@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, 2006 Free Software Foundation, Inc.
+Copyright @copyright{} 1988, 1989, 1990, 1991, 1992, 1993, 1995, 1998, 1999,
+2000, 2001, 2002, 2003, 2004, 2005, 2006, 2007, 2008, 2009, 2010 Free
+Software Foundation, Inc.
@quotation
Permission is granted to copy, distribute and/or modify this document
under the terms of the @acronym{GNU} Free Documentation License,
-Version 1.2 or any later version published by the Free Software
+Version 1.3 or any later version published by the Free Software
Foundation; with no Invariant Sections, with the Front-Cover texts
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
@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.
-* GLR Semantic Actions:: Deferred semantic actions have special concerns.
-* 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}
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
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
* Mid-Rule Actions:: Most actions go at the end of a rule.
This says when, why and how to use the exceptional
action in the middle of a rule.
+* Named References:: Using named references in actions.
Tracking Locations
* 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
* 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.
* 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
* 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
* 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
-* 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
-* Other Languages:: Parsers in Java and others
-* Beta Testing:: Experimenting development versions
-* Mailing Lists:: Meeting other Bison users
+* 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
@cindex introduction
@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.
+annotated context-free grammar into a deterministic @acronym{LR} or
+generalized @acronym{LR} (@acronym{GLR}) parser employing
+@acronym{LALR}(1), @acronym{IELR}(1), or canonical @acronym{LR}(1)
+parser tables.
+Once you are proficient with Bison, you can use it to develop a wide
+range of language parsers, from those used in simple desk calculators to
+complex programming languages.
Bison is upward compatible with Yacc: all properly-written Yacc grammars
ought to work with Bison with no change. Anyone familiar with Yacc
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
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
essentially machine-readable @acronym{BNF}.
@cindex @acronym{LALR}(1) grammars
+@cindex @acronym{IELR}(1) grammars
@cindex @acronym{LR}(1) grammars
-There are various important subclasses of context-free grammar. Although it
-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 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
-@acronym{LR}(1) grammar that fails to be @acronym{LALR}(1).
+There are various important subclasses of context-free grammars.
+Although it can handle almost all context-free grammars, Bison is
+optimized for what are called @acronym{LR}(1) grammars.
+In brief, in these grammars, it must be possible to tell how to parse
+any portion of an input string with just a single token of lookahead.
+For historical reasons, Bison by default is limited by the additional
+restrictions of @acronym{LALR}(1), which is hard to explain simply.
@xref{Mystery Conflicts, ,Mysterious Reduce/Reduce Conflicts}, for
more information on this.
+As an experimental feature, you can escape these additional restrictions by
+requesting @acronym{IELR}(1) or canonical @acronym{LR}(1) parser tables.
+@xref{Decl Summary,,lr.type}, to learn how.
@cindex @acronym{GLR} parsing
@cindex generalized @acronym{LR} (@acronym{GLR}) parsing
@cindex ambiguous grammars
@cindex nondeterministic parsing
-Parsers for @acronym{LALR}(1) grammars are @dfn{deterministic}, meaning
+Parsers for @acronym{LR}(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{lookahead}) of the remaining input. A context-free
@cindex shift/reduce conflicts
@cindex reduce/reduce conflicts
-In some grammars, Bison's standard
-@acronym{LALR}(1) parsing algorithm cannot decide whether to apply a
+In some grammars, Bison's deterministic
+@acronym{LR}(1) parsing algorithm cannot decide whether to apply a
certain grammar rule at a given point. That is, it may not be able to
decide (on the basis of the input read so far) which of two possible
reductions (applications of a grammar rule) applies, or whether to apply
(@pxref{Reduce/Reduce}), and @dfn{shift/reduce} conflicts
(@pxref{Shift/Reduce}).
-To use a grammar that is not easily modified to be @acronym{LALR}(1), a
+To use a grammar that is not easily modified to be @acronym{LR}(1), a
more general parsing algorithm is sometimes necessary. If you include
@code{%glr-parser} among the Bison declarations in your file
(@pxref{Grammar Outline}), the result is a Generalized @acronym{LR}
(@acronym{GLR}) parser. These parsers handle Bison grammars that
contain no unresolved conflicts (i.e., after applying precedence
-declarations) identically to @acronym{LALR}(1) parsers. However, when
+declarations) identically to deterministic parsers. However, when
faced with unresolved shift/reduce and reduce/reduce conflicts,
@acronym{GLR} parsers use the simple expedient of doing both,
effectively cloning the parser to follow both possibilities. Each of
merged result.
@menu
-* 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.
+* 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
@cindex shift/reduce conflicts
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 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}).
+to parse grammars that are unambiguous but fail to be @acronym{LR}(1).
+Such grammars typically require more than one symbol of lookahead.
Consider a problem that
arises in the declaration of enumerated and subrange types in the
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 lookahead it is not
+With normal @acronym{LR}(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
The effect of all this is that the parser seems to ``guess'' the
correct branch to take, or in other words, it seems to use more
-lookahead than the underlying @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.
+lookahead than the underlying @acronym{LR}(1) algorithm actually allows
+for. In this example, @acronym{LR}(2) would suffice, but also some cases
+that are not @acronym{LR}(@math{k}) for any @math{k} can be handled this way.
In general, a @acronym{GLR} parser can take quadratic or cubic worst-case time,
and the current Bison parser even takes exponential time and space
@end group
@end example
-When used as a normal @acronym{LALR}(1) grammar, Bison correctly complains
+When used as a normal @acronym{LR}(1) grammar, Bison correctly complains
about one reduce/reduce conflict. In the conflicting situation the
parser chooses one of the alternatives, arbitrarily the one
declared first. Therefore the following correct input is not
analyze the conflicts reported by Bison to make sure that @acronym{GLR}
splitting is only done where it is intended. A @acronym{GLR} parser
splitting inadvertently may cause problems less obvious than an
-@acronym{LALR} parser statically choosing the wrong alternative in a
+@acronym{LR} parser statically choosing the wrong alternative in a
conflict. Second, consider interactions with the lexer (@pxref{Semantic
Tokens}) with great care. Since a split parser consumes tokens without
performing any actions during the split, the lexer cannot obtain
(@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.
+the same as its effect in a deterministic parser.
In a deferred semantic action, its effect is undefined.
@c The effect is probably a syntax error at the split point.
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
@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
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.
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)
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
@}
@end group
@group
- | '-' exp %preg NEG @{ $$ = -$2; @}
+ | '-' exp %prec NEG @{ $$ = -$2; @}
| exp '^' exp @{ $$ = pow ($1, $3); @}
| '(' exp ')' @{ $$ = $2; @}
@end group
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.
%%
@end smallexample
-@node Mfcalc Symtab
+@node Mfcalc Symbol Table
@subsection The @code{mfcalc} Symbol Table
@cindex symbol table example
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
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 the first occurrence
+The @var{Prologue} section is terminated by the first occurrence
of @samp{%@}} that is outside a comment, a string literal, or a
character constant.
@smallexample
%@{
+ #define _GNU_SOURCE
+ #include <stdio.h>
+ #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 <stdio.h>
#include "ptypes.h"
%@}
@dots{}
@end smallexample
-@findex %before-header
-@findex %start-header
-@findex %after-header
-If you've instructed Bison to generate a header file (@pxref{Table of Symbols,
-,%defines}), you probably want @code{#include "ptypes.h"} to appear
-in that header file as well.
-In that case, use @code{%before-header}, @code{%start-header}, and
-@code{%after-header} instead of @var{Prologue} sections
-(@pxref{Table of Symbols, ,%start-header}):
+@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 <stdio.h>
+
+ /* 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 <stdio.h>
+@}
+
+%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
-%before-header @{
+%code top @{
+ #define _GNU_SOURCE
#include <stdio.h>
@}
-%start-header @{
+%code requires @{
#include "ptypes.h"
@}
%union @{
tree t; /* @r{@code{tree} is defined in @file{ptypes.h}.} */
@}
-%after-header @{
+%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 ($$); @} <field1>
+%printer @{ type1_print ($$); @} <field1>
+
+%code requires @{ #include "type2.h" @}
+%union @{ type2 field2; @}
+%destructor @{ type2_free ($$); @} <field2>
+%printer @{ type2_print ($$); @} <field2>
+@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)
equivalent groupings. The symbol name is used in writing grammar rules.
By convention, it should be all lower case.
-Symbol names can contain letters, digits (not at the beginning),
-underscores and periods. Periods make sense only in nonterminals.
+Symbol names can contain letters, underscores, periods, dashes, and (not
+at the beginning) digits. Dashes in symbol names are a GNU
+extension, incompatible with @acronym{POSIX} Yacc. Terminal symbols
+that contain periods or dashes make little sense: since they are not
+valid symbols (in most programming languages) they are not exported as
+token names.
There are three ways of writing terminal symbols in the grammar:
* Mid-Rule Actions:: Most actions go at the end of a rule.
This says when, why and how to use the exceptional
action in the middle of a rule.
+* Named References:: Using named references in actions.
@end menu
@node Value Type
@cindex action
@vindex $$
@vindex $@var{n}
+@vindex $@var{name}
+@vindex $[@var{name}]
An action accompanies a syntactic rule and contains C code to be executed
each time an instance of that rule is recognized. The task of most actions
The C code in an action can refer to the semantic values of the components
matched by the rule with the construct @code{$@var{n}}, which stands for
the value of the @var{n}th component. The semantic value for the grouping
-being constructed is @code{$$}. Bison translates both of these
+being constructed is @code{$$}. In addition, the semantic values of
+symbols can be accessed with the named references construct
+@code{$@var{name}} or @code{$[@var{name}]}. Bison translates both of these
constructs into expressions of the appropriate type when it copies the
-actions into the parser file. @code{$$} is translated to a modifiable
+actions into the parser file. @code{$$} (or @code{$@var{name}}, when it
+stands for the current grouping) is translated to a modifiable
lvalue, so it can be assigned to.
Here is a typical example:
@end group
@end example
+Or, in terms of named references:
+
+@example
+@group
+exp[result]: @dots{}
+ | exp[left] '+' exp[right]
+ @{ $result = $left + $right; @}
+@end group
+@end example
+
@noindent
This rule constructs an @code{exp} from two smaller @code{exp} groupings
connected by a plus-sign token. In the action, @code{$1} and @code{$3}
+(@code{$left} and @code{$right})
refer to the semantic values of the two component @code{exp} groupings,
which are the first and third symbols on the right hand side of the rule.
-The sum is stored into @code{$$} so that it becomes the semantic value of
+The sum is stored into @code{$$} (@code{$result}) so that it becomes the
+semantic value of
the addition-expression just recognized by the rule. If there were a
useful semantic value associated with the @samp{+} token, it could be
referred to as @code{$2}.
+@xref{Named References,,Using Named References}, for more information
+about using the named references construct.
+
Note that the vertical-bar character @samp{|} is really a rule
separator, and actions are attached to a single rule. This is a
difference with tools like Flex, for which @samp{|} stands for either
Now Bison can execute the action in the rule for @code{subroutine} without
deciding which rule for @code{compound} it will eventually use.
+@node Named References
+@subsection Using Named References
+@cindex named references
+
+While every semantic value can be accessed with positional references
+@code{$@var{n}} and @code{$$}, it's often much more convenient to refer to
+them by name. First of all, original symbol names may be used as named
+references. For example:
+
+@example
+@group
+invocation: op '(' args ')'
+ @{ $invocation = new_invocation ($op, $args, @@invocation); @}
+@end group
+@end example
+
+@noindent
+The positional @code{$$}, @code{@@$}, @code{$n}, and @code{@@n} can be
+mixed with @code{$name} and @code{@@name} arbitrarily. For example:
+
+@example
+@group
+invocation: op '(' args ')'
+ @{ $$ = new_invocation ($op, $args, @@$); @}
+@end group
+@end example
+
+@noindent
+However, sometimes regular symbol names are not sufficient due to
+ambiguities:
+
+@example
+@group
+exp: exp '/' exp
+ @{ $exp = $exp / $exp; @} // $exp is ambiguous.
+
+exp: exp '/' exp
+ @{ $$ = $1 / $exp; @} // One usage is ambiguous.
+
+exp: exp '/' exp
+ @{ $$ = $1 / $3; @} // No error.
+@end group
+@end example
+
+@noindent
+When ambiguity occurs, explicitly declared names may be used for values and
+locations. Explicit names are declared as a bracketed name after a symbol
+appearance in rule definitions. For example:
+@example
+@group
+exp[result]: exp[left] '/' exp[right]
+ @{ $result = $left / $right; @}
+@end group
+@end example
+
+@noindent
+Explicit names may be declared for RHS and for LHS symbols as well. In order
+to access a semantic value generated by a mid-rule action, an explicit name
+may also be declared by putting a bracketed name after the closing brace of
+the mid-rule action code:
+@example
+@group
+exp[res]: exp[x] '+' @{$left = $x;@}[left] exp[right]
+ @{ $res = $left + $right; @}
+@end group
+@end example
+
+@noindent
+
+In references, in order to specify names containing dots and dashes, an explicit
+bracketed syntax @code{$[name]} and @code{@@[name]} must be used:
+@example
+@group
+if-stmt: IF '(' expr ')' THEN then.stmt ';'
+ @{ $[if-stmt] = new_if_stmt ($expr, $[then.stmt]); @}
+@end group
+@end example
+
+It often happens that named references are followed by a dot, dash or other
+C punctuation marks and operators. By default, Bison will read
+@code{$name.suffix} as a reference to symbol value @code{$name} followed by
+@samp{.suffix}, i.e., an access to the @samp{suffix} field of the semantic
+value. In order to force Bison to recognize @code{name.suffix} in its entirety
+as the name of a semantic value, bracketed syntax @code{$[name.suffix]}
+must be used.
+
+
@node Locations
@section Tracking Locations
@cindex location
@} YYLTYPE;
@end example
-At the beginning of the parsing, Bison initializes all these fields to 1
-for @code{yylloc}.
+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 actions, location
@vindex @@$
@vindex @@@var{n}
+@vindex @@@var{name}
+@vindex @@[@var{name}]
Actions are not only useful for defining language semantics, but also for
describing the behavior of the output parser with locations.
@code{@@@var{n}}, while the location of the left hand side grouping is
@code{@@$}.
+In addition, the named references construct @code{@@@var{name}} and
+@code{@@[@var{name}]} may also be used to address the symbol locations.
+@xref{Named References,,Using Named References}, for more information
+about using the named references construct.
+
Here is a basic example using the default data type for locations:
@example
* Expect Decl:: Suppressing warnings about parsing conflicts.
* Start Decl:: Specifying the start symbol.
* Pure Decl:: Requesting a reentrant parser.
+* Push Decl:: Requesting a push parser.
* Decl Summary:: Table of all Bison declarations.
@end menu
Precedence}.
You can explicitly specify the numeric code for a token type by appending
-a decimal or hexadecimal integer value in the field immediately
+a nonnegative decimal or hexadecimal integer value in the field immediately
following the token name:
@example
interchangeably in further declarations or the grammar rules. The
@code{yylex} function can use the token name or the literal string to
obtain the token type code number (@pxref{Calling Convention}).
+Syntax error messages passed to @code{yyerror} from the parser will reference
+the literal string instead of the token name.
+
+The token numbered as 0 corresponds to end of file; the following line
+allows for nicer error messages referring to ``end of file'' instead
+of ``$end'':
+
+@example
+%token END 0 "end of file"
+@end example
@node Precedence Decl
@subsection Operator Precedence
@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
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
@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,
with the discarded symbol, and @code{@@$} designates its location.
The additional parser parameters are also available (@pxref{Parser Function, ,
The Parser Function @code{yyparse}}).
-@end deffn
-@deffn {Directive} %destructor @{ @var{code} @}
-@cindex default %destructor
-Invoke the braced @var{code} whenever the parser discards any user-declared
-grammar symbol for which the user has not specifically declared any
+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}.
-This is known as the default @code{%destructor}.
-As in the previous form, @code{$$}, @code{@@$}, and the additional parser
-parameters are available.
+The parser uses the @var{code} for @code{<*>} in the case of such a grammar
+symbol for which you have formally declared a semantic type tag (@code{%type}
+counts as such a declaration, but @code{$<tag>$} does not).
+The parser uses the @var{code} for @code{<>} in the case of such a grammar
+symbol that has no declared semantic type tag.
@end deffn
-For instance:
+@noindent
+For example:
@smallexample
%union @{ char *string; @}
%token <string> STRING2
%type <string> string1
%type <string> string2
-%destructor @{ free ($$); @}
+%union @{ char character; @}
+%token <character> CHR
+%type <character> chr
+%token TAGLESS
+
+%destructor @{ @} <character>
+%destructor @{ free ($$); @} <*>
%destructor @{ free ($$); printf ("%d", @@$.first_line); @} STRING1 string1
+%destructor @{ printf ("Discarding tagless symbol.\n"); @} <>
@end smallexample
@noindent
-guarantees that, when the parser discards any user-declared symbol, it passes
-its semantic value to @code{free}.
+guarantees that, when the parser discards any user-defined symbol that has a
+semantic type tag other than @code{<character>}, it passes its semantic value
+to @code{free} by default.
However, when the parser discards a @code{STRING1} or a @code{string1}, it also
prints its line number to @code{stdout}.
It performs only the second @code{%destructor} in this case, so it invokes
@code{free} only once.
+Finally, the parser merely prints a message whenever it discards any symbol,
+such as @code{TAGLESS}, that has no semantic type tag.
+
+A Bison-generated parser invokes the default @code{%destructor}s only for
+user-defined as opposed to Bison-defined symbols.
+For example, the parser will not invoke either kind of default
+@code{%destructor} for the special Bison-defined symbols @code{$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
@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.
Bison reports an error if the number of shift/reduce conflicts differs
from @var{n}, or if there are any reduce/reduce conflicts.
-For normal @acronym{LALR}(1) parsers, reduce/reduce conflicts are more
+For deterministic parsers, reduce/reduce conflicts are more
serious, and should be eliminated entirely. Bison will always report
reduce/reduce conflicts for these parsers. With @acronym{GLR}
parsers, however, both kinds of conflicts are routine; otherwise,
@code{%expect-rr} declaration as well.
@end itemize
-Now Bison will warn you if you introduce an unexpected conflict, but
-will keep silent otherwise.
+Now Bison will report an error if you introduce an unexpected conflict,
+but will keep silent otherwise.
@node Start Decl
@subsection The Start-Symbol
@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)
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.
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
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.
-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}.
+@var{qualifier} identifies the purpose of @var{code} and thus the location(s)
+where Bison should generate it.
+Not all @var{qualifier}s are accepted for all target languages.
+Unaccepted @var{qualifier}s produce an error.
+Some of the accepted @var{qualifier}s are:
-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
-the @code{YYSTYPE} macro 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}
-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}.
+@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.
-@findex %start-header
-@findex %end-header
-If you have declared @code{%start-header} or @code{%end-header}, the output
-header also contains their code.
-@xref{Table of Symbols, ,%start-header}.
-@end deffn
+@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
-@deffn {Directive} %destructor
-Specify how the parser should reclaim the memory associated to
-discarded symbols. @xref{Destructor Decl, , Freeing Discarded Symbols}.
-@end deffn
+@item provides
+@findex %code provides
-@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
+@itemize @bullet
+@item Language(s): C, C++
-@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
-the grammar uses the special @samp{@@@var{n}} tokens, but if your
-grammar does not use it, using @samp{%locations} allows for more
-accurate syntax error messages.
-@end deffn
+@item Purpose: This is the best place to write additional definitions and
+declarations that should be provided to other modules.
-@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
+@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 <stdio.h>
+@}
+@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}
+@deffnx {Directive} %define @var{variable} "@var{value}"
+Define a variable to adjust Bison's behavior.
+
+It is an error if a @var{variable} is defined by @code{%define} multiple
+times, but see @ref{Bison Options,,-D @var{name}[=@var{value}]}.
+
+@var{value} must be placed in quotation marks if it contains any
+character other than a letter, underscore, period, dash, or non-initial
+digit.
+
+Omitting @code{"@var{value}"} entirely is always equivalent to specifying
+@code{""}.
+
+Some @var{variable}s take Boolean values.
+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 @code{""} is specified).
+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.
+@end enumerate
+
+What @var{variable}s are accepted, as well as their meanings and default
+values, depend on the selected target language and/or the parser
+skeleton (@pxref{Decl Summary,,%language}, @pxref{Decl
+Summary,,%skeleton}).
+Unaccepted @var{variable}s produce an error.
+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 (deterministic parsers only)
+
+@item Purpose: Request 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
+
+@c ================================================== lr.default-reductions
+
+@item lr.default-reductions
+@cindex default reductions
+@findex %define lr.default-reductions
+@cindex delayed syntax errors
+@cindex syntax errors delayed
+@cindex @acronym{LAC}
+@findex %nonassoc
+
+@itemize @bullet
+@item Language(s): all
+
+@item Purpose: Specify the kind of states that are permitted to
+contain default reductions.
+That is, in such a state, Bison selects the reduction with the largest
+lookahead set to be the default parser action and then removes that
+lookahead set.
+(The ability to specify where default reductions should be used is
+experimental.
+More user feedback will help to stabilize it.)
+
+@item Accepted Values:
+@itemize
+@item @code{all}.
+This is the traditional Bison behavior.
+The main advantage is a significant decrease in the size of the parser
+tables.
+The disadvantage is that, when the generated parser encounters a
+syntactically unacceptable token, the parser might then perform
+unnecessary default reductions before it can detect the syntax error.
+Such delayed syntax error detection is usually inherent in
+@acronym{LALR} and @acronym{IELR} parser tables anyway due to
+@acronym{LR} state merging (@pxref{Decl Summary,,lr.type}).
+Furthermore, the use of @code{%nonassoc} can contribute to delayed
+syntax error detection even in the case of canonical @acronym{LR}.
+As an experimental feature, delayed syntax error detection can be
+overcome in all cases by enabling @acronym{LAC} (@pxref{Decl
+Summary,,parse.lac}, for details, including a discussion of the effects
+of delayed syntax error detection).
+
+@item @code{consistent}.
+@cindex consistent states
+A consistent state is a state that has only one possible action.
+If that action is a reduction, then the parser does not need to request
+a lookahead token from the scanner before performing that action.
+However, the parser recognizes the ability to ignore the lookahead token
+in this way only when such a reduction is encoded as a default
+reduction.
+Thus, if default reductions are permitted only in consistent states,
+then a canonical @acronym{LR} parser that does not employ
+@code{%nonassoc} detects a syntax error as soon as it @emph{needs} the
+syntactically unacceptable token from the scanner.
+
+@item @code{accepting}.
+@cindex accepting state
+In the accepting state, the default reduction is actually the accept
+action.
+In this case, a canonical @acronym{LR} parser that does not employ
+@code{%nonassoc} detects a syntax error as soon as it @emph{reaches} the
+syntactically unacceptable token in the input.
+That is, it does not perform any extra reductions.
+@end itemize
+
+@item Default Value:
+@itemize
+@item @code{accepting} if @code{lr.type} is @code{canonical-lr}.
+@item @code{all} otherwise.
+@end itemize
+@end itemize
+
+@c ============================================ lr.keep-unreachable-states
+
+@item lr.keep-unreachable-states
+@findex %define lr.keep-unreachable-states
+
+@itemize @bullet
+@item Language(s): all
+
+@item Purpose: Request 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
+
+@c ================================================== lr.type
+
+@item lr.type
+@findex %define lr.type
+@cindex @acronym{LALR}
+@cindex @acronym{IELR}
+@cindex @acronym{LR}
+
+@itemize @bullet
+@item Language(s): all
+
+@item Purpose: Specify the type of parser tables within the
+@acronym{LR}(1) family.
+(This feature is experimental.
+More user feedback will help to stabilize it.)
+
+@item Accepted Values:
+@itemize
+@item @code{lalr}.
+While Bison generates @acronym{LALR} parser tables by default for
+historical reasons, @acronym{IELR} or canonical @acronym{LR} is almost
+always preferable for deterministic parsers.
+The trouble is that @acronym{LALR} parser tables can suffer from
+mysterious conflicts and thus may not accept the full set of sentences
+that @acronym{IELR} and canonical @acronym{LR} accept.
+@xref{Mystery Conflicts}, for details.
+However, there are at least two scenarios where @acronym{LALR} may be
+worthwhile:
+@itemize
+@cindex @acronym{GLR} with @acronym{LALR}
+@item When employing @acronym{GLR} parsers (@pxref{GLR Parsers}), if you
+do not resolve any conflicts statically (for example, with @code{%left}
+or @code{%prec}), then the parser explores all potential parses of any
+given input.
+In this case, the use of @acronym{LALR} parser tables is guaranteed not
+to alter the language accepted by the parser.
+@acronym{LALR} parser tables are the smallest parser tables Bison can
+currently generate, so they may be preferable.
+Nevertheless, once you begin to resolve conflicts statically,
+@acronym{GLR} begins to behave more like a deterministic parser, and so
+@acronym{IELR} and canonical @acronym{LR} can be helpful to avoid
+@acronym{LALR}'s mysterious behavior.
+
+@item Occasionally during development, an especially malformed grammar
+with a major recurring flaw may severely impede the @acronym{IELR} or
+canonical @acronym{LR} parser table generation algorithm.
+@acronym{LALR} can be a quick way to generate parser tables in order to
+investigate such problems while ignoring the more subtle differences
+from @acronym{IELR} and canonical @acronym{LR}.
+@end itemize
+
+@item @code{ielr}.
+@acronym{IELR} is a minimal @acronym{LR} algorithm.
+That is, given any grammar (@acronym{LR} or non-@acronym{LR}),
+@acronym{IELR} and canonical @acronym{LR} always accept exactly the same
+set of sentences.
+However, as for @acronym{LALR}, the number of parser states is often an
+order of magnitude less for @acronym{IELR} than for canonical
+@acronym{LR}.
+More importantly, because canonical @acronym{LR}'s extra parser states
+may contain duplicate conflicts in the case of non-@acronym{LR}
+grammars, the number of conflicts for @acronym{IELR} is often an order
+of magnitude less as well.
+This can significantly reduce the complexity of developing of a grammar.
+
+@item @code{canonical-lr}.
+@cindex delayed syntax errors
+@cindex syntax errors delayed
+@cindex @acronym{LAC}
+@findex %nonassoc
+While inefficient, canonical @acronym{LR} parser tables can be an
+interesting means to explore a grammar because they have a property that
+@acronym{IELR} and @acronym{LALR} tables do not.
+That is, if @code{%nonassoc} is not used and default reductions are left
+disabled (@pxref{Decl Summary,,lr.default-reductions}), then, for every
+left context of every canonical @acronym{LR} state, the set of tokens
+accepted by that state is guaranteed to be the exact set of tokens that
+is syntactically acceptable in that left context.
+It might then seem that an advantage of canonical @acronym{LR} parsers
+in production is that, under the above constraints, they are guaranteed
+to detect a syntax error as soon as possible without performing any
+unnecessary reductions.
+However, @acronym{IELR} parsers using @acronym{LAC} (@pxref{Decl
+Summary,,parse.lac}) are also able to achieve this behavior without
+sacrificing @code{%nonassoc} or default reductions.
+@end itemize
+
+@item Default Value: @code{lalr}
+@end itemize
+
+@item namespace
+@findex %define namespace
+
+@itemize
+@item Languages(s): C++
+
+@item Purpose: Specify 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
+
+@c ================================================== parse.lac
+@item parse.lac
+@findex %define parse.lac
+@cindex @acronym{LAC}
+@cindex lookahead correction
+
+@itemize
+@item Languages(s): C
+
+@item Purpose: Enable @acronym{LAC} (lookahead correction) to improve
+syntax error handling.
+
+Canonical @acronym{LR}, @acronym{IELR}, and @acronym{LALR} can suffer
+from a couple of problems upon encountering a syntax error. First, the
+parser might perform additional parser stack reductions before
+discovering the syntax error. Such reductions perform user semantic
+actions that are unexpected because they are based on an invalid token,
+and they cause error recovery to begin in a different syntactic context
+than the one in which the invalid token was encountered. Second, when
+verbose error messages are enabled (with @code{%error-verbose} or
+@code{#define YYERROR_VERBOSE}), the expected token list in the syntax
+error message can both contain invalid tokens and omit valid tokens.
+
+The culprits for the above problems are @code{%nonassoc}, default
+reductions in inconsistent states, and parser state merging. Thus,
+@acronym{IELR} and @acronym{LALR} suffer the most. Canonical
+@acronym{LR} can suffer only if @code{%nonassoc} is used or if default
+reductions are enabled for inconsistent states.
+
+@acronym{LAC} is a new mechanism within the parsing algorithm that
+completely solves these problems for canonical @acronym{LR},
+@acronym{IELR}, and @acronym{LALR} without sacrificing @code{%nonassoc},
+default reductions, or state mering. Conceptually, the mechanism is
+straight-forward. Whenever the parser fetches a new token from the
+scanner so that it can determine the next parser action, it immediately
+suspends normal parsing and performs an exploratory parse using a
+temporary copy of the normal parser state stack. During this
+exploratory parse, the parser does not perform user semantic actions.
+If the exploratory parse reaches a shift action, normal parsing then
+resumes on the normal parser stacks. If the exploratory parse reaches
+an error instead, the parser reports a syntax error. If verbose syntax
+error messages are enabled, the parser must then discover the list of
+expected tokens, so it performs a separate exploratory parse for each
+token in the grammar.
+
+There is one subtlety about the use of @acronym{LAC}. That is, when in
+a consistent parser state with a default reduction, the parser will not
+attempt to fetch a token from the scanner because no lookahead is needed
+to determine the next parser action. Thus, whether default reductions
+are enabled in consistent states (@pxref{Decl
+Summary,,lr.default-reductions}) affects how soon the parser detects a
+syntax error: when it @emph{reaches} an erroneous token or when it
+eventually @emph{needs} that token as a lookahead. The latter behavior
+is probably more intuitive, so Bison currently provides no way to
+achieve the former behavior while default reductions are fully enabled.
+
+Thus, when @acronym{LAC} is in use, for some fixed decision of whether
+to enable default reductions in consistent states, canonical
+@acronym{LR} and @acronym{IELR} behave exactly the same for both
+syntactically acceptable and syntactically unacceptable input. While
+@acronym{LALR} still does not support the full language-recognition
+power of canonical @acronym{LR} and @acronym{IELR}, @acronym{LAC} at
+least enables @acronym{LALR}'s syntax error handling to correctly
+reflect @acronym{LALR}'s language-recognition power.
+
+Because @acronym{LAC} requires many parse actions to be performed twice,
+it can have a performance penalty. However, not all parse actions must
+be performed twice. Specifically, during a series of default reductions
+in consistent states and shift actions, the parser never has to initiate
+an exploratory parse. Moreover, the most time-consuming tasks in a
+parse are often the file I/O, the lexical analysis performed by the
+scanner, and the user's semantic actions, but none of these are
+performed during the exploratory parse. Finally, the base of the
+temporary stack used during an exploratory parse is a pointer into the
+normal parser state stack so that the stack is never physically copied.
+In our experience, the performance penalty of @acronym{LAC} has proven
+insignificant for practical grammars.
+
+@item Accepted Values: @code{none}, @code{full}
+
+@item Default Value: @code{none}
+@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
+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}"
+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
+the grammar uses the special @samp{@@@var{n}} tokens, but if your
+grammar does not use it, using @samp{%locations} allows for more
+accurate syntax error messages.
+@end deffn
+
+@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{yychar}, @code{yydebug}, and
-(if locations are used) @code{yylloc}. For example, if you use
-@samp{%name-prefix="c_"}, the names become @code{c_parse}, @code{c_lex},
-and so on. In C++ parsers, it is only the surrounding namespace which is
-named @var{prefix} instead of @samp{yy}.
+(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
@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
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}"
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
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
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
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 function 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}
@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
@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
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);
@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);
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
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@}
* 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
Algol 60 and is called the ``dangling @code{else}'' ambiguity.
To avoid warnings from Bison about predictable, legitimate shift/reduce
-conflicts, use the @code{%expect @var{n}} declaration. There will be no
-warning as long as the number of shift/reduce conflicts is exactly @var{n}.
+conflicts, use the @code{%expect @var{n}} declaration.
+There will be no warning as long as the number of shift/reduce conflicts
+is exactly @var{n}, and Bison will report an error if there is a
+different number.
@xref{Expect Decl, ,Suppressing Conflict Warnings}.
The definition of @code{if_stmt} above is solely to blame for the
@cindex @acronym{LR}(1)
@cindex @acronym{LALR}(1)
-However, Bison, like most parser generators, cannot actually handle all
-@acronym{LR}(1) grammars. In this grammar, two contexts, that after
-an @code{ID}
-at the beginning of a @code{param_spec} and likewise at the beginning of
-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
+However, for historical reasons, Bison cannot by default handle all
+@acronym{LR}(1) grammars.
+In this grammar, two contexts, that after an @code{ID} at the beginning
+of a @code{param_spec} and likewise at the beginning of 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 lookahead tokens in the two
the two contexts causes a conflict later. In parser terminology, this
occurrence means that the grammar is not @acronym{LALR}(1).
-In general, it is better to fix deficiencies than to document them. But
-this particular deficiency is intrinsically hard to fix; parser
-generators that can handle @acronym{LR}(1) grammars are hard to write
-and tend to
-produce parsers that are very large. In practice, Bison is more useful
-as it is now.
-
-When the problem arises, you can often fix it by identifying the two
-parser states that are being confused, and adding something to make them
-look distinct. In the above example, adding one rule to
+For many practical grammars (specifically those that fall into the
+non-@acronym{LR}(1) class), the limitations of @acronym{LALR}(1) result in
+difficulties beyond just mysterious reduce/reduce conflicts.
+The best way to fix all these problems is to select a different parser
+table generation algorithm.
+Either @acronym{IELR}(1) or canonical @acronym{LR}(1) would suffice, but
+the former is more efficient and easier to debug during development.
+@xref{Decl Summary,,lr.type}, for details.
+(Bison's @acronym{IELR}(1) and canonical @acronym{LR}(1) implementations
+are experimental.
+More user feedback will help to stabilize them.)
+
+If you instead wish to work around @acronym{LALR}(1)'s limitations, you
+can often fix a mysterious conflict by identifying the two parser states
+that are being confused, and adding something to make them look
+distinct. In the above example, adding one rule to
@code{return_spec} as follows makes the problem go away:
@example
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
+there are languages where Bison's default choice of how to
summarize the input seen so far loses necessary information.
When you use the @samp{%glr-parser} declaration in your grammar file,
stream.
Whenever the parser makes a transition from having multiple
-states to having one, it reverts to the normal @acronym{LALR}(1) parsing
+states to having one, it reverts to the normal deterministic parsing
algorithm, after resolving and executing the saved-up actions.
At this transition, some of the states on the stack will have semantic
values that are sets (actually multisets) of possible actions. The
the result. Otherwise, it reports an ambiguity.
It is possible to use a data structure for the @acronym{GLR} parsing tree that
-permits the processing of any @acronym{LALR}(1) grammar in linear time (in the
+permits the processing of any @acronym{LR}(1) grammar in linear time (in the
size of the input), any unambiguous (not necessarily
-@acronym{LALR}(1)) grammar in
+@acronym{LR}(1)) grammar in
quadratic worst-case time, and any general (possibly ambiguous)
context-free grammar in cubic worst-case time. However, Bison currently
uses a simpler data structure that requires time proportional to the
behaving examples, however, are not generally of practical interest.
Usually, nondeterminism in a grammar is local---the parser is ``in
doubt'' only for a few tokens at a time. Therefore, the current data
-structure should generally be adequate. On @acronym{LALR}(1) portions of a
-grammar, in particular, it is only slightly slower than with the default
-Bison parser.
+structure should generally be adequate. On @acronym{LR}(1) portions of a
+grammar, in particular, it is only slightly slower than with the
+deterministic @acronym{LR}(1) Bison parser.
For a more detailed exposition of @acronym{GLR} parsers, please see: Elizabeth
Scott, Adrian Johnstone and Shamsa Sadaf Hussain, Tomita-Style
@vindex YYINITDEPTH
You can control how much stack is allocated initially by defining the
-macro @code{YYINITDEPTH} to a positive integer. For the C
-@acronym{LALR}(1) parser, this value must be a compile-time constant
+macro @code{YYINITDEPTH} to a positive integer. For the deterministic
+parser in C, this value must be a compile-time constant
unless you are assuming C99 or some other target language or compiler
that allows variable-length arrays. The default is 200.
Do not allow @code{YYINITDEPTH} to be greater than @code{YYMAXDEPTH}.
@c FIXME: C++ output.
-Because of semantical differences between C and C++, the
-@acronym{LALR}(1) parsers in C produced by Bison cannot grow when compiled
+Because of semantic differences between C and C++, the deterministic
+parsers in C produced by Bison cannot grow when compiled
by C++ compilers. In this precise case (compiling a C parser as C++) you are
suggested to grow @code{YYINITDEPTH}. The Bison maintainers hope to fix
this deficiency in a future release.
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
@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 useless in grammar
+calc.y: warning: 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
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
'+' . exp}. Since there is no default action, any other token than
those listed above will trigger a syntax error.
+@cindex accepting state
The state 3 is named the @dfn{final state}, or the @dfn{accepting
state}:
NUM)}, which corresponds to shifting @samp{/}, or as @samp{(NUM + NUM) /
NUM}, which corresponds to reducing rule 1.
-Because in @acronym{LALR}(1) parsing a single decision can be made, Bison
+Because in deterministic parsing a single decision can be made, Bison
arbitrarily chose to disable the reduction, see @ref{Shift/Reduce, ,
Shift/Reduce Conflicts}. Discarded actions are reported in between
square brackets.
@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)
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{<stdio.h>} 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}.
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
%@{
@item --print-localedir
Print the name of the directory containing locale-dependent data.
+@item --print-datadir
+Print the name of the directory containing skeletons and XSLT.
+
@item -y
@itemx --yacc
Act more like the traditional Yacc command. This can cause
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}.
-Also, if generating an @acronym{LALR}(1) parser in C, generate @code{#define}
+Also, if generating a deterministic 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
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-yacc} will hide the warnings about
+@acronym{POSIX} Yacc incompatibilities.
@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 -D @var{name}[=@var{value}]
+@itemx --define=@var{name}[=@var{value}]
+@itemx -F @var{name}[=@var{value}]
+@itemx --force-define=@var{name}[=@var{value}]
+Each of these is equivalent to @samp{%define @var{name} "@var{value}"}
+(@pxref{Decl Summary, ,%define}) except that Bison processes multiple
+definitions for the same @var{name} as follows:
+
+@itemize
+@item
+Bison quietly ignores all command-line definitions for @var{name} except
+the last.
+@item
+If that command-line definition is specified by a @code{-D} or
+@code{--define}, Bison reports an error for any @code{%define}
+definition for @var{name}.
+@item
+If that command-line definition is specified by a @code{-F} or
+@code{--force-define} instead, Bison quietly ignores all @code{%define}
+definitions for @var{name}.
+@item
+Otherwise, Bison reports an error if there are multiple @code{%define}
+definitions for @var{name}.
+@end itemize
+
+You should avoid using @code{-F} and @code{--force-define} in your
+makefiles unless you are confident that it is safe to quietly ignore any
+conflicting @code{%define} that may be added to the grammar file.
+
+@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
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
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{%file-prefix} 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}
@table @code
@item state
Description of the grammar, conflicts (resolved and unresolved), and
-@acronym{LALR} automaton.
+parser's automaton.
@item lookahead
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
+@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}.
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 parser's
+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 parser's 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.
-
-@multitable {@option{--defines=@var{defines-file}}} {@option{-b @var{file-prefix}XXX}}
-@headitem Long Option @tab Short Option
-@item @option{--debug} @tab @option{-t}
-@item @option{--defines=@var{defines-file}} @tab @option{-d}
-@item @option{--file-prefix=@var{prefix}} @tab @option{-b @var{file-prefix}}
-@item @option{--graph=@var{graph-file}} @tab @option{-d}
-@item @option{--help} @tab @option{-h}
-@item @option{--name-prefix=@var{prefix}} @tab @option{-p @var{name-prefix}}
-@item @option{--no-lines} @tab @option{-l}
-@item @option{--no-parser} @tab @option{-n}
-@item @option{--output=@var{outfile}} @tab @option{-o @var{outfile}}
-@item @option{--print-localedir} @tab
-@item @option{--token-table} @tab @option{-k}
-@item @option{--verbose} @tab @option{-v}
-@item @option{--version} @tab @option{-V}
-@item @option{--yacc} @tab @option{-y}
+the corresponding short option and directive.
+
+@multitable {@option{--force-define=@var{name}[=@var{value}]}} {@option{-F @var{name}[=@var{value}]}} {@code{%nondeterministic-parser}}
+@headitem Long Option @tab Short Option @tab Bison Directive
+@include cross-options.texi
@end multitable
@node Yacc Library
@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
* 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
@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
-entities in the @samp{yy} namespace. Use the @samp{%name-prefix}
-directive to change the namespace name, see @ref{Decl Summary}. The
-various classes are generated in the following files:
+The C++ deterministic parser is selected using the skeleton directive,
+@samp{%skeleton "lalr1.cc"}, or the synonymous command-line option
+@option{--skeleton=lalr1.cc}.
+@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
@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
@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
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
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
additional argument for its constructor.
-@defcv {Type} {parser} {semantic_value_type}
-@defcvx {Type} {parser} {location_value_type}
+@defcv {Type} {parser} {semantic_type}
+@defcvx {Type} {parser} {location_type}
The types for semantics value and locations.
@end defcv
+@defcv {Type} {parser} {token}
+A structure that contains (only) the definition of the tokens as the
+@code{yytokentype} enumeration. To refer to the token @code{FOO}, the
+scanner should use @code{yy::parser::token::FOO}. The scanner can use
+@samp{typedef yy::parser::token token;} to ``import'' the token enumeration
+(@pxref{Calc++ Scanner}).
+@end defcv
+
@deftypemethod {parser} {} parser (@var{type1} @var{arg1}, ...)
Build a new parser object. There are no arguments by default, unless
@samp{%parse-param @{@var{type1} @var{arg1}@}} was used.
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}, ...)
+@deftypemethod {parser} {int} yylex (semantic_type* @var{yylval}, location_type* @var{yylloc}, @var{type1} @var{arg1}, ...)
Return the next token. Its type is the return value, its semantic
value and location being @var{yylval} and @var{yylloc}. Invocations of
@samp{%lex-param @{@var{type1} @var{arg1}@}} yield additional arguments.
@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,
@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
@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
@comment file: calc++-driver.hh
@example
-// Announce to Flex the prototype we want for lexing function, ...
-# define YY_DECL \
+// 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, \
@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
@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
@{
@}
-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
@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
-specifies the name of the parser class. Because the C++ skeleton
-changed several times, it is safer to require the version you designed
-the grammar for.
+the C++ deterministic parser skeleton, the creation of the parser header
+file, and specifies the name of the parser class.
+Because the C++ skeleton changed several times, it is safer to require
+the version you designed 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 %start-header
+@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{Table of Symbols, ,%start-header}.
+@xref{Decl Summary, ,%code}.
@comment file: calc++-parser.yy
@example
-%start-header @{
+%code requires @{
# include <string>
class calcxx_driver;
@}
@noindent
Then we request the location tracking feature, and initialize the
-first location's file name. Afterwards new locations are computed
+first location's file name. Afterward new locations are computed
relatively to the previous locations: the file name will be
automatically propagated.
@end example
@noindent
-@findex %after-header
-The code between @samp{%after-header @{} and @samp{@}} is output in the
+@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
-%after-header @{
+%code @{
# include "calc++-driver.hh"
@}
@end example
%token ASSIGN ":="
%token <sval> IDENTIFIER "identifier"
%token <ival> NUMBER "number"
-%type <ival> exp "expression"
+%type <ival> exp
@end example
@noindent
%printer @{ debug_stream () << *$$; @} "identifier"
%destructor @{ delete $$; @} "identifier"
-%printer @{ debug_stream () << $$; @} "number" "expression"
+%printer @{ debug_stream () << $$; @} <ival>
@end example
@noindent
assignments: assignments assignment @{@}
| /* Nothing. */ @{@};
-assignment: "identifier" ":=" exp @{ driver.variables[*$1] = $3; @};
+assignment:
+ "identifier" ":=" exp
+ @{ driver.variables[*$1] = $3; delete $1; @};
%left '+' '-';
%left '*' '/';
| exp '-' exp @{ $$ = $1 - $3; @}
| exp '*' exp @{ $$ = $1 * $3; @}
| exp '/' exp @{ $$ = $1 / $3; @}
- | "identifier" @{ $$ = driver.variables[*$1]; @}
+ | "identifier" @{ $$ = driver.variables[*$1]; delete $1; @}
| "number" @{ $$ = $1; @};
%%
@end example
@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.
@example
%@{ /* -*- C++ -*- */
# include <cstdlib>
-# include <errno.h>
-# include <limits.h>
+# include <cerrno>
+# include <climits>
# include <string>
# include "calc++-driver.hh"
# include "calc++-parser.hh"
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
@end example
@node Calc++ Top Level
-@subsection Calc++ Top Level
+@subsubsection Calc++ Top Level
The top level file, @file{calc++.cc}, poses no problem.
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 <Expression> expr assignment_expr term factor
+%type <Integer> 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 their 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 semantic 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
+
+@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
+@samp{%define stype}. Angle brackets 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 prologue 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
* I can't build Bison:: Troubleshooting
* Where can I find help?:: Troubleshouting
* Bug Reports:: Troublereporting
-* Other Languages:: Parsers in Java and others
+* More Languages:: Parsers in C++, Java, and so on
* Beta Testing:: Experimenting development versions
* Mailing Lists:: Meeting other Bison users
@end menu
@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
Send bug reports to @email{bug-bison@@gnu.org}.
-@node Other Languages
-@section Other Languages
+@node More Languages
+@section More Languages
@display
-Will Bison ever have C++ support? How about Java or @var{insert your
+Will Bison ever have C++ and Java support? How about @var{insert your
favorite language here}?
@end display
-C++ support is there now, and is documented. We'd love to add other
+C++ and Java support is there now, and is documented. We'd love to add other
languages; contributions are welcome.
@node Beta Testing
side of the rule. @xref{Locations, , Locations Overview}.
@end deffn
+@deffn {Variable} @@@var{name}
+In an action, the location of a symbol addressed by name.
+@xref{Locations, , Locations Overview}.
+@end deffn
+
+@deffn {Variable} @@[@var{name}]
+In an action, the location of a symbol addressed by name.
+@xref{Locations, , Locations Overview}.
+@end deffn
+
@deffn {Variable} $$
In an action, the semantic value of the left-hand side of the rule.
@xref{Actions}.
right-hand side of the rule. @xref{Actions}.
@end deffn
+@deffn {Variable} $@var{name}
+In an action, the semantic value of a symbol addressed by name.
+@xref{Actions}.
+@end deffn
+
+@deffn {Variable} $[@var{name}]
+In an action, the semantic value of a symbol addressed by name.
+@xref{Actions}.
+@end deffn
+
@deffn {Delimiter} %%
Delimiter used to separate the grammar rule section from the
Bison declarations section or the epilogue.
@xref{Rules, ,Syntax of Grammar Rules}.
@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} <*>
+Used to define a default tagged @code{%destructor} or default tagged
+@code{%printer}.
-@deffn {Directive} %after-header @{@var{code}@}
-Specifies code to be inserted into the code file after the contents of the
-header file.
-@xref{Table of Symbols, ,%start-header}.
-@end deffn
+This feature is experimental.
+More user feedback will help to determine whether it should become a permanent
+feature.
-@deffn {Directive} %before-header @{@var{code}@}
-Specifies code to be inserted into the code file before the contents of the
-header file.
-@xref{Table of Symbols, ,%start-header}.
+@xref{Destructor Decl, , Freeing Discarded Symbols}.
@end deffn
-@deffn {Directive} %end-header @{@var{code}@}
-Specifies code to be inserted both into the header file (if generated;
-@pxref{Table of Symbols, ,%defines}) and into the code file after any
-Bison-generated definitions.
-@xref{Table of Symbols, ,%start-header}.
-@end deffn
+@deffn {Directive} <>
+Used to define a default tagless @code{%destructor} or default tagless
+@code{%printer}.
-@deffn {Directive} %start-header @{@var{code}@}
-Specifies code to be inserted both into the header file (if generated;
-@pxref{Table of Symbols, ,%defines}) and into the code file before any
-Bison-generated definitions.
-
-@cindex Prologue
-@findex %before-header
-@findex %union
-@findex %end-header
-@findex %after-header
-For example, the following declaration order in the grammar file reflects the
-order in which Bison will output these code blocks. However, you are free to
-declare these code blocks in your grammar file in whatever order is most
-convenient for you:
-
-@smallexample
-%before-header @{
- /* Bison treats this block like a pre-prologue block: it inserts it
- * into the code file before the contents of the header file. It
- * does *not* insert it into the header file. This is a good place
- * to put #include's that you want at the top of your code file. A
- * common example is `#include "system.h"'. */
-@}
-%start-header @{
- /* Bison inserts this block into both the header file and the code
- * file. In both files, the point of insertion is before any
- * Bison-generated token, semantic type, location type, and class
- * definitions. This is a good place to define %union
- * dependencies, for example. */
-@}
-%union @{
- /* Unlike the traditional Yacc prologue blocks, the output order
- * for the %*-header blocks is not affected by their declaration
- * position relative to any %union in the grammar file. */
-@}
-%end-header @{
- /* Bison inserts this block into both the header file and the code
- * file. In both files, the point of insertion is after the
- * Bison-generated definitions. This is a good place to declare or
- * define public functions or data structures that depend on the
- * Bison-generated definitions. */
-@}
-%after-header @{
- /* Bison treats this block like a post-prologue block: it inserts
- * it into the code file after the contents of the header file. It
- * does *not* insert it into the header file. This is a good place
- * to declare or define internal functions or data structures that
- * depend on the Bison-generated definitions. */
-@}
-@end smallexample
+This feature is experimental.
+More user feedback will help to determine whether it should become a permanent
+feature.
-If you have multiple occurrences of any one of the above declarations, Bison
-will concatenate the contents in declaration order.
+@xref{Destructor Decl, , Freeing Discarded Symbols}.
+@end deffn
-@xref{Prologue, ,The Prologue}.
+@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} %debug
-Equip the parser for debugging. @xref{Decl Summary}.
+@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
@end deffn
@end ifset
+@deffn {Directive} %define @var{define-variable}
+@deffnx {Directive} %define @var{define-variable} @var{value}
+@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}.
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
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}.
@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
@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
@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}"
@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}.
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
@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
@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
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
@end deffn
@deffn {Macro} YYSTACK_USE_ALLOCA
-Macro used to control the use of @code{alloca} when the C
-@acronym{LALR}(1) parser needs to extend its stacks. If defined to 0,
+Macro used to control the use of @code{alloca} when the
+deterministic parser in C needs to extend its stacks. If defined to 0,
the parser will use @code{malloc} to extend its stacks. If defined to
1, the parser will use @code{alloca}. Values other than 0 and 1 are
reserved for future Bison extensions. If not defined,
@cindex glossary
@table @asis
+@item Accepting State
+A state whose only action is the accept action.
+The accepting state is thus a consistent state.
+@xref{Understanding,,}.
+
@item Backus-Naur Form (@acronym{BNF}; also called ``Backus Normal Form'')
Formal method of specifying context-free grammars originally proposed
by John Backus, and slightly improved by Peter Naur in his 1960-01-02
committee document contributing to what became the Algol 60 report.
@xref{Language and Grammar, ,Languages and Context-Free Grammars}.
+@item Consistent State
+A state containing only one possible action.
+@xref{Decl Summary,,lr.default-reductions}.
+
@item Context-free grammars
Grammars specified as rules that can be applied regardless of context.
Thus, if there is a rule which says that an integer can be used as an
permitted. @xref{Language and Grammar, ,Languages and Context-Free
Grammars}.
+@item Default Reduction
+The reduction that a parser should perform if the current parser state
+contains no other action for the lookahead token.
+In permitted parser states, Bison declares the reduction with the
+largest lookahead set to be the default reduction and removes that
+lookahead set.
+@xref{Decl Summary,,lr.default-reductions}.
+
@item Dynamic allocation
Allocation of memory that occurs during execution, rather than at
compile time or on entry to a function.
@item Generalized @acronym{LR} (@acronym{GLR})
A parsing algorithm that can handle all context-free grammars, including those
-that are not @acronym{LALR}(1). It resolves situations that Bison's
-usual @acronym{LALR}(1)
+that are not @acronym{LR}(1). It resolves situations that Bison's
+deterministic parsing
algorithm cannot by effectively splitting off multiple parsers, trying all
possible parsers, and discarding those that fail in the light of additional
right context. @xref{Generalized LR Parsing, ,Generalized
for example, `expression' or `declaration' in C@.
@xref{Language and Grammar, ,Languages and Context-Free Grammars}.
+@item @acronym{IELR}(1)
+A minimal @acronym{LR}(1) parser table generation algorithm.
+That is, given any context-free grammar, @acronym{IELR}(1) generates
+parser tables with the full language recognition power of canonical
+@acronym{LR}(1) but with nearly the same number of parser states as
+@acronym{LALR}(1).
+This reduction in parser states is often an order of magnitude.
+More importantly, because canonical @acronym{LR}(1)'s extra parser
+states may contain duplicate conflicts in the case of
+non-@acronym{LR}(1) grammars, the number of conflicts for
+@acronym{IELR}(1) is often an order of magnitude less as well.
+This can significantly reduce the complexity of developing of a grammar.
+@xref{Decl Summary,,lr.type}.
+
@item Infix operator
An arithmetic operator that is placed between the operands on which it
performs some operation.
@item Input stream
A continuous flow of data between devices or programs.
+@item @acronym{LAC} (Lookahead Correction)
+A parsing mechanism that fixes the problem of delayed syntax error
+detection, which is caused by LR state merging, default reductions, and
+the use of @code{%nonassoc}. Delayed syntax error detection results in
+unexpected semantic actions, initiation of error recovery in the wrong
+syntactic context, and an incorrect list of expected tokens in a verbose
+syntax error message. @xref{Decl Summary,,parse.lac}.
+
@item Language construct
One of the typical usage schemas of the language. For example, one of
the constructs of the C language is the @code{if} statement.
@item @acronym{LALR}(1)
The class of context-free grammars that Bison (like most other parser
-generators) can handle; a subset of @acronym{LR}(1). @xref{Mystery
-Conflicts, ,Mysterious Reduce/Reduce Conflicts}.
+generators) can handle by default; a subset of @acronym{LR}(1).
+@xref{Mystery Conflicts, ,Mysterious Reduce/Reduce Conflicts}.
@item @acronym{LR}(1)
The class of context-free grammars in which at most one token of
@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
@bye
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projects / bison.git / blobdiff