@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, 2007 Free Software Foundation, Inc.
+1999, 2000, 2001, 2002, 2003, 2004, 2005, 2006, 2007, 2008, 2009 Free
+Software Foundation, Inc.
@quotation
Permission is granted to copy, distribute and/or modify this document
(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.
+* 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.
+* 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
* 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
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
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
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
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.
+* 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.
+* 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
@findex %code requires
@findex %code provides
@findex %code top
-(The prologue alternatives described here are experimental.
-More user feedback will help to determine whether they should become permanent
-features.)
The functionality of @var{Prologue} sections can often be subtle and
inflexible.
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
-@code{requires}, @code{provides}, or @code{top}.
+one of @code{requires}, @code{provides}, @code{top}.
@xref{Decl Summary,,%code}.
Look again at the example of the previous section:
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.
@} 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
* 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
@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.
@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
@deffn {Directive} %code @{@var{code}@}
@findex %code
This is the unqualified form of the @code{%code} directive.
-It inserts @var{code} verbatim at the default location in the output.
-That default location is determined by the selected target language and/or
-parser skeleton.
+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 the current C/C++ skeletons, the default location is the parser source code
+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}.
-@comment For Java, the default location is inside the parser class.
-
-(Like all the Yacc prologue alternatives, this directive is experimental.
-More user feedback will help to determine whether it should become a permanent
-feature.)
+For Java, the default location is inside the parser class.
@end deffn
@deffn {Directive} %code @var{qualifier} @{@var{code}@}
Not all values of @var{qualifier} are available for all target languages:
@itemize @bullet
-@findex %code requires
@item requires
+@findex %code requires
@itemize @bullet
@item Language(s): C, C++
@item Location(s): Near the top of the parser source code file.
@end itemize
-@ignore
+
@item imports
@findex %code imports
@item Location(s): The parser Java file after any Java package directive and
before any class definitions.
@end itemize
-@end ignore
@end itemize
-(Like all the Yacc prologue alternatives, this directive is experimental.
-More user feedback will help to determine whether it should become a permanent
-feature.)
-
@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}.
@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.
-@end deffn
@xref{Tracing, ,Tracing Your Parser}.
+@end deffn
-@deffn {Directive} %define @var{define-variable}
-@deffnx {Directive} %define @var{define-variable} @var{value}
+@deffn {Directive} %define @var{variable}
+@deffnx {Directive} %define @var{variable} "@var{value}"
Define a variable to adjust Bison's behavior.
-The list of available variables and their meanings depends on the selected
-target language and/or the parser skeleton (@pxref{Decl Summary,,%language}).
-The @var{value} can be omitted for boolean variables; for
-boolean variables, the skeletons will treat a @var{value} of @samp{0}
-or @samp{false} as the boolean variable being false, and anything else
-as true.
+The possible choices for @var{variable}, as well as their meanings, depend on
+the selected target language and/or the parser skeleton (@pxref{Decl
+Summary,,%language}, @pxref{Decl Summary,,%skeleton}).
+
+Bison will warn if a @var{variable} is defined multiple times.
+
+Omitting @code{"@var{value}"} is always equivalent to specifying it as
+@code{""}.
+
+Some @var{variable}s may be used as Booleans.
+In this case, Bison will complain if the variable definition does not meet one
+of the following four conditions:
+
+@enumerate
+@item @code{"@var{value}"} is @code{"true"}
+
+@item @code{"@var{value}"} is omitted (or is @code{""}).
+This is equivalent to @code{"true"}.
+
+@item @code{"@var{value}"} is @code{"false"}.
+
+@item @var{variable} is never defined.
+In this case, Bison selects a default value, which may depend on the selected
+target language and/or parser skeleton.
+@end enumerate
+
+Some of the accepted @var{variable}s are:
+
+@itemize @bullet
+@item api.pure
+@findex %define api.pure
+
+@itemize @bullet
+@item Language(s): C
+
+@item Purpose: Request a pure (reentrant) parser program.
+@xref{Pure Decl, ,A Pure (Reentrant) Parser}.
+
+@item Accepted Values: Boolean
+
+@item Default Value: @code{"false"}
+@end itemize
+
+@item api.push_pull
+@findex %define api.push_pull
+
+@itemize @bullet
+@item Language(s): C (LALR(1) only)
+
+@item Purpose: Requests a pull parser, a push parser, or both.
+@xref{Push Decl, ,A Push Parser}.
+(The current push parsing interface is experimental and may evolve.
+More user feedback will help to stabilize it.)
+
+@item Accepted Values: @code{"pull"}, @code{"push"}, @code{"both"}
+
+@item Default Value: @code{"pull"}
+@end itemize
+
+@item lr.keep_unreachable_states
+@findex %define lr.keep_unreachable_states
+
+@itemize @bullet
+@item Language(s): all
+
+@item Purpose: Requests that Bison allow unreachable parser states to remain in
+the parser tables.
+Bison considers a state to be unreachable if there exists no sequence of
+transitions from the start state to that state.
+A state can become unreachable during conflict resolution if Bison disables a
+shift action leading to it from a predecessor state.
+Keeping unreachable states is sometimes useful for analysis purposes, but they
+are useless in the generated parser.
+
+@item Accepted Values: Boolean
+
+@item Default Value: @code{"false"}
+
+@item Caveats:
+
+@itemize @bullet
+
+@item Unreachable states may contain conflicts and may use rules not used in
+any other state.
+Thus, keeping unreachable states may induce warnings that are irrelevant to
+your parser's behavior, and it may eliminate warnings that are relevant.
+Of course, the change in warnings may actually be relevant to a parser table
+analysis that wants to keep unreachable states, so this behavior will likely
+remain in future Bison releases.
+
+@item While Bison is able to remove unreachable states, it is not guaranteed to
+remove other kinds of useless states.
+Specifically, when Bison disables reduce actions during conflict resolution,
+some goto actions may become useless, and thus some additional states may
+become useless.
+If Bison were to compute which goto actions were useless and then disable those
+actions, it could identify such states as unreachable and then remove those
+states.
+However, Bison does not compute which goto actions are useless.
+@end itemize
+@end itemize
+
+@item namespace
+@findex %define namespace
+
+@itemize
+@item Languages(s): C++
+
+@item Purpose: Specifies the namespace for the parser class.
+For example, if you specify:
+
+@smallexample
+%define namespace "foo::bar"
+@end smallexample
+
+Bison uses @code{foo::bar} verbatim in references such as:
+
+@smallexample
+foo::bar::parser::semantic_type
+@end smallexample
+
+However, to open a namespace, Bison removes any leading @code{::} and then
+splits on any remaining occurrences:
+
+@smallexample
+namespace foo @{ namespace bar @{
+ class position;
+ class location;
+@} @}
+@end smallexample
+
+@item Accepted Values: Any absolute or relative C++ namespace reference without
+a trailing @code{"::"}.
+For example, @code{"foo"} or @code{"::foo::bar"}.
+
+@item Default Value: The value specified by @code{%name-prefix}, which defaults
+to @code{yy}.
+This usage of @code{%name-prefix} is for backward compatibility and can be
+confusing since @code{%name-prefix} also specifies the textual prefix for the
+lexical analyzer function.
+Thus, if you specify @code{%name-prefix}, it is best to also specify
+@code{%define namespace} so that @code{%name-prefix} @emph{only} affects the
+lexical analyzer function.
+For example, if you specify:
+
+@smallexample
+%define namespace "foo"
+%name-prefix "bar::"
+@end smallexample
+
+The parser namespace is @code{foo} and @code{yylex} is referenced as
+@code{bar::lex}.
+@end itemize
+@end itemize
+
@end deffn
@deffn {Directive} %defines
@deffn {Directive} %language "@var{language}"
Specify the programming language for the generated parser. Currently
-supported languages include C and C++.
+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
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
@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}"
@deffn {Directive} %skeleton "@var{file}"
Specify the skeleton to use.
-You probably don't need this option unless you are developing Bison.
-You should use @code{%language} if you want to specify the skeleton for a
-different language, because it is clearer and because it will always choose the
-correct skeleton for non-deterministic or push parsers.
+@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.
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
Do not allow @code{YYINITDEPTH} to be greater than @code{YYMAXDEPTH}.
@c FIXME: C++ output.
-Because of semantical differences between C and C++, the
+Because of semantic differences between C and C++, the
@acronym{LALR}(1) 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
@command{bison} reports:
@example
-calc.y: warning: 1 useless nonterminal and 1 useless rule
-calc.y:11.1-7: warning: useless nonterminal: useless
-calc.y:11.10-12: warning: useless rule: useless: STR
+calc.y: warning: 1 nonterminal and 1 rule useless in grammar
+calc.y:11.1-7: warning: nonterminal useless in grammar: useless
+calc.y:11.10-12: warning: rule useless in grammar: useless: STR
calc.y: conflicts: 7 shift/reduce
@end example
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
@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{YYFPRINTF} is defined to @code{fprintf}.
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
like @samp{%glr-parser}, Bison might not be Yacc-compatible even if
this option is specified.
+@item -W [@var{category}]
+@itemx --warnings[=@var{category}]
+Output warnings falling in @var{category}. @var{category} can be one
+of:
+@table @code
+@item midrule-values
+Warn about mid-rule values that are set but not used within any of the actions
+of the parent rule.
+For example, warn about unused @code{$2} in:
+
+@example
+exp: '1' @{ $$ = 1; @} '+' exp @{ $$ = $1 + $4; @};
+@end example
+
+Also warn about mid-rule values that are used but not set.
+For example, warn about unset @code{$$} in the mid-rule action in:
+
+@example
+ exp: '1' @{ $1 = 1; @} '+' exp @{ $$ = $2 + $4; @};
+@end example
+
+These warnings are not enabled by default since they sometimes prove to
+be false alarms in existing grammars employing the Yacc constructs
+@code{$0} or @code{$-@var{n}} (where @var{n} is some positive integer).
+
+
+@item yacc
+Incompatibilities with @acronym{POSIX} Yacc.
+
+@item all
+All the warnings.
+@item none
+Turn off all the warnings.
+@item error
+Treat warnings as errors.
+@end table
+
+A category can be turned off by prefixing its name with @samp{no-}. For
+instance, @option{-Wno-syntax} will hide the warnings about unused
+variables.
@end table
@noindent
@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 and C++.
+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}.
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}).
-You probably don't need this option unless you are developing Bison.
-You should use @option{--language} if you want to specify the skeleton for a
-different language, because it is clearer and because it will always
-choose the correct skeleton for non-deterministic or push parsers.
+@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.
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}
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
The other output files' names are constructed from @var{file} as
described under the @samp{-v} and @samp{-d} options.
-@item -g
+@item -g[@var{file}]
+@itemx --graph[=@var{file}]
Output a graphical representation of the @acronym{LALR}(1) grammar
automaton computed by Bison, in @uref{http://www.graphviz.org/, Graphviz}
@uref{http://www.graphviz.org/doc/info/lang.html, @acronym{DOT}} format.
-If the grammar file is @file{foo.y}, the output file will
-be @file{foo.dot}.
-
-@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.
+@code{@var{file}} is optional.
+If omitted and the grammar file is @file{foo.y}, the output file will be
+@file{foo.dot}.
+
+@item -x[@var{file}]
+@itemx --xml[=@var{file}]
+Output an XML report of the @acronym{LALR}(1) automaton computed by Bison.
+@code{@var{file}} is optional.
+If omitted and the grammar file is @file{foo.y}, the output file will be
+@file{foo.xml}.
+(The current XML schema is experimental and may evolve.
+More user feedback will help to stabilize it.)
@end table
@node Option Cross Key
@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}
+@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
@subsection C++ Bison Interface
-@c - %language "C++"
+@c - %skeleton "lalr1.cc"
@c - Always pure
@c - initial action
-The C++ @acronym{LALR}(1) parser is selected using the language directive,
-@samp{%language "C++"}, or the synonymous command-line option
-@option{--language=c++}.
+The C++ @acronym{LALR}(1) parser is selected using the skeleton directive,
+@samp{%skeleton "lalr1.c"}, or the synonymous command-line option
+@option{--skeleton=lalr1.c}.
@xref{Decl Summary}.
-When run, @command{bison} will create several
-entities in the @samp{yy} namespace. Use the @samp{%name-prefix}
-directive to change the namespace name, see @ref{Decl Summary}. The
-various classes are generated in the following files:
+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
The parser invokes the scanner by calling @code{yylex}. Contrary to C
parsers, C++ parsers are always pure: there is no point in using the
-@code{%pure-parser} directive. Therefore the interface is as follows.
+@code{%define api.pure} directive. Therefore the interface is as follows.
@deftypemethod {parser} {int} yylex (semantic_value_type& @var{yylval}, location_type& @var{yylloc}, @var{type1} @var{arg1}, ...)
Return the next token. Its type is the return value, its semantic
@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
@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
@comment file: calc++-parser.yy
@example
-%language "C++" /* -*- C++ -*- */
+%skeleton "lalr1.cc" /* -*- C++ -*- */
%require "@value{VERSION}"
%defines
%define parser_class_name "calcxx_parser"
@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
@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"
@end example
@node Calc++ Top Level
-@subsection Calc++ Top Level
+@subsubsection Calc++ Top Level
The top level file, @file{calc++.cc}, poses no problem.
@}
@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
Equip the parser for debugging. @xref{Decl Summary}.
@end deffn
-@deffn {Directive} %debug
-Equip the parser for debugging. @xref{Decl Summary}.
-@end deffn
-
@ifset defaultprec
@deffn {Directive} %default-prec
Assign a precedence to rules that lack an explicit @samp{%prec}
@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}"
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
@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
+@c Local Variables:
+@c fill-column: 76
+@c End:
+
@c LocalWords: texinfo setfilename settitle setchapternewpage finalout
@c LocalWords: ifinfo smallbook shorttitlepage titlepage GPL FIXME iftex
@c LocalWords: akim fn cp syncodeindex vr tp synindex dircategory direntry
@c LocalWords: ifset vskip pt filll insertcopying sp ISBN Etienne Suvasa
@c LocalWords: ifnottex yyparse detailmenu GLR RPN Calc var Decls Rpcalc
-@c LocalWords: rpcalc Lexer Gen Comp Expr ltcalc mfcalc Decl Symtab yylex
+@c LocalWords: rpcalc Lexer Expr ltcalc mfcalc yylex
@c LocalWords: yyerror pxref LR yylval cindex dfn LALR samp gpl BNF xref
@c LocalWords: const int paren ifnotinfo AC noindent emph expr stmt findex
@c LocalWords: glr YYSTYPE TYPENAME prog dprec printf decl init stmtMerge
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