X-Git-Url: https://git.saurik.com/bison.git/blobdiff_plain/f8e1c9e55b6f51b5144ad19a7fc11d2a774c5d58..a022ff418685a490925aed4adf19ebf8ed31239d:/doc/bison.texinfo diff --git a/doc/bison.texinfo b/doc/bison.texinfo index 671d1c4e..8072ae22 100644 --- a/doc/bison.texinfo +++ b/doc/bison.texinfo @@ -12,25 +12,15 @@ @c the smallbook format. @c @smallbook -@c Set following if you have the new `shorttitlepage' command -@c @clear shorttitlepage-enabled -@c @set shorttitlepage-enabled - @c Set following if you want to document %default-prec and %no-default-prec. @c This feature is experimental and may change in future Bison versions. @c @set defaultprec -@c ISPELL CHECK: done, 14 Jan 1993 --bob - -@c Check COPYRIGHT dates. should be updated in the titlepage, ifinfo -@c titlepage; should NOT be changed in the GPL. --mew - -@c FIXME: I don't understand this `iftex'. Obsolete? --akim. -@iftex +@ifnotinfo @syncodeindex fn cp @syncodeindex vr cp @syncodeindex tp cp -@end iftex +@end ifnotinfo @ifinfo @synindex fn cp @synindex vr cp @@ -40,11 +30,12 @@ @copying -This manual is for @acronym{GNU} Bison (version @value{VERSION}, -@value{UPDATED}), the @acronym{GNU} parser generator. +This manual (@value{UPDATED}) is for @acronym{GNU} Bison (version +@value{VERSION}), the @acronym{GNU} parser generator. Copyright @copyright{} 1988, 1989, 1990, 1991, 1992, 1993, 1995, 1998, -1999, 2000, 2001, 2002, 2003, 2004, 2005 Free Software Foundation, Inc. +1999, 2000, 2001, 2002, 2003, 2004, 2005, 2006, 2007, 2008, 2009 Free +Software Foundation, Inc. @quotation Permission is granted to copy, distribute and/or modify this document @@ -55,10 +46,10 @@ being ``A @acronym{GNU} Manual,'' and with the Back-Cover Texts as in (a) below. A copy of the license is included in the section entitled ``@acronym{GNU} Free Documentation License.'' -(a) The @acronym{FSF}'s Back-Cover Text is: ``You have freedom to copy -and modify this @acronym{GNU} Manual, like @acronym{GNU} software. -Copies published by the Free Software Foundation raise funds for -@acronym{GNU} development.'' +(a) The FSF's Back-Cover Text is: ``You have the freedom to copy and +modify this @acronym{GNU} manual. Buying copies from the @acronym{FSF} +supports it in developing @acronym{GNU} and promoting software +freedom.'' @end quotation @end copying @@ -67,9 +58,6 @@ Copies published by the Free Software Foundation raise funds for * bison: (bison). @acronym{GNU} parser generator (Yacc replacement). @end direntry -@ifset shorttitlepage-enabled -@shorttitlepage Bison -@end ifset @titlepage @title Bison @subtitle The Yacc-compatible Parser Generator @@ -101,75 +89,76 @@ Cover art by Etienne Suvasa. @menu * Introduction:: * Conditions:: -* Copying:: The @acronym{GNU} General Public License says - how you can copy and share Bison +* Copying:: The @acronym{GNU} General Public License says + how you can copy and share Bison. Tutorial sections: -* Concepts:: Basic concepts for understanding Bison. -* Examples:: Three simple explained examples of using Bison. +* Concepts:: Basic concepts for understanding Bison. +* Examples:: Three simple explained examples of using Bison. Reference sections: -* Grammar File:: Writing Bison declarations and rules. -* Interface:: C-language interface to the parser function @code{yyparse}. -* Algorithm:: How the Bison parser works at run-time. -* Error Recovery:: Writing rules for error recovery. +* Grammar File:: Writing Bison declarations and rules. +* Interface:: C-language interface to the parser function @code{yyparse}. +* Algorithm:: How the Bison parser works at run-time. +* Error Recovery:: Writing rules for error recovery. * Context Dependency:: What to do if your language syntax is too - messy for Bison to handle straightforwardly. -* Debugging:: Understanding or debugging Bison parsers. -* Invocation:: How to run Bison (to produce the parser source file). -* C++ Language Interface:: Creating C++ parser objects. -* FAQ:: Frequently Asked Questions -* Table of Symbols:: All the keywords of the Bison language are explained. -* Glossary:: Basic concepts are explained. -* Copying This Manual:: License for copying this manual. -* Index:: Cross-references to the text. + messy for Bison to handle straightforwardly. +* Debugging:: Understanding or debugging Bison parsers. +* Invocation:: How to run Bison (to produce the parser source file). +* Other Languages:: Creating C++ and Java parsers. +* FAQ:: Frequently Asked Questions +* Table of Symbols:: All the keywords of the Bison language are explained. +* Glossary:: Basic concepts are explained. +* Copying This Manual:: License for copying this manual. +* Index:: Cross-references to the text. @detailmenu --- The Detailed Node Listing --- The Concepts of Bison -* Language and Grammar:: Languages and context-free grammars, - as mathematical ideas. -* Grammar in Bison:: How we represent grammars for Bison's sake. -* Semantic Values:: Each token or syntactic grouping can have - a semantic value (the value of an integer, - the name of an identifier, etc.). -* Semantic Actions:: Each rule can have an action containing C code. -* GLR Parsers:: Writing parsers for general context-free languages. -* Locations Overview:: Tracking Locations. -* Bison Parser:: What are Bison's input and output, - how is the output used? -* Stages:: Stages in writing and running Bison grammars. -* Grammar Layout:: Overall structure of a Bison grammar file. +* Language and Grammar:: Languages and context-free grammars, + as mathematical ideas. +* Grammar in Bison:: How we represent grammars for Bison's sake. +* Semantic Values:: Each token or syntactic grouping can have + a semantic value (the value of an integer, + the name of an identifier, etc.). +* Semantic Actions:: Each rule can have an action containing C code. +* GLR Parsers:: Writing parsers for general context-free languages. +* Locations Overview:: Tracking Locations. +* Bison Parser:: What are Bison's input and output, + how is the output used? +* Stages:: Stages in writing and running Bison grammars. +* Grammar Layout:: Overall structure of a Bison grammar file. Writing @acronym{GLR} Parsers -* Simple GLR Parsers:: Using @acronym{GLR} parsers on unambiguous grammars -* Merging GLR Parses:: Using @acronym{GLR} parsers to resolve ambiguities -* Compiler Requirements:: @acronym{GLR} parsers require a modern C compiler +* Simple GLR Parsers:: Using @acronym{GLR} parsers on unambiguous grammars. +* Merging GLR Parses:: Using @acronym{GLR} parsers to resolve ambiguities. +* GLR Semantic Actions:: Deferred semantic actions have special concerns. +* Compiler Requirements:: @acronym{GLR} parsers require a modern C compiler. Examples -* RPN Calc:: Reverse polish notation calculator; - a first example with no operator precedence. -* Infix Calc:: Infix (algebraic) notation calculator. - Operator precedence is introduced. +* RPN Calc:: Reverse polish notation calculator; + a first example with no operator precedence. +* Infix Calc:: Infix (algebraic) notation calculator. + Operator precedence is introduced. * Simple Error Recovery:: Continuing after syntax errors. * Location Tracking Calc:: Demonstrating the use of @@@var{n} and @@$. -* Multi-function Calc:: Calculator with memory and trig functions. - It uses multiple data-types for semantic values. -* Exercises:: Ideas for improving the multi-function calculator. +* Multi-function Calc:: Calculator with memory and trig functions. + It uses multiple data-types for semantic values. +* Exercises:: Ideas for improving the multi-function calculator. Reverse Polish Notation Calculator -* Decls: Rpcalc Decls. Prologue (declarations) for rpcalc. -* Rules: Rpcalc Rules. Grammar Rules for rpcalc, with explanation. -* Lexer: Rpcalc Lexer. The lexical analyzer. -* Main: Rpcalc Main. The controlling function. -* Error: Rpcalc Error. The error reporting function. -* Gen: Rpcalc Gen. Running Bison on the grammar file. -* Comp: Rpcalc Compile. Run the C compiler on the output code. +* Rpcalc Declarations:: Prologue (declarations) for rpcalc. +* Rpcalc Rules:: Grammar Rules for rpcalc, with explanation. +* Rpcalc Lexer:: The lexical analyzer. +* Rpcalc Main:: The controlling function. +* Rpcalc Error:: The error reporting function. +* Rpcalc Generate:: Running Bison on the grammar file. +* Rpcalc Compile:: Run the C compiler on the output code. Grammar Rules for @code{rpcalc} @@ -179,15 +168,15 @@ Grammar Rules for @code{rpcalc} Location Tracking Calculator: @code{ltcalc} -* Decls: Ltcalc Decls. Bison and C declarations for ltcalc. -* Rules: Ltcalc Rules. Grammar rules for ltcalc, with explanations. -* Lexer: Ltcalc Lexer. The lexical analyzer. +* Ltcalc Declarations:: Bison and C declarations for ltcalc. +* Ltcalc Rules:: Grammar rules for ltcalc, with explanations. +* Ltcalc Lexer:: The lexical analyzer. Multi-Function Calculator: @code{mfcalc} -* Decl: Mfcalc Decl. Bison declarations for multi-function calculator. -* Rules: Mfcalc Rules. Grammar rules for the calculator. -* Symtab: Mfcalc Symtab. Symbol table management subroutines. +* Mfcalc Declarations:: Bison declarations for multi-function calculator. +* Mfcalc Rules:: Grammar rules for the calculator. +* Mfcalc Symbol Table:: Symbol table management subroutines. Bison Grammar Files @@ -202,10 +191,11 @@ Bison Grammar Files Outline of a Bison Grammar -* Prologue:: Syntax and usage of the prologue. -* Bison Declarations:: Syntax and usage of the Bison declarations section. -* Grammar Rules:: Syntax and usage of the grammar rules section. -* Epilogue:: Syntax and usage of the epilogue. +* Prologue:: Syntax and usage of the prologue. +* Prologue Alternatives:: Syntax and usage of alternatives to the prologue. +* Bison Declarations:: Syntax and usage of the Bison declarations section. +* Grammar Rules:: Syntax and usage of the grammar rules section. +* Epilogue:: Syntax and usage of the epilogue. Defining Language Semantics @@ -235,38 +225,43 @@ Bison Declarations * Expect Decl:: Suppressing warnings about parsing conflicts. * Start Decl:: Specifying the start symbol. * Pure Decl:: Requesting a reentrant parser. +* Push Decl:: Requesting a push parser. * Decl Summary:: Table of all Bison declarations. Parser C-Language Interface -* Parser Function:: How to call @code{yyparse} and what it returns. -* Lexical:: You must supply a function @code{yylex} - which reads tokens. -* Error Reporting:: You must supply a function @code{yyerror}. -* Action Features:: Special features for use in actions. -* Internationalization:: How to let the parser speak in the user's - native language. +* Parser Function:: How to call @code{yyparse} and what it returns. +* Push Parser Function:: How to call @code{yypush_parse} and what it returns. +* Pull Parser Function:: How to call @code{yypull_parse} and what it returns. +* Parser Create Function:: How to call @code{yypstate_new} and what it returns. +* Parser Delete Function:: How to call @code{yypstate_delete} and what it returns. +* Lexical:: You must supply a function @code{yylex} + which reads tokens. +* Error Reporting:: You must supply a function @code{yyerror}. +* Action Features:: Special features for use in actions. +* Internationalization:: How to let the parser speak in the user's + native language. The Lexical Analyzer Function @code{yylex} * Calling Convention:: How @code{yyparse} calls @code{yylex}. -* Token Values:: How @code{yylex} must return the semantic value - of the token it has read. -* Token Locations:: How @code{yylex} must return the text location - (line number, etc.) of the token, if the - actions want that. -* Pure Calling:: How the calling convention differs - in a pure parser (@pxref{Pure Decl, ,A Pure (Reentrant) Parser}). +* Token Values:: How @code{yylex} must return the semantic value + of the token it has read. +* Token Locations:: How @code{yylex} must return the text location + (line number, etc.) of the token, if the + actions want that. +* Pure Calling:: How the calling convention differs in a pure parser + (@pxref{Pure Decl, ,A Pure (Reentrant) Parser}). The Bison Parser Algorithm -* Look-Ahead:: Parser looks one token ahead when deciding what to do. +* Lookahead:: Parser looks one token ahead when deciding what to do. * Shift/Reduce:: Conflicts: when either shifting or reduction is valid. * Precedence:: Operator precedence works by resolving conflicts. * Contextual Precedence:: When an operator's precedence depends on context. * Parser States:: The parser is a finite-state-machine with stack. * Reduce/Reduce:: When two rules are applicable in the same situation. -* Mystery Conflicts:: Reduce/reduce conflicts that look unjustified. +* Mystery Conflicts:: Reduce/reduce conflicts that look unjustified. * Generalized LR Parsing:: Parsing arbitrary context-free grammars. * Memory Management:: What happens when memory is exhausted. How to avoid it. @@ -296,10 +291,10 @@ Invoking Bison * Option Cross Key:: Alphabetical list of long options. * Yacc Library:: Yacc-compatible @code{yylex} and @code{main}. -C++ Language Interface +Parsers Written In Other Languages * C++ Parsers:: The interface to generate C++ parser classes -* A Complete C++ Example:: Demonstrating their use +* Java Parsers:: The interface to generate Java parser classes C++ Parsers @@ -308,6 +303,7 @@ C++ Parsers * C++ Location Values:: The position and location classes * C++ Parser Interface:: Instantiating and running the parser * C++ Scanner Interface:: Exchanges between yylex and parse +* A Complete C++ Example:: Demonstrating their use A Complete C++ Example @@ -317,16 +313,35 @@ A Complete C++ Example * Calc++ Scanner:: A pure C++ Flex scanner * Calc++ Top Level:: Conducting the band +Java Parsers + +* Java Bison Interface:: Asking for Java parser generation +* Java Semantic Values:: %type and %token vs. Java +* Java Location Values:: The position and location classes +* Java Parser Interface:: Instantiating and running the parser +* Java Scanner Interface:: Specifying the scanner for the parser +* Java Action Features:: Special features for use in actions +* Java Differences:: Differences between C/C++ and Java Grammars +* Java Declarations Summary:: List of Bison declarations used with Java + Frequently Asked Questions -* Memory Exhausted:: Breaking the Stack Limits -* How Can I Reset the Parser:: @code{yyparse} Keeps some State -* Strings are Destroyed:: @code{yylval} Loses Track of Strings -* Implementing Gotos/Loops:: Control Flow in the Calculator +* Memory Exhausted:: Breaking the Stack Limits +* How Can I Reset the Parser:: @code{yyparse} Keeps some State +* Strings are Destroyed:: @code{yylval} Loses Track of Strings +* Implementing Gotos/Loops:: Control Flow in the Calculator +* Multiple start-symbols:: Factoring closely related grammars +* Secure? Conform?:: Is Bison @acronym{POSIX} safe? +* I can't build Bison:: Troubleshooting +* Where can I find help?:: Troubleshouting +* Bug Reports:: Troublereporting +* More Languages:: Parsers in C++, Java, and so on +* Beta Testing:: Experimenting development versions +* Mailing Lists:: Meeting other Bison users Copying This Manual -* GNU Free Documentation License:: License for copying this manual. +* Copying This Manual:: License for copying this manual. @end detailmenu @end menu @@ -335,16 +350,16 @@ Copying This Manual @unnumbered Introduction @cindex introduction -@dfn{Bison} is a general-purpose parser generator that converts a -grammar description for an @acronym{LALR}(1) context-free grammar into a C -program to parse that grammar. Once you are proficient with Bison, -you may use it to develop a wide range of language parsers, from those +@dfn{Bison} is a general-purpose parser generator that converts an +annotated context-free grammar into an @acronym{LALR}(1) or +@acronym{GLR} parser for that grammar. 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 programming in order to use Bison or to understand this manual. +C or C++ 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 @@ -360,9 +375,10 @@ This edition corresponds to version @value{VERSION} of Bison. @node Conditions @unnumbered Conditions for Using Bison -As of Bison version 1.24, we have changed the distribution terms for -@code{yyparse} to permit using Bison's output in nonfree programs when -Bison is generating C code for @acronym{LALR}(1) parsers. Formerly, these +The 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 @acronym{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 @acronym{GNU} programming tools, such as the @acronym{GNU} C @@ -374,10 +390,10 @@ License to all of the Bison source code. The output of the Bison utility---the Bison parser file---contains a verbatim copy of a sizable piece of Bison, which is the code for the -@code{yyparse} function. (The actions from your grammar are inserted -into this function at one point, but the rest of the function is not -changed.) When we applied the @acronym{GPL} terms to the code for -@code{yyparse}, +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 @acronym{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 @@ -387,15 +403,15 @@ 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 @acronym{GNU} tools. -This exception applies only when Bison is generating C code for an -@acronym{LALR}(1) parser; otherwise, the @acronym{GPL} terms operate -as usual. You can -tell whether the exception applies to your @samp{.c} output file by -inspecting it to see whether it says ``As a special exception, when -this file is copied by Bison into a Bison output file, you may use -that output file without restriction.'' +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@dots{}''. The text spells out the exact terms of the +exception. -@include gpl.texi +@node Copying +@unnumbered GNU GENERAL PUBLIC LICENSE +@include gpl-3.0.texi @node Concepts @chapter The Concepts of Bison @@ -405,19 +421,19 @@ 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. @menu -* Language and Grammar:: Languages and context-free grammars, - as mathematical ideas. -* Grammar in Bison:: How we represent grammars for Bison's sake. -* Semantic Values:: Each token or syntactic grouping can have - a semantic value (the value of an integer, - the name of an identifier, etc.). -* Semantic Actions:: Each rule can have an action containing C code. -* GLR Parsers:: Writing parsers for general context-free languages. -* Locations Overview:: Tracking Locations. -* Bison Parser:: What are Bison's input and output, - how is the output used? -* Stages:: Stages in writing and running Bison grammars. -* Grammar Layout:: Overall structure of a Bison grammar file. +* Language and Grammar:: Languages and context-free grammars, + as mathematical ideas. +* Grammar in Bison:: How we represent grammars for Bison's sake. +* Semantic Values:: Each token or syntactic grouping can have + a semantic value (the value of an integer, + the name of an identifier, etc.). +* Semantic Actions:: Each rule can have an action containing C code. +* GLR Parsers:: Writing parsers for general context-free languages. +* Locations Overview:: Tracking Locations. +* Bison Parser:: What are Bison's input and output, + how is the output used? +* Stages:: Stages in writing and running Bison grammars. +* Grammar Layout:: Overall structure of a Bison grammar file. @end menu @node Language and Grammar @@ -450,7 +466,7 @@ can handle almost all context-free grammars, Bison is optimized for what are called @acronym{LALR}(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 look-ahead. Strictly speaking, that is a description of an +token of lookahead. Strictly speaking, that is a description of an @acronym{LR}(1) grammar, and @acronym{LALR}(1) involves additional restrictions that are hard to explain simply; but it is rare in actual practice to find an @@ -466,11 +482,11 @@ more information on this. Parsers for @acronym{LALR}(1) grammars are @dfn{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 @dfn{look-ahead}) of the remaining input. A context-free +(called a @dfn{lookahead}) of the remaining input. A context-free grammar can be @dfn{ambiguous}, meaning that there are multiple ways to apply the grammar rules to get the same inputs. Even unambiguous grammars can be @dfn{nondeterministic}, meaning that no fixed -look-ahead always suffices to determine the next grammar rule to apply. +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 @acronym{GLR} parsing (for Generalized @acronym{LR}). Bison's @acronym{GLR} parsers @@ -507,8 +523,8 @@ int /* @r{keyword `int'} */ square (int x) /* @r{identifier, open-paren, keyword `int',} @r{identifier, close-paren} */ @{ /* @r{open-brace} */ - return x * x; /* @r{keyword `return', identifier, asterisk, - identifier, semicolon} */ + return x * x; /* @r{keyword `return', identifier, asterisk,} + @r{identifier, semicolon} */ @} /* @r{close-brace} */ @end example @end ifinfo @@ -733,9 +749,10 @@ user-defined function on the resulting values to produce an arbitrary merged result. @menu -* Simple GLR Parsers:: Using @acronym{GLR} parsers on unambiguous grammars -* Merging GLR Parses:: Using @acronym{GLR} parsers to resolve ambiguities -* Compiler Requirements:: @acronym{GLR} parsers require a modern C compiler +* Simple GLR Parsers:: Using @acronym{GLR} parsers on unambiguous grammars. +* Merging GLR Parses:: Using @acronym{GLR} parsers to resolve ambiguities. +* GLR Semantic Actions:: Deferred semantic actions have special concerns. +* Compiler Requirements:: @acronym{GLR} parsers require a modern C compiler. @end menu @node Simple GLR Parsers @@ -750,7 +767,7 @@ merged result. In the simplest cases, you can use the @acronym{GLR} algorithm to parse grammars that are unambiguous, but fail to be @acronym{LALR}(1). -Such grammars typically require more than one symbol of look-ahead, +Such grammars typically require more than one symbol of lookahead, or (in rare cases) fall into the category of grammars in which the @acronym{LALR}(1) algorithm throws away too much information (they are in @acronym{LR}(1), but not @acronym{LALR}(1), @ref{Mystery Conflicts}). @@ -790,7 +807,7 @@ type enum = (a); valid, and more-complicated cases can come up in practical programs.) These two declarations look identical until the @samp{..} token. -With normal @acronym{LALR}(1) one-token look-ahead it is not +With normal @acronym{LALR}(1) one-token lookahead it is not possible to decide between the two forms when the identifier @samp{a} is parsed. It is, however, desirable for a parser to decide this, since in the latter case @@ -829,7 +846,7 @@ 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 -look-ahead than the underlying @acronym{LALR}(1) algorithm actually allows +lookahead than the underlying @acronym{LALR}(1) algorithm actually allows for. In this example, @acronym{LALR}(2) would suffice, but also some cases that are not @acronym{LALR}(@math{k}) for any @math{k} can be handled this way. @@ -1094,6 +1111,55 @@ productions that participate in any particular merge have identical and the parser will report an error during any parse that results in the offending merge. +@node GLR Semantic Actions +@subsection GLR Semantic Actions + +@cindex deferred semantic actions +By 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 @acronym{GLR} parser. + +@vindex yychar +@cindex @acronym{GLR} parsers and @code{yychar} +@vindex yylval +@cindex @acronym{GLR} parsers and @code{yylval} +@vindex yylloc +@cindex @acronym{GLR} parsers and @code{yylloc} +In any semantic action, you can examine @code{yychar} to determine the type of +the lookahead token present at the time of the associated reduction. +After checking that @code{yychar} is not set to @code{YYEMPTY} or @code{YYEOF}, +you can then examine @code{yylval} and @code{yylloc} 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. +@xref{Lookahead, ,Lookahead Tokens}. + +@findex yyclearin +@cindex @acronym{GLR} parsers and @code{yyclearin} +In a deferred semantic action, it's too late to influence syntax analysis. +In this case, @code{yychar}, @code{yylval}, and @code{yylloc} 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 @code{yyclearin} (@pxref{Action Features}) or to attempt to free +memory referenced by @code{yylval}. + +@findex YYERROR +@cindex @acronym{GLR} parsers and @code{YYERROR} +Another Bison feature requiring special consideration is @code{YYERROR} +(@pxref{Action Features}), which you can invoke in a semantic action to +initiate error recovery. +During deterministic @acronym{GLR} operation, the effect of @code{YYERROR} is +the same as its effect in an @acronym{LALR}(1) parser. +In a deferred semantic action, its effect is undefined. +@c The effect is probably a syntax error at the split point. + +Also, see @ref{Location Default Action, ,Default Action for Locations}, which +describes a special usage of @code{YYLLOC_DEFAULT} in @acronym{GLR} parsers. + @node Compiler Requirements @subsection Considerations when Compiling @acronym{GLR} Parsers @cindex @code{inline} @@ -1310,22 +1376,19 @@ under BSD Unix 4.3; each produces a usable, though limited, interactive desk-top calculator. These examples are simple, but Bison grammars for real programming -languages are written the same way. -@ifinfo -You can copy these examples out of the Info file and into a source file -to try them. -@end ifinfo +languages are written the same way. You can copy these examples into a +source file to try them. @menu -* RPN Calc:: Reverse polish notation calculator; - a first example with no operator precedence. -* Infix Calc:: Infix (algebraic) notation calculator. - Operator precedence is introduced. +* RPN Calc:: Reverse polish notation calculator; + a first example with no operator precedence. +* Infix Calc:: Infix (algebraic) notation calculator. + Operator precedence is introduced. * Simple Error Recovery:: Continuing after syntax errors. * Location Tracking Calc:: Demonstrating the use of @@@var{n} and @@$. -* Multi-function Calc:: Calculator with memory and trig functions. - It uses multiple data-types for semantic values. -* Exercises:: Ideas for improving the multi-function calculator. +* Multi-function Calc:: Calculator with memory and trig functions. + It uses multiple data-types for semantic values. +* Exercises:: Ideas for improving the multi-function calculator. @end menu @node RPN Calc @@ -1344,16 +1407,16 @@ The source code for this calculator is named @file{rpcalc.y}. The @samp{.y} extension is a convention used for Bison input files. @menu -* Decls: Rpcalc Decls. Prologue (declarations) for rpcalc. -* Rules: Rpcalc Rules. Grammar Rules for rpcalc, with explanation. -* Lexer: Rpcalc Lexer. The lexical analyzer. -* Main: Rpcalc Main. The controlling function. -* Error: Rpcalc Error. The error reporting function. -* Gen: Rpcalc Gen. Running Bison on the grammar file. -* Comp: Rpcalc Compile. Run the C compiler on the output code. +* Rpcalc Declarations:: Prologue (declarations) for rpcalc. +* Rpcalc Rules:: Grammar Rules for rpcalc, with explanation. +* Rpcalc Lexer:: The lexical analyzer. +* Rpcalc Main:: The controlling function. +* Rpcalc Error:: The error reporting function. +* Rpcalc Generate:: Running Bison on the grammar file. +* Rpcalc Compile:: Run the C compiler on the output code. @end menu -@node Rpcalc Decls +@node Rpcalc Declarations @subsection Declarations for @code{rpcalc} Here are the C and Bison declarations for the reverse polish notation @@ -1433,7 +1496,7 @@ exp: NUM @{ $$ = $1; @} The groupings of the rpcalc ``language'' defined here are the expression (given the name @code{exp}), the line of input (@code{line}), and the complete input transcript (@code{input}). Each of these nonterminal -symbols has several alternate rules, joined by the @samp{|} punctuator +symbols has several alternate rules, joined by the vertical bar @samp{|} which is read as ``or''. The following sections explain what these rules mean. @@ -1603,7 +1666,7 @@ therefore, @code{NUM} becomes a macro for @code{yylex} to use. The semantic value of the token (if it has one) is stored into the global variable @code{yylval}, which is where the Bison parser will look for it. (The C data type of @code{yylval} is @code{YYSTYPE}, which was -defined at the beginning of the grammar; @pxref{Rpcalc Decls, +defined at the beginning of the grammar; @pxref{Rpcalc Declarations, ,Declarations for @code{rpcalc}}.) A token type code of zero is returned if the end-of-input is encountered. @@ -1699,7 +1762,7 @@ 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. -@node Rpcalc Gen +@node Rpcalc Generate @subsection Running Bison to Make the Parser @cindex running Bison (introduction) @@ -1918,12 +1981,12 @@ most of the work needed to use locations will be done in the lexical analyzer. @menu -* Decls: Ltcalc Decls. Bison and C declarations for ltcalc. -* Rules: Ltcalc Rules. Grammar rules for ltcalc, with explanations. -* Lexer: Ltcalc Lexer. The lexical analyzer. +* Ltcalc Declarations:: Bison and C declarations for ltcalc. +* Ltcalc Rules:: Grammar rules for ltcalc, with explanations. +* Ltcalc Lexer:: The lexical analyzer. @end menu -@node Ltcalc Decls +@node Ltcalc Declarations @subsection Declarations for @code{ltcalc} The C and Bison declarations for the location tracking calculator are @@ -1956,7 +2019,9 @@ type for storing locations is not needed: we will use the type provided by default (@pxref{Location Type, ,Data Types of Locations}), which is a four member structure with the following integer fields: @code{first_line}, @code{first_column}, @code{last_line} and -@code{last_column}. +@code{last_column}. By conventions, and in accordance with the GNU +Coding Standards and common practice, the line and column count both +start at 1. @node Ltcalc Rules @subsection Grammar Rules for @code{ltcalc} @@ -2003,7 +2068,7 @@ exp : NUM @{ $$ = $1; @} @} @end group @group - | '-' exp %preg NEG @{ $$ = -$2; @} + | '-' exp %prec NEG @{ $$ = -$2; @} | exp '^' exp @{ $$ = pow ($1, $3); @} | '(' exp ')' @{ $$ = $2; @} @end group @@ -2157,12 +2222,12 @@ $ Note that multiple assignment and nested function calls are permitted. @menu -* Decl: Mfcalc Decl. Bison declarations for multi-function calculator. -* Rules: Mfcalc Rules. Grammar rules for the calculator. -* Symtab: Mfcalc Symtab. Symbol table management subroutines. +* Mfcalc Declarations:: Bison declarations for multi-function calculator. +* Mfcalc Rules:: Grammar rules for the calculator. +* Mfcalc Symbol Table:: Symbol table management subroutines. @end menu -@node Mfcalc Decl +@node Mfcalc Declarations @subsection Declarations for @code{mfcalc} Here are the C and Bison declarations for the multi-function calculator. @@ -2258,7 +2323,7 @@ exp: NUM @{ $$ = $1; @} %% @end smallexample -@node Mfcalc Symtab +@node Mfcalc Symbol Table @subsection The @code{mfcalc} Symbol Table @cindex symbol table example @@ -2571,10 +2636,11 @@ As a @acronym{GNU} extension, @samp{//} introduces a comment that continues until end of line. @menu -* Prologue:: Syntax and usage of the prologue. -* Bison Declarations:: Syntax and usage of the Bison declarations section. -* Grammar Rules:: Syntax and usage of the grammar rules section. -* Epilogue:: Syntax and usage of the epilogue. +* Prologue:: Syntax and usage of the prologue. +* Prologue Alternatives:: Syntax and usage of alternatives to the prologue. +* Bison Declarations:: Syntax and usage of the Bison declarations section. +* Grammar Rules:: Syntax and usage of the grammar rules section. +* Epilogue:: Syntax and usage of the epilogue. @end menu @node Prologue @@ -2591,6 +2657,10 @@ they precede the definition of @code{yyparse}. You can use don't need any C declarations, you may omit the @samp{%@{} and @samp{%@}} delimiters that bracket this section. +The @var{Prologue} section is terminated by the first occurrence +of @samp{%@}} that is outside a comment, a string literal, or a +character constant. + You may have more than one @var{Prologue} section, intermixed with the @var{Bison declarations}. This allows you to have C and Bison declarations that refer to each other. For example, the @code{%union} @@ -2601,6 +2671,54 @@ can be done with two @var{Prologue} blocks, one before and one after the @smallexample %@{ + #define _GNU_SOURCE + #include + #include "ptypes.h" +%@} + +%union @{ + long int n; + tree t; /* @r{@code{tree} is defined in @file{ptypes.h}.} */ +@} + +%@{ + static void print_token_value (FILE *, int, YYSTYPE); + #define YYPRINT(F, N, L) print_token_value (F, N, L) +%@} + +@dots{} +@end smallexample + +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 @code{_GNU_SOURCE} or +@code{_POSIX_C_SOURCE} should appear before all Bison declarations, as +feature test macros can affect the behavior of Bison-generated +@code{#include} directives. + +@node Prologue Alternatives +@subsection Prologue Alternatives +@cindex Prologue Alternatives + +@findex %code +@findex %code requires +@findex %code provides +@findex %code top + +The functionality of @var{Prologue} sections can often be subtle and +inflexible. +As an alternative, Bison provides a %code 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 @code{requires}, @code{provides}, @code{top}. +@xref{Decl Summary,,%code}. + +Look again at the example of the previous section: + +@smallexample +%@{ + #define _GNU_SOURCE #include #include "ptypes.h" %@} @@ -2618,6 +2736,250 @@ can be done with two @var{Prologue} blocks, one before and one after the @dots{} @end smallexample +@noindent +Notice that there are two @var{Prologue} sections here, but there's a subtle +distinction between their functionality. +For example, if you decide to override Bison's default definition for +@code{YYLTYPE}, in which @var{Prologue} section should you write your new +definition? +You should write it in the first since Bison will insert that code into the +parser source code file @emph{before} the default @code{YYLTYPE} definition. +In which @var{Prologue} section should you prototype an internal function, +@code{trace_token}, that accepts @code{YYLTYPE} and @code{yytokentype} as +arguments? +You should prototype it in the second since Bison will insert that code +@emph{after} the @code{YYLTYPE} and @code{yytokentype} definitions. + +This distinction in functionality between the two @var{Prologue} sections is +established by the appearance of the @code{%union} between them. +This behavior raises a few questions. +First, why should the position of a @code{%union} affect definitions related to +@code{YYLTYPE} and @code{yytokentype}? +Second, what if there is no @code{%union}? +In that case, the second kind of @var{Prologue} section is not available. +This behavior is not intuitive. + +To avoid this subtle @code{%union} dependency, rewrite the example using a +@code{%code top} and an unqualified @code{%code}. +Let's go ahead and add the new @code{YYLTYPE} definition and the +@code{trace_token} prototype at the same time: + +@smallexample +%code top @{ + #define _GNU_SOURCE + #include + + /* WARNING: The following code really belongs + * in a `%code requires'; see below. */ + + #include "ptypes.h" + #define YYLTYPE YYLTYPE + typedef struct YYLTYPE + @{ + int first_line; + int first_column; + int last_line; + int last_column; + char *filename; + @} YYLTYPE; +@} + +%union @{ + long int n; + tree t; /* @r{@code{tree} is defined in @file{ptypes.h}.} */ +@} + +%code @{ + static void print_token_value (FILE *, int, YYSTYPE); + #define YYPRINT(F, N, L) print_token_value (F, N, L) + static void trace_token (enum yytokentype token, YYLTYPE loc); +@} + +@dots{} +@end smallexample + +@noindent +In this way, @code{%code top} and the unqualified @code{%code} achieve the same +functionality as the two kinds of @var{Prologue} sections, but it's always +explicit which kind you intend. +Moreover, both kinds are always available even in the absence of @code{%union}. + +The @code{%code top} block above logically contains two parts. +The first two lines before the warning need to appear near the top of the +parser source code file. +The first line after the warning is required by @code{YYSTYPE} and thus also +needs to appear in the parser source code file. +However, if you've instructed Bison to generate a parser header file +(@pxref{Decl Summary, ,%defines}), you probably want that line to appear before +the @code{YYSTYPE} definition in that header file as well. +The @code{YYLTYPE} definition should also appear in the parser header file to +override the default @code{YYLTYPE} definition there. + +In other words, in the @code{%code top} block above, all but the first two +lines are dependency code required by the @code{YYSTYPE} and @code{YYLTYPE} +definitions. +Thus, they belong in one or more @code{%code requires}: + +@smallexample +%code top @{ + #define _GNU_SOURCE + #include +@} + +%code requires @{ + #include "ptypes.h" +@} +%union @{ + long int n; + tree t; /* @r{@code{tree} is defined in @file{ptypes.h}.} */ +@} + +%code requires @{ + #define YYLTYPE YYLTYPE + typedef struct YYLTYPE + @{ + int first_line; + int first_column; + int last_line; + int last_column; + char *filename; + @} YYLTYPE; +@} + +%code @{ + static void print_token_value (FILE *, int, YYSTYPE); + #define YYPRINT(F, N, L) print_token_value (F, N, L) + static void trace_token (enum yytokentype token, YYLTYPE loc); +@} + +@dots{} +@end smallexample + +@noindent +Now Bison will insert @code{#include "ptypes.h"} and the new @code{YYLTYPE} +definition before the Bison-generated @code{YYSTYPE} and @code{YYLTYPE} +definitions in both the parser source code file and the parser header file. +(By the same reasoning, @code{%code requires} would also be the appropriate +place to write your own definition for @code{YYSTYPE}.) + +When you are writing dependency code for @code{YYSTYPE} and @code{YYLTYPE}, you +should prefer @code{%code requires} over @code{%code top} 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 +source code file and that has no special need to appear at the top of that +file, you should prefer the unqualified @code{%code} over @code{%code top}. +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 @code{%code} and +@code{%code requires} to be the most important of the four @var{Prologue} +alternatives. + +At some point while developing your parser, you might decide to provide +@code{trace_token} 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 source code file. +Since this function is not a dependency required by @code{YYSTYPE} or +@code{YYLTYPE}, it doesn't make sense to move its prototype to a +@code{%code requires}. +More importantly, since it depends upon @code{YYLTYPE} and @code{yytokentype}, +@code{%code requires} is not sufficient. +Instead, move its prototype from the unqualified @code{%code} to a +@code{%code provides}: + +@smallexample +%code top @{ + #define _GNU_SOURCE + #include +@} + +%code requires @{ + #include "ptypes.h" +@} +%union @{ + long int n; + tree t; /* @r{@code{tree} is defined in @file{ptypes.h}.} */ +@} + +%code requires @{ + #define YYLTYPE YYLTYPE + typedef struct YYLTYPE + @{ + int first_line; + int first_column; + int last_line; + int last_column; + char *filename; + @} YYLTYPE; +@} + +%code provides @{ + void trace_token (enum yytokentype token, YYLTYPE loc); +@} + +%code @{ + static void print_token_value (FILE *, int, YYSTYPE); + #define YYPRINT(F, N, L) print_token_value (F, N, L) +@} + +@dots{} +@end smallexample + +@noindent +Bison will insert the @code{trace_token} prototype into both the parser header +file and the parser source code file after the definitions for +@code{yytokentype}, @code{YYLTYPE}, and @code{YYSTYPE}. + +The above examples are careful to write directives in an order that reflects +the layout of the generated parser source code and header files: +@code{%code top}, @code{%code requires}, @code{%code provides}, and then +@code{%code}. +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: + +@smallexample +%code requires @{ #include "type1.h" @} +%union @{ type1 field1; @} +%destructor @{ type1_free ($$); @} +%printer @{ type1_print ($$); @} + +%code requires @{ #include "type2.h" @} +%union @{ type2 field2; @} +%destructor @{ type2_free ($$); @} +%printer @{ type2_print ($$); @} +@end smallexample + +@noindent +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 @code{%union}) in the +definitions section is going to adversely affect their functionality in some +counter-intuitive manner just because it comes first. +Such an organization is not possible using @var{Prologue} sections. + +This section has been concerned with explaining the advantages of the four +@var{Prologue} alternatives over the original Yacc @var{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. +@code{%code} is the most generic label. +Move code to @code{%code requires}, @code{%code provides}, or @code{%code top} +as needed. + @node Bison Declarations @subsection The Bison Declarations Section @cindex Bison declarations (introduction) @@ -2851,6 +3213,22 @@ the semantics of the rule. An action looks like this: @end example @noindent +@cindex braced code +This is an example of @dfn{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 output 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 @samp{<%} and @samp{%>} that represent +braces. At the top level braced code must be terminated by @samp{@}} +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. @xref{Actions}. @@ -2858,15 +3236,6 @@ Usually there is only one action and it follows the components. Multiple rules for the same @var{result} can be written separately or can be joined with the vertical-bar character @samp{|} as follows: -@ifinfo -@example -@var{result}: @var{rule1-components}@dots{} - | @var{rule2-components}@dots{} - @dots{} - ; -@end example -@end ifinfo -@iftex @example @group @var{result}: @var{rule1-components}@dots{} @@ -2875,7 +3244,6 @@ be joined with the vertical-bar character @samp{|} as follows: ; @end group @end example -@end iftex @noindent They are still considered distinct rules even when joined in this way. @@ -3007,7 +3375,8 @@ the semantic values of all language constructs. This was true in the @acronym{RPN} and infix calculator examples (@pxref{RPN Calc, ,Reverse Polish Notation Calculator}). -Bison's default is to use type @code{int} for all semantic values. To +Bison normally uses the type @code{int} for semantic values if your +program uses the same data type for all language constructs. To specify some other type, define @code{YYSTYPE} as a macro, like this: @example @@ -3015,6 +3384,8 @@ specify some other type, define @code{YYSTYPE} as a macro, like this: @end example @noindent +@code{YYSTYPE}'s replacement list should be a type name +that does not contain parentheses or square brackets. This macro definition must go in the prologue of the grammar file (@pxref{Grammar Outline, ,Outline of a Bison Grammar}). @@ -3032,9 +3403,11 @@ requires you to do two things: @itemize @bullet @item -Specify the entire collection of possible data types, with the +Specify the entire collection of possible data types, either by using the @code{%union} Bison declaration (@pxref{Union Decl, ,The Collection of -Value Types}). +Value Types}), or by using a @code{typedef} or a @code{#define} to +define @code{YYSTYPE} to be a union type whose member names are +the type tags. @item Choose one of those types for each symbol (terminal or nonterminal) for @@ -3055,14 +3428,8 @@ 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 C statements surrounded by braces, much like a -compound statement in C@. An action can contain any sequence of C -statements. Bison does not look for trigraphs, though, so if your C -code uses trigraphs you should ensure that they do not affect the -nesting of braces or the boundaries of comments, strings, or character -literals. - -An action can be placed at any position in the rule; +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 (@pxref{Mid-Rule @@ -3140,6 +3507,12 @@ As long as @code{bar} is used only in the fashion shown here, @code{$0} always refers to the @code{expr} which precedes @code{bar} in the definition of @code{foo}. +@vindex yylval +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 @code{yylval}. +@xref{Action Features, ,Special Features for Use in Actions}. + @node Action Types @subsection Data Types of Values in Actions @cindex action data types @@ -3249,6 +3622,46 @@ earlier action is used to restore the prior list of variables. This removes the temporary @code{let}-variable from the list so that it won't appear to exist while the rest of the program is parsed. +@findex %destructor +@cindex discarded symbols, mid-rule actions +@cindex error recovery, mid-rule actions +In the above example, if the parser initiates error recovery (@pxref{Error +Recovery}) while parsing the tokens in the embedded statement @code{stmt}, +it might discard the previous semantic context @code{$5} without +restoring it. +Thus, @code{$5} needs a destructor (@pxref{Destructor Decl, , Freeing +Discarded Symbols}). +However, Bison currently provides no means to declare a destructor specific to +a particular mid-rule action's semantic value. + +One solution is to bury the mid-rule action inside a nonterminal symbol and to +declare a destructor for that symbol: + +@example +@group +%type let +%destructor @{ pop_context ($$); @} let + +%% + +stmt: let stmt + @{ $$ = $2; + pop_context ($1); @} + ; + +let: LET '(' var ')' + @{ $$ = push_context (); + declare_variable ($3); @} + ; + +@end group +@end example + +@noindent +Note that the action is now at the end of its rule. +Any mid-rule action can be converted to an end-of-rule action in this way, and +this is what Bison actually does to implement mid-rule actions. + Taking 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 mid-rule actions, @@ -3283,8 +3696,8 @@ Now the parser is forced to decide whether to run the mid-rule 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 @dfn{look-ahead} token at this time, since the parser is still -deciding what to do about it. @xref{Look-Ahead, ,Look-Ahead Tokens}.) +the @dfn{lookahead} token at this time, since the parser is still +deciding what to do about it. @xref{Lookahead, ,Lookahead Tokens}.) You might think that you could correct the problem by putting identical actions into the two rules, like this: @@ -3342,10 +3755,7 @@ compound: subroutine @noindent Now Bison can execute the action in the rule for @code{subroutine} without -deciding which rule for @code{compound} it will eventually use. Note that -the action is now at the end of its rule. Any mid-rule action can be -converted to an end-of-rule action in this way, and this is what Bison -actually does to implement mid-rule actions. +deciding which rule for @code{compound} it will eventually use. @node Locations @section Tracking Locations @@ -3374,7 +3784,9 @@ actions to take when rules are matched. Defining a data type for locations is much simpler than for semantic values, since all tokens and groupings always use the same type. -The type of locations is specified by defining a macro called @code{YYLTYPE}. +You can specify the type of locations by defining a macro called +@code{YYLTYPE}, just as you can specify the semantic value type by +defining a @code{YYSTYPE} macro (@pxref{Value Type}). When @code{YYLTYPE} is not defined, Bison uses a default structure type with four members: @@ -3388,6 +3800,12 @@ typedef struct YYLTYPE @} YYLTYPE; @end example +When @code{YYLTYPE} is not defined, at the beginning of the parsing, Bison +initializes all these fields to 1 for @code{yylloc}. To initialize +@code{yylloc} with a custom location type (or to chose a different +initialization), use the @code{%initial-action} directive. @xref{Initial +Action Decl, , Performing Actions before Parsing}. + @node Actions and Locations @subsection Actions and Locations @cindex location actions @@ -3457,9 +3875,16 @@ exp: @dots{} @end group @end example +@vindex yylloc +It is also possible to access the location of the lookahead token, if any, +from a semantic action. +This location is stored in @code{yylloc}. +@xref{Action Features, ,Special Features for Use in Actions}. + @node Location Default Action @subsection Default Action for Locations @vindex YYLLOC_DEFAULT +@cindex @acronym{GLR} parsers and @code{YYLLOC_DEFAULT} Actually, actions are not the best place to compute locations. Since locations are much more general than semantic values, there is room in @@ -3467,6 +3892,9 @@ the output parser to redefine the default action to take for each rule. The @code{YYLLOC_DEFAULT} 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 @acronym{GLR} +parser invokes @code{YYLLOC_DEFAULT} 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. @@ -3475,9 +3903,11 @@ The @code{YYLLOC_DEFAULT} 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 processing -a syntax error, the second parameter identifies locations of -the symbols that were discarded during error processing, and the third +parameter is the size of the rule's right hand side. +When a @acronym{GLR} parser reports an ambiguity, which of multiple candidate +right hand sides it passes to @code{YYLLOC_DEFAULT} 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, @code{YYLLOC_DEFAULT} is defined this way: @@ -3558,6 +3988,7 @@ Grammars}). * Expect Decl:: Suppressing warnings about parsing conflicts. * Start Decl:: Specifying the start symbol. * Pure Decl:: Requesting a reentrant parser. +* Push Decl:: Requesting a push parser. * Decl Summary:: Table of all Bison declarations. @end menu @@ -3598,7 +4029,7 @@ associativity and precedence. @xref{Precedence Decl, ,Operator Precedence}. You can explicitly specify the numeric code for a token type by appending -a decimal or hexadecimal integer value in the field immediately +a nonnegative decimal or hexadecimal integer value in the field immediately following the token name: @example @@ -3651,6 +4082,16 @@ Once you equate the literal string and the token name, you can use them interchangeably in further declarations or the grammar rules. The @code{yylex} function can use the token name or the literal string to obtain the token type code number (@pxref{Calling Convention}). +Syntax error messages passed to @code{yyerror} from the parser will reference +the literal string instead of the token name. + +The token numbered as 0 corresponds to end of file; the following line +allows for nicer error messages referring to ``end of file'' instead +of ``$end'': + +@example +%token END 0 "end of file" +@end example @node Precedence Decl @subsection Operator Precedence @@ -3664,7 +4105,7 @@ once. These are called @dfn{precedence declarations}. @xref{Precedence, ,Operator Precedence}, for general information on operator precedence. -The syntax of a precedence declaration is the same as that of +The syntax of a precedence declaration is nearly the same as that of @code{%token}: either @example @@ -3702,16 +4143,28 @@ When two tokens declared in different precedence declarations associate, the one declared later has the higher precedence and is grouped first. @end itemize +For backward compatibility, there is a confusing difference between the +argument lists of @code{%token} and precedence declarations. +Only a @code{%token} can associate a literal string with a token type name. +A precedence declaration always interprets a literal string as a reference to a +separate token. +For example: + +@example +%left OR "<=" // Does not declare an alias. +%left OR 134 "<=" 135 // Declares 134 for OR and 135 for "<=". +@end example + @node Union Decl @subsection The Collection of Value Types @cindex declaring value types @cindex value types, declaring @findex %union -The @code{%union} declaration specifies the entire collection of possible -data types for semantic values. The keyword @code{%union} is followed by a -pair of braces containing the same thing that goes inside a @code{union} in -C. +The @code{%union} declaration specifies the entire collection of +possible data types for semantic values. The keyword @code{%union} is +followed by braced code containing the same thing that goes inside a +@code{union} in C@. For example: @@ -3742,13 +4195,47 @@ As an extension to @acronym{POSIX}, a tag is allowed after the @end group @end example +@noindent specifies the union tag @code{value}, so the corresponding C type is @code{union value}. If you do not specify a tag, it defaults to @code{YYSTYPE}. +As another extension to @acronym{POSIX}, you may specify multiple +@code{%union} declarations; their contents are concatenated. However, +only the first @code{%union} declaration can specify a tag. + Note that, unlike making a @code{union} declaration in C, you need not write a semicolon after the closing brace. +Instead of @code{%union}, you can define and use your own union type +@code{YYSTYPE} if your grammar contains at least one +@samp{<@var{type}>} tag. For example, you can put the following into +a header file @file{parser.h}: + +@example +@group +union YYSTYPE @{ + double val; + symrec *tptr; +@}; +typedef union YYSTYPE YYSTYPE; +@end group +@end example + +@noindent +and then your grammar can use the following +instead of @code{%union}: + +@example +@group +%@{ +#include "parser.h" +%@} +%type expr +%token ID +@end group +@end example + @node Type Decl @subsection Nonterminal Symbols @cindex declaring value types, nonterminals @@ -3787,9 +4274,9 @@ code. @deffn {Directive} %initial-action @{ @var{code} @} @findex %initial-action -Declare that the @var{code} must be invoked before parsing each time +Declare that the braced @var{code} must be invoked before parsing each time @code{yyparse} is called. The @var{code} may use @code{$$} and -@code{@@$} --- initial value and location of the look-ahead --- and the +@code{@@$} --- initial value and location of the lookahead --- and the @code{%parse-param}. @end deffn @@ -3808,7 +4295,8 @@ For instance, if your locations use a file name, you may use @subsection Freeing Discarded Symbols @cindex freeing discarded symbols @findex %destructor - +@findex <*> +@findex <> During error recovery (@pxref{Error Recovery}), symbols already pushed on the stack and tokens coming from the rest of the file are discarded until the parser falls on its feet. If the parser runs out of memory, @@ -3826,28 +4314,101 @@ symbol is automatically discarded. @deffn {Directive} %destructor @{ @var{code} @} @var{symbols} @findex %destructor -Invoke @var{code} whenever the parser discards one of the @var{symbols}. +Invoke the braced @var{code} whenever the parser discards one of the +@var{symbols}. Within @var{code}, @code{$$} designates the semantic value associated -with the discarded symbol. The additional parser parameters are also -available (@pxref{Parser Function, , The Parser Function -@code{yyparse}}). +with the discarded symbol, and @code{@@$} designates its location. +The additional parser parameters are also available (@pxref{Parser Function, , +The Parser Function @code{yyparse}}). + +When a symbol is listed among @var{symbols}, its @code{%destructor} is called a +per-symbol @code{%destructor}. +You may also define a per-type @code{%destructor} by listing a semantic type +tag among @var{symbols}. +In that case, the parser will invoke this @var{code} whenever it discards any +grammar symbol that has that semantic type tag unless that symbol has its own +per-symbol @code{%destructor}. + +Finally, you can define two different kinds of default @code{%destructor}s. +(These default forms are experimental. +More user feedback will help to determine whether they should become permanent +features.) +You can place each of @code{<*>} and @code{<>} in the @var{symbols} list of +exactly one @code{%destructor} declaration in your grammar file. +The parser will invoke the @var{code} associated with one of these whenever it +discards any user-defined grammar symbol that has no per-symbol and no per-type +@code{%destructor}. +The parser uses the @var{code} for @code{<*>} in the case of such a grammar +symbol for which you have formally declared a semantic type tag (@code{%type} +counts as such a declaration, but @code{$$} does not). +The parser uses the @var{code} for @code{<>} in the case of such a grammar +symbol that has no declared semantic type tag. @end deffn -For instance: +@noindent +For example: @smallexample -%union -@{ - char *string; -@} -%token STRING -%type string -%destructor @{ free ($$); @} STRING string +%union @{ char *string; @} +%token STRING1 +%token STRING2 +%type string1 +%type string2 +%union @{ char character; @} +%token CHR +%type chr +%token TAGLESS + +%destructor @{ @} +%destructor @{ free ($$); @} <*> +%destructor @{ free ($$); printf ("%d", @@$.first_line); @} STRING1 string1 +%destructor @{ printf ("Discarding tagless symbol.\n"); @} <> @end smallexample @noindent -guarantees that when a @code{STRING} or a @code{string} is discarded, -its associated memory will be freed. +guarantees that, when the parser discards any user-defined symbol that has a +semantic type tag other than @code{}, it passes its semantic value +to @code{free} by default. +However, when the parser discards a @code{STRING1} or a @code{string1}, it also +prints its line number to @code{stdout}. +It performs only the second @code{%destructor} in this case, so it invokes +@code{free} only once. +Finally, the parser merely prints a message whenever it discards any symbol, +such as @code{TAGLESS}, that has no semantic type tag. + +A Bison-generated parser invokes the default @code{%destructor}s only for +user-defined as opposed to Bison-defined symbols. +For example, the parser will not invoke either kind of default +@code{%destructor} for the special Bison-defined symbols @code{$accept}, +@code{$undefined}, or @code{$end} (@pxref{Table of Symbols, ,Bison Symbols}), +none of which you can reference in your grammar. +It also will not invoke either for the @code{error} token (@pxref{Table of +Symbols, ,error}), 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 @code{$end} to, for example, @code{END}: + +@smallexample +%token END 0 +@end smallexample + +@cindex actions in mid-rule +@cindex mid-rule actions +Finally, Bison will never invoke a @code{%destructor} for an unreferenced +mid-rule semantic value (@pxref{Mid-Rule Actions,,Actions in Mid-Rule}). +That is, Bison does not consider a mid-rule to have a semantic value if you do +not reference @code{$$} in the mid-rule's action or @code{$@var{n}} (where +@var{n} is the RHS symbol position of the mid-rule) in any later action in that +rule. +However, if you do reference either, the Bison-generated parser will invoke the +@code{<>} @code{%destructor} whenever it discards the mid-rule symbol. + +@ignore +@noindent +In the future, it may be possible to redefine the @code{error} token as a +nonterminal that captures the discarded symbols. +In that case, the parser will invoke the default destructor for it as well. +@end ignore @sp 1 @@ -3860,7 +4421,7 @@ stacked symbols popped during the first phase of error recovery, @item incoming terminals during the second phase of error recovery, @item -the current look-ahead and the entire stack (except the current +the current lookahead and the entire stack (except the current right-hand side symbols) when the parser returns immediately, and @item the start symbol, when the parser succeeds. @@ -3870,7 +4431,7 @@ The parser can @dfn{return immediately} because of an explicit call to @code{YYABORT} or @code{YYACCEPT}, or failed error recovery, or memory exhaustion. -Right-hand size symbols of a rule that explicitly triggers a syntax +Right-hand side symbols of a rule that explicitly triggers a syntax error via @code{YYERROR} are not discarded automatically. As a rule of thumb, destructors are invoked only when user actions cannot manage the memory. @@ -3955,7 +4516,7 @@ may override this restriction with the @code{%start} declaration as follows: @subsection A Pure (Reentrant) Parser @cindex reentrant parser @cindex pure parser -@findex %pure-parser +@findex %define api.pure A @dfn{reentrant} program is one which does not alter in the course of execution; in other words, it consists entirely of @dfn{pure} (read-only) @@ -3971,19 +4532,20 @@ statically allocated variables for communication with @code{yylex}, including @code{yylval} and @code{yylloc}.) Alternatively, you can generate a pure, reentrant parser. The Bison -declaration @code{%pure-parser} says that you want the parser to be +declaration @code{%define api.pure} says that you want the parser to be reentrant. It looks like this: @example -%pure-parser +%define api.pure @end example The result is that the communication variables @code{yylval} and @code{yylloc} become local variables in @code{yyparse}, and a different calling convention is used for the lexical analyzer function @code{yylex}. @xref{Pure Calling, ,Calling Conventions for Pure -Parsers}, for the details of this. The variable @code{yynerrs} also -becomes local in @code{yyparse} (@pxref{Error Reporting, ,The Error +Parsers}, for the details of this. The variable @code{yynerrs} +becomes local in @code{yyparse} in pull mode but it becomes a member +of yypstate in push mode. (@pxref{Error Reporting, ,The Error Reporting Function @code{yyerror}}). The convention for calling @code{yyparse} itself is unchanged. @@ -3991,6 +4553,116 @@ 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. +@node Push Decl +@subsection A Push Parser +@cindex push parser +@cindex push parser +@findex %define api.push_pull + +(The current push parsing interface is experimental and may evolve. +More user feedback will help to stabilize it.) + +A 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 (@pxref{Decl Summary,,%define api.push_pull}): + +@example +%define api.push_pull "push" +@end example + +In almost all cases, you want to ensure that your push parser is also +a pure parser (@pxref{Pure Decl, ,A Pure (Reentrant) Parser}). 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: + +@example +%define api.pure +%define api.push_pull "push" +@end example + +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. @code{yypstate} is a structure that the generated +parser uses to store the parser's state. @code{yypstate_new} is the +function that will create a new parser instance. @code{yypstate_delete} +will free the resources associated with the corresponding parser instance. +Finally, @code{yypush_parse} 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: + +@example +int status; +yypstate *ps = yypstate_new (); +do @{ + status = yypush_parse (ps, yylex (), NULL); +@} while (status == YYPUSH_MORE); +yypstate_delete (ps); +@end example + +If the user decided to use an impure push parser, a few things about +the generated parser will change. The @code{yychar} variable becomes +a global variable instead of a variable in the @code{yypush_parse} function. +For this reason, the signature of the @code{yypush_parse} function is +changed to remove the token as a parameter. A nonreentrant push parser +example would thus look like this: + +@example +extern int yychar; +int status; +yypstate *ps = yypstate_new (); +do @{ + yychar = yylex (); + status = yypush_parse (ps); +@} while (status == YYPUSH_MORE); +yypstate_delete (ps); +@end example + +That's it. Notice the next token is put into the global variable @code{yychar} +for use by the next invocation of the @code{yypush_parse} 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 @code{%define api.push_pull "push"} declaration with the +@code{%define api.push_pull "both"} declaration. Doing this will create all of +the symbols mentioned earlier along with the two extra symbols, @code{yyparse} +and @code{yypull_parse}. @code{yyparse} 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 @code{yypull_parse}. +This makes the @code{yyparse} function that is generated with the +@code{%define api.push_pull "both"} declaration slower than the normal +@code{yyparse} function. If the user +calls the @code{yypull_parse} function it will parse the rest of the input +stream. It is possible to @code{yypush_parse} tokens to select a subgrammar +and then @code{yypull_parse} 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 @code{yypull_parse} function that knows when to quit looking +for input. An example of using the @code{yypull_parse} function would look +like this: + +@example +yypstate *ps = yypstate_new (); +yypull_parse (ps); /* Will call the lexer */ +yypstate_delete (ps); +@end example + +Adding the @code{%define api.pure} declaration does exactly the same thing to +the generated parser with @code{%define api.push_pull "both"} as it did for +@code{%define api.push_pull "push"}. + @node Decl Summary @subsection Bison Declaration Summary @cindex Bison declaration summary @@ -4053,41 +4725,312 @@ Declare the expected number of shift-reduce conflicts In order to change the behavior of @command{bison}, use the following directives: -@deffn {Directive} %debug -In the parser file, define the macro @code{YYDEBUG} to 1 if it is not -already defined, so that the debugging facilities are compiled. +@deffn {Directive} %code @{@var{code}@} +@findex %code +This is the unqualified form of the @code{%code} directive. +It inserts @var{code} verbatim at a language-dependent default location in the +output@footnote{The default location is actually skeleton-dependent; + writers of non-standard skeletons however should choose the default location + consistently with the behavior of the standard Bison skeletons.}. + +@cindex Prologue +For C/C++, the default location is the parser source code +file after the usual contents of the parser header file. +Thus, @code{%code} replaces the traditional Yacc prologue, +@code{%@{@var{code}%@}}, for most purposes. +For a detailed discussion, see @ref{Prologue Alternatives}. + +For Java, the default location is inside the parser class. @end deffn -@xref{Tracing, ,Tracing Your Parser}. -@deffn {Directive} %defines -Write a header file containing macro definitions for the token type -names defined in the grammar as well as a few other declarations. -If the parser output file is named @file{@var{name}.c} then this file -is named @file{@var{name}.h}. +@deffn {Directive} %code @var{qualifier} @{@var{code}@} +This is the qualified form of the @code{%code} directive. +If you need to specify location-sensitive verbatim @var{code} that does not +belong at the default location selected by the unqualified @code{%code} form, +use this form instead. -Unless @code{YYSTYPE} is already defined as a macro, the output header -declares @code{YYSTYPE}. Therefore, if you are using a @code{%union} -(@pxref{Multiple Types, ,More Than One Value Type}) with components that -require other definitions, or if you have defined a @code{YYSTYPE} macro -(@pxref{Value Type, ,Data Types of Semantic Values}), 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 @code{YYSTYPE}. +@var{qualifier} identifies the purpose of @var{code} and thus the location(s) +where Bison should generate it. +Not all values of @var{qualifier} are available for all target languages: -Unless your parser is pure, the output header declares @code{yylval} -as an external variable. @xref{Pure Decl, ,A Pure (Reentrant) -Parser}. +@itemize @bullet +@item requires +@findex %code requires -If you have also used locations, the output header declares -@code{YYLTYPE} and @code{yylloc} using a protocol similar to that of -@code{YYSTYPE} and @code{yylval}. @xref{Locations, ,Tracking -Locations}. +@itemize @bullet +@item Language(s): C, C++ -This output file is normally essential if you wish to put the definition -of @code{yylex} in a separate source file, because @code{yylex} +@item Purpose: This is the best place to write dependency code required for +@code{YYSTYPE} and @code{YYLTYPE}. +In other words, it's the best place to define types referenced in @code{%union} +directives, and it's the best place to override Bison's default @code{YYSTYPE} +and @code{YYLTYPE} definitions. + +@item Location(s): The parser header file and the parser source code file +before the Bison-generated @code{YYSTYPE} and @code{YYLTYPE} definitions. +@end itemize + +@item provides +@findex %code provides + +@itemize @bullet +@item Language(s): C, C++ + +@item Purpose: This is the best place to write additional definitions and +declarations that should be provided to other modules. + +@item Location(s): The parser header file and the parser source code file after +the Bison-generated @code{YYSTYPE}, @code{YYLTYPE}, and token definitions. +@end itemize + +@item top +@findex %code top + +@itemize @bullet +@item Language(s): C, C++ + +@item Purpose: The unqualified @code{%code} or @code{%code requires} should +usually be more appropriate than @code{%code top}. +However, occasionally it is necessary to insert code much nearer the top of the +parser source code file. +For example: + +@smallexample +%code top @{ + #define _GNU_SOURCE + #include +@} +@end smallexample + +@item Location(s): Near the top of the parser source code file. +@end itemize + +@item imports +@findex %code imports + +@itemize @bullet +@item Language(s): Java + +@item Purpose: This is the best place to write Java import directives. + +@item Location(s): The parser Java file after any Java package directive and +before any class definitions. +@end itemize +@end itemize + +@cindex Prologue +For a detailed discussion of how to use @code{%code} in place of the +traditional Yacc prologue for C/C++, see @ref{Prologue Alternatives}. +@end deffn + +@deffn {Directive} %debug +In the parser file, define the macro @code{YYDEBUG} to 1 if it is not +already defined, so that the debugging facilities are compiled. +@xref{Tracing, ,Tracing Your Parser}. +@end deffn + +@deffn {Directive} %define @var{variable} +@deffnx {Directive} %define @var{variable} "@var{value}" +Define a variable to adjust Bison's behavior. +The possible choices for @var{variable}, as well as their meanings, depend on +the selected target language and/or the parser skeleton (@pxref{Decl +Summary,,%language}, @pxref{Decl Summary,,%skeleton}). + +Bison will warn if a @var{variable} is defined multiple times. + +Omitting @code{"@var{value}"} is always equivalent to specifying it as +@code{""}. + +Some @var{variable}s may be used as Booleans. +In this case, Bison will complain if the variable definition does not meet one +of the following four conditions: + +@enumerate +@item @code{"@var{value}"} is @code{"true"} + +@item @code{"@var{value}"} is omitted (or is @code{""}). +This is equivalent to @code{"true"}. + +@item @code{"@var{value}"} is @code{"false"}. + +@item @var{variable} is never defined. +In this case, Bison selects a default value, which may depend on the selected +target language and/or parser skeleton. +@end enumerate + +Some of the accepted @var{variable}s are: + +@itemize @bullet +@item api.pure +@findex %define api.pure + +@itemize @bullet +@item Language(s): C + +@item Purpose: Request a pure (reentrant) parser program. +@xref{Pure Decl, ,A Pure (Reentrant) Parser}. + +@item Accepted Values: Boolean + +@item Default Value: @code{"false"} +@end itemize + +@item api.push_pull +@findex %define api.push_pull + +@itemize @bullet +@item Language(s): C (LALR(1) only) + +@item Purpose: Requests a pull parser, a push parser, or both. +@xref{Push Decl, ,A Push Parser}. +(The current push parsing interface is experimental and may evolve. +More user feedback will help to stabilize it.) + +@item Accepted Values: @code{"pull"}, @code{"push"}, @code{"both"} + +@item Default Value: @code{"pull"} +@end itemize + +@item lr.keep_unreachable_states +@findex %define lr.keep_unreachable_states + +@itemize @bullet +@item Language(s): all + +@item Purpose: Requests that Bison allow unreachable parser states to remain in +the parser tables. +Bison considers a state to be unreachable if there exists no sequence of +transitions from the start state to that state. +A state can become unreachable during conflict resolution if Bison disables a +shift action leading to it from a predecessor state. +Keeping unreachable states is sometimes useful for analysis purposes, but they +are useless in the generated parser. + +@item Accepted Values: Boolean + +@item Default Value: @code{"false"} + +@item Caveats: + +@itemize @bullet + +@item Unreachable states may contain conflicts and may use rules not used in +any other state. +Thus, keeping unreachable states may induce warnings that are irrelevant to +your parser's behavior, and it may eliminate warnings that are relevant. +Of course, the change in warnings may actually be relevant to a parser table +analysis that wants to keep unreachable states, so this behavior will likely +remain in future Bison releases. + +@item While Bison is able to remove unreachable states, it is not guaranteed to +remove other kinds of useless states. +Specifically, when Bison disables reduce actions during conflict resolution, +some goto actions may become useless, and thus some additional states may +become useless. +If Bison were to compute which goto actions were useless and then disable those +actions, it could identify such states as unreachable and then remove those +states. +However, Bison does not compute which goto actions are useless. +@end itemize +@end itemize + +@item namespace +@findex %define namespace + +@itemize +@item Languages(s): C++ + +@item Purpose: Specifies the namespace for the parser class. +For example, if you specify: + +@smallexample +%define namespace "foo::bar" +@end smallexample + +Bison uses @code{foo::bar} verbatim in references such as: + +@smallexample +foo::bar::parser::semantic_type +@end smallexample + +However, to open a namespace, Bison removes any leading @code{::} and then +splits on any remaining occurrences: + +@smallexample +namespace foo @{ namespace bar @{ + class position; + class location; +@} @} +@end smallexample + +@item Accepted Values: Any absolute or relative C++ namespace reference without +a trailing @code{"::"}. +For example, @code{"foo"} or @code{"::foo::bar"}. + +@item Default Value: The value specified by @code{%name-prefix}, which defaults +to @code{yy}. +This usage of @code{%name-prefix} is for backward compatibility and can be +confusing since @code{%name-prefix} also specifies the textual prefix for the +lexical analyzer function. +Thus, if you specify @code{%name-prefix}, it is best to also specify +@code{%define namespace} so that @code{%name-prefix} @emph{only} affects the +lexical analyzer function. +For example, if you specify: + +@smallexample +%define namespace "foo" +%name-prefix "bar::" +@end smallexample + +The parser namespace is @code{foo} and @code{yylex} is referenced as +@code{bar::lex}. +@end itemize +@end itemize + +@end deffn + +@deffn {Directive} %defines +Write a header file containing macro definitions for the token type +names defined in the grammar as well as a few other declarations. +If the parser output file is named @file{@var{name}.c} then this file +is named @file{@var{name}.h}. + +For C parsers, the output header declares @code{YYSTYPE} unless +@code{YYSTYPE} is already defined as a macro or you have used a +@code{<@var{type}>} tag without using @code{%union}. +Therefore, if you are using a @code{%union} +(@pxref{Multiple Types, ,More Than One Value Type}) with components that +require other definitions, or if you have defined a @code{YYSTYPE} macro +or type definition +(@pxref{Value Type, ,Data Types of Semantic Values}), 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 @code{YYSTYPE}. + +Unless your parser is pure, the output header declares @code{yylval} +as an external variable. @xref{Pure Decl, ,A Pure (Reentrant) +Parser}. + +If you have also used locations, the output header declares +@code{YYLTYPE} and @code{yylloc} using a protocol similar to that of +the @code{YYSTYPE} macro and @code{yylval}. @xref{Locations, ,Tracking +Locations}. + +This output file is normally essential if you wish to put the definition +of @code{yylex} in a separate source file, because @code{yylex} typically needs to be able to refer to the above-mentioned declarations and to the token type codes. @xref{Token Values, ,Semantic Values of Tokens}. + +@findex %code requires +@findex %code provides +If you have declared @code{%code requires} or @code{%code provides}, the output +header also contains their code. +@xref{Decl Summary, ,%code}. +@end deffn + +@deffn {Directive} %defines @var{defines-file} +Same as above, but save in the file @var{defines-file}. @end deffn @deffn {Directive} %destructor @@ -4095,11 +5038,20 @@ Specify how the parser should reclaim the memory associated to discarded symbols. @xref{Destructor Decl, , Freeing Discarded Symbols}. @end deffn -@deffn {Directive} %file-prefix="@var{prefix}" +@deffn {Directive} %file-prefix "@var{prefix}" Specify a prefix to use for all Bison output file names. The names are chosen as if the input file were named @file{@var{prefix}.y}. @end deffn +@deffn {Directive} %language "@var{language}" +Specify the programming language for the generated parser. Currently +supported languages include C, C++, and Java. +@var{language} is case-insensitive. + +This directive is experimental and its effect may be modified in future +releases. +@end deffn + @deffn {Directive} %locations Generate the code processing the locations (@pxref{Action Features, ,Special Features for Use in Actions}). This mode is enabled as soon as @@ -4108,15 +5060,20 @@ grammar does not use it, using @samp{%locations} allows for more accurate syntax error messages. @end deffn -@deffn {Directive} %name-prefix="@var{prefix}" +@deffn {Directive} %name-prefix "@var{prefix}" Rename the external symbols used in the parser so that they start with @var{prefix} instead of @samp{yy}. The precise list of symbols renamed +in C parsers is @code{yyparse}, @code{yylex}, @code{yyerror}, @code{yynerrs}, -@code{yylval}, @code{yylloc}, @code{yychar}, @code{yydebug}, and -possible @code{yylloc}. For example, if you use -@samp{%name-prefix="c_"}, the names become @code{c_parse}, @code{c_lex}, -and so on. @xref{Multiple Parsers, ,Multiple Parsers in the Same -Program}. +@code{yylval}, @code{yychar}, @code{yydebug}, and +(if locations are used) @code{yylloc}. If you use a push parser, +@code{yypush_parse}, @code{yypull_parse}, @code{yypstate}, +@code{yypstate_new} and @code{yypstate_delete} will +also be renamed. For example, if you use @samp{%name-prefix "c_"}, the +names become @code{c_parse}, @code{c_lex}, and so on. +For C++ parsers, see the @code{%define namespace} documentation in this +section. +@xref{Multiple Parsers, ,Multiple Parsers in the Same Program}. @end deffn @ifset defaultprec @@ -4127,16 +5084,6 @@ Precedence}). @end deffn @end ifset -@deffn {Directive} %no-parser -Do not include any C code in the parser file; generate tables only. The -parser file contains just @code{#define} directives and static variable -declarations. - -This option also tells Bison to write the C code for the grammar actions -into a file named @file{@var{file}.act}, in the form of a -brace-surrounded body fit for a @code{switch} statement. -@end deffn - @deffn {Directive} %no-lines Don't generate any @code{#line} preprocessor commands in the parser file. Ordinarily Bison writes these commands in the parser file so that @@ -4146,13 +5093,13 @@ associate errors with the parser file, treating it an independent source file in its own right. @end deffn -@deffn {Directive} %output="@var{file}" +@deffn {Directive} %output "@var{file}" Specify @var{file} for the parser file. @end deffn @deffn {Directive} %pure-parser -Request a pure (reentrant) parser program (@pxref{Pure Decl, ,A Pure -(Reentrant) Parser}). +Deprecated version of @code{%define api.pure} (@pxref{Decl Summary, ,%define}), +for which Bison is more careful to warn about unreasonable usage. @end deffn @deffn {Directive} %require "@var{version}" @@ -4160,6 +5107,21 @@ Require version @var{version} or higher of Bison. @xref{Require Decl, , Require a Version of Bison}. @end deffn +@deffn {Directive} %skeleton "@var{file}" +Specify the skeleton to use. + +@c You probably don't need this option unless you are developing Bison. +@c You should use @code{%language} if you want to specify the skeleton for a +@c different language, because it is clearer and because it will always choose the +@c correct skeleton for non-deterministic or push parsers. + +If @var{file} does not contain a @code{/}, @var{file} is the name of a skeleton +file in the Bison installation directory. +If it does, @var{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. +@end deffn + @deffn {Directive} %token-table Generate an array of token names in the parser file. The name of the array is @code{yytname}; @code{yytname[@var{i}]} is the name of the @@ -4196,7 +5158,7 @@ The number of parser states (@pxref{Parser States}). @deffn {Directive} %verbose Write an extra output file containing verbose descriptions of the -parser states and what is done for each type of look-ahead token in +parser states and what is done for each type of lookahead token in that state. @xref{Understanding, , Understanding Your Parser}, for more information. @end deffn @@ -4223,8 +5185,11 @@ names that do not conflict. The precise list of symbols renamed is @code{yyparse}, @code{yylex}, @code{yyerror}, @code{yynerrs}, @code{yylval}, @code{yylloc}, -@code{yychar} and @code{yydebug}. For example, if you use @samp{-p c}, -the names become @code{cparse}, @code{clex}, and so on. +@code{yychar} and @code{yydebug}. If you use a push parser, +@code{yypush_parse}, @code{yypull_parse}, @code{yypstate}, +@code{yypstate_new} and @code{yypstate_delete} will also be renamed. +For example, if you use @samp{-p c}, the names become @code{cparse}, +@code{clex}, and so on. @strong{All the other variables and macros associated with Bison are not renamed.} These others are not global; there is no conflict if the same @@ -4252,13 +5217,17 @@ identifier (aside from those in this manual) in an action or in epilogue in the grammar file, you are likely to run into trouble. @menu -* Parser Function:: How to call @code{yyparse} and what it returns. -* Lexical:: You must supply a function @code{yylex} - which reads tokens. -* Error Reporting:: You must supply a function @code{yyerror}. -* Action Features:: Special features for use in actions. -* Internationalization:: How to let the parser speak in the user's - native language. +* Parser Function:: How to call @code{yyparse} and what it returns. +* Push Parser Function:: How to call @code{yypush_parse} and what it returns. +* Pull Parser Function:: How to call @code{yypull_parse} and what it returns. +* Parser Create Function:: How to call @code{yypstate_new} and what it returns. +* Parser Delete Function:: How to call @code{yypstate_delete} and what it returns. +* Lexical:: You must supply a function @code{yylex} + which reads tokens. +* Error Reporting:: You must supply a function @code{yyerror}. +* Action Features:: Special features for use in actions. +* Internationalization:: How to let the parser speak in the user's + native language. @end menu @node Parser Function @@ -4302,8 +5271,8 @@ declaration @code{%parse-param}: @deffn {Directive} %parse-param @{@var{argument-declaration}@} @findex %parse-param -Declare that an argument declared by @code{argument-declaration} is an -additional @code{yyparse} argument. +Declare that an argument declared by the braced-code +@var{argument-declaration} is an additional @code{yyparse} argument. The @var{argument-declaration} is used when declaring functions or prototypes. The last identifier in @var{argument-declaration} must be the argument name. @@ -4335,6 +5304,75 @@ In the grammar actions, use expressions like this to refer to the data: exp: @dots{} @{ @dots{}; *randomness += 1; @dots{} @} @end example +@node Push Parser Function +@section The Push Parser Function @code{yypush_parse} +@findex yypush_parse + +(The current push parsing interface is experimental and may evolve. +More user feedback will help to stabilize it.) + +You call the function @code{yypush_parse} to parse a single token. This +function is available if either the @code{%define api.push_pull "push"} or +@code{%define api.push_pull "both"} declaration is used. +@xref{Push Decl, ,A Push Parser}. + +@deftypefun int yypush_parse (yypstate *yyps) +The value returned by @code{yypush_parse} is the same as for yyparse with the +following exception. @code{yypush_parse} will return YYPUSH_MORE if more input +is required to finish parsing the grammar. +@end deftypefun + +@node Pull Parser Function +@section The Pull Parser Function @code{yypull_parse} +@findex yypull_parse + +(The current push parsing interface is experimental and may evolve. +More user feedback will help to stabilize it.) + +You call the function @code{yypull_parse} to parse the rest of the input +stream. This function is available if the @code{%define api.push_pull "both"} +declaration is used. +@xref{Push Decl, ,A Push Parser}. + +@deftypefun int yypull_parse (yypstate *yyps) +The value returned by @code{yypull_parse} is the same as for @code{yyparse}. +@end deftypefun + +@node Parser Create Function +@section The Parser Create Function @code{yystate_new} +@findex yypstate_new + +(The current push parsing interface is experimental and may evolve. +More user feedback will help to stabilize it.) + +You call the function @code{yypstate_new} to create a new parser instance. +This function is available if either the @code{%define api.push_pull "push"} or +@code{%define api.push_pull "both"} declaration is used. +@xref{Push Decl, ,A Push Parser}. + +@deftypefun yypstate *yypstate_new (void) +The fuction will return a valid parser instance if there was memory available +or 0 if no memory was available. +In impure mode, it will also return 0 if a parser instance is currently +allocated. +@end deftypefun + +@node Parser Delete Function +@section The Parser Delete Function @code{yystate_delete} +@findex yypstate_delete + +(The current push parsing interface is experimental and may evolve. +More user feedback will help to stabilize it.) + +You call the function @code{yypstate_delete} to delete a parser instance. +function is available if either the @code{%define api.push_pull "push"} or +@code{%define api.push_pull "both"} declaration is used. +@xref{Push Decl, ,A Push Parser}. + +@deftypefun void yypstate_delete (yypstate *yyps) +This function will reclaim the memory associated with a parser instance. +After this call, you should no longer attempt to use the parser instance. +@end deftypefun @node Lexical @section The Lexical Analyzer Function @code{yylex} @@ -4356,13 +5394,13 @@ that need it. @xref{Invocation, ,Invoking Bison}. @menu * Calling Convention:: How @code{yyparse} calls @code{yylex}. -* Token Values:: How @code{yylex} must return the semantic value - of the token it has read. -* Token Locations:: How @code{yylex} must return the text location - (line number, etc.) of the token, if the - actions want that. -* Pure Calling:: How the calling convention differs - in a pure parser (@pxref{Pure Decl, ,A Pure (Reentrant) Parser}). +* Token Values:: How @code{yylex} must return the semantic value + of the token it has read. +* Token Locations:: How @code{yylex} must return the text location + (line number, etc.) of the token, if the + actions want that. +* Pure Calling:: How the calling convention differs in a pure parser + (@pxref{Pure Decl, ,A Pure (Reentrant) Parser}). @end menu @node Calling Convention @@ -4516,7 +5554,7 @@ The data type of @code{yylloc} has the name @code{YYLTYPE}. @node Pure Calling @subsection Calling Conventions for Pure Parsers -When you use the Bison declaration @code{%pure-parser} to request a +When you use the Bison declaration @code{%define api.pure} to request a pure, reentrant parser, the global communication variables @code{yylval} and @code{yylloc} cannot be used. (@xref{Pure Decl, ,A Pure (Reentrant) Parser}.) In such parsers the two global variables are replaced by @@ -4547,8 +5585,8 @@ Function}). @deffn {Directive} lex-param @{@var{argument-declaration}@} @findex %lex-param -Declare that @code{argument-declaration} is an additional @code{yylex} -argument declaration. +Declare that the braced-code @var{argument-declaration} is an +additional @code{yylex} argument declaration. @end deffn For instance: @@ -4567,7 +5605,7 @@ int yylex (int *nastiness); int yyparse (int *nastiness, int *randomness); @end example -If @code{%pure-parser} is added: +If @code{%define api.pure} is added: @example int yylex (YYSTYPE *lvalp, int *nastiness); @@ -4575,7 +5613,7 @@ int yyparse (int *nastiness, int *randomness); @end example @noindent -and finally, if both @code{%pure-parser} and @code{%locations} are used: +and finally, if both @code{%define api.pure} and @code{%locations} are used: @example int yylex (YYSTYPE *lvalp, YYLTYPE *llocp, int *nastiness); @@ -4641,7 +5679,7 @@ Obviously, in location tracking pure parsers, @code{yyerror} should have an access to the current location. This is indeed the case for the @acronym{GLR} parsers, but not for the Yacc parser, for historical reasons. I.e., if -@samp{%locations %pure-parser} is passed then the prototypes for +@samp{%locations %define api.pure} is passed then the prototypes for @code{yyerror} are: @example @@ -4659,13 +5697,14 @@ void yyerror (int *nastiness, char const *msg); /* GLR parsers. */ Finally, @acronym{GLR} and Yacc parsers share the same @code{yyerror} calling convention for absolutely pure parsers, i.e., when the calling convention of @code{yylex} @emph{and} the calling convention of -@code{%pure-parser} are pure. I.e.: +@code{%define api.pure} are pure. +I.e.: @example /* Location tracking. */ %locations /* Pure yylex. */ -%pure-parser +%define api.pure %lex-param @{int *nastiness@} /* Pure yyparse. */ %parse-param @{int *nastiness@} @@ -4744,14 +5783,14 @@ Return immediately from @code{yyparse}, indicating success. @deffn {Macro} YYBACKUP (@var{token}, @var{value}); @findex YYBACKUP Unshift a token. This macro is allowed only for rules that reduce -a single value, and only when there is no look-ahead token. +a single value, and only when there is no lookahead token. It is also disallowed in @acronym{GLR} parsers. -It installs a look-ahead token with token type @var{token} and +It installs a lookahead token with token type @var{token} and semantic value @var{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 look-ahead token already, then it reports a syntax error with +a lookahead token already, then it reports a syntax error with a message @samp{cannot back up} and performs ordinary error recovery. @@ -4760,7 +5799,13 @@ In either case, the rest of the action is not executed. @deffn {Macro} YYEMPTY @vindex YYEMPTY -Value stored in @code{yychar} when there is no look-ahead token. +Value stored in @code{yychar} when there is no lookahead token. +@end deffn + +@deffn {Macro} YYEOF +@vindex YYEOF +Value stored in @code{yychar} when the lookahead is the end of the input +stream. @end deffn @deffn {Macro} YYERROR; @@ -4773,21 +5818,27 @@ the @samp{YYERROR;} statement. @xref{Error Recovery}. @end deffn @deffn {Macro} YYRECOVERING -This macro stands for an expression that has the value 1 when the parser -is recovering from a syntax error, and 0 the rest of the time. +@findex YYRECOVERING +The expression @code{YYRECOVERING ()} yields 1 when the parser +is recovering from a syntax error, and 0 otherwise. @xref{Error Recovery}. @end deffn @deffn {Variable} yychar -Variable containing the current look-ahead token. (In a pure parser, -this is actually a local variable within @code{yyparse}.) When there is -no look-ahead token, the value @code{YYEMPTY} is stored in the variable. -@xref{Look-Ahead, ,Look-Ahead Tokens}. +Variable containing either the lookahead token, or @code{YYEOF} when the +lookahead is the end of the input stream, or @code{YYEMPTY} when no lookahead +has been performed so the next token is not yet known. +Do not modify @code{yychar} in a deferred semantic action (@pxref{GLR Semantic +Actions}). +@xref{Lookahead, ,Lookahead Tokens}. @end deffn @deffn {Macro} yyclearin; -Discard the current look-ahead token. This is useful primarily in -error rules. @xref{Error Recovery}. +Discard the current lookahead token. This is useful primarily in +error rules. +Do not invoke @code{yyclearin} in a deferred semantic action (@pxref{GLR +Semantic Actions}). +@xref{Error Recovery}. @end deffn @deffn {Macro} yyerrok; @@ -4796,6 +5847,22 @@ errors. This is useful primarily in error rules. @xref{Error Recovery}. @end deffn +@deffn {Variable} yylloc +Variable containing the lookahead token location when @code{yychar} is not set +to @code{YYEMPTY} or @code{YYEOF}. +Do not modify @code{yylloc} in a deferred semantic action (@pxref{GLR Semantic +Actions}). +@xref{Actions and Locations, ,Actions and Locations}. +@end deffn + +@deffn {Variable} yylval +Variable containing the lookahead token semantic value when @code{yychar} is +not set to @code{YYEMPTY} or @code{YYEOF}. +Do not modify @code{yylval} in a deferred semantic action (@pxref{GLR Semantic +Actions}). +@xref{Actions, ,Actions}. +@end deffn + @deffn {Value} @@$ @findex @@$ Acts like a structure variable containing information on the textual location @@ -4970,20 +6037,20 @@ to a single grouping whose symbol is the grammar's start-symbol This kind of parser is known in the literature as a bottom-up parser. @menu -* Look-Ahead:: Parser looks one token ahead when deciding what to do. +* Lookahead:: Parser looks one token ahead when deciding what to do. * Shift/Reduce:: Conflicts: when either shifting or reduction is valid. * Precedence:: Operator precedence works by resolving conflicts. * Contextual Precedence:: When an operator's precedence depends on context. * Parser States:: The parser is a finite-state-machine with stack. * Reduce/Reduce:: When two rules are applicable in the same situation. -* Mystery Conflicts:: Reduce/reduce conflicts that look unjustified. +* Mystery Conflicts:: Reduce/reduce conflicts that look unjustified. * Generalized LR Parsing:: Parsing arbitrary context-free grammars. * Memory Management:: What happens when memory is exhausted. How to avoid it. @end menu -@node Look-Ahead -@section Look-Ahead Tokens -@cindex look-ahead token +@node Lookahead +@section Lookahead Tokens +@cindex lookahead token The Bison parser does @emph{not} always reduce immediately as soon as the last @var{n} tokens and groupings match a rule. This is because such a @@ -4992,15 +6059,15 @@ 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 -@dfn{look-ahead token}, which is not on the stack. Now the parser can +@dfn{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 look-ahead token remains off to the side. When no more reductions -should take place, the look-ahead token is shifted onto the stack. This +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 type of the look-ahead token, some rules may choose to delay their +token type of the lookahead token, some rules may choose to delay their application. -Here is a simple case where look-ahead is needed. These three rules define +Here is a simple case where lookahead is needed. These three rules define expressions which contain binary addition operators and postfix unary factorial operators (@samp{!}), and allow parentheses for grouping. @@ -5033,7 +6100,11 @@ doing so would produce on the stack the sequence of symbols @code{expr '!'}. No rule allows that sequence. @vindex yychar -The current look-ahead token is stored in the variable @code{yychar}. +@vindex yylval +@vindex yylloc +The lookahead token is stored in the variable @code{yychar}. +Its semantic value and location, if any, are stored in the variables +@code{yylval} and @code{yylloc}. @xref{Action Features, ,Special Features for Use in Actions}. @node Shift/Reduce @@ -5059,7 +6130,7 @@ if_stmt: Here we assume that @code{IF}, @code{THEN} and @code{ELSE} are terminal symbols for specific keyword tokens. -When the @code{ELSE} token is read and becomes the look-ahead token, the +When the @code{ELSE} 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 @code{ELSE}, because that would lead to eventual reduction by the second @@ -5193,7 +6264,7 @@ operators we prefer the former, which is called @dfn{left association}. The latter alternative, @dfn{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 @w{@samp{1 - 2}} and the look-ahead token is @samp{-}: shifting +contains @w{@samp{1 - 2}} and the lookahead token is @samp{-}: shifting makes right-associativity. @node Using Precedence @@ -5254,7 +6325,7 @@ specify explicitly the precedence of a rule. @xref{Contextual Precedence, ,Context-Dependent Precedence}.) Finally, the resolution of conflicts works by comparing the precedence -of the rule being considered with that of the look-ahead token. If the +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 @@ -5263,7 +6334,7 @@ precedence level. The verbose output file made by @samp{-v} resolved. Not all rules and not all tokens have precedence. If either the rule or -the look-ahead token has no precedence, then the default is to shift. +the lookahead token has no precedence, then the default is to shift. @node Contextual Precedence @section Context-Dependent Precedence @@ -5357,9 +6428,9 @@ 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 look-ahead token is read, the current parser state together -with the type of look-ahead token are looked up in a table. This table -entry can say, ``Shift the look-ahead token.'' In this case, it also +Each time a lookahead token is read, the current parser state together +with the type 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 @var{n}.'' This means that a certain number of tokens or groupings are taken off @@ -5367,7 +6438,7 @@ 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 look-ahead token +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 (@pxref{Error Recovery}). @@ -5525,7 +6596,7 @@ name_list: @end example It would seem that this grammar can be parsed with only a single token -of look-ahead: when a @code{param_spec} is being read, an @code{ID} is +of lookahead: when a @code{param_spec} is being read, an @code{ID} is a @code{name} if a comma or colon follows, or a @code{type} if another @code{ID} follows. In other words, this grammar is @acronym{LR}(1). @@ -5539,7 +6610,7 @@ a @code{return_spec}, 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 @code{name} and that for reducing to a @code{type}. Bison is unable to determine at that stage of processing -that the rules would require different look-ahead tokens in the two +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 @acronym{LALR}(1). @@ -5612,13 +6683,13 @@ pp.@: 615--649 @uref{http://doi.acm.org/10.1145/69622.357187}. Bison produces @emph{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 look-ahead. +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 -look-ahead, since the parser lacks the information necessary to make a +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 (@pxref{Mystery Conflicts}), there are languages where Bison's particular choice of how to @@ -5795,7 +6866,7 @@ and objects from the stack until it gets back to a state in which the @code{error} token is acceptable. (This means that the subexpressions already parsed are discarded, back to the last complete @code{stmnts}.) At this point the @code{error} token can be shifted. Then, if the old -look-ahead token is not acceptable to be shifted next, the parser reads +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 @@ -5846,22 +6917,23 @@ error messages will be suppressed. This macro requires no arguments; @samp{yyerrok;} is a valid C statement. @findex yyclearin -The previous look-ahead token is reanalyzed immediately after an error. If +The previous lookahead token is reanalyzed immediately after an error. If this is unacceptable, then the macro @code{yyclearin} may be used to clear this token. Write the statement @samp{yyclearin;} in the error rule's action. +@xref{Action Features, ,Special Features for Use in Actions}. 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 look-ahead token ought to be discarded +probably correct. The previous lookahead token ought to be discarded with @samp{yyclearin;}. @vindex YYRECOVERING -The macro @code{YYRECOVERING} stands for an expression that has the -value 1 when the parser is recovering from a syntax error, and 0 the -rest of the time. A value of 1 indicates that error messages are -currently suppressed for new syntax errors. +The expression @code{YYRECOVERING ()} 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. @node Context Dependency @chapter Handling Context Dependencies @@ -6095,8 +7167,7 @@ As documented elsewhere (@pxref{Algorithm, ,The Bison Parser Algorithm}) Bison parsers are @dfn{shift/reduce automata}. In some cases (much more frequent than one would hope), looking at this automaton is required to tune or simply fix a parser. Bison provides two different -representation of it, either textually or graphically (as a @acronym{VCG} -file). +representation of it, either textually or graphically (as a DOT file). The textual file is generated when the options @option{--report} or @option{--verbose} are specified, see @xref{Invocation, , Invoking @@ -6126,9 +7197,9 @@ useless: STR; @command{bison} reports: @example -calc.y: warning: 1 useless nonterminal and 1 useless rule -calc.y:11.1-7: warning: useless nonterminal: useless -calc.y:11.10-12: warning: useless rule: useless: STR +calc.y: warning: 1 nonterminal and 1 rule useless in grammar +calc.y:11.1-7: warning: nonterminal useless in grammar: useless +calc.y:11.10-12: warning: rule useless in grammar: useless: STR calc.y: conflicts: 7 shift/reduce @end example @@ -6167,17 +7238,17 @@ State 11 conflicts: 4 shift/reduce The next section reports useless tokens, nonterminal 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 ``not used'' +scanner (note the difference between ``useless'' and ``unused'' below): @example -Useless nonterminals: +Nonterminals useless in grammar: useless -Terminals which are not used: +Terminals unused in grammar: STR -Useless rules: +Rules useless in grammar: #6 useless: STR; @end example @@ -6242,16 +7313,16 @@ beginning of the parsing, in the initial rule, right before the start symbol (here, @code{exp}). When the parser returns to this state right after having reduced a rule that produced an @code{exp}, the control flow jumps to state 2. If there is no such transition on a nonterminal -symbol, and the look-ahead is a @code{NUM}, then this token is shifted on +symbol, and the lookahead is a @code{NUM}, then this token is shifted on the parse stack, and the control flow jumps to state 1. Any other -look-ahead triggers a syntax error.'' +lookahead triggers a syntax error.'' @cindex core, item set @cindex item set core @cindex kernel, item set @cindex item set core Even though the only active rule in state 0 seems to be rule 0, the -report lists @code{NUM} as a look-ahead token because @code{NUM} can be +report lists @code{NUM} as a lookahead token because @code{NUM} can be at the beginning of any rule deriving an @code{exp}. By default Bison reports the so-called @dfn{core} or @dfn{kernel} of the item set, but if you want to see more detail you can invoke @command{bison} with @@ -6285,7 +7356,7 @@ state 1 @end example @noindent -the rule 5, @samp{exp: NUM;}, is completed. Whatever the look-ahead token +the rule 5, @samp{exp: NUM;}, is completed. Whatever the lookahead token (@samp{$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 (@samp{exp: go to state 2}). @@ -6308,7 +7379,7 @@ state 2 @noindent In state 2, the automaton can only shift a symbol. For instance, -because of the item @samp{exp -> exp . '+' exp}, if the look-ahead if +because of the item @samp{exp -> exp . '+' exp}, if the lookahead if @samp{+}, it will be shifted on the parse stack, and the automaton control will jump to state 4, corresponding to the item @samp{exp -> exp '+' . exp}. Since there is no default action, any other token than @@ -6385,7 +7456,7 @@ state 8 $default reduce using rule 1 (exp) @end example -Indeed, there are two actions associated to the look-ahead @samp{/}: +Indeed, there are two actions associated to the lookahead @samp{/}: 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 @@ -6403,19 +7474,19 @@ 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 @emph{and} reducing is possible or when @emph{several} reductions are -possible, the look-ahead is required to select the action. State 8 is -one such state: if the look-ahead is @samp{*} or @samp{/} then the action +possible, the lookahead is required to select the action. State 8 is +one such state: if the lookahead is @samp{*} or @samp{/} 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 -look-ahead token is @samp{*}, since we specified that @samp{*} has higher +lookahead token is @samp{*}, since we specified that @samp{*} has higher precedence than @samp{+}. More generally, some items are eligible only -with some set of possible look-ahead tokens. When run with -@option{--report=look-ahead}, Bison specifies these look-ahead tokens: +with some set of possible lookahead tokens. When run with +@option{--report=lookahead}, Bison specifies these lookahead tokens: @example state 8 - exp -> exp . '+' exp [$, '+', '-', '/'] (rule 1) + exp -> exp . '+' exp (rule 1) exp -> exp '+' exp . [$, '+', '-', '/'] (rule 1) exp -> exp . '-' exp (rule 2) exp -> exp . '*' exp (rule 3) @@ -6524,10 +7595,10 @@ always possible. The trace facility outputs messages with macro calls of the form @code{YYFPRINTF (stderr, @var{format}, @var{args})} where -@var{format} and @var{args} are the usual @code{printf} format and +@var{format} and @var{args} are the usual @code{printf} format and variadic arguments. If you define @code{YYDEBUG} to a nonzero value but do not define @code{YYFPRINTF}, @code{} is automatically included -and @code{YYPRINTF} is defined to @code{fprintf}. +and @code{YYFPRINTF} is defined to @code{fprintf}. Once you have compiled the program with trace facilities, the way to request a trace is to store a nonzero value in the variable @code{yydebug}. @@ -6576,7 +7647,7 @@ standard I/O stream, the numeric code for the token type, and the token value (from @code{yylval}). Here is an example of @code{YYPRINT} suitable for the multi-function -calculator (@pxref{Mfcalc Decl, ,Declarations for @code{mfcalc}}): +calculator (@pxref{Mfcalc Declarations, ,Declarations for @code{mfcalc}}): @smallexample %@{ @@ -6677,43 +7748,101 @@ Print the version number of Bison and exit. @item --print-localedir Print the name of the directory containing locale-dependent data. -@need 1750 +@item --print-datadir +Print the name of the directory containing skeletons and XSLT. + @item -y @itemx --yacc -Equivalent to @samp{-o y.tab.c}; the parser output file is called +Act more like the traditional Yacc command. This can cause +different diagnostics to be generated, and may change behavior in +other minor ways. Most importantly, imitate Yacc's output +file name conventions, so that the parser output file is called @file{y.tab.c}, and the other outputs are called @file{y.output} and -@file{y.tab.h}. The purpose of this option is to imitate Yacc's output -file name conventions. Thus, the following shell script can substitute -for Yacc, and the Bison distribution contains such a script for -compatibility with @acronym{POSIX}: +@file{y.tab.h}. +Also, if generating an @acronym{LALR}(1) parser in C, generate @code{#define} +statements in addition to an @code{enum} to associate token numbers with token +names. +Thus, the following shell script can substitute for Yacc, and the Bison +distribution contains such a script for compatibility with @acronym{POSIX}: @example #! /bin/sh bison -y "$@@" @end example + +The @option{-y}/@option{--yacc} option is intended for use with +traditional Yacc grammars. If your grammar uses a Bison extension +like @samp{%glr-parser}, Bison might not be Yacc-compatible even if +this option is specified. + +@item -W [@var{category}] +@itemx --warnings[=@var{category}] +Output warnings falling in @var{category}. @var{category} can be one +of: +@table @code +@item midrule-values +Warn about mid-rule values that are set but not used within any of the actions +of the parent rule. +For example, warn about unused @code{$2} in: + +@example +exp: '1' @{ $$ = 1; @} '+' exp @{ $$ = $1 + $4; @}; +@end example + +Also warn about mid-rule values that are used but not set. +For example, warn about unset @code{$$} in the mid-rule action in: + +@example + exp: '1' @{ $1 = 1; @} '+' exp @{ $$ = $2 + $4; @}; +@end example + +These warnings are not enabled by default since they sometimes prove to +be false alarms in existing grammars employing the Yacc constructs +@code{$0} or @code{$-@var{n}} (where @var{n} is some positive integer). + + +@item yacc +Incompatibilities with @acronym{POSIX} Yacc. + +@item all +All the warnings. +@item none +Turn off all the warnings. +@item error +Treat warnings as errors. +@end table + +A category can be turned off by prefixing its name with @samp{no-}. For +instance, @option{-Wno-syntax} will hide the warnings about unused +variables. @end table @noindent Tuning the parser: @table @option -@item -S @var{file} -@itemx --skeleton=@var{file} -Specify the skeleton to use. You probably don't need this option unless -you are developing Bison. - @item -t @itemx --debug In the parser file, define the macro @code{YYDEBUG} to 1 if it is not already defined, so that the debugging facilities are compiled. @xref{Tracing, ,Tracing Your Parser}. +@item -L @var{language} +@itemx --language=@var{language} +Specify the programming language for the generated parser, as if +@code{%language} was specified (@pxref{Decl Summary, , Bison Declaration +Summary}). Currently supported languages include C, C++, and Java. +@var{language} is case-insensitive. + +This option is experimental and its effect may be modified in future +releases. + @item --locations Pretend that @code{%locations} was specified. @xref{Decl Summary}. @item -p @var{prefix} @itemx --name-prefix=@var{prefix} -Pretend that @code{%name-prefix="@var{prefix}"} was specified. +Pretend that @code{%name-prefix "@var{prefix}"} was specified. @xref{Decl Summary}. @item -l @@ -6724,9 +7853,21 @@ and debuggers will associate errors with your source file, the grammar file. This option causes them to associate errors with the parser file, treating it as an independent source file in its own right. -@item -n -@itemx --no-parser -Pretend that @code{%no-parser} was specified. @xref{Decl Summary}. +@item -S @var{file} +@itemx --skeleton=@var{file} +Specify the skeleton to use, similar to @code{%skeleton} +(@pxref{Decl Summary, , Bison Declaration Summary}). + +@c You probably don't need this option unless you are developing Bison. +@c You should use @option{--language} if you want to specify the skeleton for a +@c different language, because it is clearer and because it will always +@c choose the correct skeleton for non-deterministic or push parsers. + +If @var{file} does not contain a @code{/}, @var{file} is the name of a skeleton +file in the Bison installation directory. +If it does, @var{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. @item -k @itemx --token-table @@ -6737,18 +7878,19 @@ Pretend that @code{%token-table} was specified. @xref{Decl Summary}. Adjust the output: @table @option -@item -d -@itemx --defines +@item --defines[=@var{file}] Pretend that @code{%defines} was specified, i.e., write an extra output file containing macro definitions for the token type names defined in the grammar, as well as a few other declarations. @xref{Decl Summary}. -@item --defines=@var{defines-file} -Same as above, but save in the file @var{defines-file}. +@item -d +This is the same as @code{--defines} except @code{-d} does not accept a +@var{file} argument since POSIX Yacc requires that @code{-d} can be bundled +with other short options. @item -b @var{file-prefix} @itemx --file-prefix=@var{prefix} -Pretend that @code{%verbose} was specified, i.e, specify prefix to use +Pretend that @code{%file-prefix} was specified, i.e., specify prefix to use for all Bison output file names. @xref{Decl Summary}. @item -r @var{things} @@ -6761,20 +7903,21 @@ separated list of @var{things} among: Description of the grammar, conflicts (resolved and unresolved), and @acronym{LALR} automaton. -@item look-ahead +@item lookahead Implies @code{state} and augments the description of the automaton with -each rule's look-ahead set. +each rule's lookahead set. @item itemset Implies @code{state} and augments the description of the automaton with the full set of items for each state, instead of its core only. @end table -For instance, on the following grammar +@item --report-file=@var{file} +Specify the @var{file} for the verbose description. @item -v @itemx --verbose -Pretend that @code{%verbose} was specified, i.e, write an extra output +Pretend that @code{%verbose} was specified, i.e., write an extra output file containing verbose descriptions of the grammar and parser. @xref{Decl Summary}. @@ -6785,63 +7928,36 @@ Specify the @var{file} for the parser file. The other output files' names are constructed from @var{file} as described under the @samp{-v} and @samp{-d} options. -@item -g -Output a @acronym{VCG} definition of the @acronym{LALR}(1) grammar -automaton computed by Bison. If the grammar file is @file{foo.y}, the -@acronym{VCG} output file will -be @file{foo.vcg}. - -@item --graph=@var{graph-file} -The behavior of @var{--graph} is the same than @samp{-g}. The only -difference is that it has an optional argument which is the name of -the output graph file. +@item -g[@var{file}] +@itemx --graph[=@var{file}] +Output a graphical representation of the @acronym{LALR}(1) grammar +automaton computed by Bison, in @uref{http://www.graphviz.org/, Graphviz} +@uref{http://www.graphviz.org/doc/info/lang.html, @acronym{DOT}} format. +@code{@var{file}} is optional. +If omitted and the grammar file is @file{foo.y}, the output file will be +@file{foo.dot}. + +@item -x[@var{file}] +@itemx --xml[=@var{file}] +Output an XML report of the @acronym{LALR}(1) automaton computed by Bison. +@code{@var{file}} is optional. +If omitted and the grammar file is @file{foo.y}, the output file will be +@file{foo.xml}. +(The current XML schema is experimental and may evolve. +More user feedback will help to stabilize it.) @end table @node Option Cross Key @section Option Cross Key +@c FIXME: How about putting the directives too? Here is a list of options, alphabetized by long option, to help you find the corresponding short option. -@tex -\def\leaderfill{\leaders\hbox to 1em{\hss.\hss}\hfill} - -{\tt -\line{ --debug \leaderfill -t} -\line{ --defines \leaderfill -d} -\line{ --file-prefix \leaderfill -b} -\line{ --graph \leaderfill -g} -\line{ --help \leaderfill -h} -\line{ --name-prefix \leaderfill -p} -\line{ --no-lines \leaderfill -l} -\line{ --no-parser \leaderfill -n} -\line{ --output \leaderfill -o} -\line{ --print-localedir} -\line{ --token-table \leaderfill -k} -\line{ --verbose \leaderfill -v} -\line{ --version \leaderfill -V} -\line{ --yacc \leaderfill -y} -} -@end tex - -@ifinfo -@example ---debug -t ---defines=@var{defines-file} -d ---file-prefix=@var{prefix} -b @var{file-prefix} ---graph=@var{graph-file} -d ---help -h ---name-prefix=@var{prefix} -p @var{name-prefix} ---no-lines -l ---no-parser -n ---output=@var{outfile} -o @var{outfile} ---print-localedir ---token-table -k ---verbose -v ---version -V ---yacc -y -@end example -@end ifinfo +@multitable {@option{--defines=@var{defines-file}}} {@option{-b @var{file-prefix}XXX}} +@headitem Long Option @tab Short Option +@include cross-options.texi +@end multitable @node Yacc Library @section Yacc Library @@ -6871,12 +7987,12 @@ int yyparse (void); @c ================================================= C++ Bison -@node C++ Language Interface -@chapter C++ Language Interface +@node Other Languages +@chapter Parsers Written In Other Languages @menu * C++ Parsers:: The interface to generate C++ parser classes -* A Complete C++ Example:: Demonstrating their use +* Java Parsers:: The interface to generate Java parser classes @end menu @node C++ Parsers @@ -6888,6 +8004,7 @@ int yyparse (void); * C++ Location Values:: The position and location classes * C++ Parser Interface:: Instantiating and running the parser * C++ Scanner Interface:: Exchanges between yylex and parse +* A Complete C++ Example:: Demonstrating their use @end menu @node C++ Bison Interface @@ -6896,11 +8013,18 @@ int yyparse (void); @c - Always pure @c - initial action -The C++ parser @acronym{LALR}(1) skeleton is named @file{lalr1.cc}. To select -it, you may either pass the option @option{--skeleton=lalr1.cc} to -Bison, or include the directive @samp{%skeleton "lalr1.cc"} in the -grammar preamble. When run, @command{bison} will create several -files: +The C++ @acronym{LALR}(1) parser is selected using the skeleton directive, +@samp{%skeleton "lalr1.c"}, or the synonymous command-line option +@option{--skeleton=lalr1.c}. +@xref{Decl Summary}. + +When run, @command{bison} will create several entities in the @samp{yy} +namespace. +@findex %define namespace +Use the @samp{%define namespace} directive to change the namespace name, see +@ref{Decl Summary}. +The various classes are generated in the following files: + @table @file @item position.hh @itemx location.hh @@ -6912,13 +8036,13 @@ An auxiliary class @code{stack} used by the parser. @item @var{file}.hh @itemx @var{file}.cc -The declaration and implementation of the C++ parser class. -@var{file} is the name of the output file. It follows the same -rules as with regular C parsers. +(Assuming the extension of the input file was @samp{.yy}.) The +declaration and implementation of the C++ parser class. The basename +and extension of these two files follow the same rules as with regular C +parsers (@pxref{Invocation}). -Note that @file{@var{file}.hh} is @emph{mandatory}, the C++ cannot -work without the parser class declaration. Therefore, you must either -pass @option{-d}/@option{--defines} to @command{bison}, or use the +The header is @emph{mandatory}; you must either pass +@option{-d}/@option{--defines} to @command{bison}, or use the @samp{%defines} directive. @end table @@ -6928,7 +8052,7 @@ for a complete and accurate documentation. @node C++ Semantic Values @subsection C++ Semantic Values @c - No objects in unions -@c - YSTYPE +@c - YYSTYPE @c - Printer and destructor The @code{%union} directive works as for C, see @ref{Union Decl, ,The @@ -6958,7 +8082,7 @@ Symbols}. @c - %locations @c - class Position @c - class Location -@c - %define "filename_type" "const symbol::Symbol" +@c - %define filename_type "const symbol::Symbol" When the directive @code{%locations} is used, the C++ parser supports location tracking, see @ref{Locations, , Locations Overview}. Two @@ -6970,7 +8094,7 @@ and a @code{location}, a range composed of a pair of The name of the file. It will always be handled as a pointer, the parser will never duplicate nor deallocate it. As an experimental feature you may change it to @samp{@var{type}*} using @samp{%define -"filename_type" "@var{type}"}. +filename_type "@var{type}"}. @end deftypemethod @deftypemethod {position} {unsigned int} line @@ -7034,7 +8158,7 @@ Move @code{begin} onto @code{end}. The output files @file{@var{output}.hh} and @file{@var{output}.cc} declare and define the parser class in the namespace @code{yy}. The class name defaults to @code{parser}, but may be changed using -@samp{%define "parser_class_name" "@var{name}"}. The interface of +@samp{%define parser_class_name "@var{name}"}. The interface of this class is detailed below. It can be extended using the @code{%parse-param} feature: its semantics is slightly changed since it describes an additional member of the parser class, and an @@ -7081,7 +8205,7 @@ described by @var{m}. The parser invokes the scanner by calling @code{yylex}. Contrary to C parsers, C++ parsers are always pure: there is no point in using the -@code{%pure-parser} directive. Therefore the interface is as follows. +@code{%define api.pure} directive. Therefore the interface is as follows. @deftypemethod {parser} {int} yylex (semantic_value_type& @var{yylval}, location_type& @var{yylloc}, @var{type1} @var{arg1}, ...) Return the next token. Its type is the return value, its semantic @@ -7091,7 +8215,7 @@ value and location being @var{yylval} and @var{yylloc}. Invocations of @node A Complete C++ Example -@section A Complete C++ Example +@subsection A Complete C++ Example This section demonstrates the use of a C++ parser with a simple but complete example. This example should be available on your system, @@ -7111,7 +8235,7 @@ actually easier to interface with. @end menu @node Calc++ --- C++ Calculator -@subsection Calc++ --- C++ Calculator +@subsubsection Calc++ --- C++ Calculator Of course the grammar is dedicated to arithmetics, a single expression, possibly preceded by variable assignments. An @@ -7126,7 +8250,7 @@ seven * seven @end example @node Calc++ Parsing Driver -@subsection Calc++ Parsing Driver +@subsubsection Calc++ Parsing Driver @c - An env @c - A place to store error messages @c - A place for the result @@ -7162,11 +8286,12 @@ factor both as follows. @comment file: calc++-driver.hh @example -// Announce to Flex the prototype we want for lexing function, ... -# define YY_DECL \ - int yylex (yy::calcxx_parser::semantic_type* yylval, \ - yy::calcxx_parser::location_type* yylloc, \ - calcxx_driver& driver) +// Tell Flex the lexer's prototype ... +# define YY_DECL \ + yy::calcxx_parser::token_type \ + yylex (yy::calcxx_parser::semantic_type* yylval, \ + yy::calcxx_parser::location_type* yylloc, \ + calcxx_driver& driver) // ... and declare it for the parser's sake. YY_DECL; @end example @@ -7192,7 +8317,6 @@ public: @noindent To encapsulate the coordination with the Flex scanner, it is useful to have two members function to open and close the scanning phase. -members. @comment file: calc++-driver.hh @example @@ -7207,8 +8331,8 @@ Similarly for the parser itself. @comment file: calc++-driver.hh @example - // Handling the parser. - void parse (const std::string& f); + // Run the parser. Return 0 on success. + int parse (const std::string& f); std::string file; bool trace_parsing; @end example @@ -7249,15 +8373,16 @@ calcxx_driver::~calcxx_driver () @{ @} -void +int calcxx_driver::parse (const std::string &f) @{ file = f; scan_begin (); yy::calcxx_parser parser (*this); parser.set_debug_level (trace_parsing); - parser.parse (); + int res = parser.parse (); scan_end (); + return res; @} void @@ -7274,7 +8399,7 @@ calcxx_driver::error (const std::string& m) @end example @node Calc++ Parser -@subsection Calc++ Parser +@subsubsection Calc++ Parser The parser definition file @file{calc++-parser.yy} starts by asking for the C++ LALR(1) skeleton, the creation of the parser header file, and @@ -7285,25 +8410,27 @@ the grammar for. @comment file: calc++-parser.yy @example %skeleton "lalr1.cc" /* -*- C++ -*- */ -%require "2.1a" +%require "@value{VERSION}" %defines -%define "parser_class_name" "calcxx_parser" +%define parser_class_name "calcxx_parser" @end example @noindent +@findex %code requires Then come the declarations/inclusions needed to define the @code{%union}. Because the parser uses the parsing driver and reciprocally, both cannot include the header of the other. 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 simply use a forward declaration of the driver. +@xref{Decl Summary, ,%code}. @comment file: calc++-parser.yy @example -%@{ +%code requires @{ # include class calcxx_driver; -%@} +@} @end example @noindent @@ -7359,15 +8486,15 @@ them. @end example @noindent -The code between @samp{%@{} and @samp{%@}} after the introduction of the -@samp{%union} is output in the @file{*.cc} file; it needs detailed -knowledge about the driver. +@findex %code +The code between @samp{%code @{} and @samp{@}} is output in the +@file{*.cc} file; it needs detailed knowledge about the driver. @comment file: calc++-parser.yy @example -%@{ +%code @{ # include "calc++-driver.hh" -%@} +@} @end example @@ -7384,19 +8511,20 @@ avoid name clashes. %token ASSIGN ":=" %token IDENTIFIER "identifier" %token NUMBER "number" -%type exp "expression" +%type exp @end example @noindent To enable memory deallocation during error recovery, use @code{%destructor}. +@c FIXME: Document %printer, and mention that it takes a braced-code operand. @comment file: calc++-parser.yy @example %printer @{ debug_stream () << *$$; @} "identifier" %destructor @{ delete $$; @} "identifier" -%printer @{ debug_stream () << $$; @} "number" "expression" +%printer @{ debug_stream () << $$; @} @end example @noindent @@ -7411,7 +8539,9 @@ unit: assignments exp @{ driver.result = $2; @}; assignments: assignments assignment @{@} | /* Nothing. */ @{@}; -assignment: "identifier" ":=" exp @{ driver.variables[*$1] = $3; @}; +assignment: + "identifier" ":=" exp + @{ driver.variables[*$1] = $3; delete $1; @}; %left '+' '-'; %left '*' '/'; @@ -7419,7 +8549,7 @@ exp: exp '+' exp @{ $$ = $1 + $3; @} | exp '-' exp @{ $$ = $1 - $3; @} | exp '*' exp @{ $$ = $1 * $3; @} | exp '/' exp @{ $$ = $1 / $3; @} - | "identifier" @{ $$ = driver.variables[*$1]; @} + | "identifier" @{ $$ = driver.variables[*$1]; delete $1; @} | "number" @{ $$ = $1; @}; %% @end example @@ -7439,7 +8569,7 @@ yy::calcxx_parser::error (const yy::calcxx_parser::location_type& l, @end example @node Calc++ Scanner -@subsection Calc++ Scanner +@subsubsection Calc++ Scanner The Flex scanner first includes the driver declaration, then the parser's to get the set of defined tokens. @@ -7448,11 +8578,23 @@ parser's to get the set of defined tokens. @example %@{ /* -*- C++ -*- */ # include -# include -# include +# include +# include # include # include "calc++-driver.hh" # include "calc++-parser.hh" + +/* Work around an incompatibility in flex (at least versions + 2.5.31 through 2.5.33): it generates code that does + not conform to C89. See Debian bug 333231 + . */ +# undef yywrap +# define yywrap() 1 + +/* By default yylex returns int, we use token_type. + Unfortunately yyterminate by default returns 0, which is + not of token_type. */ +#define yyterminate() return token::END %@} @end example @@ -7510,8 +8652,8 @@ It is convenient to use a typedef to shorten %@{ typedef yy::calcxx_parser::token token; %@} - -[-+*/] return yytext[0]; + /* Convert ints to the actual type of tokens. */ +[-+*/] return yy::calcxx_parser::token_type (yytext[0]); ":=" return token::ASSIGN; @{int@} @{ errno = 0; @@ -7536,8 +8678,13 @@ void calcxx_driver::scan_begin () @{ yy_flex_debug = trace_scanning; - if (!(yyin = fopen (file.c_str (), "r"))) - error (std::string ("cannot open ") + file); + if (file == "-") + yyin = stdin; + else if (!(yyin = fopen (file.c_str (), "r"))) + @{ + error (std::string ("cannot open ") + file); + exit (1); + @} @} void @@ -7548,7 +8695,7 @@ calcxx_driver::scan_end () @end example @node Calc++ Top Level -@subsection Calc++ Top Level +@subsubsection Calc++ Top Level The top level file, @file{calc++.cc}, poses no problem. @@ -7566,14 +8713,583 @@ main (int argc, char *argv[]) driver.trace_parsing = true; else if (*argv == std::string ("-s")) driver.trace_scanning = true; - else - @{ - driver.parse (*argv); - std::cout << driver.result << std::endl; - @} + else if (!driver.parse (*argv)) + std::cout << driver.result << std::endl; @} @end example +@node Java Parsers +@section Java Parsers + +@menu +* Java Bison Interface:: Asking for Java parser generation +* Java Semantic Values:: %type and %token vs. Java +* Java Location Values:: The position and location classes +* Java Parser Interface:: Instantiating and running the parser +* Java Scanner Interface:: Specifying the scanner for the parser +* Java Action Features:: Special features for use in actions +* Java Differences:: Differences between C/C++ and Java Grammars +* Java Declarations Summary:: List of Bison declarations used with Java +@end menu + +@node Java Bison Interface +@subsection Java Bison Interface +@c - %language "Java" + +(The current Java interface is experimental and may evolve. +More user feedback will help to stabilize it.) + +The Java parser skeletons are selected using the @code{%language "Java"} +directive or the @option{-L java}/@option{--language=java} option. + +@c FIXME: Documented bug. +When generating a Java parser, @code{bison @var{basename}.y} will create +a single Java source file named @file{@var{basename}.java}. Using an +input file without a @file{.y} suffix is currently broken. The basename +of the output file can be changed by the @code{%file-prefix} directive +or the @option{-p}/@option{--name-prefix} option. The entire output file +name can be changed by the @code{%output} directive or the +@option{-o}/@option{--output} option. The output 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 @code{%pure-parser} +and @code{%define api.pure} directives does not do anything when used in +Java. + +Push parsers are currently unsupported in Java and @code{%define +api.push_pull} have no effect. + +@acronym{GLR} parsers are currently unsupported in Java. Do not use the +@code{glr-parser} directive. + +No header file can be generated for Java parsers. Do not use the +@code{%defines} directive or the @option{-d}/@option{--defines} options. + +@c FIXME: Possible code change. +Currently, support for debugging and verbose errors are always compiled +in. Thus the @code{%debug} and @code{%token-table} directives and the +@option{-t}/@option{--debug} and @option{-k}/@option{--token-table} +options have no effect. This may change in the future to eliminate +unused code in the generated parser, so use @code{%debug} and +@code{%verbose-error} explicitly if needed. Also, in the future the +@code{%token-table} directive might enable a public interface to +access the token names and codes. + +@node Java Semantic Values +@subsection Java Semantic Values +@c - No %union, specify type in %type/%token. +@c - YYSTYPE +@c - Printer and destructor + +There is no @code{%union} directive in Java parsers. Instead, the +semantic values' types (class names) should be specified in the +@code{%type} or @code{%token} directive: + +@example +%type expr assignment_expr term factor +%type number +@end example + +By default, the semantic stack is declared to have @code{Object} 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 @code{%define stype} +directive. For example, after the following declaration: + +@example +%define stype "ASTNode" +@end example + +@noindent +any @code{%type} or @code{%token} specifying a semantic type which +is not a subclass of ASTNode, will cause a compile-time error. + +@c FIXME: Documented bug. +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 @code{%destructor}, 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 @code{%printer}, as @code{toString()} +can be used to print the semantic values. This however may change +(in a backwards-compatible way) in future versions of Bison. + + +@node Java Location Values +@subsection Java Location Values +@c - %locations +@c - class Position +@c - class Location + +When the directive @code{%locations} is used, the Java parser +supports location tracking, see @ref{Locations, , Locations Overview}. +An auxiliary user-defined class defines a @dfn{position}, a single point +in a file; Bison itself defines a class representing a @dfn{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 @code{Location} by default, and may also be renamed using +@code{%define location_type "@var{class-name}}. + +The location class treats the position as a completely opaque value. +By default, the class name is @code{Position}, but this can be changed +with @code{%define position_type "@var{class-name}"}. This class must +be supplied by the user. + + +@deftypeivar {Location} {Position} begin +@deftypeivarx {Location} {Position} end +The first, inclusive, position of the range, and the first beyond. +@end deftypeivar + +@deftypeop {Constructor} {Location} {} Location (Position @var{loc}) +Create a @code{Location} denoting an empty range located at a given point. +@end deftypeop + +@deftypeop {Constructor} {Location} {} Location (Position @var{begin}, Position @var{end}) +Create a @code{Location} from the endpoints of the range. +@end deftypeop + +@deftypemethod {Location} {String} toString () +Prints the range represented by the location. For this to work +properly, the position class should override the @code{equals} and +@code{toString} methods appropriately. +@end deftypemethod + + +@node Java Parser Interface +@subsection Java Parser Interface +@c - define parser_class_name +@c - Ctor +@c - parse, error, set_debug_level, debug_level, set_debug_stream, +@c debug_stream. +@c - Reporting errors + +The name of the generated parser class defaults to @code{YYParser}. The +@code{YY} prefix may be changed using the @code{%name-prefix} directive +or the @option{-p}/@option{--name-prefix} option. Alternatively, use +@code{%define parser_class_name "@var{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 +@code{%define public} will change to public visibility. Remember that, +according to the Java language specification, the name of the @file{.java} +file should match the name of the class in this case. Similarly, you can +use @code{abstract}, @code{final} and @code{strictfp} with the +@code{%define} declaration to add other modifiers to the parser class. + +The Java package name of the parser class can be specified using the +@code{%define package} directive. The superclass and the implemented +interfaces of the parser class can be specified with the @code{%define +extends} and @code{%define implements} directives. + +The parser class defines an inner class, @code{Location}, that is used +for location tracking (see @ref{Java Location Values}), and a inner +interface, @code{Lexer} (see @ref{Java Scanner Interface}). Other than +these inner class/interface, and the members described in the interface +below, all the other members and fields are preceded with a @code{yy} or +@code{YY} prefix to avoid clashes with user code. + +@c FIXME: The following constants and variables are still undocumented: +@c @code{bisonVersion}, @code{bisonSkeleton} and @code{errorVerbose}. + +The parser class can be extended using the @code{%parse-param} +directive. Each occurrence of the directive will add a @code{protected +final} field to the parser class, and an argument to its constructor, +which initialize them automatically. + +Token names defined by @code{%token} and the predefined @code{EOF} token +name are added as constant fields to the parser class. + +@deftypeop {Constructor} {YYParser} {} YYParser (@var{lex_param}, @dots{}, @var{parse_param}, @dots{}) +Build a new parser object with embedded @code{%code lexer}. There are +no parameters, unless @code{%parse-param}s and/or @code{%lex-param}s are +used. +@end deftypeop + +@deftypeop {Constructor} {YYParser} {} YYParser (Lexer @var{lexer}, @var{parse_param}, @dots{}) +Build a new parser object using the specified scanner. There are no +additional parameters unless @code{%parse-param}s are used. + +If the scanner is defined by @code{%code lexer}, this constructor is +declared @code{protected} and is called automatically with a scanner +created with the correct @code{%lex-param}s. +@end deftypeop + +@deftypemethod {YYParser} {boolean} parse () +Run the syntactic analysis, and return @code{true} on success, +@code{false} otherwise. +@end deftypemethod + +@deftypemethod {YYParser} {boolean} recovering () +During the syntactic analysis, return @code{true} if recovering +from a syntax error. +@xref{Error Recovery}. +@end deftypemethod + +@deftypemethod {YYParser} {java.io.PrintStream} getDebugStream () +@deftypemethodx {YYParser} {void} setDebugStream (java.io.printStream @var{o}) +Get or set the stream used for tracing the parsing. It defaults to +@code{System.err}. +@end deftypemethod + +@deftypemethod {YYParser} {int} getDebugLevel () +@deftypemethodx {YYParser} {void} setDebugLevel (int @var{l}) +Get or set the tracing level. Currently its value is either 0, no trace, +or nonzero, full tracing. +@end deftypemethod + + +@node Java Scanner Interface +@subsection Java Scanner Interface +@c - %code lexer +@c - %lex-param +@c - Lexer interface + +There are two possible ways to interface a Bison-generated Java parser +with a scanner: the scanner may be defined by @code{%code lexer}, or +defined elsewhere. In either case, the scanner has to implement the +@code{Lexer} inner interface of the parser class. + +In the first case, the body of the scanner class is placed in +@code{%code lexer} blocks. If you want to pass parameters from the +parser constructor to the scanner constructor, specify them with +@code{%lex-param}; they are passed before @code{%parse-param}s to the +constructor. + +In the second case, the scanner has to implement the @code{Lexer} interface, +which is defined within the parser class (e.g., @code{YYParser.Lexer}). +The constructor of the parser object will then accept an object +implementing the interface; @code{%lex-param} is not used in this +case. + +In both cases, the scanner has to implement the following methods. + +@deftypemethod {Lexer} {void} yyerror (Location @var{loc}, String @var{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 @code{%define location_type "@var{class-name}".} +@end deftypemethod + +@deftypemethod {Lexer} {int} yylex () +Return the next token. Its type is the return value, its semantic +value and location are saved and returned by the ther methods in the +interface. + +Use @code{%define lex_throws} to specify any uncaught exceptions. +Default is @code{java.io.IOException}. +@end deftypemethod + +@deftypemethod {Lexer} {Position} getStartPos () +@deftypemethodx {Lexer} {Position} getEndPos () +Return respectively the first position of the last token that +@code{yylex} returned, and the first position beyond it. These +methods are not needed unless location tracking is active. + +The return type can be changed using @code{%define position_type +"@var{class-name}".} +@end deftypemethod + +@deftypemethod {Lexer} {Object} getLVal () +Return the semantical value of the last token that yylex returned. + +The return type can be changed using @code{%define stype +"@var{class-name}".} +@end deftypemethod + + +@node Java Action Features +@subsection Special Features for Use in Java Actions + +The following special constructs can be uses in Java actions. +Other analogous C action features are currently unavailable for Java. + +Use @code{%define throws} to specify any uncaught exceptions from parser +actions, and initial actions specified by @code{%initial-action}. + +@defvar $@var{n} +The semantic value for the @var{n}th component of the current rule. +This may not be assigned to. +@xref{Java Semantic Values}. +@end defvar + +@defvar $<@var{typealt}>@var{n} +Like @code{$@var{n}} but specifies a alternative type @var{typealt}. +@xref{Java Semantic Values}. +@end defvar + +@defvar $$ +The semantic value for the grouping made by the current rule. As a +value, this is in the base type (@code{Object} or as specified by +@code{%define stype}) as in not cast to the declared subtype because +casts are not allowed on the left-hand side of Java assignments. +Use an explicit Java cast if the correct subtype is needed. +@xref{Java Semantic Values}. +@end defvar + +@defvar $<@var{typealt}>$ +Same as @code{$$} since Java always allow assigning to the base type. +Perhaps we should use this and @code{$<>$} for the value and @code{$$} +for setting the value but there is currently no easy way to distinguish +these constructs. +@xref{Java Semantic Values}. +@end defvar + +@defvar @@@var{n} +The location information of the @var{n}th component of the current rule. +This may not be assigned to. +@xref{Java Location Values}. +@end defvar + +@defvar @@$ +The location information of the grouping made by the current rule. +@xref{Java Location Values}. +@end defvar + +@deffn {Statement} {return YYABORT;} +Return immediately from the parser, indicating failure. +@xref{Java Parser Interface}. +@end deffn + +@deffn {Statement} {return YYACCEPT;} +Return immediately from the parser, indicating success. +@xref{Java Parser Interface}. +@end deffn + +@deffn {Statement} {return YYERROR;} +Start error recovery without printing an error message. +@xref{Error Recovery}. +@end deffn + +@deffn {Statement} {return YYFAIL;} +Print an error message and start error recovery. +@xref{Error Recovery}. +@end deffn + +@deftypefn {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. +@xref{Error Recovery}. +@end deftypefn + +@deftypefn {Function} {protected void} yyerror (String msg) +@deftypefnx {Function} {protected void} yyerror (Position pos, String msg) +@deftypefnx {Function} {protected void} yyerror (Location loc, String msg) +Print an error message using the @code{yyerror} method of the scanner +instance in use. +@end deftypefn + + +@node Java Differences +@subsection Differences between C/C++ and Java Grammars + +The different structure of the Java language forces several differences +between C/C++ grammars, and grammars designed for Java parsers. This +section summarizes these differences. + +@itemize +@item +Java lacks a preprocessor, so the @code{YYERROR}, @code{YYACCEPT}, +@code{YYABORT} symbols (@pxref{Table of Symbols}) cannot obviously be +macros. Instead, they should be preceded by @code{return} when they +appear in an action. The actual definition of these symbols is +opaque to the Bison grammar, and it might change in the future. The +only meaningful operation that you can do, is to return them. +See @pxref{Java Action Features}. + +Note that of these three symbols, only @code{YYACCEPT} and +@code{YYABORT} will cause a return from the @code{yyparse} +method@footnote{Java parsers include the actions in a separate +method than @code{yyparse} in order to have an intuitive syntax that +corresponds to these C macros.}. + +@item +Java lacks unions, so @code{%union} has no effect. Instead, semantic +values have a common base type: @code{Object} or as specified by +@code{%define stype}. Angle backets on @code{%token}, @code{type}, +@code{$@var{n}} and @code{$$} specify subtypes rather than fields of +an union. The type of @code{$$}, even with angle brackets, is the base +type since Java casts are not allow on the left-hand side of assignments. +Also, @code{$@var{n}} and @code{@@@var{n}} are not allowed on the +left-hand side of assignments. See @pxref{Java Semantic Values} and +@pxref{Java Action Features}. + +@item +The prolog declarations have a different meaning than in C/C++ code. +@table @asis +@item @code{%code imports} +blocks are placed at the beginning of the Java source code. They may +include copyright notices. For a @code{package} declarations, it is +suggested to use @code{%define package} instead. + +@item unqualified @code{%code} +blocks are placed inside the parser class. + +@item @code{%code lexer} +blocks, if specified, should include the implementation of the +scanner. If there is no such block, the scanner can be any class +that implements the appropriate interface (see @pxref{Java Scanner +Interface}). +@end table + +Other @code{%code} blocks are not supported in Java parsers. +In particular, @code{%@{ @dots{} %@}} blocks should not be used +and may give an error in future versions of Bison. + +The epilogue has the same meaning as in C/C++ code and it can +be used to define other classes used by the parser @emph{outside} +the parser class. +@end itemize + + +@node Java Declarations Summary +@subsection Java Declarations Summary + +This summary only include declarations specific to Java or have special +meaning when used in a Java parser. + +@deffn {Directive} {%language "Java"} +Generate a Java class for the parser. +@end deffn + +@deffn {Directive} %lex-param @{@var{type} @var{name}@} +A parameter for the lexer class defined by @code{%code lexer} +@emph{only}, added as parameters to the lexer constructor and the parser +constructor that @emph{creates} a lexer. Default is none. +@xref{Java Scanner Interface}. +@end deffn + +@deffn {Directive} %name-prefix "@var{prefix}" +The prefix of the parser class name @code{@var{prefix}Parser} if +@code{%define parser_class_name} is not used. Default is @code{YY}. +@xref{Java Bison Interface}. +@end deffn + +@deffn {Directive} %parse-param @{@var{type} @var{name}@} +A parameter for the parser class added as parameters to constructor(s) +and as fields initialized by the constructor(s). Default is none. +@xref{Java Parser Interface}. +@end deffn + +@deffn {Directive} %token <@var{type}> @var{token} @dots{} +Declare tokens. Note that the angle brackets enclose a Java @emph{type}. +@xref{Java Semantic Values}. +@end deffn + +@deffn {Directive} %type <@var{type}> @var{nonterminal} @dots{} +Declare the type of nonterminals. Note that the angle brackets enclose +a Java @emph{type}. +@xref{Java Semantic Values}. +@end deffn + +@deffn {Directive} %code @{ @var{code} @dots{} @} +Code appended to the inside of the parser class. +@xref{Java Differences}. +@end deffn + +@deffn {Directive} {%code imports} @{ @var{code} @dots{} @} +Code inserted just after the @code{package} declaration. +@xref{Java Differences}. +@end deffn + +@deffn {Directive} {%code lexer} @{ @var{code} @dots{} @} +Code added to the body of a inner lexer class within the parser class. +@xref{Java Scanner Interface}. +@end deffn + +@deffn {Directive} %% @var{code} @dots{} +Code (after the second @code{%%}) appended to the end of the file, +@emph{outside} the parser class. +@xref{Java Differences}. +@end deffn + +@deffn {Directive} %@{ @var{code} @dots{} %@} +Not supported. Use @code{%code import} instead. +@xref{Java Differences}. +@end deffn + +@deffn {Directive} {%define abstract} +Whether the parser class is declared @code{abstract}. Default is false. +@xref{Java Bison Interface}. +@end deffn + +@deffn {Directive} {%define extends} "@var{superclass}" +The superclass of the parser class. Default is none. +@xref{Java Bison Interface}. +@end deffn + +@deffn {Directive} {%define final} +Whether the parser class is declared @code{final}. Default is false. +@xref{Java Bison Interface}. +@end deffn + +@deffn {Directive} {%define implements} "@var{interfaces}" +The implemented interfaces of the parser class, a comma-separated list. +Default is none. +@xref{Java Bison Interface}. +@end deffn + +@deffn {Directive} {%define lex_throws} "@var{exceptions}" +The exceptions thrown by the @code{yylex} method of the lexer, a +comma-separated list. Default is @code{java.io.IOException}. +@xref{Java Scanner Interface}. +@end deffn + +@deffn {Directive} {%define location_type} "@var{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 @command{bison}. Default is @code{Location}. +@xref{Java Location Values}. +@end deffn + +@deffn {Directive} {%define package} "@var{package}" +The package to put the parser class in. Default is none. +@xref{Java Bison Interface}. +@end deffn + +@deffn {Directive} {%define parser_class_name} "@var{name}" +The name of the parser class. Default is @code{YYParser} or +@code{@var{name-prefix}Parser}. +@xref{Java Bison Interface}. +@end deffn + +@deffn {Directive} {%define position_type} "@var{class}" +The name of the class used for positions. This class must be supplied by +the user. Default is @code{Position}. +@xref{Java Location Values}. +@end deffn + +@deffn {Directive} {%define public} +Whether the parser class is declared @code{public}. Default is false. +@xref{Java Bison Interface}. +@end deffn + +@deffn {Directive} {%define stype} "@var{class}" +The base type of semantic values. Default is @code{Object}. +@xref{Java Semantic Values}. +@end deffn + +@deffn {Directive} {%define strictfp} +Whether the parser class is declared @code{strictfp}. Default is false. +@xref{Java Bison Interface}. +@end deffn + +@deffn {Directive} {%define throws} "@var{exceptions}" +The exceptions thrown by user-supplied parser actions and +@code{%initial-action}, a comma-separated list. Default is none. +@xref{Java Parser Interface}. +@end deffn + + @c ================================================= FAQ @node FAQ @@ -7585,10 +9301,18 @@ Several questions about Bison come up occasionally. Here some of them are addressed. @menu -* Memory Exhausted:: Breaking the Stack Limits -* How Can I Reset the Parser:: @code{yyparse} Keeps some State -* Strings are Destroyed:: @code{yylval} Loses Track of Strings -* Implementing Gotos/Loops:: Control Flow in the Calculator +* Memory Exhausted:: Breaking the Stack Limits +* How Can I Reset the Parser:: @code{yyparse} Keeps some State +* Strings are Destroyed:: @code{yylval} Loses Track of Strings +* Implementing Gotos/Loops:: Control Flow in the Calculator +* Multiple start-symbols:: Factoring closely related grammars +* Secure? Conform?:: Is Bison @acronym{POSIX} safe? +* I can't build Bison:: Troubleshooting +* Where can I find help?:: Troubleshouting +* Bug Reports:: Troublereporting +* More Languages:: Parsers in C++, Java, and so on +* Beta Testing:: Experimenting development versions +* Mailing Lists:: Meeting other Bison users @end menu @node Memory Exhausted @@ -7620,7 +9344,7 @@ or @display My parser includes support for an @samp{#include}-like feature, in which case I run @code{yyparse} from @code{yyparse}. This fails -although I did specify I needed a @code{%pure-parser}. +although I did specify @code{%define api.pure}. @end display These problems typically come not from Bison itself, but from @@ -7704,7 +9428,7 @@ them. Instead of reporting @samp{"foo", "bar"}, it reports 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 scanner. Consider the following Lex code: +of the scanner. Consider the following Lex code: @verbatim %{ @@ -7782,6 +9506,172 @@ This topic is way beyond the scope of this manual, and the reader is invited to consult the dedicated literature. +@node Multiple start-symbols +@section Multiple start-symbols + +@display +I 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. +@end display + +Bison does not support multiple start-symbols, but there is a very +simple means to simulate them. If @code{foo} and @code{bar} are the two +pseudo start-symbols, then introduce two new tokens, say +@code{START_FOO} and @code{START_BAR}, and use them as switches from the +real start-symbol: + +@example +%token START_FOO START_BAR; +%start start; +start: START_FOO foo + | START_BAR bar; +@end example + +These tokens prevents 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 @samp{%@{ ... %@}} +after the first @code{%%} is copied verbatim in the top of the generated +@code{yylex} function. Make sure a variable @code{start_token} is +available in the scanner (e.g., a global variable or using +@code{%lex-param} etc.), and use the following: + +@example + /* @r{Prologue.} */ +%% +%@{ + if (start_token) + @{ + int t = start_token; + start_token = 0; + return t; + @} +%@} + /* @r{The rules.} */ +@end example + + +@node Secure? Conform? +@section Secure? Conform? + +@display +Is Bison secure? Does it conform to POSIX? +@end display + +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 +@acronym{POSIX} specification for Yacc. If you run into problems, +please send us a bug report. + +@node I can't build Bison +@section I can't build Bison + +@display +I can't build Bison because @command{make} complains that +@code{msgfmt} is not found. +What should I do? +@end display + +Like most GNU packages with internationalization support, that feature +is turned on by default. If you have problems building in the @file{po} +subdirectory, it indicates that your system's internationalization +support is lacking. You can re-configure Bison with +@option{--disable-nls} to turn off this support, or you can install GNU +gettext from @url{ftp://ftp.gnu.org/gnu/gettext/} and re-configure +Bison. See the file @file{ABOUT-NLS} for more information. + + +@node Where can I find help? +@section Where can I find help? + +@display +I'm having trouble using Bison. Where can I find help? +@end display + +First, read this fine manual. Beyond that, you can send mail to +@email{help-bison@@gnu.org}. 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. + +@node Bug Reports +@section Bug Reports + +@display +I found a bug. What should I include in the bug report? +@end display + +Before you send a bug report, make sure you are using the latest +version. Check @url{ftp://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 +`configure'. 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 can not provide a fix. + +Send bug reports to @email{bug-bison@@gnu.org}. + +@node More Languages +@section More Languages + +@display +Will Bison ever have C++ and Java support? How about @var{insert your +favorite language here}? +@end display + +C++ and Java support is there now, and is documented. We'd love to add other +languages; contributions are welcome. + +@node Beta Testing +@section Beta Testing + +@display +What is involved in being a beta tester? +@end display + +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. + +@node Mailing Lists +@section Mailing Lists + +@display +How do I join the help-bison and bug-bison mailing lists? +@end display + +See @url{http://lists.gnu.org/}. @c ================================================= Table of Symbols @@ -7842,12 +9732,40 @@ Separates alternate rules for the same result nonterminal. @xref{Rules, ,Syntax of Grammar Rules}. @end deffn +@deffn {Directive} <*> +Used to define a default tagged @code{%destructor} or default tagged +@code{%printer}. + +This feature is experimental. +More user feedback will help to determine whether it should become a permanent +feature. + +@xref{Destructor Decl, , Freeing Discarded Symbols}. +@end deffn + +@deffn {Directive} <> +Used to define a default tagless @code{%destructor} or default tagless +@code{%printer}. + +This feature is experimental. +More user feedback will help to determine whether it should become a permanent +feature. + +@xref{Destructor Decl, , Freeing Discarded Symbols}. +@end deffn + @deffn {Symbol} $accept The predefined nonterminal whose only rule is @samp{$accept: @var{start} $end}, where @var{start} is the start symbol. @xref{Start Decl, , The Start-Symbol}. It cannot be used in the grammar. @end deffn +@deffn {Directive} %code @{@var{code}@} +@deffnx {Directive} %code @var{qualifier} @{@var{code}@} +Insert @var{code} verbatim into output parser source. +@xref{Decl Summary,,%code}. +@end deffn + @deffn {Directive} %debug Equip the parser for debugging. @xref{Decl Summary}. @end deffn @@ -7860,11 +9778,22 @@ Precedence}. @end deffn @end ifset +@deffn {Directive} %define @var{define-variable} +@deffnx {Directive} %define @var{define-variable} @var{value} +Define a variable to adjust Bison's behavior. +@xref{Decl Summary,,%define}. +@end deffn + @deffn {Directive} %defines Bison declaration to create a header file meant for the scanner. @xref{Decl Summary}. @end deffn +@deffn {Directive} %defines @var{defines-file} +Same as above, but save in the file @var{defines-file}. +@xref{Decl Summary}. +@end deffn + @deffn {Directive} %destructor Specify how the parser should reclaim the memory associated to discarded symbols. @xref{Destructor Decl, , Freeing Discarded Symbols}. @@ -7886,8 +9815,8 @@ 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 @code{error} becomes the current look-ahead token. Actions -corresponding to @code{error} are then executed, and the look-ahead +token @code{error} becomes the current lookahead token. Actions +corresponding to @code{error} are then executed, and the lookahead token is reset to the token that originally caused the violation. @xref{Error Recovery}. @end deffn @@ -7897,7 +9826,7 @@ Bison declaration to request verbose, specific error message strings when @code{yyerror} is called. @end deffn -@deffn {Directive} %file-prefix="@var{prefix}" +@deffn {Directive} %file-prefix "@var{prefix}" Bison declaration to set the prefix of the output files. @xref{Decl Summary}. @end deffn @@ -7911,6 +9840,11 @@ Parsers, ,Writing @acronym{GLR} Parsers}. Run user code before parsing. @xref{Initial Action Decl, , Performing Actions before Parsing}. @end deffn +@deffn {Directive} %language +Specify the programming language for the generated parser. +@xref{Decl Summary}. +@end deffn + @deffn {Directive} %left Bison declaration to assign left associativity to token(s). @xref{Precedence Decl, ,Operator Precedence}. @@ -7929,7 +9863,7 @@ function is applied to the two semantic values to get a single result. @xref{GLR Parsers, ,Writing @acronym{GLR} Parsers}. @end deffn -@deffn {Directive} %name-prefix="@var{prefix}" +@deffn {Directive} %name-prefix "@var{prefix}" Bison declaration to rename the external symbols. @xref{Decl Summary}. @end deffn @@ -7951,7 +9885,7 @@ Bison declaration to assign nonassociativity to token(s). @xref{Precedence Decl, ,Operator Precedence}. @end deffn -@deffn {Directive} %output="@var{file}" +@deffn {Directive} %output "@var{file}" Bison declaration to set the name of the parser file. @xref{Decl Summary}. @end deffn @@ -7968,8 +9902,8 @@ Bison declaration to assign a precedence to a specific rule. @end deffn @deffn {Directive} %pure-parser -Bison declaration to request a pure (reentrant) parser. -@xref{Pure Decl, ,A Pure (Reentrant) Parser}. +Deprecated version of @code{%define api.pure} (@pxref{Decl Summary, ,%define}), +for which Bison is more careful to warn about unreasonable usage. @end deffn @deffn {Directive} %require "@var{version}" @@ -7982,6 +9916,11 @@ Bison declaration to assign right associativity to token(s). @xref{Precedence Decl, ,Operator Precedence}. @end deffn +@deffn {Directive} %skeleton +Specify the skeleton to use; usually for development. +@xref{Decl Summary}. +@end deffn + @deffn {Directive} %start Bison declaration to specify the start symbol. @xref{Start Decl, ,The Start-Symbol}. @@ -8018,29 +9957,35 @@ Macro to pretend that an unrecoverable syntax error has occurred, by making @code{yyparse} return 1 immediately. The error reporting function @code{yyerror} is not called. @xref{Parser Function, ,The Parser Function @code{yyparse}}. + +For Java parsers, this functionality is invoked using @code{return YYABORT;} +instead. @end deffn @deffn {Macro} YYACCEPT Macro to pretend that a complete utterance of the language has been read, by making @code{yyparse} return 0 immediately. @xref{Parser Function, ,The Parser Function @code{yyparse}}. + +For Java parsers, this functionality is invoked using @code{return YYACCEPT;} +instead. @end deffn @deffn {Macro} YYBACKUP -Macro to discard a value from the parser stack and fake a look-ahead +Macro to discard a value from the parser stack and fake a lookahead token. @xref{Action Features, ,Special Features for Use in Actions}. @end deffn @deffn {Variable} yychar -External integer variable that contains the integer value of the current -look-ahead token. (In a pure parser, it is a local variable within +External integer variable that contains the integer value of the +lookahead token. (In a pure parser, it is a local variable within @code{yyparse}.) Error-recovery rule actions may examine this variable. @xref{Action Features, ,Special Features for Use in Actions}. @end deffn @deffn {Variable} yyclearin Macro used in error-recovery rule actions. It clears the previous -look-ahead token. @xref{Error Recovery}. +lookahead token. @xref{Error Recovery}. @end deffn @deffn {Macro} YYDEBUG @@ -8064,6 +10009,9 @@ Macro to pretend that a syntax error has just been detected: call @code{yyerror} and then perform normal error recovery if possible (@pxref{Error Recovery}), or (if recovery is impossible) make @code{yyparse} return 1. @xref{Error Recovery}. + +For Java parsers, this functionality is invoked using @code{return YYERROR;} +instead. @end deffn @deffn {Function} yyerror @@ -8093,7 +10041,7 @@ the next token. @xref{Lexical, ,The Lexical Analyzer Function @deffn {Macro} YYLEX_PARAM An obsolete macro for specifying an extra argument (or list of extra -arguments) for @code{yyparse} to pass to @code{yylex}. he use of this +arguments) for @code{yyparse} to pass to @code{yylex}. The use of this macro is deprecated, and is supported only for Yacc like parsers. @xref{Pure Calling,, Calling Conventions for Pure Parsers}. @end deffn @@ -8102,9 +10050,12 @@ macro is deprecated, and is supported only for Yacc like parsers. External variable in which @code{yylex} should place the line and column numbers associated with a token. (In a pure parser, it is a local variable within @code{yyparse}, and its address is passed to -@code{yylex}.) You can ignore this variable if you don't use the -@samp{@@} feature in the grammar actions. @xref{Token Locations, -,Textual Locations of Tokens}. +@code{yylex}.) +You can ignore this variable if you don't use the @samp{@@} feature in the +grammar actions. +@xref{Token Locations, ,Textual Locations of Tokens}. +In semantic actions, it stores the location of the lookahead token. +@xref{Actions and Locations, ,Actions and Locations}. @end deffn @deffn {Type} YYLTYPE @@ -8116,7 +10067,10 @@ members. @xref{Location Type, , Data Types of Locations}. External variable in which @code{yylex} should place the semantic value associated with a token. (In a pure parser, it is a local variable within @code{yyparse}, and its address is passed to -@code{yylex}.) @xref{Token Values, ,Semantic Values of Tokens}. +@code{yylex}.) +@xref{Token Values, ,Semantic Values of Tokens}. +In semantic actions, it stores the semantic value of the lookahead token. +@xref{Actions, ,Actions}. @end deffn @deffn {Macro} YYMAXDEPTH @@ -8126,7 +10080,8 @@ Management}. @deffn {Variable} yynerrs Global variable which Bison increments each time it reports a syntax error. -(In a pure parser, it is a local variable within @code{yyparse}.) +(In a pure parser, it is a local variable within @code{yyparse}. In a +pure push parser, it is a member of yypstate.) @xref{Error Reporting, ,The Error Reporting Function @code{yyerror}}. @end deffn @@ -8135,6 +10090,41 @@ The parser function produced by Bison; call this function to start parsing. @xref{Parser Function, ,The Parser Function @code{yyparse}}. @end deffn +@deffn {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. +@xref{Parser Delete Function, ,The Parser Delete Function +@code{yypstate_delete}}. +(The current push parsing interface is experimental and may evolve. +More user feedback will help to stabilize it.) +@end deffn + +@deffn {Function} yypstate_new +The function to create a parser instance, produced by Bison in push mode; +call this function to create a new parser. +@xref{Parser Create Function, ,The Parser Create Function +@code{yypstate_new}}. +(The current push parsing interface is experimental and may evolve. +More user feedback will help to stabilize it.) +@end deffn + +@deffn {Function} yypull_parse +The parser function produced by Bison in push mode; call this function to +parse the rest of the input stream. +@xref{Pull Parser Function, ,The Pull Parser Function +@code{yypull_parse}}. +(The current push parsing interface is experimental and may evolve. +More user feedback will help to stabilize it.) +@end deffn + +@deffn {Function} yypush_parse +The parser function produced by Bison in push mode; call this function to +parse a single token. @xref{Push Parser Function, ,The Push Parser Function +@code{yypush_parse}}. +(The current push parsing interface is experimental and may evolve. +More user feedback will help to stabilize it.) +@end deffn + @deffn {Macro} YYPARSE_PARAM An obsolete macro for specifying the name of a parameter that @code{yyparse} should accept. The use of this macro is deprecated, and @@ -8143,8 +10133,9 @@ Conventions for Pure Parsers}. @end deffn @deffn {Macro} YYRECOVERING -Macro whose value indicates whether the parser is recovering from a -syntax error. @xref{Action Features, ,Special Features for Use in Actions}. +The expression @code{YYRECOVERING ()} yields 1 when the parser +is recovering from a syntax error, and 0 otherwise. +@xref{Action Features, ,Special Features for Use in Actions}. @end deffn @deffn {Macro} YYSTACK_USE_ALLOCA @@ -8254,8 +10245,8 @@ tokens are parsed. @xref{Lexical Tie-ins}. @item Literal string token A token which consists of two or more fixed characters. @xref{Symbols}. -@item Look-ahead token -A token already read but not yet shifted. @xref{Look-Ahead, ,Look-Ahead +@item Lookahead token +A token already read but not yet shifted. @xref{Lookahead, ,Lookahead Tokens}. @item @acronym{LALR}(1) @@ -8265,7 +10256,7 @@ Conflicts, ,Mysterious Reduce/Reduce Conflicts}. @item @acronym{LR}(1) The class of context-free grammars in which at most one token of -look-ahead is needed to disambiguate the parsing of any piece of input. +lookahead is needed to disambiguate the parsing of any piece of input. @item Nonterminal symbol A grammar symbol standing for a grammatical construct that can @@ -8342,11 +10333,6 @@ grammatically indivisible. The piece of text it represents is a token. @node Copying This Manual @appendix Copying This Manual - -@menu -* GNU Free Documentation License:: License for copying this manual. -@end menu - @include fdl.texi @node Index @@ -8356,32 +10342,36 @@ grammatically indivisible. The piece of text it represents is a token. @bye +@c Local Variables: +@c fill-column: 76 +@c End: + @c LocalWords: texinfo setfilename settitle setchapternewpage finalout @c LocalWords: ifinfo smallbook shorttitlepage titlepage GPL FIXME iftex @c LocalWords: akim fn cp syncodeindex vr tp synindex dircategory direntry @c LocalWords: ifset vskip pt filll insertcopying sp ISBN Etienne Suvasa @c LocalWords: ifnottex yyparse detailmenu GLR RPN Calc var Decls Rpcalc -@c LocalWords: rpcalc Lexer Gen Comp Expr ltcalc mfcalc Decl Symtab yylex +@c LocalWords: rpcalc Lexer Expr ltcalc mfcalc yylex @c LocalWords: yyerror pxref LR yylval cindex dfn LALR samp gpl BNF xref @c LocalWords: const int paren ifnotinfo AC noindent emph expr stmt findex @c LocalWords: glr YYSTYPE TYPENAME prog dprec printf decl init stmtMerge @c LocalWords: pre STDC GNUC endif yy YY alloca lf stddef stdlib YYDEBUG @c LocalWords: NUM exp subsubsection kbd Ctrl ctype EOF getchar isdigit @c LocalWords: ungetc stdin scanf sc calc ulator ls lm cc NEG prec yyerrok -@c LocalWords: longjmp fprintf stderr preg yylloc YYLTYPE cos ln +@c LocalWords: longjmp fprintf stderr yylloc YYLTYPE cos ln @c LocalWords: smallexample symrec val tptr FNCT fnctptr func struct sym @c LocalWords: fnct putsym getsym fname arith fncts atan ptr malloc sizeof @c LocalWords: strlen strcpy fctn strcmp isalpha symbuf realloc isalnum @c LocalWords: ptypes itype YYPRINT trigraphs yytname expseq vindex dtype -@c LocalWords: Rhs YYRHSLOC LE nonassoc op deffn typeless typefull yynerrs +@c LocalWords: Rhs YYRHSLOC LE nonassoc op deffn typeless yynerrs @c LocalWords: yychar yydebug msg YYNTOKENS YYNNTS YYNRULES YYNSTATES @c LocalWords: cparse clex deftypefun NE defmac YYACCEPT YYABORT param @c LocalWords: strncmp intval tindex lvalp locp llocp typealt YYBACKUP -@c LocalWords: YYEMPTY YYRECOVERING yyclearin GE def UMINUS maybeword +@c LocalWords: YYEMPTY YYEOF YYRECOVERING yyclearin GE def UMINUS maybeword @c LocalWords: Johnstone Shamsa Sadaf Hussain Tomita TR uref YYMAXDEPTH -@c LocalWords: YYINITDEPTH stmnts ref stmnt initdcl maybeasm VCG notype +@c LocalWords: YYINITDEPTH stmnts ref stmnt initdcl maybeasm notype @c LocalWords: hexflag STR exdent itemset asis DYYDEBUG YYFPRINTF args -@c LocalWords: YYPRINTF infile ypp yxx outfile itemx vcg tex leaderfill +@c LocalWords: infile ypp yxx outfile itemx tex leaderfill @c LocalWords: hbox hss hfill tt ly yyin fopen fclose ofirst gcc ll -@c LocalWords: yyrestart nbar yytext fst snd osplit ntwo strdup AST +@c LocalWords: nbar yytext fst snd osplit ntwo strdup AST @c LocalWords: YYSTACK DVI fdl printindex