is shown as a blue diamond, labeled “Acc”. Graphical Representation of GotosThe ‘go to’ jump transitions are represented as dotted lines bearing the name of the rule being jumped to. 8.4 Visualizing your parser in multiple formatsBison supports two major report formats: textual output (see ) when invoked with option --verbose, and DOT (see ) when invoked with option --graph. However, another alternative is to output an XML file that may then be, with program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 010, rendered as either a raw text format equivalent to the verbose file, or as an HTML version of the same file, with clickable transitions, or even as a DOT. The .output and DOT files obtained via XSLT have no difference whatsoever with those obtained by invoking %% type_decl: TYPE ID '=' type ';' ; 61 with options --verbose or --graph. The XML file is generated when the options -x or --xml[=FILE] are specified, see . If not specified, its name is made by removing ‘.tab.c’ or ‘.c’ from the parser implementation file name, and adding ‘.xml’ instead. For instance, if the grammar file is foo.y, the default XML output file is foo.xml. Bison ships with a data/xslt directory, containing XSL Transformation files to apply to the XML file. Their names are non-ambiguous: xml2dot.xsl Used to output a copy of the DOT visualization of the automaton. xml2text.xsl Used to output a copy of the ‘.output’ file. xml2xhtml.xsl Used to output an xhtml enhancement of the ‘.output’ file. Sample usage (requires program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 010): expr: expr '+' expr { $$ = $1 + $3; } ; 19 expr: expr '+' expr { $$ = $1 + $3; } ; 20 expr: expr '+' expr { $$ = $1 + $3; } ; 21 8.5 Tracing Your ParserWhen a Bison grammar compiles properly but parses “incorrectly”, the %left '+' '-' %left '*' '/' 48 parser-trace feature helps figuring out why. 8.5.1 Enabling TracesThere are several means to enable compilation of trace facilities, in decreasing order of preference: the variable ‘parse.trace’ Add the ‘%define parse.trace’ directive (see ), or pass the -Dparse.trace option (see ). This is a Bison extension. Unless POSIX and Yacc portability matter to you, this is the preferred solution. the option -t (POSIX Yacc compliant) the option --debug (Bison extension) Use the -t option when you run Bison (see ). With ‘%define api.prefix {c}’, it defines program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 015 to 1, otherwise it defines type subrange = (a) .. b; 63 to 1. the directive ‘%debug’ (deprecated) Add the program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 017 directive (see ). This Bison extension is maintained for backward compatibility; use program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 018 instead. the macro type subrange = (a) .. b; 63 (C/C++ only) Define the macro type subrange = (a) .. b; 63 to a nonzero value when you compile the parser. This is compliant with POSIX Yacc. You could use -DYYDEBUG=1 as a compiler option or you could put ‘ define YYDEBUG 1’ in the prologue of the grammar file (see ).If the type subrange = (a) .. b; 80 variable one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 315 is used (see ), for instance ‘%define api.prefix {c}’, then if program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 015 is defined, its value controls the tracing feature (enabled if and only if nonzero); otherwise tracing is enabled if and only if type subrange = (a) .. b; 63 is nonzero. In C++, where POSIX compliance makes no sense, avoid this option, and prefer ‘%define parse.trace’. If you %% type_decl: TYPE ID '=' type ';' ; 80 the type subrange = (a) .. b; 63 macro at the wrong place (e.g., in ‘%code top’ instead of ‘%code require’), the parser class will have two different definitions, thus leading to ODR violations and happy debugging times. We suggest that you always enable the trace option so that debugging is always possible. In C the trace facility outputs messages with macro calls of the form program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 027 where format and args are the usual program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 028 format and variadic arguments. If you define type subrange = (a) .. b; 63 to a nonzero value but do not define program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 030, program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 031 is automatically included and program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 030 is defined to program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 033. Once you have compiled the program with trace facilities, the way to request a trace is to store a nonzero value in the variable %left '+' '-' %left '*' '/' 48. You can do this by making the C code do it (in type subrange = (a) .. b; 53, perhaps), or you can alter the value with a C debugger. Each step taken by the parser when %left '+' '-' %left '*' '/' 48 is nonzero produces a line or two of trace information, written on program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 037. The trace messages tell you these things:
To make sense of this information, it helps to refer to the automaton description file (see ). This file shows the meaning of each state in terms of positions in various rules, and also what each state will do with each possible input token. As you read the successive trace messages, you can see that the parser is functioning according to its specification in the listing file. Eventually you will arrive at the place where something undesirable happens, and you will see which parts of the grammar are to blame. The parser implementation file is a C/C++/D/Java program and you can use debuggers on it, but it’s not easy to interpret what it is doing. The parser function is a finite-state machine interpreter, and aside from the actions it executes the same code over and over. Only the values of variables show where in the grammar it is working. 8.5.2 Enabling Debug Traces fortype subrange = (a) .. b; 71 The debugging information normally gives the token kind of each token read, but not its semantic value. The one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 078 directive allows specify how semantic values are reported, see . As a demonstration of one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 078, consider the multi-function calculator, type subrange = (a) .. b; 71 (see ). To enable run-time traces, and semantic value reports, insert the following directives in its prologue: expr: expr '+' expr { $$ = $1 + $3; } ; 22 The type subrange = (a) .. b; 80 directive instructs Bison to generate run-time trace support. Then, activation of these traces is controlled at run-time by the %left '+' '-' %left '*' '/' 48 variable, which is disabled by default. Because these traces will refer to the “states” of the parser, it is helpful to ask for the creation of a description of that parser; this is the purpose of (admittedly ill-named) program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 046 directive. The set of one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 078 directives demonstrates how to format the semantic value in the traces. Note that the specification can be done either on the symbol type (e.g., %left '+' '-' %left '*' '/' 11 or %left '+' '-' %left '*' '/' 12), or on the type tag: since program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 050 is the type for both type subrange = (a) .. b; 86 and type subrange = (a) .. b; 88, this printer will be used for them. Here is a sample of the information provided by run-time traces. The traces are sent onto standard error. expr: expr '+' expr { $$ = $1 + $3; } ; 23 This first batch shows a specific feature of this grammar: the first rule (which is in line 34 of mfcalc.y can be reduced without even having to look for the first token. The resulting left-hand symbol ( type subrange = (a) .. b;
type subrange = (a) .. b; 90 nonterminal ( program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 055). Then the parser calls the scanner. expr: expr '+' expr { $$ = $1 + $3; } ; 24 That token ( program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details.
%left '+' '-' %left '*' '/'
one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 078 specification: ‘sin()’. The parser stores ( program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details.
expr: expr '+' expr { $$ = $1 + $3; } ; 25 The previous reduction demonstrates the one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 078 directive for program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 050: both the token type subrange = (a) .. b; 86 and the resulting nonterminal type subrange = (a) .. b; 88 have ‘1’ as value. expr: expr '+' expr { $$ = $1 + $3; } ; 26 The rule for the subtraction was just reduced. The parser is about to discover the end of the call to %token TYPE DOTDOT ID 97. expr: expr '+' expr { $$ = $1 + $3; } ; 27 Finally, the end-of-line allow the parser to complete the computation, and display its result. expr: expr '+' expr { $$ = $1 + $3; } ; 28 The parser has returned into state 1, in which it is waiting for the next expression to evaluate, or for the end-of-file token, which causes the completion of the parsing. expr: expr '+' expr { $$ = $1 + $3; } ; 29 9 Invoking BisonThe usual way to invoke Bison is as follows: Here file is the grammar file name, which usually ends in ‘.y’. The parser implementation file’s name is made by replacing the ‘.y’ with ‘.tab.c’ and removing any leading directory. Thus, the ‘bison foo.y’ file name yields foo.tab.c, and the ‘bison hack/foo.y’ file name yields foo.tab.c. It’s also possible, in case you are writing C++ code instead of C in your grammar file, to name it foo.ypp or foo.y++. Then, the output files will take an extension like the given one as input (respectively foo.tab.cpp and foo.tab.c++). This feature takes effect with all options that manipulate file names like -o or -d. For example: will produce file.tab.cxx and file.tab.hxx, and expr: expr '+' expr { $$ = $1 + $3; } ; 30 will produce output.c++ and output.h++. For compatibility with POSIX, the standard Bison distribution also contains a shell script called program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 065 that invokes Bison with the -y option. The exit status of %% type_decl: TYPE ID '=' type ';' ; 61 is: 0 (success) when there were no errors. Warnings, which are diagnostics about dubious constructs, do not change the exit status, unless they are turned into errors (see ). 1 (failure) when there were errors. No file was generated (except the reports generated by --verbose, etc.). In particular, the output files that possibly existed were not changed. 63 (mismatch) when %% type_decl: TYPE ID '=' type ';' ; 61 does not meet the version requirements of the grammar file. See . No file was generated or changed. 9.1 Bison OptionsBison supports both traditional single-letter options and mnemonic long option names. Long option names are indicated with -- instead of -. Abbreviations for option names are allowed as long as they are unique. When a long option takes an argument, like --file-prefix, connect the option name and the argument with ‘=’. Here is a list of options that can be used with Bison. It is followed by a cross key alphabetized by long option. 9.1.1 Operation ModesOptions controlling the global behavior of %% type_decl: TYPE ID '=' type ';' ; 61. -h --help Print a summary of the command-line options to Bison and exit. -V --version Print the version number of Bison and exit. --print-localedir Print the name of the directory containing locale-dependent data. --print-datadir Print the name of the directory containing skeletons, CSS and XSLT. -u --update Update the grammar file (remove duplicates, update deprecated directives, etc.) and exit (i.e., do not generate any of the output files). Leaves a backup of the original file with a program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 069 appended. For instance: expr: expr '+' expr { $$ = $1 + $3; } ; 31 expr: expr '+' expr { $$ = $1 + $3; } ; 32 expr: expr '+' expr { $$ = $1 + $3; } ; 33 See the documentation of --feature=fixit below for more details. -f [feature] --feature[=feature] Activate miscellaneous features. Feature can be one of: program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 070 program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 071 Show caret errors, in a manner similar to GCC’s -fdiagnostics-show-caret, or Clang’s -fcaret-diagnostics. The location provided with the message is used to quote the corresponding line of the source file, underlining the important part of it with carets (‘^’). Here is an example, using the following file in.y: expr: expr '+' expr { $$ = $1 + $3; } ; 34 When invoked with -fcaret (or nothing), Bison will report: expr: expr '+' expr { $$ = $1 + $3; } ; 35 expr: expr '+' expr { $$ = $1 + $3; } ; 36 expr: expr '+' expr { $$ = $1 + $3; } ; 37 expr: expr '+' expr { $$ = $1 + $3; } ; 38 expr: expr '+' expr { $$ = $1 + $3; } ; 39 Whereas, when invoked with -fno-caret, Bison will only report: expr: expr '+' expr { $$ = $1 + $3; } ; 40 This option is activated by default. program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 072 program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 073 Show machine-readable fixes, in a manner similar to GCC’s and Clang’s -fdiagnostics-parseable-fixits. Fix-its are generated for duplicate directives: expr: expr '+' expr { $$ = $1 + $3; } ; 41 one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 1 expr: expr '+' expr { $$ = $1 + $3; } ; 43 They are also generated to update deprecated directives, unless -Wno-deprecated was given: expr: expr '+' expr { $$ = $1 + $3; } ; 44 expr: expr '+' expr { $$ = $1 + $3; } ; 45 The fix-its are applied by %% type_decl: TYPE ID '=' type ';' ; 61 itself when given the option -u/--update. See its documentation above. program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 075 Do not generate the output files. The name of this feature is somewhat misleading as more than just checking the syntax is done: every stage is run (including checking for conflicts for instance), except the generation of the output files. 9.1.2 DiagnosticsOptions controlling the diagnostics. program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 076 program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 077 Output warnings falling in category. category can be one of: program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 078 program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 079 S/R and R/R conflicts. These warnings are enabled by default. However, if the one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 235 or one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 237 directive is specified, an unexpected number of conflicts is an error, and an expected number of conflicts is not reported, so -W and --warning then have no effect on the conflict report. program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 082 program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 083 Provide counterexamples for conflicts. See . Counterexamples take time to compute. The option -Wcex should be used by the developer when working on the grammar; it hardly makes sense to use it in a CI. program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 084 Report string literals that are not bound to a token symbol. String literals, which allow for better error messages, are (too) liberally accepted by Bison, which might result in silent errors. For instance expr: expr '+' expr { $$ = $1 + $3; } ; 46 does not define “condition” as a string alias to program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 085—nonterminal symbols do not have string aliases. It is rather equivalent to expr: expr '+' expr { $$ = $1 + $3; } ; 47 i.e., it gives the ‘"condition"’ token the type program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 086. Also, because string aliases do not need to be defined, typos such as ‘"baz"’ instead of ‘"bar"’ will be not reported. The option -Wdangling-alias catches these situations. On expr: expr '+' expr { $$ = $1 + $3; } ; 48 ‘bison -Wdangling-alias’ reports expr: expr '+' expr { $$ = $1 + $3; } ; 49 program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 087 Deprecated constructs whose support will be removed in future versions of Bison. program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 088 Empty rules without %token TYPE DOTDOT ID 02. See . Disabled by default, but enabled by uses of %token TYPE DOTDOT ID 02, unless -Wno-empty-rule was specified. program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 091 Warn about midrule values that are set but not used within any of the actions of the parent rule. For example, warn about unused type subrange = (a) .. b; 94 in: expr: expr '+' expr { $$ = $1 + $3; } ; 50 Also warn about midrule values that are used but not set. For example, warn about unset type subrange = (a) .. b; 91 in the midrule action in: expr: expr '+' expr { $$ = $1 + $3; } ; 51 These warnings are not enabled by default since they sometimes prove to be false alarms in existing grammars employing the Yacc constructs one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 043 or program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 095 (where n is some positive integer). program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 096 Useless precedence and associativity directives. Disabled by default. Consider for instance the following grammar: expr: expr '+' expr { $$ = $1 + $3; } ; 52 int / keyword ‘int’ /
square (int x) / identifier, open-paren, keyword ‘int’, 6 expr: expr '+' expr { $$ = $1 + $3; } ; 54 one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 1 expr: expr '+' expr { $$ = $1 + $3; } ; 56 Bison reports: expr: expr '+' expr { $$ = $1 + $3; } ; 57 expr: expr '+' expr { $$ = $1 + $3; } ; 58 expr: expr '+' expr { $$ = $1 + $3; } ; 59 One would get the exact same parser with the following directives instead: expr: expr '+' expr { $$ = $1 + $3; } ; 60 program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 097 Incompatibilities with POSIX Yacc. program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 098 All warnings not categorized above. These warnings are enabled by default. This category is provided merely for the sake of completeness. Future releases of Bison may move warnings from this category to new, more specific categories. program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 099 All the warnings except program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 100, program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 101 and program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 065. program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 103 Turn off all the warnings. type subrange = lo .. hi; type enum = (a, b, c); 84 See -Werror, below. A category can be turned off by prefixing its name with ‘no-’. For instance, -Wno-yacc will hide the warnings about POSIX Yacc incompatibilities. program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 105 Turn enabled warnings for every category into errors, unless they are explicitly disabled by -Wno-error=category. program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 106 Enable warnings falling in category, and treat them as errors. category is the same as for --warnings, with the exception that it may not be prefixed with ‘no-’ (see above). Note that the precedence of the ‘=’ and ‘,’ operators is such that the following commands are not equivalent, as the first will not treat S/R conflicts as errors. expr: expr '+' expr { $$ = $1 + $3; } ; 61 program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 107 Do not turn enabled warnings for every category into errors, unless they are explicitly enabled by -Werror=category. program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 108 Deactivate the error treatment for this category. However, the warning itself won’t be disabled, or enabled, by this option. program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 109 Equivalent to --color=always. program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 110 Control whether diagnostics are colorized, depending on when: program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 111 program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 112 Enable colorized diagnostics. program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 113 program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 114 Disable colorized diagnostics. program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 115 program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 116 Diagnostics will be colorized if the output device is a tty, i.e. when the output goes directly to a text screen or terminal emulator window. program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 117 Specifies the CSS style file to use when colorizing. It has an effect only when the --color option is effective. The bison-default.css file provide a good example from which to define your own style file. See the documentation of libtextstyle for more details. 9.1.3 Tuning the ParserOptions changing the generated parsers. -t --debug In the parser implementation file, define the macro type subrange = (a) .. b; 63 to 1 if it is not already defined, so that the debugging facilities are compiled. See . -D name[=value] --define=name[=value] -F name[=value] --force-define=name[=value] Each of these is equivalent to ‘%define name value’ (see ). Note that the delimiters are part of value: -Dapi.value.type=union, -Dapi.value.type={union} and -Dapi.value.type="union" correspond to ‘%define api.value.type union’, ‘%define api.value.type {union}’ and ‘%define api.value.type "union"’. Bison processes multiple definitions for the same name as follows:
You should avoid using -F and --force-define in your make files unless you are confident that it is safe to quietly ignore any conflicting type subrange = (a) .. b; 80 that may be added to the grammar file. -L language --language=language Specify the programming language for the generated parser, as if program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 123 was specified (see ). Currently supported languages include C, C++, D and Java. language is case-insensitive. --locations Pretend that one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 579 was specified. See . -p prefix --name-prefix=prefix Pretend that program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 125 was specified (see ). The option -p is specified by POSIX. When POSIX compatibility is not a requirement, -Dapi.prefix=prefix is a better option (see ). -l --no-lines Don’t put any one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 322 preprocessor commands in the parser implementation file. Ordinarily Bison puts them in the parser implementation file so that the C compiler and debuggers will associate errors with your source file, the grammar file. This option causes them to associate errors with the parser implementation file, treating it as an independent source file in its own right. -S file --skeleton=file Specify the skeleton to use, similar to program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 127 (see ). If file does not contain a one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 323, file is the name of a skeleton file in the Bison installation directory. If it does, file is an absolute file name or a file name relative to the current working directory. This is similar to how most shells resolve commands. -k --token-table Pretend that one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 334 was specified. See . -y --yacc Act more like the traditional program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 065 command:
The -y/--yacc option is intended for use with traditional Yacc grammars. This option only makes sense for the default C skeleton, yacc.c. If your grammar uses Bison extensions Bison cannot be Yacc-compatible, even if this option is specified. Thus, the following shell script can substitute for Yacc, and the Bison distribution contains such a program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 065 script for compatibility with POSIX: 9.1.4 Output FilesOptions controlling the output. -H [file] --header=[file] Pretend that one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 282 was specified, i.e., write an extra output file containing definitions for the token kind names defined in the grammar, as well as a few other declarations. See . --defines[=file] Historical name for option --header before Bison 3.8. -d This is the same as --header except -d does not accept a file argument since POSIX Yacc requires that -d can be bundled with other short options. -b file-prefix --file-prefix=prefix Pretend that program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 144 was specified, i.e., specify prefix to use for all Bison output file names. See . -r things --report=things Write an extra output file containing verbose description of the comma separated list of things among: program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 145 Description of the grammar, conflicts (resolved and unresolved), and parser’s automaton. program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 146 Implies program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 145 and augments the description of the automaton with the full set of items for each state, instead of its core only. program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 148 Implies program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 145 and augments the description of the automaton with each rule’s lookahead set. program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 150 Implies program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 145. Explain how conflicts were solved thanks to precedence and associativity directives. program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 100 program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 083 Look for counterexamples for the conflicts. See . Counterexamples take time to compute. The option -rcex should be used by the developer when working on the grammar; it hardly makes sense to use it in a CI. program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 154 Enable all the items. one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 379 Do not generate the report. --report-file=file Specify the file for the verbose description. -v --verbose Pretend that program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 046 was specified, i.e., write an extra output file containing verbose descriptions of the grammar and parser. See . -o file --output=file Specify the file for the parser implementation file. The names of the other output files are constructed from file as described under the -v and -d options. -g [file] --graph[=file] Output a graphical representation of the parser’s automaton computed by Bison, in Graphviz DOT format. program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 157 is optional. If omitted and the grammar file is foo.y, the output file will be foo.gv. -x [file] --xml[=file] Output an XML report of the parser’s automaton computed by Bison. program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 157 is optional. If omitted and the grammar file is foo.y, the output file will be foo.xml. -M old=new --file-prefix-map=old=new Replace prefix old with new when writing file paths in output files. 9.2 Option Cross KeyHere is a list of options, alphabetized by long option, to help you find the corresponding short option and directive. Long OptionShort OptionBison Directive --color[=when] --debug-t program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 017 --define=name[=value]-D name[=value] program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 160 --feature[=features]-f [features] --file-prefix-map=old=new-M old=new --file-prefix=prefix-b prefix program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 161 --force-define=name[=value]-F name[=value] program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 160 --graph[=file]-g [file] --header=[file]-H [file] program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 163 --help-h --html[=file] --language=language-L language program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 164 --locations one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 579 --name-prefix=prefix-p prefix program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 125 --no-lines-l program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 167 --output=file-o file program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 168 --print-datadir --print-localedir --report-file=file --report=things-r things --skeleton=file-S file program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 169 --style=file --token-table-k one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 334 --update-u --verbose-v program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 046 --version-V --warnings[=category]-W [category] --xml[=file]-x [file] --yacc-y one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 000 9.3 Yacc LibraryThe Yacc library contains default implementations of the type subrange = (a) .. b; 56 and type subrange = (a) .. b; 53 functions. These default implementations are normally not useful, but POSIX requires them. To use the Yacc library, link your program with the -ly option. Note that Bison’s implementation of the Yacc library is distributed under the terms of the GNU General Public License (see ). If you use the Yacc library’s type subrange = (a) .. b; 56 function, you should declare type subrange = (a) .. b; 56 as follows: expr: expr '+' expr { $$ = $1 + $3; } ; 63 The type subrange = (a) .. b; 83 value returned by this type subrange = (a) .. b; 56 is ignored. The implementation of Yacc library’s type subrange = (a) .. b; 53 function is: expr: expr '+' expr { $$ = $1 + $3; } ; 64 so if you use it, the internationalization support is enabled (e.g., error messages are translated), and your type subrange = (a) .. b; 52 function should have the following type signature: 10 Parsers Written In Other LanguagesIn addition to C, Bison can generate parsers in C++, D and Java. This chapter is devoted to these languages. The reader is expected to understand how Bison works; read the introductory chapters first if you don’t. 10.1 C++ ParsersThe Bison parser in C++ is an object, an instance of the class program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 181. 10.1.1 A Simple C++ ExampleThis tutorial about C++ parsers is based on a simple, self contained example. The following sections are the reference manual for Bison with C++, the last one showing a fully blown example (see ). To look nicer, our example will be in C++14. It is not required: Bison supports the original C++98 standard. A Bison file has three parts. In the first part, the prologue, we start by making sure we run a version of Bison which is recent enough, and that we generate C++. expr: expr '+' expr { $$ = $1 + $3; } ; 65 Let’s dive directly into the middle part: the grammar. Our input is a simple list of strings, that we display once the parsing is done. int / keyword ‘int’ /
square (int x) / identifier, open-paren, keyword ‘int’, 6 expr: expr '+' expr { $$ = $1 + $3; } ; 67 expr: expr '+' expr { $$ = $1 + $3; } ; 68 expr: expr '+' expr { $$ = $1 + $3; } ; 69 We used a vector of strings as a semantic value! To use genuine C++ objects as semantic values—not just PODs—we cannot rely on the union that Bison uses by default to store them, we need variants (see ): expr: expr '+' expr { $$ = $1 + $3; } ; 70 Obviously, the rule for program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 182 needs to print a vector of strings. In the prologue, we add: expr: expr '+' expr { $$ = $1 + $3; } ; 71 expr: expr '+' expr { $$ = $1 + $3; } ; 72 expr: expr '+' expr { $$ = $1 + $3; } ; 73 You may want to move it into the one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 399 namespace to avoid leaking it in your default namespace. We recommend that you keep the actions simple, and move details into auxiliary functions, as we did with program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 184. Our list of strings will be built from two types of items: numbers and strings: expr: expr '+' expr { $$ = $1 + $3; } ; 74 expr: expr '+' expr { $$ = $1 + $3; } ; 75 In the case of program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 185, the implicit default action applies: one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 040. Our scanner deserves some attention. The traditional interface of type subrange = (a) .. b; 51 is not type safe: since the token kind and the token value are not correlated, you may return a program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 188 with a string as semantic value. To avoid this, we use token constructors (see ). This directive: expr: expr '+' expr { $$ = $1 + $3; } ; 76 requests that Bison generates the functions program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 189 and program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 190, but also program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 191, for the end of input. Everything is in place for our scanner: expr: expr '+' expr { $$ = $1 + $3; } ; 77 expr: expr '+' expr { $$ = $1 + $3; } ; 78 expr: expr '+' expr { $$ = $1 + $3; } ; 79 expr: expr '+' expr { $$ = $1 + $3; } ; 80 expr: expr '+' expr { $$ = $1 + $3; } ; 81 expr: expr '+' expr { $$ = $1 + $3; } ; 82 In the epilogue, the third part of a Bison grammar file, we leave simple details: the error reporting function, and the main function. expr: expr '+' expr { $$ = $1 + $3; } ; 83 Compile, and run! expr: expr '+' expr { $$ = $1 + $3; } ; 84 expr: expr '+' expr { $$ = $1 + $3; } ; 85 10.1.2 C++ Bison InterfaceThe C++ deterministic parser is selected using the skeleton directive, ‘%skeleton "lalr1.cc"’. See . When run, %% type_decl: TYPE ID '=' type ';' ; 61 will create several entities in the ‘yy’ namespace.Use the ‘%define api.namespace’ directive to change the namespace name, see . The various classes are generated in the following files: file.hh (Assuming the extension of the grammar file was ‘.yy’.) The declaration of the C++ parser class and auxiliary types. By default, this file is not generated (see ). file.cc The implementation of the C++ parser class. The basename and extension of these two files (file.hh and file.cc) follow the same rules as with regular C parsers (see ). location.hh Generated when both one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 282 and one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 579 are enabled, this file contains the definition of the classes one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 381 and one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 382, used for location tracking. It is not generated if ‘%define api.location.file none’ is specified, or if user defined locations are used. See . position.hh stack.hh Useless legacy files. To get rid of then, use ‘%require "3.2"’ or newer. All these files are documented using Doxygen; run program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 197 for a complete and accurate documentation. 10.1.3 C++ Parser InterfaceThe output files file.hh and file.cc declare and define the parser class in the namespace one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 399. The class name defaults to one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 400, but may be changed using ‘%define api.parser.class {name}’. The interface of this class is detailed below. It can be extended using the one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 168 feature: its semantics is slightly changed since it describes an additional member of the parser class, and an additional argument for its constructor. Type of parser: token A structure that contains (only) the program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 201 enumeration, which defines the tokens. To refer to the token program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 202, use program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 203. The scanner can use ‘typedef yy::parser::token token;’ to “import” the token enumeration (see ). Type of parser: token_kind_type An enumeration of the token kinds. Its enumerators are forged from the token names, with a possible token prefix (see ): expr: expr '+' expr { $$ = $1 + $3; } ; 86 Type of parser: value_type The types for semantic values. See . Type of parser: location_type The type of locations, if location tracking is enabled. See . Type of parser: syntax_error This class derives from program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 205. Throw instances of it from the scanner or from the actions to raise parse errors. This is equivalent with first invoking type subrange = lo .. hi; type enum = (a, b, c); 84 to report the location and message of the syntax error, and then to invoke type subrange = (a) .. b; 34 to enter the error-recovery mode. But contrary to type subrange = (a) .. b; 34 which can only be invoked from user actions (i.e., written in the action itself), the exception can be thrown from functions invoked from the user action. Constructor on parser: parser () Constructor on parser: parser (type1 arg1, ...) Build a new parser object. There are no arguments, unless ‘%parse-param {type1 arg1}’ was used. Constructor on syntax_error: syntax_error ( program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 209 l, program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 210 m) Constructor on syntax_error: syntax_error ( program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 210 m) Instantiate a syntax-error exception. Method on parser: int operator() () Method on parser: int parse () Run the syntactic analysis, and return 0 on success, 1 otherwise. Both routines are equivalent, program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 212 being more C++ish. The whole function is wrapped in a program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 213/ program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 214 block, so that when an exception is thrown, the one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 079s are called to release the lookahead symbol, and the symbols pushed on the stack. Exception related code in the generated parser is protected by CPP guards ( program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details.
Method on parser: std::ostream& debug_stream () Method on parser: void set_debug_stream ( one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 222 o) Get or set the stream used for tracing the parsing. It defaults to program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 218. Method on parser: debug_level_type debug_level () Method on parser: void set_debug_level (debug_level_type l) Get or set the tracing level (an integral). Currently its value is either 0, no trace, or nonzero, full tracing. Method on parser: void error ( program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 209 l, program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 210 m) Method on parser: void error ( program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 210 m) The definition for this member function must be supplied by the user: the parser uses it to report a parser error occurring at l, described by m. If location tracking is not enabled, the second signature is used. 10.1.4 C++ Semantic ValuesBison supports two different means to handle semantic values in C++. One is alike the C interface, and relies on unions. As C++ practitioners know, unions are inconvenient in C++, therefore another approach is provided, based on variants. 10.1.4.1 C++ UnionsThe %left '+' '-' %left '*' '/' 54 directive works as for C, see . In particular it produces a genuine %left '+' '-' %left '*' '/' 06, which have a few specific features in C++.
Because objects have to be stored via pointers, memory is not reclaimed automatically: using the one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 079 directive is the only means to avoid leaks. See . 10.1.4.2 C++ VariantsBison provides a variant based implementation of semantic values for C++. This alleviates all the limitations reported in the previous section, and in particular, object types can be used without pointers. To enable variant-based semantic values, set the type subrange = (a) .. b; 80 variable type subrange = (a) .. b; 81 to one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 072 (see ). Then %left '+' '-' %left '*' '/' 54 is ignored; instead of using the name of the fields of the %left '+' '-' %left '*' '/' 54 to “type” the symbols, use genuine types. For instance, instead of: expr: expr '+' expr { $$ = $1 + $3; } ; 87 write: expr: expr '+' expr { $$ = $1 + $3; } ; 88 program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 232 is no longer a pointer, which should fairly simplify the user actions in the grammar and in the scanner (in particular the memory management). Since C++ features destructors, and since it is customary to specialize program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 184 to support uniform printing of values, variants also typically simplify Bison printers and destructors. Variants are stricter than unions. When based on unions, you may play any dirty game with type subrange = (a) .. b; 27, say storing an type subrange = (a) .. b; 83, reading a program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 236, and then storing a %token TYPE DOTDOT ID 26 in it. This is no longer possible with variants: they must be initialized, then assigned to, and eventually, destroyed. As a matter of fact, Bison variants forbid the use of alternative types such as ‘$<int>2’ or ‘$<std::string>$’, even in midrule actions. It is mandatory to use typed midrule actions (see ). Method on value_type: T& emplace<T> () Method on value_type: T& emplace<T> ( program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 238 t) Available in C++98/C++03 only. Default construct/copy-construct from t. Return a reference to where the actual value may be stored. Requires that the variant was not initialized yet. Method on value_type: T& emplace<T, U> ( program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 239 u) Available in C++11 and later only. Build a variant of type program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 240 from the variadic forwarding references u.... Warning: We do not use Boost.Variant, for two reasons. First, it appeared unacceptable to require Boost on the user’s machine (i.e., the machine on which the generated parser will be compiled, not the machine on which %% type_decl: TYPE ID '=' type ';' ; 61 was run). Second, for each possible semantic value, Boost.Variant not only stores the value, but also a tag specifying its type. But the parser already “knows” the type of the semantic value, so that would be duplicating the information. We do not use C++17’s program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 242 either: we want to support all the C++ standards, and of course program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 242 also stores a tag to record the current type. Therefore we developed light-weight variants whose type tag is external (so they are really like program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 244 for C++ actually). There is a number of limitations in (the current implementation of) variants:
As far as we know, these limitations can be alleviated. All it takes is some time and/or some talented C++ hacker willing to contribute to Bison. 10.1.5 C++ Location ValuesWhen the directive one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 579 is used, the C++ parser supports location tracking, see . By default, two auxiliary classes define a one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 381, a single point in a file, and a one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 382, a range composed of a pair of one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 381s (possibly spanning several files). If the type subrange = (a) .. b; 80 variable one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 096 is defined, then these classes will not be generated, and the user defined type will be used. 10.1.5.1 C++one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 381 Type of position: filename_type The base type for file names. Defaults to one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 364. See , to change its definition. Type of position: counter_type The type used to store line and column numbers. Defined as type subrange = (a) .. b; 83. Constructor on position: position ( program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 259 file = nullptr, program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 260 line = 1, program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 260 col = 1) Create a one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 381 denoting a given point. Note that program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 157 is not reclaimed when the one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 381 is destroyed: memory managed must be handled elsewhere. Method on position: void initialize ( program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 259 file = nullptr, program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 260 line = 1, program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 260 col = 1) Reset the position to the given values. Instance Variable of position: filename_type* file The name of the file. It will always be handled as a pointer, the parser will never duplicate nor deallocate it. Instance Variable of position: counter_type line The line, starting at 1. Method on position: void lines ( program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 260 height = 1) If height is not null, advance by height lines, resetting the column number. The resulting line number cannot be less than 1. Instance Variable of position: counter_type column The column, starting at 1. Method on position: void columns ( program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 260 width = 1) Advance by width columns, without changing the line number. The resulting column number cannot be less than 1. Method on position: position& operator+= ( program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 260 width) Method on position: position operator+ ( program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 260 width) Method on position: position& operator-= ( program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 260 width) Method on position: position operator- ( program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 260 width) Various forms of syntactic sugar for program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 274. Method on position: bool operator== ( program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 275 that) Method on position: bool operator!= ( program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 275 that) Whether program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 277 and program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 278 denote equal/different positions. Function: std::ostream& operator<< ( one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 222 o, program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 275 p) Report p on o like this: ‘file:line.column’, or ‘line.column’ if file is null. 10.1.5.2 C++one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 382 Constructor on location: location ( program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 275 begin, program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 275 end) Create a program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 284 from the endpoints of the range. Constructor on location: location ( program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 275 pos = position()) Constructor on location: location ( program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 259 file, program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 260 line, program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 260 col) Create a program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 284 denoting an empty range located at a given point. Method on location: void initialize ( program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 259 file = nullptr, program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 260 line = 1, program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 260 col = 1) Reset the location to an empty range at the given values. Instance Variable of location: position begin Instance Variable of location: position end The first, inclusive, position of the range, and the first beyond. Method on location: void columns ( program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 260 width = 1) Method on location: void lines ( program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 260 height = 1) Forwarded to the program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 295 position. Method on location: location operator+ ( program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 260 width) Method on location: location operator+= ( program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 260 width) Method on location: location operator- ( program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 260 width) Method on location: location operator-= ( program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 260 width) Various forms of syntactic sugar for program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 274. Method on location: location operator+ ( program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 301 end) Method on location: location operator+= ( program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 301 end) Join two locations: starts at the position of the first one, and ends at the position of the second. Method on location: void step () Move program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 303 onto program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 295. Method on location: bool operator== ( program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 301 that) Method on location: bool operator!= ( program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 301 that) Whether program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 277 and program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 278 denote equal/different ranges of positions. Function: std::ostream& operator<< ( one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 222 o, program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 301 p) Report p on o, taking care of special cases such as: no program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 311 defined, or equal filename/line or column. 10.1.5.3 Exposing the Location ClassesWhen both one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 282 and one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 579 are enabled, Bison generates an additional file: location.hh. If you don’t use locations outside of the parser, you may avoid its creation with ‘%define api.location.file none’. However this file is useful if, for instance, your parser builds an abstract syntax tree decorated with locations: you may use Bison’s one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 382 type independently of Bison’s parser. You may name the file differently, e.g., ‘%define api.location.file "include/ast/location.hh"’: this name can have directory components, or even be absolute. The way the location file is included is controlled by program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 315. This way it is possible to have several parsers share the same location file. For instance, in src/foo/parser.yy, generate the include/ast/loc.hh file: expr: expr '+' expr { $$ = $1 + $3; } ; 89 and use it in src/bar/parser.yy: expr: expr '+' expr { $$ = $1 + $3; } ; 90 Absolute file names are supported; it is safe in your Makefile to pass the flag -Dapi.location.file='"$(top_srcdir)/include/ast/loc.hh"' to %% type_decl: TYPE ID '=' type ';' ; 61 for src/foo/parser.yy. The generated file will not have references to this absolute path, thanks to ‘%define api.location.include {<ast/loc.hh>}’. Adding ‘-I $(top_srcdir)/include’ to your program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 317 will suffice for the compiler to find ast/loc.hh. 10.1.5.4 User Defined Location TypeInstead of using the built-in types you may use the type subrange = (a) .. b; 80 variable one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 096 to specify your own type: expr: expr '+' expr { $$ = $1 + $3; } ; 91 The requirements over your LocationType are:
In programs with several C++ parsers, you may also use the type subrange = (a) .. b; 80 variable one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 096 to share a common set of built-in definitions for one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 381 and one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 382. For instance, one parser master/parser.yy might use: expr: expr '+' expr { $$ = $1 + $3; } ; 93 to generate the master/position.hh and master/location.hh files, reused by other parsers as follows: expr: expr '+' expr { $$ = $1 + $3; } ; 94 10.1.6 C++ Parser ContextWhen ‘%define parse.error custom’ is used (see ), the user must define the following function. Method on parser: void report_syntax_error ( program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 328ctx) program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 329 Report a syntax error to the user. Whether it uses type subrange = (a) .. b; 56 is up to the user. Use the following types and functions to build the error message. Type of parser: context A type that captures the circumstances of the syntax error. Type of parser: symbol_kind_type An enum of all the grammar symbols, tokens and nonterminals. Its enumerators are forged from the symbol names: expr: expr '+' expr { $$ = $1 + $3; } ; 95 Method on context: const symbol_type& lookahead () program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 329 The “unexpected” token: the lookahead that caused the syntax error. Method on context: symbol_kind_type token () program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 329 The symbol kind of the lookahead token that caused the syntax error. Returns program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 333 if there is no lookahead. Method on context: const location& location () program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 329 The location of the syntax error (that of the lookahead). Method on context: int expected_tokens ( program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 335 argv one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 602, type subrange = (a) .. b; 83 argc) program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 329 Fill argv with the expected tokens, which never includes program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 333, program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 340, or program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 341. Never put more than argc elements into argv, and on success return the number of tokens stored in argv. If there are more expected tokens than argc, fill argv up to argc and return 0. If there are no expected tokens, also return 0, but set one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 607 to program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 333. If argv is null, return the size needed to store all the possible values, which is always less than one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 335. Method on parser: const char * symbol_name ( one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 727 symbol) program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 329 The name of the symbol whose kind is symbol, possibly translated. Returns a one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 366 when one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 348 is one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 477. A custom syntax error function looks as follows. This implementation is inappropriate for internationalization, see the c/bistromathic example for a better alternative. expr: expr '+' expr { $$ = $1 + $3; } ; 96 You still must provide a type subrange = (a) .. b; 56 function, used for instance to report memory exhaustion. 10.1.7 C++ Scanner InterfaceThe parser invokes the scanner by calling type subrange = (a) .. b; 51. Contrary to C parsers, C++ parsers are always pure: there is no point in using the ‘%define api.pure’ directive. The actual interface with type subrange = (a) .. b; 51 depends whether you use unions, or variants. 10.1.7.1 Split SymbolsThe generated parser expects type subrange = (a) .. b; 51 to have the following prototype. Function: int yylex ( program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 354 yylval, program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 355 yylloc, type1 arg1, …) Function: int yylex ( program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 354 yylval, type1 arg1, …) Return the next token. Its kind is the return value, its semantic value and location (if enabled) being yylval and yylloc. Invocations of ‘%lex-param {type1 arg1}’ yield additional arguments. Note that when using variants, the interface for type subrange = (a) .. b; 51 is the same, but type subrange = (a) .. b; 27 is handled differently. Regular union-based code in Lex scanner typically looks like: expr: expr '+' expr { $$ = $1 + $3; } ; 97 Using variants, type subrange = (a) .. b; 27 is already constructed, but it is not initialized. So the code would look like: expr: expr '+' expr { $$ = $1 + $3; } ; 98 or expr: expr '+' expr { $$ = $1 + $3; } ; 99 10.1.7.2 Complete SymbolsWith both program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 360 and program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 361, the parser defines the type program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 362, and expects type subrange = (a) .. b; 51 to have the following prototype. Function: parser::symbol_type yylex () Function: parser::symbol_type yylex (type1 arg1, …) Return a complete symbol, aggregating its type (i.e., the traditional value returned by type subrange = (a) .. b; 51), its semantic value, and possibly its location. Invocations of ‘%lex-param {type1 arg1}’ yield additional arguments. Type of parser: symbol_type A “complete symbol”, that binds together its kind, value and (when applicable) location. Method on symbol_type: symbol_kind_type kind () program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 329 The kind of this symbol. Method on symbol_type: const char * name () program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 329 The name of the kind of this symbol. Returns a one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 366 when one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 348 is one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 477. For each token kind, Bison generates named constructors as follows. Constructor on parser::symbol_type: symbol_type ( type subrange = (a) .. b; 83 token, program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 371 value, program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 209 location) Constructor on parser::symbol_type: symbol_type ( type subrange = (a) .. b; 83 token, program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 209 location) Constructor on parser::symbol_type: symbol_type ( type subrange = (a) .. b; 83 token, program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 371 value) Constructor on parser::symbol_type: symbol_type ( type subrange = (a) .. b; 83 token) Build a complete terminal symbol for the token kind token (including the %% type_decl: TYPE ID '=' type ';' ; 99), whose semantic value, if it has one, is value of adequate value_type. Pass the location iff location tracking is enabled. Consistency between token and value_type is checked via an program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 379. For instance, given the following declarations: type subrange = lo .. hi; type enum = (a, b, c); 00 you may use these constructors: type subrange = lo .. hi; type enum = (a, b, c); 01 Correct matching between token kinds and value types is checked via program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 379; for instance, ‘symbol_type (ID, 42)’ would abort. Named constructors are preferable (see below), as they offer better type safety (for instance ‘make_ID (42)’ would not even compile), but symbol_type constructors may help when token kinds are discovered at run-time, e.g., type subrange = lo .. hi; type enum = (a, b, c); 02 Note that it is possible to generate and compile type incorrect code (e.g. ‘symbol_type (':', yytext, loc)’). It will fail at run time, provided the assertions are enabled (i.e., -DNDEBUG was not passed to the compiler). Bison supports an alternative that guarantees that type incorrect code will not even compile. Indeed, it generates named constructors as follows. Method on parser: symbol_type make_token ( program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 371 value, program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 209 location) Method on parser: symbol_type make_token ( program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 209 location) Method on parser: symbol_type make_token ( program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 371 value) Method on parser: symbol_type make_token () Build a complete terminal symbol for the token kind token (not including the %% type_decl: TYPE ID '=' type ';' ; 99), whose semantic value, if it has one, is value of adequate value_type. Pass the location iff location tracking is enabled. For instance, given the following declarations: type subrange = lo .. hi; type enum = (a, b, c); 03 Bison generates: type subrange = lo .. hi; type enum = (a, b, c); 04 which should be used in a scanner as follows. type subrange = lo .. hi; type enum = (a, b, c); 05 Tokens that do not have an identifier are not accessible: you cannot simply use characters such as program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 386, they must be declared with %token TYPE DOTDOT ID 57, including the end-of-file token. 10.1.8 A Complete C++ ExampleThis section demonstrates the use of a C++ parser with a simple but complete example. This example should be available on your system, ready to compile, in the directory examples/c++/calc++. It focuses on the use of Bison, therefore the design of the various C++ classes is very naive: no accessors, no encapsulation of members etc. We will use a Lex scanner, and more precisely, a Flex scanner, to demonstrate the various interactions. A hand-written scanner is actually easier to interface with. 10.1.8.1 Calc++ — C++ CalculatorOf course the grammar is dedicated to arithmetic, a single expression, possibly preceded by variable assignments. An environment containing possibly predefined variables such as program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 388 and program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 389, is exchanged with the parser. An example of valid input follows. type subrange = lo .. hi; type enum = (a, b, c); 06 10.1.8.2 Calc++ Parsing DriverTo support a pure interface with the parser (and the scanner) the technique of the “parsing context” is convenient: a structure containing all the data to exchange. Since, in addition to simply launch the parsing, there are several auxiliary tasks to execute (open the file for scanning, instantiate the parser etc.), we recommend transforming the simple parsing context structure into a fully blown parsing driver class. The declaration of this driver class, in driver.hh, is as follows. The first part includes the CPP guard and imports the required standard library components, and the declaration of the parser class. type subrange = lo .. hi; type enum = (a, b, c); 07 Then comes the declaration of the scanning function. Flex expects the signature of type subrange = (a) .. b; 51 to be defined in the macro program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 391, and the C++ parser expects it to be declared. We can factor both as follows. type subrange = lo .. hi; type enum = (a, b, c); 08 The program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 392 class is then declared with its most obvious members. type subrange = lo .. hi; type enum = (a, b, c); 09 The main routine is of course calling the parser. type subrange = lo .. hi; type enum = (a, b, c); 10 To encapsulate the coordination with the Flex scanner, it is useful to have member functions to open and close the scanning phase. type subrange = lo .. hi; type enum = (a, b, c); 11 The implementation of the driver (driver.cc) is straightforward. type subrange = lo .. hi; type enum = (a, b, c); 12 type subrange = lo .. hi; type enum = (a, b, c); 13 The one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 213 member function deserves some attention. type subrange = lo .. hi; type enum = (a, b, c); 14 10.1.8.3 Calc++ ParserThe grammar file parser.yy starts by asking for the C++ deterministic parser skeleton, the creation of the parser header file. Because the C++ skeleton changed several times, it is safer to require the version you designed the grammar for. type subrange = lo .. hi; type enum = (a, b, c); 15 Because our scanner returns only genuine tokens and never simple characters (i.e., it returns ‘PLUS’, not ‘'+'’), we can avoid conversions. This example uses genuine C++ objects as semantic values, therefore, we require the variant-based storage of semantic values. To make sure we properly use it, we enable assertions. To fully benefit from type-safety and more natural definition of “symbol”, we enable program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 394. type subrange = lo .. hi; type enum = (a, b, c); 16 Then come the declarations/inclusions needed by the semantic values. Because the parser uses the parsing driver and reciprocally, both would like to include the header of the other, which is, of course, insane. This mutual dependency will be broken using forward declarations. Because the driver’s header needs detailed knowledge about the parser class (in particular its inner types), it is the parser’s header which will use a forward declaration of the driver. See . type subrange = lo .. hi; type enum = (a, b, c); 17 The driver is passed by reference to the parser and to the scanner. This provides a simple but effective pure interface, not relying on global variables. type subrange = lo .. hi; type enum = (a, b, c); 18 Then we request location tracking. Use the following two directives to enable parser tracing and detailed error messages. However, detailed error messages can contain incorrect information if lookahead correction is not enabled (see ). type subrange = lo .. hi; type enum = (a, b, c); 19 The code between ‘%code {’ and ‘}’ is output in the *.cc file; it needs detailed knowledge about the driver. type subrange = lo .. hi; type enum = (a, b, c); 20 User friendly names are provided for each symbol. To avoid name clashes in the generated files (see ), prefix tokens with program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 395 (see ). type subrange = lo .. hi; type enum = (a, b, c); 21 Since we use variant-based semantic values, %left '+' '-' %left '*' '/' 54 is not used, and %token TYPE DOTDOT ID 57, %left '+' '-' %left '*' '/' 16 and %% type_decl: TYPE ID '=' type ';' ; 84 expect genuine types, not type tags. type subrange = lo .. hi; type enum = (a, b, c); 22 No one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 079 is needed to enable memory deallocation during error recovery; the memory, for strings for instance, will be reclaimed by the regular destructors. All the values are printed using their program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 184 (see ). type subrange = lo .. hi; type enum = (a, b, c); 23 The grammar itself is straightforward (see ). type subrange = lo .. hi; type enum = (a, b, c); 24 Finally the type subrange = lo .. hi; type enum = (a, b, c); 84 member function reports the errors. type subrange = lo .. hi; type enum = (a, b, c); 25 10.1.8.4 Calc++ ScannerIn addition to standard headers, the Flex scanner includes the driver’s, then the parser’s to get the set of defined tokens. type subrange = lo .. hi; type enum = (a, b, c); 26 Since our calculator has no type subrange = (a) .. b; 66-like feature, we don’t need program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 405. We don’t need the program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 406 and type subrange = (a) .. b; 90 functions either, and we parse an actual file, this is not an interactive session with the user. Finally, we enable scanner tracing. type subrange = lo .. hi; type enum = (a, b, c); 27 The following function will be handy to convert a string denoting a number into a program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 188 token. type subrange = lo .. hi; type enum = (a, b, c); 28 Abbreviations allow for more readable rules. type subrange = lo .. hi; type enum = (a, b, c); 29 The following paragraph suffices to track locations accurately. Each time type subrange = (a) .. b; 51 is invoked, the begin position is moved onto the end position. Then when a pattern is matched, its width is added to the end column. When matching ends of lines, the end cursor is adjusted, and each time blanks are matched, the begin cursor is moved onto the end cursor to effectively ignore the blanks preceding tokens. Comments would be treated equally. type subrange = lo .. hi; type enum = (a, b, c); 30 int / keyword ‘int’ /
square (int x) / identifier, open-paren, keyword ‘int’, 6 type subrange = lo .. hi; type enum = (a, b, c); 32 type subrange = lo .. hi; type enum = (a, b, c); 33 The rules are simple. The driver is used to report errors. type subrange = lo .. hi; type enum = (a, b, c); 34 type subrange = lo .. hi; type enum = (a, b, c); 35 type subrange = lo .. hi; type enum = (a, b, c); 36 You should keep your rules simple, both in the parser and in the scanner. Throwing from the auxiliary functions is then very handy to report errors. type subrange = lo .. hi; type enum = (a, b, c); 37 Finally, because the scanner-related driver’s member-functions depend on the scanner’s data, it is simpler to implement them in this file. type subrange = lo .. hi; type enum = (a, b, c); 38 one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 1 type subrange = lo .. hi; type enum = (a, b, c); 40 10.1.8.5 Calc++ Top LevelThe top level file, calc++.cc, poses no problem. type subrange = lo .. hi; type enum = (a, b, c); 41 type subrange = lo .. hi; type enum = (a, b, c); 42 10.2 D Parsers10.2.1 D Bison InterfaceThe D parser skeletons are selected using the program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 410 directive or the -L D/--language=D option. When generating a D parser, ‘bison basename.y’ will create a single D source file named basename.d containing the parser implementation. Using a grammar file without a .y suffix is currently broken. The basename of the parser implementation file can be changed by the program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 144 directive or the -b/--file-prefix option. The entire parser implementation file name can be changed by the program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 412 directive or the -o/--output option. The parser implementation file contains a single class for the parser. You can create documentation for generated parsers using Ddoc. GLR parsers are currently unsupported in D. Do not use the program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 413 directive. No header file can be generated for D parsers. Do not use the one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 282 directive or the -d/--header options. 10.2.2 D Semantic ValuesSemantic types are handled by %left '+' '-' %left '*' '/' 54 and ‘%define api.value.type union’, similar to C/C++ parsers. In the latter case, the union of the values is handled by the backend. In D, unions can hold classes, structs, etc., so this directive is more similar to ‘%define api.value.type variant’ from C++. D parsers do not support one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 079, since the language adopts garbage collection. The parser will try to hold references to semantic values for as little time as needed. D parsers support one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 078. An example for the output of type type subrange = (a) .. b; 83, where one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 220 is the parser’s debug output: type subrange = lo .. hi; type enum = (a, b, c); 43 10.2.3 D Location ValuesWhen the directive one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 579 is used, the D parser supports location tracking, see . The position and the location structures are provided. Instance Variable of Location: Position begin Instance Variable of Location: Position end The first, inclusive, position of the range, and the first beyond. Constructor on Location: this( program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 421 loc) Create a program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 284 denoting an empty range located at a given point. Constructor on Location: this( program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 421 begin, program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 421 end) Create a program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 284 from the endpoints of the range. Method on Location: string toString() The range represented by the location as a string. 10.2.4 D Parser InterfaceThe name of the generated parser class defaults to one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 401. The one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 404 prefix may be changed using the ‘%define api.prefix’. Alternatively, use ‘%define api.parser.class {name}’ to give a custom name to the class. The interface of this class is detailed below. By default, the parser class has public visibility. To add modifiers to the parser class, type subrange = (a) .. b; 80 program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 429, program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 430 and/or program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 431. The superclass and the implemented interfaces of the parser class can be specified with the ‘%define api.parser.extends’ and ‘%define api.parser.implements’ directives. The parser class defines an interface, program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 432 (see ). Other than this interface and the members described in the interface below, all the other members and fields are preceded with a one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 399 or one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 404 prefix to avoid clashes with user code. The parser class can be extended using the one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 168 directive. Each occurrence of the directive will add a by default public field to the parser class, and an argument to its constructor, which initializes them automatically. Constructor on YYParser: this(lex_param, …, parse_param, …) Build a new parser object with embedded ‘%code lexer’. There are no parameters, unless one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 668s and/or one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 168s and/or one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 663s are used. Constructor on YYParser: this( program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 432 lexer, parse_param, …) Build a new parser object using the specified scanner. There are no additional parameters unless one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 668s and/or one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 168s are used. Method on YYParser: boolean parse() Run the syntactic analysis, and return one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 356 on success, one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 361 otherwise. Method on YYParser: boolean getErrorVerbose() Method on YYParser: void setErrorVerbose(boolean verbose) Get or set the option to produce verbose error messages. These are only available with ‘%define parse.error detailed’, which also turns on verbose error messages. Method on YYParser: void yyerror( program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 444 msg) Method on YYParser: void yyerror( program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 284 loc, program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 444 msg) Print an error message using the type subrange = (a) .. b; 56 method of the scanner instance in use. The program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 284 and program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 421 parameters are available only if location tracking is active. Method on YYParser: boolean recovering() During the syntactic analysis, return one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 356 if recovering from a syntax error. See . Method on YYParser: File getDebugStream() Method on YYParser: void setDebugStream( program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 451 o) Get or set the stream used for tracing the parsing. It defaults to program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 037. Method on YYParser: int getDebugLevel() Method on YYParser: void setDebugLevel( type subrange = (a) .. b; 83 l) Get or set the tracing level. Currently its value is either 0, no trace, or nonzero, full tracing. Constant of YYParser: string bisonVersion Constant of YYParser: string bisonSkeleton Identify the Bison version and skeleton used to generate this parser. The internationalization in D is very similar to the one in C. The D parser uses program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 454 for translating Bison messages. To enable internationalization, compile using ‘-version ENABLE_NLS -version YYENABLE_NLS’ and import program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 455 and program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 456 from C: type subrange = lo .. hi; type enum = (a, b, c); 44 The main function should load the translation catalogs, similarly to the c/bistromathic example: type subrange = lo .. hi; type enum = (a, b, c); 45 For user message translations, the user must implement the ‘string _(const char* msg)’ function. It is recommended to use one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 763: type subrange = lo .. hi; type enum = (a, b, c); 46 10.2.5 D Parser Context InterfaceThe parser context provides information to build error reports when you invoke ‘%define parse.error custom’. Type of YYParser: SymbolKind A struct containing an enum of all the grammar symbols, tokens and nonterminals. Its enumerators are forged from the symbol names. Use ‘void toString(W)(W sink)’ to get the symbol names. Method on YYParser.Context: YYParser.SymbolKind getToken() The kind of the lookahead. Return program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 458 iff there is no lookahead. Method on YYParser.Context: YYParser.Location getLocation() The location of the lookahead. Method on YYParser.Context: int getExpectedTokens( program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 459 argv, type subrange = (a) .. b; 83 argc) Fill argv with the expected tokens, which never includes program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 461, or program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 462. Never put more than argc elements into argv, and on success return the number of tokens stored in argv. If there are more expected tokens than argc, fill argv up to argc and return 0. If there are no expected tokens, also return 0, but set one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 607 to program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 458. If argv is null, return the size needed to store all the possible values, which is always less than one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 335. 10.2.6 D Scanner InterfaceThere are two possible ways to interface a Bison-generated D parser with a scanner: the scanner may be defined by program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 466, or defined elsewhere. In either case, the scanner has to implement the program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 432 inner interface of the parser class. This interface also contains constants for all user-defined token names and the predefined type subrange = (a) .. b; 26 token. In the first case, the body of the scanner class is placed in program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 466 blocks. If you want to pass parameters from the parser constructor to the scanner constructor, specify them with one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 663; they are passed before one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 168s to the constructor. In the second case, the scanner has to implement the program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 432 interface, which is defined within the parser class (e.g., program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 473). The constructor of the parser object will then accept an object implementing the interface; one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 663 is not used in this case. In both cases, the scanner has to implement the following methods. Method on Lexer: void yyerror( program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 284 loc, program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 444 msg) This method is defined by the user to emit an error message. The first parameter is omitted if location tracking is not active. Method on Lexer: Symbol yylex() Return the next token. The return value is of type program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 477, which binds together the kind, the semantic value and the location. Method on Lexer: void reportSyntaxError( program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 478 ctx) If you invoke ‘%define parse.error custom’ (see ), then the parser no longer passes syntax error messages to type subrange = (a) .. b; 56, rather it delegates that task to the user by calling the program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 480 function. Whether it uses type subrange = (a) .. b; 56 is up to the user. Here is an example of a reporting function (see ). type subrange = lo .. hi; type enum = (a, b, c); 47 This implementation is inappropriate for internationalization, see the c/bistromathic example for a better alternative. 10.2.7 Special Features for Use in D ActionsHere is a table of Bison constructs, variables and functions that are useful in actions. Variable: $$ Acts like a variable that contains the semantic value for the grouping made by the current rule. See . Variable: $n Acts like a variable that contains the semantic value for the nth component of the current rule. See . Function: yyerrok Resume generating error messages immediately for subsequent syntax errors. This is useful primarily in error rules. See . 10.2.8 D Push Parser InterfaceNormally, Bison generates a pull parser for D. The following Bison declaration says that you want the parser to be a push parser (see ): program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 50 Most of the discussion about the D pull Parser Interface, (see ) applies to the push parser interface as well. When generating a push parser, the method program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 482 is created with the following signature: Method on YYParser: int pushParse ( program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 477 sym) The primary difference with respect to a pull parser is that the parser method program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 482 is invoked repeatedly to parse each token. This function is available if either the ‘%define api.push-pull push’ or ‘%define api.push-pull both’ declaration is used (see ). The value returned by the program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 482 method is one of the following: program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 486, program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 487, or program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 488. This new value, program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 488, may be returned if more input is required to finish parsing the input. If program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 490 is defined as one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 423, then the generated parser class will also implement the one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 213 method. This method’s body is a loop that repeatedly invokes the scanner and then passes the values obtained from the scanner to the program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 482 method. 10.2.9 D Complete SymbolsTo build return values for type subrange = (a) .. b; 51, call the program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 477 method of the same name as the token kind reported, and adding the parameters for value and location if necessary. These methods generate compile-time errors if the parameters are inconsistent. Token constructors work with both %left '+' '-' %left '*' '/' 54 and ‘%define api.value.type union’. The order of the parameters is the same as for the program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 477 constructor. An example for the token kind type subrange = (a) .. b; 86, which has value program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 499 and with location tracking activated: type subrange = lo .. hi; type enum = (a, b, c); 49 10.3 Java Parsers10.3.1 Java Bison InterfaceThe Java parser skeletons are selected using the program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 500 directive or the -L java/--language=java option. When generating a Java parser, ‘bison basename.y’ will create a single Java source file named basename.java containing the parser implementation. Using a grammar file without a .y suffix is currently broken. The basename of the parser implementation file can be changed by the program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 144 directive or the -b/--file-prefix option. The entire parser implementation file name can be changed by the program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 412 directive or the -o/--output option. The parser implementation file contains a single class for the parser. You can create documentation for generated parsers using Javadoc. Contrary to C parsers, Java parsers do not use global variables; the state of the parser is always local to an instance of the parser class. Therefore, all Java parsers are “pure”, and the one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 578 directive does nothing when used in Java. GLR parsers are currently unsupported in Java. Do not use the program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 413 directive. No header file can be generated for Java parsers. Do not use the one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 282 directive or the -d/-H/--header options. Currently, support for tracing is always compiled in. Thus the ‘%define parse.trace’ and ‘%token-table’ directives and the -t/--debug and -k/--token-table options have no effect. This may change in the future to eliminate unused code in the generated parser, so use ‘%define parse.trace’ explicitly if needed. Also, in the future the one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 334 directive might enable a public interface to access the token names and codes. Getting a “code too large” error from the Java compiler means the code hit the 64KB bytecode per method limitation of the Java class file. Try reducing the amount of code in actions and static initializers; otherwise, report a bug so that the parser skeleton will be improved. 10.3.2 Java Semantic ValuesThere is no %left '+' '-' %left '*' '/' 54 directive in Java parsers. Instead, the semantic values’ types (class names) should be specified in the %left '+' '-' %left '*' '/' 16 or %token TYPE DOTDOT ID 57 directive: type subrange = lo .. hi; type enum = (a, b, c); 50 By default, the semantic stack is declared to have program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 510 members, which means that the class types you specify can be of any class. To improve the type safety of the parser, you can declare the common superclass of all the semantic values using the ‘%define api.value.type’ directive. For example, after the following declaration: type subrange = lo .. hi; type enum = (a, b, c); 51 any %token TYPE DOTDOT ID 57, %left '+' '-' %left '*' '/' 16 or %% type_decl: TYPE ID '=' type ';' ; 84 specifying a semantic type which is not a subclass of program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 514, will cause a compile-time error. Types used in the directives may be qualified with a package name. Primitive data types are accepted for Java version 1.5 or later. Note that in this case the autoboxing feature of Java 1.5 will be used. Generic types may not be used; this is due to a limitation in the implementation of Bison, and may change in future releases. Java parsers do not support one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 079, since the language adopts garbage collection. The parser will try to hold references to semantic values for as little time as needed. Java parsers do not support one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 078, as program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 517 can be used to print the semantic values. This however may change (in a backwards-compatible way) in future versions of Bison. 10.3.3 Java Location ValuesWhen the directive one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 579 is used, the Java parser supports location tracking, see . An auxiliary user-defined class defines a position, a single point in a file; Bison itself defines a class representing a location, a range composed of a pair of positions (possibly spanning several files). The location class is an inner class of the parser; the name is program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 284 by default, and may also be renamed using program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 520. The location class treats the position as a completely opaque value. By default, the class name is program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 421, but this can be changed with program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 522. This class must be supplied by the user. Instance Variable of Location: Position begin Instance Variable of Location: Position end The first, inclusive, position of the range, and the first beyond. Constructor on Location: Location ( program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 421 loc) Create a program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 284 denoting an empty range located at a given point. Constructor on Location: Location ( program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 421 begin, program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 421 end) Create a program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 284 from the endpoints of the range. Method on Location: String toString () Prints the range represented by the location. For this to work properly, the position class should override the program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 528 and program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 529 methods appropriately. 10.3.4 Java Parser InterfaceThe name of the generated parser class defaults to one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 401. The one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 404 prefix may be changed using the ‘%define api.prefix’. Alternatively, use ‘%define api.parser.class {name}’ to give a custom name to the class. The interface of this class is detailed below. By default, the parser class has package visibility. A declaration ‘%define api.parser.public’ will change to public visibility. Remember that, according to the Java language specification, the name of the .java file should match the name of the class in this case. Similarly, you can use program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 430, program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 431 and program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 534 with the type subrange = (a) .. b; 80 declaration to add other modifiers to the parser class. A single ‘%define api.parser.annotations {annotations}’ directive can be used to add any number of annotations to the parser class. The Java package name of the parser class can be specified using the ‘%define package’ directive. The superclass and the implemented interfaces of the parser class can be specified with the program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 536 and ‘%define api.parser.implements’ directives. The parser class defines an inner class, program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 284, that is used for location tracking (see ), and a inner interface, program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 432 (see ). Other than these inner class/interface, and the members described in the interface below, all the other members and fields are preceded with a one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 399 or one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 404 prefix to avoid clashes with user code. The parser class can be extended using the one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 168 directive. Each occurrence of the directive will add a program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 542 field to the parser class, and an argument to its constructor, which initializes them automatically. Constructor on YYParser: YYParser (lex_param, …, parse_param, …) Build a new parser object with embedded program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 466. There are no parameters, unless one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 668s and/or one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 168s and/or one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 663s are used. Use program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 547 for code added to the start of the constructor body. This is especially useful to initialize superclasses. Use ‘%define init_throws’ to specify any uncaught exceptions. Constructor on YYParser: YYParser ( program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 432 lexer, parse_param, …) Build a new parser object using the specified scanner. There are no additional parameters unless one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 668s and/or one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 168s are used. If the scanner is defined by program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 466, this constructor is declared program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 552 and is called automatically with a scanner created with the correct one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 668s and/or one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 663s. Use program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 547 for code added to the start of the constructor body. This is especially useful to initialize superclasses. Use ‘%define init_throws’ to specify any uncaught exceptions. Method on YYParser: boolean parse () Run the syntactic analysis, and return one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 356 on success, one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 361 otherwise. Method on YYParser: boolean getErrorVerbose () Method on YYParser: void setErrorVerbose (boolean verbose) Get or set the option to produce verbose error messages. These are only available with ‘%define parse.error detailed’ (or ‘verbose’), which also turns on verbose error messages. Method on YYParser: void yyerror ( program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 558 msg) Method on YYParser: void yyerror ( program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 421 pos, program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 558 msg) Method on YYParser: void yyerror ( program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 284 loc, program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 558 msg) Print an error message using the type subrange = (a) .. b; 56 method of the scanner instance in use. The program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 284 and program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 421 parameters are available only if location tracking is active. Method on YYParser: boolean recovering () During the syntactic analysis, return one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 356 if recovering from a syntax error. See . Method on YYParser: java.io.PrintStream getDebugStream () Method on YYParser: void setDebugStream ( program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 567 o) Get or set the stream used for tracing the parsing. It defaults to program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 568. Method on YYParser: int getDebugLevel () Method on YYParser: void setDebugLevel ( type subrange = (a) .. b; 83 l) Get or set the tracing level. Currently its value is either 0, no trace, or nonzero, full tracing. Constant of YYParser: String bisonVersion Constant of YYParser: String bisonSkeleton Identify the Bison version and skeleton used to generate this parser. If you enabled token internationalization (see ), you must provide the parser with the following function: Static Method of YYParser: String i18n ( program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 444 s) Return the translation of s in the user’s language. As an example: type subrange = lo .. hi; type enum = (a, b, c); 52 10.3.5 Java Parser Context InterfaceThe parser context provides information to build error reports when you invoke ‘%define parse.error custom’. Type of YYParser: SymbolKind An enum of all the grammar symbols, tokens and nonterminals. Its enumerators are forged from the symbol names: type subrange = lo .. hi; type enum = (a, b, c); 53 Method on YYParser.SymbolKind: String getName () The name of this symbol, possibly translated. Method on YYParser.Context: YYParser.SymbolKind getToken () The kind of the lookahead. Return program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 458 iff there is no lookahead. Method on YYParser.Context: YYParser.Location getLocation () The location of the lookahead. Method on YYParser.Context: int getExpectedTokens ( program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 459 argv, type subrange = (a) .. b; 83 argc) Fill argv with the expected tokens, which never includes program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 574, or program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 575. Never put more than argc elements into argv, and on success return the number of tokens stored in argv. If there are more expected tokens than argc, fill argv up to argc and return 0. If there are no expected tokens, also return 0, but set one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 607 to program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 458. If argv is null, return the size needed to store all the possible values, which is always less than one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 335. 10.3.6 Java Scanner InterfaceThere are two possible ways to interface a Bison-generated Java parser with a scanner: the scanner may be defined by program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 466, or defined elsewhere. In either case, the scanner has to implement the program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 432 inner interface of the parser class. This interface also contains constants for all user-defined token names and the predefined type subrange = (a) .. b; 26 token. In the first case, the body of the scanner class is placed in program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 466 blocks. If you want to pass parameters from the parser constructor to the scanner constructor, specify them with one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 663; they are passed before one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 168s to the constructor. In the second case, the scanner has to implement the program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 432 interface, which is defined within the parser class (e.g., program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 473). The constructor of the parser object will then accept an object implementing the interface; one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 663 is not used in this case. In both cases, the scanner has to implement the following methods. Method on Lexer: void yyerror ( program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 284 loc, program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 558 msg) This method is defined by the user to emit an error message. The first parameter is omitted if location tracking is not active. Its type can be changed using program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 520. Method on Lexer: int yylex () Return the next token. Its type is the return value, its semantic value and location are saved and returned by the their methods in the interface. Not needed for push-only parsers. Use ‘%define lex_throws’ to specify any uncaught exceptions. Default is program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 591. Method on Lexer: Position getStartPos () Method on Lexer: Position getEndPos () Return respectively the first position of the last token that type subrange = (a) .. b; 51 returned, and the first position beyond it. These methods are not needed unless location tracking and pull parsing are active. They should return new objects for each call, to avoid that all the symbol share the same Position boundaries. The return type can be changed using program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 593. Method on Lexer: Object getLVal () Return the semantic value of the last token that yylex returned. Not needed for push-only parsers. The return type can be changed using ‘%define api.value.type {class-name}’. Method on Lexer: void reportSyntaxError ( program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 478 ctx) If you invoke ‘%define parse.error custom’ (see ), then the parser no longer passes syntax error messages to type subrange = (a) .. b; 56, rather it delegates that task to the user by calling the program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 480 function. Whether it uses type subrange = (a) .. b; 56 is up to the user. Here is an example of a reporting function (see ). type subrange = lo .. hi; type enum = (a, b, c); 54 This implementation is inappropriate for internationalization, see the c/bistromathic example for a better alternative. 10.3.7 Special Features for Use in Java ActionsThe following special constructs can be uses in Java actions. Other analogous C action features are currently unavailable for Java. Use ‘%define throws’ to specify any uncaught exceptions from parser actions, and initial actions specified by one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 100. Variable: $n The semantic value for the nth component of the current rule. This may not be assigned to. See . Variable: $<typealt>n Like one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 024 but specifies a alternative type typealt. See . Variable: $$ The semantic value for the grouping made by the current rule. As a value, this is in the base type ( program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 510 or as specified by ‘%define api.value.type’) as in not cast to the declared subtype because casts are not allowed on the left-hand side of Java assignments. Use an explicit Java cast if the correct subtype is needed. See . Variable: $<typealt>$ Same as type subrange = (a) .. b; 91 since Java always allow assigning to the base type. Perhaps we should use this and program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 602 for the value and type subrange = (a) .. b; 91 for setting the value but there is currently no easy way to distinguish these constructs. See . Variable: @n The location information of the nth component of the current rule. This may not be assigned to. See . Variable: @$ The location information of the grouping made by the current rule. See . Statement: return YYABORT one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 109 Return immediately from the parser, indicating failure. See . Statement: return YYACCEPT one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 109 Return immediately from the parser, indicating success. See . Statement: return YYERROR one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 109 Start error recovery (without printing an error message). See . Function: boolean recovering () Return whether error recovery is being done. In this state, the parser reads token until it reaches a known state, and then restarts normal operation. See . Function: void yyerror ( program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 558 msg) Function: void yyerror ( program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 421 loc, program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 558 msg) Function: void yyerror ( program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 284 loc, program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 558 msg) Print an error message using the type subrange = (a) .. b; 56 method of the scanner instance in use. The program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 284 and program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 421 parameters are available only if location tracking is active. 10.3.8 Java Push Parser InterfaceNormally, Bison generates a pull parser for Java. The following Bison declaration says that you want the parser to be a push parser (see ): program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 50 Most of the discussion about the Java pull Parser Interface, (see ) applies to the push parser interface as well. When generating a push parser, the method program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 615 is created with the following signature (depending on if locations are enabled). Method on YYParser: void push_parse ( type subrange = (a) .. b; 83 token, program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 510 yylval) Method on YYParser: void push_parse ( type subrange = (a) .. b; 83 token, program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 510 yylval, program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 284 yyloc) Method on YYParser: void push_parse ( type subrange = (a) .. b; 83 token, program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 510 yylval, program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 421 yypos) The primary difference with respect to a pull parser is that the parser method program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 615 is invoked repeatedly to parse each token. This function is available if either the ‘%define api.push-pull push’ or ‘%define api.push-pull both’ declaration is used (see ). The program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 284 and program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 421 parameters are available only if location tracking is active. The value returned by the program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 615 method is one of the following: 0 (success), 1 (abort), 2 (memory exhaustion), or one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 588. This new value, one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 588, may be returned if more input is required to finish parsing the grammar. If program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 490 is defined as one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 423, then the generated parser class will also implement the one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 213 method. This method’s body is a loop that repeatedly invokes the scanner and then passes the values obtained from the scanner to the program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 615 method. There is one additional complication. Technically, the push parser does not need to know about the scanner (i.e. an object implementing the program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 473 interface), but it does need access to the type subrange = (a) .. b; 56 method. Currently, the type subrange = (a) .. b; 56 method is defined in the program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 473 interface. Hence, an implementation of that interface is still required in order to provide an implementation of type subrange = (a) .. b; 56. The current approach (and subject to change) is to require the one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 401 constructor to be given an object implementing the program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 473 interface. This object need only implement the type subrange = (a) .. b; 56 method; the other methods can be stubbed since they will never be invoked. The simplest way to do this is to add a trivial scanner implementation to your grammar file using whatever implementation of type subrange = (a) .. b; 56 is desired. The following code sample shows a simple way to accomplish this. type subrange = lo .. hi; type enum = (a, b, c); 56 10.3.9 Differences between C/C++ and Java GrammarsThe different structure of the Java language forces several differences between C/C++ grammars, and grammars designed for Java parsers. This section summarizes these differences.
10.3.10 Java Declarations SummaryThis summary only include declarations specific to Java or have special meaning when used in a Java parser. Directive: %language "Java" Generate a Java class for the parser. Directive: %lex-param {type name} A parameter for the lexer class defined by program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 466 only, added as parameters to the lexer constructor and the parser constructor that creates a lexer. Default is none. See . Directive: %parse-param {type name} A parameter for the parser class added as parameters to constructor(s) and as fields initialized by the constructor(s). Default is none. See . Directive: %token <type> token … Declare tokens. Note that the angle brackets enclose a Java type. See . Directive: %nterm <type> nonterminal … Declare the type of nonterminals. Note that the angle brackets enclose a Java type. See . Directive: %code { code … } Code appended to the inside of the parser class. See . Directive: %code imports { code … } Code inserted just after the program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 660 declaration. See . Directive: %code init { code … } Code inserted at the beginning of the parser constructor body. See . Directive: %code lexer { code … } Code added to the body of a inner lexer class within the parser class. See . Directive: %% code … Code (after the second program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details.
Directive: %{ code … %} Not supported. Use program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 659 instead. See . Directive: %define api.prefix {prefix} The prefix of the parser class name program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 669 if ‘%define api.parser.class’ is not used. Default is one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 404. See . Directive: %define api.parser.abstract Whether the parser class is declared program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 671. Default is false. See . Directive: %define api.parser.annotations {annotations} The Java annotations for the parser class. Default is none. See . Directive: %define api.parser.class {name} The name of the parser class. Default is one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 401 or one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 402. See . Directive: %define api.parser.extends {superclass} The superclass of the parser class. Default is none. See . Directive: %define api.parser.final Whether the parser class is declared program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 674. Default is false. See . Directive: %define api.parser.implements {interfaces} The implemented interfaces of the parser class, a comma-separated list. Default is none. See . Directive: %define api.parser.public Whether the parser class is declared program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 675. Default is false. See . Directive: %define api.parser.strictfp Whether the parser class is declared program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 676. Default is false. See . Directive: %define init_throws {exceptions} The exceptions thrown by program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 547 from the parser class constructor. Default is none. See . Directive: %define lex_throws {exceptions} The exceptions thrown by the type subrange = (a) .. b; 51 method of the lexer, a comma-separated list. Default is program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 591. See . Directive: %define api.location.type {class} The name of the class used for locations (a range between two positions). This class is generated as an inner class of the parser class by %% type_decl: TYPE ID '=' type ';' ; 61. Default is program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 284. Formerly named one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 393. See . Directive: %define api.package {package} The package to put the parser class in. Default is none. See . Renamed from program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 660 in Bison 3.7. Directive: %define api.position.type {class} The name of the class used for positions. This class must be supplied by the user. Default is program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 421. Formerly named program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 685. See . Directive: %define api.value.type {class} The base type of semantic values. Default is program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 510. See . Directive: %define throws {exceptions} The exceptions thrown by user-supplied parser actions and one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 100, a comma-separated list. Default is none. See . 11 A Brief History of the Greater Ungulates11.1 The ancestral YaccBison originated as a workalike of a program called Yacc — Yet Another Compiler Compiler. Yacc was written at Bell Labs as part of the very early development of Unix; one of its first uses was to develop the original Portable C Compiler, pcc. The same person, Steven C. Johnson, wrote Yacc and the original pcc. According to the author , Yacc was first invented in 1971 and reached a form recognizably similar to the C version in 1973. Johnson published A Portable Compiler: Theory and Practice (see ). Yacc was not itself originally written in C but in its predecessor language, B. This goes far to explain its odd interface, which exposes a large number of global variables rather than bundling them into a C struct. All other Yacc-like programs are descended from the C port of Yacc. Yacc, through both its deployment in pcc and as a standalone tool for generating other parsers, helped drive the early spread of Unix. Yacc itself, however, passed out of use after around 1990 when workalikes with less restrictive licenses and more features became available. Original Yacc became generally available when Caldera released the sources of old versions of Unix up to V7 and 32V in 2002. By that time it had been long superseded in practical use by Bison even on Yacc’s native Unix variants. 11.2 yacchackOne of the deficiencies of original Yacc was its inability to produce reentrant parsers. This was first remedied by a set of drop-in modifications called “yacchack”, published by Eric S. Raymond on USENET around 1983. This code was quickly forgotten when zoo and Berkeley Yacc became available a few years later. 11.3 Berkeley YaccBerkeley Yacc was originated in 1985 by Robert Corbett (see ). It was originally named “zoo”, but by October 1989 it became known as Berkeley Yacc or byacc. Berkeley Yacc had three advantages over the ancestral Yacc: it generated faster parsers, it could generate reentrant parsers, and the source code was released to the public domain rather than being under an AT&T proprietary license. The better performance came from implementing techniques from DeRemer and Penello’s seminal paper on LALR parsing (see ). Use of byacc spread rapidly due to its public domain license. However, once Bison became available, byacc itself passed out of general use. 11.4 BisonRobert Corbett actually wrote two (closely related) LALR parsers in 1985, both using the DeRemer/Penello techniques. One was “zoo”, the other was “Byson”. In 1987 Richard Stallman began working on Byson; the name changed to Bison and the interface became Yacc-compatible. The main visible difference between Yacc and Byson/Bison at the time of Byson’s first release is that Byson supported the %token TYPE DOTDOT ID 85 construct (giving access to the starting and ending line number and character number associated with any of the symbols in the current rule). There was also the command ‘%expect n’ which said not to mention the conflicts if there are n shift/reduce conflicts and no reduce/reduce conflicts. In more recent versions of Bison, one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 235 and its one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 237 variant for reduce/reduce conflicts can be applied to individual rules. Later versions of Bison added many more new features. Bison error reporting has been improved in various ways. Notably. ancestral Yacc and Byson did not have carets in error messages. Compared to Yacc Bison uses a faster but less space-efficient encoding for the parse tables (see ), and more modern techniques for generating the lookahead sets (see ). This approach is the standard one since then. (It has also been plausibly alleged the differences in the algorithms stem mainly from the horrible kludges that Johnson had to perpetrate to make the original Yacc fit in a PDP-11.) Named references, semantic predicates, one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 579, type subrange = lo .. hi; type enum = (a, b, c); 94, one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 078, %destructor, dumps to DOT, one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 168, one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 663, and dumps to XSLT, LAC, and IELR(1) generation are new in Bison. Bison also has many features to support C++ that were not present in the ancestral Yacc or Byson. Bison obsolesced all previous Yacc variants and workalikes generating C by 1995. 11.5 Other UngulatesThe Yacc concept has frequently been ported to other languages. Some of the early ports are extinct along with the languages that hosted them; others have been superseded by parser skeletons shipped with Bison. However, independent implementations persist. One of the best-known still in use is David Beazley’s “PLY” (Python Lex-Yacc) for Python. Another is goyacc, supporting the Go language. An “ocamlyacc” is shipped as part of the Ocaml compiler suite. 12 Bison Version Compatibility: Best PracticesBison provides a Yacc compatibility mode in which it strives to conform with the POSIX standard. Grammar files which are written to the POSIX standard, and do not take advantage of any of the special capabilities of Bison, should work with many versions of Bison without modification. All other features of Bison are particular to Bison, and are changing. Bison is actively maintained and continuously evolving. It should come as no surprise that an older version of Bison will not accept Bison source code which uses newer features that do no not exist at all in the older Bison. Regrettably, in spite of reasonable effort to maintain compatibility, the reverse situation may also occur: it may happen that code developed using an older version of Bison does not build with a newer version of Bison without modifications. Because Bison is a code generation tool, it is possible to retain its output and distribute that to the users of the program. The users are then not required to have Bison installed at all, only an implementation of the programming language, such as C, which is required for processing the generated output. It is the output of Bison that is intended to be of the utmost portability. So, that is to say, whereas the Bison grammar source code may have a dependency on specific versions of Bison, the generated parser from any version of Bison should work with with a large number of implementations of C, or whatever language is applicable. The recommended best practice for using Bison (in the context of software that is distributed in source code form) is to ship the generated parser to the downstream users. Only those downstream users who engage in active development of the program who need to make changes to the grammar file need to have Bison installed at all, and those users can install the specific version of Bison which is required. Following this recommended practice also makes it possible to use a more recent Bison than what is available to users through operating system distributions, thereby taking advantage of the latest techniques that Bison allows. Some features of Bison have been, or are being adopted into other Yacc-like programs. Therefore it might seem that is a good idea to write grammar code which targets multiple implementations, similarly to the way C programs are often written to target multiple compilers and language versions. Other than the Yacc subset described by POSIX, the Bison language is not rigorously standardized. When a Bison feature is adopted by another parser generator, it may be initially compatible with that version of Bison on which it was based, but the compatibility may degrade going forward. Developers who strive to make their Bison code simultaneously compatible with other parser generators are encouraged to nevertheless use specific versions of all generators, and still follow the recommended practice of shipping generated output. For example, a project can internally maintain compatibility with multiple generators, and choose the output of a particular one to ship to the users. Or else, the project could ship all of the outputs, arranging for a way for the user to specify which one is used to build the program. 13 Frequently Asked QuestionsSeveral questions about Bison come up occasionally. Here some of them are addressed. 13.1 Memory ExhaustedMy parser returns with error with a ‘memory exhausted’ message. What can I do? This question is already addressed elsewhere, see . 13.2 How Can I Reset the ParserThe following phenomenon has several symptoms, resulting in the following typical questions: I invoke or My parser includes support for an ‘ These problems typically come not from Bison itself, but from Lex-generated scanners. Because these scanners use large buffers for speed, they might not notice a change of input file. As a demonstration, consider the following source file, first-line.l: type subrange = lo .. hi; type enum = (a, b, c); 57 type subrange = lo .. hi; type enum = (a, b, c); 58 type subrange = lo .. hi; type enum = (a, b, c); 59 type subrange = lo .. hi; type enum = (a, b, c); 60 one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 1 type subrange = lo .. hi; type enum = (a, b, c); 62 If the file input contains type subrange = lo .. hi; type enum = (a, b, c); 63 then instead of getting the first line twice, you get: type subrange = lo .. hi; type enum = (a, b, c); 64 Therefore, whenever you change program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 700, you must tell the Lex-generated scanner to discard its current buffer and switch to the new one. This depends upon your implementation of Lex; see its documentation for more. For Flex, it suffices to call ‘YY_FLUSH_BUFFER’ after each change to program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 700. If your Flex-generated scanner needs to read from several input streams to handle features like include files, you might consider using Flex functions like ‘yy_switch_to_buffer’ that manipulate multiple input buffers. If your Flex-generated scanner uses start conditions (see in The Flex Manual), you might also want to reset the scanner’s state, i.e., go back to the initial start condition, through a call to ‘BEGIN (0)’. 13.3 Strings are DestroyedMy parser seems to destroy old strings, or maybe it loses track of them. Instead of reporting ‘"foo", "bar"’, it reports ‘"bar", "bar"’, or even ‘"foo\nbar", "bar"’. This error is probably the single most frequent “bug report” sent to Bison lists, but is only concerned with a misunderstanding of the role of the scanner. Consider the following Lex code: type subrange = lo .. hi; type enum = (a, b, c); 65 type subrange = lo .. hi; type enum = (a, b, c); 66 type subrange = lo .. hi; type enum = (a, b, c); 67 If you compile and run this code, you get: type subrange = lo .. hi; type enum = (a, b, c); 68 this is because program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 702 is a buffer provided for reading in the action, but if you want to keep it, you have to duplicate it (e.g., using program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 703). Note that the output may depend on how your implementation of Lex handles program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 702. For instance, when given the Lex compatibility option -l (which triggers the option ‘%array’) Flex generates a different behavior: type subrange = lo .. hi; type enum = (a, b, c); 69 13.4 Implementing Gotos/LoopsMy simple calculator supports variables, assignments, and functions, but how can I implement gotos, or loops? Although very pedagogical, the examples included in the document blur the distinction to make between the parser—whose job is to recover the structure of a text and to transmit it to subsequent modules of the program—and the processing (such as the execution) of this structure. This works well with so called straight line programs, i.e., precisely those that have a straightforward execution model: execute simple instructions one after the others. If you want a richer model, you will probably need to use the parser to construct a tree that does represent the structure it has recovered; this tree is usually called the abstract syntax tree, or AST for short. Then, walking through this tree, traversing it in various ways, will enable treatments such as its execution or its translation, which will result in an interpreter or a compiler. This topic is way beyond the scope of this manual, and the reader is invited to consult the dedicated literature. 13.5 Multiple start-symbolsI have several closely related grammars, and I would like to share their implementations. In fact, I could use a single grammar but with multiple entry points. Bison does not support multiple start-symbols, but there is a very simple means to simulate them. If one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 046 and one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 042 are the two pseudo start-symbols, then introduce two new tokens, say program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 707 and program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 708, and use them as switches from the real start-symbol: type subrange = lo .. hi; type enum = (a, b, c); 70 These tokens prevent the introduction of new conflicts. As far as the parser goes, that is all that is needed. Now the difficult part is ensuring that the scanner will send these tokens first. If your scanner is hand-written, that should be straightforward. If your scanner is generated by Lex, them there is simple means to do it: recall that anything between ‘%{ ... %}’ after the first program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 667 is copied verbatim in the top of the generated type subrange = (a) .. b; 51 function. Make sure a variable program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 711 is available in the scanner (e.g., a global variable or using one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 663 etc.), and use the following: type subrange = lo .. hi; type enum = (a, b, c); 71 13.6 Secure? Conform?Is Bison secure? Does it conform to POSIX? If you’re looking for a guarantee or certification, we don’t provide it. However, Bison is intended to be a reliable program that conforms to the POSIX specification for Yacc. If you run into problems, please send us a bug report. 13.7 Enabling RelocatabilityIt has been a pain for many users of GNU packages for a long time that packages are not relocatable. It means a user cannot copy a program, installed by another user on the same machine, to his home directory, and have it work correctly (including i18n). So many users need to go through program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 713 with all its dependencies, options, and hurdles. Most package management systems, that allow the user to install pre-built binaries of the packages, solve the “ease of installation” problem, but they hardwire path names, usually to /usr or /usr/local. This means that users need root privileges to install a binary package, and prevents installing two different versions of the same binary package. A relocatable program can be moved or copied to a different location on the file system. It is possible to make symlinks to the installed and moved programs, and invoke them through the symlink. It is possible to do the same thing with a hard link only if the hard link file is in the same directory as the real program. To configure a program to be relocatable, add --enable-relocatable to the one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 766 command line. On some OSes the executables remember the location of shared libraries and prefer them over any other search path. Therefore, such an executable will look for its shared libraries first in the original installation directory and only then in the current installation directory. Thus, for reliability, it is best to also give a --prefix option pointing to a directory that does not exist now and which never will be created, e.g. --prefix=/nonexistent. You may use program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 715 on the %token TYPE DOTDOT ID 44 command line to avoid installing into that directory. We do not recommend using a prefix writable by unprivileged users (e.g. /tmp/inst$$) because such a directory can be recreated by an unprivileged user after the original directory has been removed. We also do not recommend prefixes that might be behind an automounter (e.g. $HOME/inst$$) because of the performance impact of directory searching. Here’s a sample installation run that takes into account all these recommendations: type subrange = lo .. hi; type enum = (a, b, c); 72 Installation with --enable-relocatable will not work for setuid or setgid executables, because such executables search only system library paths for security reasons. The runtime penalty and size penalty are negligible on GNU/Linux (just one system call more when an executable is launched), and small on other systems (the wrapper program just sets an environment variable and executes the real program). 13.8 I can’t build BisonI can’t build Bison because Like most GNU packages with internationalization support, that feature is turned on by default. If you have problems building in the po subdirectory, it indicates that your system’s internationalization support is lacking. You can re-configure Bison with --disable-nls to turn off this support, or you can install GNU gettext from https://ftp.gnu.org/gnu/gettext/ and re-configure Bison. See the file ABOUT-NLS for more information. I can’t build Bison because my C compiler is too old. Except for GLR parsers (which require C99), the C code that Bison generates requires only C89 or later. However, Bison itself requires common C99 features such as declarations after statements. Bison’s one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 766 script attempts to enable C99 (or later) support on compilers that default to pre-C99. If your compiler lacks these C99 features entirely, GCC may well be a better choice; or you can try upgrading to your compiler’s latest version. 13.9 Where can I find help?I’m having trouble using Bison. Where can I find help? First, read this fine manual. Beyond that, you can send mail to [email protected]. This mailing list is intended to be populated with people who are willing to answer questions about using and installing Bison. Please keep in mind that (most of) the people on the list have aspects of their lives which are not related to Bison (!), so you may not receive an answer to your question right away. This can be frustrating, but please try not to honk them off; remember that any help they provide is purely voluntary and out of the kindness of their hearts. 13.10 Bug ReportsI found a bug. What should I include in the bug report? Before sending a bug report, make sure you are using the latest version. Check https://ftp.gnu.org/pub/gnu/bison/ or one of its mirrors. Be sure to include the version number in your bug report. If the bug is present in the latest version but not in a previous version, try to determine the most recent version which did not contain the bug. If the bug is parser-related, you should include the smallest grammar you can which demonstrates the bug. The grammar file should also be complete (i.e., I should be able to run it through Bison without having to edit or add anything). The smaller and simpler the grammar, the easier it will be to fix the bug. Include information about your compilation environment, including your operating system’s name and version and your compiler’s name and version. If you have trouble compiling, you should also include a transcript of the build session, starting with the invocation of one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 766. Depending on the nature of the bug, you may be asked to send additional files as well (such as config.h or config.cache). Patches are most welcome, but not required. That is, do not hesitate to send a bug report just because you cannot provide a fix. Send bug reports to [email protected]. 13.11 More LanguagesWill Bison ever have C++ and Java support? How about insert your favorite language here? C++, D and Java are supported. We’d love to add other languages; contributions are welcome. 13.12 Beta TestingWhat is involved in being a beta tester? It’s not terribly involved. Basically, you would download a test release, compile it, and use it to build and run a parser or two. After that, you would submit either a bug report or a message saying that everything is okay. It is important to report successes as well as failures because test releases eventually become mainstream releases, but only if they are adequately tested. If no one tests, development is essentially halted. Beta testers are particularly needed for operating systems to which the developers do not have easy access. They currently have easy access to recent GNU/Linux and Solaris versions. Reports about other operating systems are especially welcome. Appendix A Bison SymbolsVariable: @$ In an action, the location of the left-hand side of the rule. See . Variable: @n Symbol: @n In an action, the location of the n-th symbol of the right-hand side of the rule. See . In a grammar, the Bison-generated nonterminal symbol for a midrule action with a semantic value. See . Variable: @name Variable: @[name] In an action, the location of a symbol addressed by name. See . Symbol: $@n In a grammar, the Bison-generated nonterminal symbol for a midrule action with no semantics value. See . Variable: $$ In an action, the semantic value of the left-hand side of the rule. See . Variable: $n In an action, the semantic value of the n-th symbol of the right-hand side of the rule. See . Variable: $name Variable: $[name] In an action, the semantic value of a symbol addressed by name. See . Delimiter: %% Delimiter used to separate the grammar rule section from the Bison declarations section or the epilogue. See . Delimiter: %{code%} All code listed between ‘%{’ and ‘%}’ is copied verbatim to the parser implementation file. Such code forms the prologue of the grammar file. See . Directive: %?{expression} Predicate actions. This is a type of action clause that may appear in rules. The expression is evaluated, and if false, causes a syntax error. In GLR parsers during nondeterministic operation, this silently causes an alternative parse to die. During deterministic operation, it is the same as the effect of YYERROR. See . Construct: /* … */ Construct: // … Comments, as in C/C++. Delimiter: : Separates a rule’s result from its components. See . Delimiter: ; Terminates a rule. See . Delimiter: | Separates alternate rules for the same result nonterminal. See . Directive: <*> Used to define a default tagged one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 079 or default tagged one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 078. See . Directive: <> Used to define a default tagless one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 079 or default tagless one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 078. See . Symbol: $accept The predefined nonterminal whose only rule is ‘$accept: start $end’, where start is the start symbol. See . It cannot be used in the grammar. Directive: %code {code} Directive: %code qualifier {code} Insert code verbatim into the output parser source at the default location or at the location specified by qualifier. See . Directive: %debug Equip the parser for debugging. See . Directive: %define variable Directive: %define variable value Directive: %define variable {value} Directive: %define variable "value" Define a variable to adjust Bison’s behavior. See . Directive: %defines Directive: %defines defines-file Historical name for one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 282. See . Directive: %destructor Specify how the parser should reclaim the memory associated to discarded symbols. See . Directive: %dprec Bison declaration to assign a precedence to a rule that is used at parse time to resolve reduce/reduce conflicts. See . Directive: %empty Bison declaration to declare make explicit that a rule has an empty right-hand side. See . Symbol: $end The predefined token marking the end of the token stream. It cannot be used in the grammar. Symbol: error A token name reserved for error recovery. This token may be used in grammar rules so as to allow the Bison parser to recognize an error in the grammar without halting the process. In effect, a sentence containing an error may be recognized as valid. On a syntax error, the token type subrange = lo .. hi; type enum = (a, b, c); 84 becomes the current lookahead token. Actions corresponding to type subrange = lo .. hi; type enum = (a, b, c); 84 are then executed, and the lookahead token is reset to the token that originally caused the violation. See . Directive: %error-verbose An obsolete directive standing for ‘%define parse.error verbose’. Directive: %file-prefix "prefix" Bison declaration to set the prefix of the output files. See . Directive: %glr-parser Bison declaration to produce a GLR parser. See . Bison declaration to create a parser header file, which is usually meant for the scanner. See . Same as above, but save in the file header-file. See . Directive: %initial-action Run user code before parsing. See . Directive: %language Specify the programming language for the generated parser. See . Directive: %left Bison declaration to assign precedence and left associativity to token(s). See . Directive: %lex-param {argument-declaration} … Bison declaration to specifying additional arguments that type subrange = (a) .. b; 51 should accept. See . Directive: %merge Bison declaration to assign a merging function to a rule. If there is a reduce/reduce conflict with a rule having the same merging function, the function is applied to the two semantic values to get a single result. See . Directive: %name-prefix "prefix" Obsoleted by the type subrange = (a) .. b; 80 variable one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 315 (see ). Rename the external symbols (variables and functions) used in the parser so that they start with prefix instead of ‘yy’. Contrary to one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 315, do no rename types and macros. The precise list of symbols renamed in C parsers is type subrange = (a) .. b; 52, type subrange = (a) .. b; 51, type subrange = (a) .. b; 56, one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 256, type subrange = (a) .. b; 27, type subrange = (a) .. b; 23, %left '+' '-' %left '*' '/' 48, and (if locations are used) type subrange = (a) .. b; 28. If you use a push parser, one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 264, one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 271, one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 258, one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 262 and one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 263 will also be renamed. For example, if you use ‘%name-prefix "c_"’, the names become one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 313, one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 314, and so on. For C++ parsers, see the program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 747 documentation in this section. Directive: %no-lines Bison declaration to avoid generating one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 322 directives in the parser implementation file. See . Directive: %nonassoc Bison declaration to assign precedence and nonassociativity to token(s). See . Directive: %nterm Bison declaration to declare nonterminals. See . Directive: %output "file" Bison declaration to set the name of the parser implementation file. See . Directive: %param {argument-declaration} … Bison declaration to specify additional arguments that both type subrange = (a) .. b; 51 and type subrange = (a) .. b; 52 should accept. See . Directive: %parse-param {argument-declaration} … Bison declaration to specify additional arguments that type subrange = (a) .. b; 52 should accept. See . Directive: %prec Bison declaration to assign a precedence to a specific rule. See . Directive: %precedence Bison declaration to assign precedence to token(s), but no associativity See . Directive: %pure-parser Deprecated version of ‘%define api.pure’ (see ), for which Bison is more careful to warn about unreasonable usage. Directive: %require "version" Require version version or higher of Bison. See . Directive: %right Bison declaration to assign precedence and right associativity to token(s). See . Directive: %skeleton Specify the skeleton to use; usually for development. See . Directive: %start Bison declaration to specify the start symbol. See . Directive: %token Bison declaration to declare token(s) without specifying precedence. See . Directive: %token-table Bison declaration to include a token name table in the parser implementation file. See . Directive: %type Bison declaration to declare symbol value types. See . Symbol: $undefined The predefined token onto which all undefined values returned by type subrange = (a) .. b; 51 are mapped. It cannot be used in the grammar, rather, use type subrange = lo .. hi; type enum = (a, b, c); 84. Directive: %union Bison declaration to specify several possible data types for semantic values. See . Macro: YYABORT Macro to pretend that an unrecoverable syntax error has occurred, by making type subrange = (a) .. b; 52 return 1 immediately. The error reporting function type subrange = (a) .. b; 56 is not called. See . For Java parsers, this functionality is invoked using program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 759 instead. Macro: YYACCEPT Macro to pretend that a complete utterance of the language has been read, by making type subrange = (a) .. b; 52 return 0 immediately. See . For Java parsers, this functionality is invoked using program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 762 instead. Macro: YYBACKUP Macro to discard a value from the parser stack and fake a lookahead token. See . Macro: YYBISON The version of Bison as an integer, for instance 30704 for version 3.7.4. Defined in yacc.c only. Before version 3.7.4, program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 763 was defined to 1. Variable: yychar External integer variable that contains the integer value of the lookahead token. (In a pure parser, it is a local variable within type subrange = (a) .. b; 52.) Error-recovery rule actions may examine this variable. See . Variable: yyclearin Macro used in error-recovery rule actions. It clears the previous lookahead token. See . Macro: YYDEBUG Macro to define to equip the parser with tracing code. See . Variable: yydebug External integer variable set to zero by default. If %left '+' '-' %left '*' '/' 48 is given a nonzero value, the parser will output information on input symbols and parser action. See . Value: YYEMPTY The pseudo token kind when there is no lookahead token. Value: YYEOF The token kind denoting is the end of the input stream. Macro: yyerrok Macro to cause parser to recover immediately to its normal mode after a syntax error. See . Macro: YYERROR Cause an immediate syntax error. This statement initiates error recovery just as if the parser itself had detected an error; however, it does not call type subrange = (a) .. b; 56, and does not print any message. If you want to print an error message, call type subrange = (a) .. b; 56 explicitly before the ‘YYERROR;’ statement. See . For Java parsers, this functionality is invoked using program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 768 instead. Function: yyerror User-supplied function to be called by type subrange = (a) .. b; 52 on error. See . Macro: YYFPRINTF Macro used to output run-time traces in C. See . Macro: YYINITDEPTH Macro for specifying the initial size of the parser stack. See . Function: yylex User-supplied lexical analyzer function, called with no arguments to get the next token. See . Variable: yylloc External variable in which type subrange = (a) .. b; 51 should place the line and column numbers associated with a token. (In a pure parser, it is a local variable within type subrange = (a) .. b; 52, and its address is passed to type subrange = (a) .. b; 51.) You can ignore this variable if you don’t use the ‘@’ feature in the grammar actions. See . In semantic actions, it stores the location of the lookahead token. See . Type: YYLTYPE Data type of type subrange = (a) .. b; 28. By default in C, a structure with four members (start/end line/column). See . Variable: yylval External variable in which type subrange = (a) .. b; 51 should place the semantic value associated with a token. (In a pure parser, it is a local variable within type subrange = (a) .. b; 52, and its address is passed to type subrange = (a) .. b; 51.) See . In semantic actions, it stores the semantic value of the lookahead token. See . Macro: YYMAXDEPTH Macro for specifying the maximum size of the parser stack. See . Variable: yynerrs Global variable which Bison increments each time it reports a syntax error. (In a pure parser, it is a local variable within type subrange = (a) .. b; 52. In a pure push parser, it is a member of one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 258.) See . Macro: YYNOMEM Macro to pretend that memory is exhausted, by making type subrange = (a) .. b; 52 return 2 immediately. The error reporting function type subrange = (a) .. b; 56 is called. See . Function: yyparse The parser function produced by Bison; call this function to start parsing. See . Function: yypstate_delete The function to delete a parser instance, produced by Bison in push mode; call this function to delete the memory associated with a parser. See . Does nothing when called with a null pointer. Function: yypstate_new The function to create a parser instance, produced by Bison in push mode; call this function to create a new parser. See . Function: yypull_parse The parser function produced by Bison in push mode; call this function to parse the rest of the input stream. See . Function: yypush_parse The parser function produced by Bison in push mode; call this function to parse a single token. See . Macro: YYRECOVERING The expression one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 748 yields 1 when the parser is recovering from a syntax error, and 0 otherwise. See . Macro: YYSTACK_USE_ALLOCA Macro used to control the use of program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 791 when the deterministic parser in C needs to extend its stacks. If defined to 0, the parser will use program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 792 to extend its stacks and memory exhaustion occurs if program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 792 fails (see ). If defined to 1, the parser will use program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 791. Values other than 0 and 1 are reserved for future Bison extensions. If not defined, type subrange = (a) .. b; 64 defaults to 0. In the all-too-common case where your code may run on a host with a limited stack and with unreliable stack-overflow checking, you should set one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 934 to a value that cannot possibly result in unchecked stack overflow on any of your target hosts when program Copyright (C) year name of author This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’. This is free software, and you are welcome to redistribute it under certain conditions; type ‘show c’ for details. 791 is called. You can inspect the code that Bison generates in order to determine the proper numeric values. This will require some expertise in low-level implementation details. Type: YYSTYPE In C, data type of semantic values; type subrange = (a) .. b; 83 by default. Deprecated in favor of the type subrange = (a) .. b; 80 variable type subrange = (a) .. b; 81. See . Type: yysymbol_kind_t An enum of all the symbols, tokens and nonterminals, of the grammar. See . The symbol kinds are used internally by the parser, and should not be confused with the token kinds: the symbol kind of a terminal symbol is not equal to its token kind! (Unless ‘%define api.token.raw’ was used.) Type: yytoken_kind_t An enum of all the token kinds declared with %token TYPE DOTDOT ID 57 (see ). These are the return values for type subrange = (a) .. b; 51. They should not be confused with the symbol kinds, used internally by the parser. Value: YYUNDEF The token kind denoting an unknown token. Appendix B GlossaryAccepting state A state whose only action is the accept action. The accepting state is thus a consistent state. See . Backus-Naur Form (BNF; also called “Backus Normal Form”) Formal method of specifying context-free grammars originally proposed by John Backus, and slightly improved by Peter Naur in his 1960-01-02 committee document contributing to what became the Algol 60 report. See . Consistent state A state containing only one possible action. See . Context-free grammars Grammars specified as rules that can be applied regardless of context. Thus, if there is a rule which says that an integer can be used as an expression, integers are allowed anywhere an expression is permitted. See . Counterexample A sequence of tokens and/or nonterminals, with one dot, that demonstrates a conflict. The dot marks the place where the conflict occurs. A unifying counterexample is a single string that has two different parses; its existence proves that the grammar is ambiguous. When a unifying counterexample cannot be found in reasonable time, a nonunifying counterexample is built: two different string sharing the prefix up to the dot. See Default reduction The reduction that a parser should perform if the current parser state contains no other action for the lookahead token. In permitted parser states, Bison declares the reduction with the largest lookahead set to be the default reduction and removes that lookahead set. See . Defaulted state A consistent state with a default reduction. See . Dynamic allocation Allocation of memory that occurs during execution, rather than at compile time or on entry to a function. Empty string Analogous to the empty set in set theory, the empty string is a character string of length zero. Finite-state stack machine A “machine” that has discrete states in which it is said to exist at each instant in time. As input to the machine is processed, the machine moves from state to state as specified by the logic of the machine. In the case of the parser, the input is the language being parsed, and the states correspond to various stages in the grammar rules. See . Generalized LR (GLR) A parsing algorithm that can handle all context-free grammars, including those that are not LR(1). It resolves situations that Bison’s deterministic parsing algorithm cannot by effectively splitting off multiple parsers, trying all possible parsers, and discarding those that fail in the light of additional right context. See . Grouping A language construct that is (in general) grammatically divisible; for example, ‘expression’ or ‘declaration’ in C. See . IELR(1) (Inadequacy Elimination LR(1)) A minimal LR(1) parser table construction algorithm. That is, given any context-free grammar, IELR(1) generates parser tables with the full language-recognition power of canonical LR(1) but with nearly the same number of parser states as LALR(1). This reduction in parser states is often an order of magnitude. More importantly, because canonical LR(1)’s extra parser states may contain duplicate conflicts in the case of non-LR(1) grammars, the number of conflicts for IELR(1) is often an order of magnitude less as well. This can significantly reduce the complexity of developing a grammar. See . Infix operator An arithmetic operator that is placed between the operands on which it performs some operation. Input stream A continuous flow of data between devices or programs. Kind “Token” and “symbol” are each overloaded to mean either a grammar symbol (kind) or all parse info (kind, value, location) associated with occurrences of that grammar symbol from the input. To disambiguate,
In summary: When you see “kind”, interpret “symbol” or “token” to mean a grammar symbol. When you don’t see “kind” (including when you see “type”), interpret “symbol” or “token” to mean a parsed symbol. LAC (Lookahead Correction) A parsing mechanism that fixes the problem of delayed syntax error detection, which is caused by LR state merging, default reductions, and the use of one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 135. Delayed syntax error detection results in unexpected semantic actions, initiation of error recovery in the wrong syntactic context, and an incorrect list of expected tokens in a verbose syntax error message. See . Language construct One of the typical usage schemas of the language. For example, one of the constructs of the C language is the one line to give the program's name and a brief idea of what it does. Copyright (C) year name of author This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <https://www.gnu.org/licenses/>. 820 statement. See . Left associativity Operators having left associativity are analyzed from left to right: ‘a+b+c’ first computes ‘a+b’ and then combines with ‘c’. See . Left recursion A rule whose result symbol is also its first component symbol; for example, ‘expseq1 : expseq1 ',' exp;’. See . Left-to-right parsing Parsing a sentence of a language by analyzing it token by token from left to right. See . Lexical analyzer (scanner) A function that reads an input stream and returns tokens one by one. See . Lexical tie-in A flag, set by actions in the grammar rules, which alters the way tokens are parsed. See . Literal string token A token which consists of two or more fixed characters. See . Lookahead token A token already read but not yet shifted. See . LALR(1) The class of context-free grammars that Bison (like most other parser generators) can handle by default; a subset of LR(1). See . LR(1) The class of context-free grammars in which at most one token of lookahead is needed to disambiguate the parsing of any piece of input. Nonterminal symbol A grammar symbol standing for a grammatical construct that can be expressed through rules in terms of smaller constructs; in other words, a construct that is not a token. See . Parser A function that recognizes valid sentences of a language by analyzing the syntax structure of a set of tokens passed to it from a lexical analyzer. Postfix operator An arithmetic operator that is placed after the operands upon which it performs some operation. Reduction Replacing a string of nonterminals and/or terminals with a single nonterminal, according to a grammar rule. See . Reentrant A reentrant subprogram is a subprogram which can be in invoked any number of times in parallel, without interference between the various invocations. See . Reverse Polish Notation A language in which all operators are postfix operators. Right recursion A rule whose result symbol is also its last component symbol; for example, ‘expseq1: exp ',' expseq1;’. See . Semantics In computer languages, the semantics are specified by the actions taken for each instance of the language, i.e., the meaning of each statement. See . Shift A parser is said to shift when it makes the choice of analyzing further input from the stream rather than reducing immediately some already-recognized rule. See . Single-character literal A single character that is recognized and interpreted as is. See . Start symbol The nonterminal symbol that stands for a complete valid utterance in the language being parsed. The start symbol is usually listed as the first nonterminal symbol in a language specification. See . Symbol kind A (finite) enumeration of the grammar symbols, as processed by the parser. See . Symbol table A data structure where symbol names and associated data are stored during parsing to allow for recognition and use of existing information in repeated uses of a symbol. See . Syntax error An error encountered during parsing of an input stream due to invalid syntax. See . Terminal symbol A grammar symbol that has no rules in the grammar and therefore is grammatically indivisible. The piece of text it represents is a token. See . Token A basic, grammatically indivisible unit of a language. The symbol that describes a token in the grammar is a terminal symbol. The input of the Bison parser is a stream of tokens which comes from the lexical analyzer. See . Token kind A (finite) enumeration of the grammar terminals, as discriminated by the scanner. See . Unreachable state A parser state to which there does not exist a sequence of transitions from the parser’s start state. A state can become unreachable during conflict resolution. See . Appendix C GNU Free Documentation LicenseVersion 1.3, 3 November 2008 type subrange = lo .. hi; type enum = (a, b, c); 73
ADDENDUM: How to use this License for your documentsTo use this License in a document you have written, include a copy of the License in the document and put the following copyright and license notices just after the title page: type subrange = lo .. hi; type enum = (a, b, c); 74 If you have Invariant Sections, Front-Cover Texts and Back-Cover Texts, replace the “with…Texts.” line with this: type subrange = lo .. hi; type enum = (a, b, c); 75 If you have Invariant Sections without Cover Texts, or some other combination of the three, merge those two alternatives to suit the situation. If your document contains nontrivial examples of program code, we recommend releasing these examples in parallel under your choice of free software license, such as the GNU General Public License, to permit their use in free software. Bibliography[Corbett 1984] Robert Paul Corbett, Static Semantics in Compiler Error Recovery Ph.D. Dissertation, Report No. UCB/CSD 85/251, Department of Electrical Engineering and Computer Science, Compute Science Division, University of California, Berkeley, California (June 1985). https://digicoll.lib.berkeley.edu/record/135875 [Denny 2008] Joel E. Denny and Brian A. Malloy, IELR(1): Practical LR(1) Parser Tables for Non-LR(1) Grammars with Conflict Resolution, in Proceedings of the 2008 ACM Symposium on Applied Computing (SAC’08), ACM, New York, NY, USA, pp. 240–245. https://dx.doi.org/10.1145/1363686.1363747 [Denny 2010 May] Joel E. Denny, PSLR(1): Pseudo-Scannerless Minimal LR(1) for the Deterministic Parsing of Composite Languages, Ph.D. Dissertation, Clemson University, Clemson, SC, USA (May 2010). https://tigerprints.clemson.edu/all_dissertations/519/ [Denny 2010 November] Joel E. Denny and Brian A. Malloy, The IELR(1) Algorithm for Generating Minimal LR(1) Parser Tables for Non-LR(1) Grammars with Conflict Resolution, in Science of Computer Programming, Vol. 75, Issue 11 (November 2010), pp. 943–979. https://dx.doi.org/10.1016/j.scico.2009.08.001 [DeRemer 1982] Frank DeRemer and Thomas Pennello, Efficient Computation of LALR(1) Look-Ahead Sets, in ACM Transactions on Programming Languages and Systems, Vol. 4, No. 4 (October 1982), pp. 615–649. https://dx.doi.org/10.1145/69622.357187 [Isradisaikul 2015] Chinawat Isradisaikul, Andrew Myers, Finding Counterexamples from Parsing Conflicts, in Proceedings of the 36th ACM SIGPLAN Conference on Programming Language Design and Implementation (PLDI ’15), ACM, pp. 555–564. https://www.cs.cornell.edu/andru/papers/cupex/cupex.pdf [Johnson 1978] Steven C. Johnson, A portable compiler: theory and practice, in Proceedings of the 5th ACM SIGACT-SIGPLAN symposium on Principles of programming languages (POPL ’78), pp. 97–104. https://dx.doi.org/10.1145/512760.512771. [Knuth 1965] Donald E. Knuth, On the Translation of Languages from Left to Right, in Information and Control, Vol. 8, Issue 6 (December 1965), pp. 607–639. https://dx.doi.org/10.1016/S0019-9958(65)90426-2 [Scott 2000] Elizabeth Scott, Adrian Johnstone, and Shamsa Sadaf Hussain, Tomita-Style Generalised LR Parsers, Royal Holloway, University of London, Department of Computer Science, TR-00-12 (December 2000). https://www.cs.rhul.ac.uk/research/languages/publications/tomita_style_1.ps |
