@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, 2008 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
@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).
-* 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.
+ 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
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.
Operator Precedence
* Why Precedence:: An example showing why precedence is needed.
-* Using Precedence:: How to specify precedence in Bison grammars.
+* Using Precedence:: How to specify precedence and associativity.
+* Precedence Only:: How to specify precedence only.
* Precedence Examples:: How these features are used in the previous example.
* How Precedence:: How they work.
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:: Java scanners, and pure parsers
-* Java Differences:: Differences between C/C++ and Java Grammars
+* 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
-* Copying This Manual:: 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 or @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
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.
+To escape these additional restrictions, you can request
+@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)
%token NUM
%left '-' '+'
%left '*' '/'
-%left NEG /* negation--unary minus */
-%right '^' /* exponentiation */
+%precedence NEG /* negation--unary minus */
+%right '^' /* exponentiation */
%% /* The grammar follows. */
input: /* empty */
types and says they are left-associative operators. The declarations
@code{%left} and @code{%right} (right associativity) take the place of
@code{%token} which is used to declare a token type name without
-associativity. (These tokens are single-character literals, which
+associativity/precedence. (These tokens are single-character literals, which
ordinarily don't need to be declared. We declare them here to specify
-the associativity.)
+the associativity/precedence.)
Operator precedence is determined by the line ordering of the
declarations; the higher the line number of the declaration (lower on
the page or screen), the higher the precedence. Hence, exponentiation
has the highest precedence, unary minus (@code{NEG}) is next, followed
-by @samp{*} and @samp{/}, and so on. @xref{Precedence, ,Operator
+by @samp{*} and @samp{/}, and so on. Unary minus is not associative,
+only precedence matters (@code{%precedence}. @xref{Precedence, ,Operator
Precedence}.
The other important new feature is the @code{%prec} in the grammar
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
%left '-' '+'
%left '*' '/'
-%left NEG
+%precedence NEG
%right '^'
%% /* The grammar follows. */
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.
%right '='
%left '-' '+'
%left '*' '/'
-%left NEG /* negation--unary minus */
-%right '^' /* exponentiation */
+%precedence NEG /* negation--unary minus */
+%right '^' /* exponentiation */
@end group
%% /* The grammar follows. */
@end smallexample
%%
@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
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, period, and (not at the
+beginning) digits and dashes. 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:
the parser, so that the function @code{yylex} (if it is in this file)
can use the name @var{name} to stand for this token type's code.
-Alternatively, you can use @code{%left}, @code{%right}, or
+Alternatively, you can use @code{%left}, @code{%right},
+@code{%precedence}, or
@code{%nonassoc} instead of @code{%token}, if you wish to specify
associativity and precedence. @xref{Precedence Decl, ,Operator
Precedence}.
@cindex declaring operator precedence
@cindex operator precedence, declaring
-Use the @code{%left}, @code{%right} or @code{%nonassoc} declaration to
+Use the @code{%left}, @code{%right}, @code{%nonassoc}, or
+@code{%precedence} declaration to
declare a token and specify its precedence and associativity, all at
once. These are called @dfn{precedence declarations}.
@xref{Precedence, ,Operator Precedence}, for general information on
means that @samp{@var{x} @var{op} @var{y} @var{op} @var{z}} is
considered a syntax error.
+@code{%precedence} gives only precedence to the @var{symbols}, and
+defines no associativity at all. Use this to define precedence only,
+and leave any potential conflict due to associativity enabled.
+
@item
The precedence of an operator determines how it nests with other operators.
All the tokens declared in a single precedence declaration have equal
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,
@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.
-@end deffn
+Instrument the output parser for traces. Obsoleted by @samp{%define
+parse.trace}.
@xref{Tracing, ,Tracing Your Parser}.
+@end deffn
@deffn {Directive} %define @var{variable}
@deffnx {Directive} %define @var{variable} "@var{value}"
Define a variable to adjust Bison's behavior.
The possible choices for @var{variable}, as well as their meanings, depend on
the selected target language and/or the parser skeleton (@pxref{Decl
-Summary,,%language}).
+Summary,,%language}, @pxref{Decl Summary,,%skeleton}).
Bison will warn if a @var{variable} is defined multiple times.
Some of the accepted @var{variable}s are:
-@itemize @bullet
+@table @code
@item api.pure
@findex %define api.pure
@item Default Value: @code{"false"}
@end itemize
+@c api.pure
@item api.push_pull
@findex %define api.push_pull
@itemize @bullet
-@item Language(s): C (LALR(1) only)
+@item Language(s): C (deterministic parsers only)
@item Purpose: Requests a pull parser, a push parser, or both.
@xref{Push Decl, ,A Push Parser}.
@item Default Value: @code{"pull"}
@end itemize
+@c api.push_pull
+
+@item error-verbose
+@findex %define error-verbose
+@itemize
+@item Languages(s):
+all.
+@item Purpose:
+Enable the generation of more verbose error messages than a instead of
+just plain @w{@code{"syntax error"}}. @xref{Error Reporting, ,The Error
+Reporting Function @code{yyerror}}.
+@item Accepted Values:
+Boolean
+@item Default Value:
+@code{false}
+@end itemize
+@c error-verbose
+
+
+@item lr.default_rules
+@cindex default rules
+@findex %define lr.default_rules
+@cindex delayed syntax errors
+@cindex syntax errors delayed
+
+@itemize @bullet
+@item Language(s): all
+
+@item Purpose: Specifies the kind of states that are permitted to
+contain default rules.
+That is, in such a state, Bison declares the rule with the largest
+lookahead set to be the default rule by which to reduce and then removes
+that lookahead set.
+The advantages of default rules are discussed below.
+The disadvantage is that, when the generated parser encounters a
+syntactically unacceptable token, the parser might then perform
+unnecessary reductions by default rules before it can detect the syntax
+error.
+
+(This feature is experimental.
+More user feedback will help to stabilize it.)
+
+@item Accepted Values:
+@itemize
+@item @code{"all"}.
+For @acronym{LALR} and @acronym{IELR} parsers (@pxref{Decl
+Summary,,lr.type}) by default, all states are permitted to contain
+default rules.
+The advantage is that parser table sizes can be significantly reduced.
+The reason Bison does not by default attempt to address the disadvantage
+of delayed syntax error detection is that this disadvantage is already
+inherent in @acronym{LALR} and @acronym{IELR} parser tables.
+That is, unlike a canonical @acronym{LR} state, an @acronym{LALR} or
+@acronym{IELR} state can contain syntactically incorrect tokens in the
+lookahead sets of its rules.
+
+@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 only recognizes the ability to ignore the lookahead
+token when such a reduction is encoded as a default rule.
+Thus, if default rules are permitted in and only in consistent states,
+then a canonical @acronym{LR} parser reports a syntax error as soon as
+it @emph{needs} the syntactically unacceptable token from the scanner.
+
+@item @code{"accepting"}.
+@cindex accepting state
+By default, the only default rule permitted in a canonical @acronym{LR}
+parser is the accept rule in the accepting state, which the parser
+reaches only after reading all tokens from the input.
+Thus, the default canonical @acronym{LR} parser reports a syntax error
+as soon as it @emph{reaches} the syntactically unacceptable token
+without performing 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
@item lr.keep_unreachable_states
@findex %define lr.keep_unreachable_states
However, Bison does not compute which goto actions are useless.
@end itemize
@end itemize
+@c lr.keep_unreachable_states
+
+@item lr.type
+@findex %define lr.type
+@cindex @acronym{LALR}
+@cindex @acronym{IELR}
+@cindex @acronym{LR}
+
+@itemize @bullet
+@item Language(s): all
+
+@item Purpose: Specifies 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 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.
+Thus, 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.
+
+@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
+The only advantage of canonical @acronym{LR} over @acronym{IELR} is that
+every canonical @acronym{LR} state encodes that state's exact set of
+syntactically acceptable tokens.
+The only difference in parsing behavior is then that the canonical
+@acronym{LR} parser can report a syntax error as soon as possible
+without performing any unnecessary reductions.
+@xref{Decl Summary,,lr.default_rules}, for further details.
+Even when canonical @acronym{LR} behavior is ultimately desired,
+@acronym{IELR}'s elimination of duplicate conflicts should still
+facilitate the development of a grammar.
+@end itemize
+
+@item Default Value: @code{"LALR"}
+@end itemize
@item namespace
@findex %define namespace
The parser namespace is @code{foo} and @code{yylex} is referenced as
@code{bar::lex}.
@end itemize
+@c namespace
+
+@item parse.assert
+@findex %define parse.assert
+
+@itemize
+@item Languages(s): C++
+
+@item Purpose: Issue runtime assertions to catch invalid uses.
+In C++, when variants are used, symbols must be constructed and
+destroyed properly. This option checks these constraints.
+
+@item Accepted Values: Boolean
+
+@item Default Value: @code{false}
@end itemize
+@c parse.assert
+
+@item parse.trace
+@findex %define parse.trace
+
+@itemize
+@item Languages(s): C, C++
+
+@item Purpose: Require parser instrumentation for tracing.
+In C/C++, define the macro @code{YYDEBUG} to 1 in the parser file if it
+is not already defined, so that the debugging facilities are compiled.
+@xref{Tracing, ,Tracing Your Parser}.
+@item Accepted Values: Boolean
+
+@item Default Value: @code{false}
+@end itemize
+@end table
+@c parse.trace
@end deffn
+@c %define
@deffn {Directive} %defines
Write a header file containing macro definitions for the token type
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
@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.
in the grammar file, you are likely to run into trouble.
@menu
-* 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.
+* 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
@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
receives one argument. For a syntax error, the string is normally
@w{@code{"syntax error"}}.
-@findex %error-verbose
-If you invoke the directive @code{%error-verbose} in the Bison
+@findex %define error-verbose
+If you invoke the directive @code{%define error-verbose} in the Bison
declarations section (@pxref{Bison Declarations, ,The Bison Declarations
Section}), then Bison provides a more verbose and specific error message
string instead of just plain @w{@code{"syntax error"}}.
* 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
@menu
* Why Precedence:: An example showing why precedence is needed.
-* Using Precedence:: How to specify precedence in Bison grammars.
+* Using Precedence:: How to specify precedence and associativity.
+* Precedence Only:: How to specify precedence only.
* Precedence Examples:: How these features are used in the previous example.
* How Precedence:: How they work.
@end menu
@node Using Precedence
@subsection Specifying Operator Precedence
@findex %left
-@findex %right
@findex %nonassoc
+@findex %precedence
+@findex %right
Bison allows you to specify these choices with the operator precedence
declarations @code{%left} and @code{%right}. Each such declaration
them right-associative. A third alternative is @code{%nonassoc}, which
declares that it is a syntax error to find the same operator twice ``in a
row''.
+The last alternative, @code{%precedence}, allows to define only
+precedence and no associativity at all. As a result, any
+associativity-related conflict that remains will be reported as an
+compile-time error. The directive @code{%nonassoc} creates run-time
+error: using the operator in a associative way is a syntax error. The
+directive @code{%precedence} creates compile-time errors: an operator
+@emph{can} be involved in an associativity-related conflict, contrary to
+what expected the grammar author.
The relative precedence of different operators is controlled by the
-order in which they are declared. The first @code{%left} or
-@code{%right} declaration in the file declares the operators whose
+order in which they are declared. The first precedence/associativity
+declaration in the file declares the operators whose
precedence is lowest, the next such declaration declares the operators
whose precedence is a little higher, and so on.
+@node Precedence Only
+@subsection Specifying Precedence Only
+@findex %precedence
+
+Since @acronym{POSIX} Yacc defines only @code{%left}, @code{%right}, and
+@code{%nonassoc}, which all defines precedence and associativity, little
+attention is paid to the fact that precedence cannot be defined without
+defining associativity. Yet, sometimes, when trying to solve a
+conflict, precedence suffices. In such a case, using @code{%left},
+@code{%right}, or @code{%nonassoc} might hide future (associativity
+related) conflicts that would remain hidden.
+
+The dangling @code{else} ambiguity (@pxref{Shift/Reduce, , Shift/Reduce
+Conflicts}) can be solved explictly. This shift/reduce conflicts occurs
+in the following situation, where the period denotes the current parsing
+state:
+
+@example
+if @var{e1} then if @var{e2} then @var{s1} . else @var{s2}
+@end example
+
+The conflict involves the reduction of the rule @samp{IF expr THEN
+stmt}, which precedence is by default that of its last token
+(@code{THEN}), and the shifting of the token @code{ELSE}. The usual
+disambiguation (attach the @code{else} to the closest @code{if}),
+shifting must be preferred, i.e., the precedence of @code{ELSE} must be
+higher than that of @code{THEN}. But neither is expected to be involved
+in an associativity related conflict, which can be specified as follows.
+
+@example
+%precedence THEN
+%precedence ELSE
+@end example
+
+The unary-minus is another typical example where associativity is
+usually over-specified, see @ref{Infix Calc, , Infix Notation
+Calculator: @code{calc}}. The @code{%left} directive is traditionaly
+used to declare the precedence of @code{NEG}, which is more than needed
+since it also defines its associativity. While this is harmless in the
+traditional example, who knows how @code{NEG} might be used in future
+evolutions of the grammar@dots{}
+
@node Precedence Examples
@subsection Precedence Examples
sign typically has a very high precedence as a unary operator, and a
somewhat lower precedence (lower than multiplication) as a binary operator.
-The Bison precedence declarations, @code{%left}, @code{%right} and
-@code{%nonassoc}, can only be used once for a given token; so a token has
+The Bison precedence declarations
+can only be used once for a given token; so a token has
only one precedence declared in this way. For context-dependent
precedence, you need to use an additional mechanism: the @code{%prec}
modifier for rules.
@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 semantical 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.
@command{bison} reports:
@example
-calc.y: warning: 1 nonterminal and 1 rule useless in grammar
+tmp.y: warning: 1 nonterminal useless in grammar
+tmp.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
'+' . 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.
@item the directive @samp{%debug}
@findex %debug
-Add the @code{%debug} directive (@pxref{Decl Summary, ,Bison
-Declaration Summary}). This is a Bison extension, which will prove
-useful when Bison will output parsers for languages that don't use a
-preprocessor. Unless @acronym{POSIX} and Yacc portability matter to
-you, this is
-the preferred solution.
+Add the @code{%debug} directive (@pxref{Decl Summary, ,Bison Declaration
+Summary}). This Bison extension is maintained for backward
+compatibility with previous versions of Bison.
+
+@item the variable @samp{parse.trace}
+@findex %define parse.trace
+Add the @samp{%define parse.trace} directive (@pxref{Decl Summary,
+,Bison Declaration Summary}), or pass the @option{-Dparse.trace} option
+(@pxref{Bison Options}). This is a Bison extension, which is especially
+useful for languages that don't use a preprocessor. Unless
+@acronym{POSIX} and Yacc portability matter to you, this is the
+preferred solution.
@end table
-We suggest that you always enable the debug option so that debugging is
+We suggest that you always enable the trace option so that debugging is
always possible.
The trace facility outputs messages with macro calls of the form
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
%@{
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
-@itemx --warnings
+@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 about mid-rule values that are set but not used within any of
-the actions of the parent rule. For example, Bison warns about unused
-@code{$2} in:
+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
-It also warns about mid-rule values that are used but not set. For
-example, Bison warns about unset @code{$$} in the mid-rule action in:
+Also warn about mid-rule values that are used but not set.
+For example, warn about unset @code{$$} in the mid-rule action in:
@example
exp: '1' @{ $1 = 1; @} '+' exp @{ $$ = $2 + $4; @};
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{b}} (where @var{n} is some positive integer).
+@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
+All the warnings.
@item none
-turn off all the warnings
+Turn off all the warnings.
@item error
-treat warnings as errors
+Treat warnings as errors.
@end table
A category can be turned off by prefixing its name with @samp{no-}. For
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}]
+Same as running @samp{%define @var{name} "@var{value}"} (@pxref{Decl
+Summary, ,%define}).
+
@item -L @var{language}
@itemx --language=@var{language}
Specify the programming language for the generated parser, as if
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}.
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}
@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 other output files' names are constructed from @var{file} as
described under the @samp{-v} and @samp{-d} options.
-@item -g
-Output a graphical representation of the @acronym{LALR}(1) grammar
+@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.
-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 as @samp{-g}. The only
-difference is that it has an optional argument which is the name of
-the output graph file.
-
-@item -x
-@itemx --xml=@var{file}
-Output an XML report of the @acronym{LALR}(1) automaton computed by Bison.
-@code{=@var{file}} is optional.
+@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.
@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
+@multitable {@option{--defines=@var{defines-file}}} {@option{-D @var{name}[=@var{value}]}} {@code{%nondeterministic-parser}}
+@headitem Long Option @tab Short Option @tab Bison Directive
@include cross-options.texi
@end multitable
@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++ deterministic 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}
@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
-%language "C++" /* -*- C++ -*- */
+%skeleton "lalr1.cc" /* -*- C++ -*- */
%require "@value{VERSION}"
%defines
%define parser_class_name "calcxx_parser"
@comment file: calc++-parser.yy
@example
-%debug
-%error-verbose
+%define parse.trace
+%define error-verbose
@end example
@noindent
| exp '-' exp @{ $$ = $1 - $3; @}
| exp '*' exp @{ $$ = $1 * $3; @}
| exp '/' exp @{ $$ = $1 / $3; @}
+ | '(' exp ')' @{ $$ = $2; @}
| "identifier" @{ $$ = driver.variables[*$1]; delete $1; @}
| "number" @{ $$ = $1; @};
%%
typedef yy::calcxx_parser::token token;
%@}
/* Convert ints to the actual type of tokens. */
-[-+*/] return yy::calcxx_parser::token_type (yytext[0]);
+[-+*/()] return yy::calcxx_parser::token_type (yytext[0]);
":=" return token::ASSIGN;
@{int@} @{
errno = 0;
int
main (int argc, char *argv[])
@{
+ int res = 0;
calcxx_driver driver;
for (++argv; argv[0]; ++argv)
if (*argv == std::string ("-p"))
driver.trace_scanning = true;
else if (!driver.parse (*argv))
std::cout << driver.result << std::endl;
+ else
+ res = 1;
+ return res;
@}
@end example
@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:: Java scanners, and pure parsers
-* Java Differences:: Differences between C/C++ and Java Grammars
+* 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"
-@c - initial action
(The current Java interface is experimental and may evolve.
More user feedback will help to stabilize it.)
-The Java parser skeletons are selected using a language directive,
-@samp{%language "Java"}, or the synonymous command-line option
-@option{--language=java}.
+The Java parser skeletons are selected using the @code{%language "Java"}
+directive or the @option{-L java}/@option{--language=java} option.
-When run, @command{bison} will create several entities whose name
-starts with @samp{YY}. Use the @samp{%name-prefix} directive to
-change the prefix, see @ref{Decl Summary}; classes can be placed
-in an arbitrary Java package using a @samp{%define package} section.
+@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.
-The parser class defines an inner class, @code{Location}, that is used
-for location tracking. If the parser is pure, it also defines an
-inner interface, @code{Lexer}; see @ref{Java Scanner Interface} for the
-meaning of pure parsers when the Java language is chosen. Other than
-these inner class/interface, and the members described in @ref{Java
-Parser Interface}, all the other members and fields are preceded
-with a @code{yy} prefix to avoid clashes with user code.
-
-No header file can be generated for Java parsers; you must not pass
-@option{-d}/@option{--defines} to @command{bison}, nor use the
-@samp{%defines} directive.
+You can create documentation for generated parsers using Javadoc.
-By default, the @samp{YYParser} class has package visibility. A
-declaration @samp{%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.
+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.
-Similarly, a declaration @samp{%define "abstract"} will make your
-class abstract.
+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 tracing is always compiled
+in. Thus the @samp{%define parse.trace} and @samp{%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 @samp{%define parse.trace}
+explicitly
+if needed. Also, in the future the
+@code{%token-table} directive might enable a public interface to
+access the token names and codes.
+
+Getting a ``code too large'' error from the Java compiler means the code
+hit the 64KB bytecode per method limination of the Java class file.
+Try reducing the amount of code in actions and static initializers;
+otherwise, report a bug so that the parser skeleton will be improved.
-You can create documentation for generated parsers using Javadoc.
@node Java Semantic Values
@subsection Java Semantic Values
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 @samp{%define} directive.
-For example, after the following declaration:
+superclass of all the semantic values using the @code{%define stype}
+directive. For example, after the following declaration:
@example
-%define "stype" "ASTNode"
+%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
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, may also be renamed using @code{%define
-"location_type" "@var{class-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}"}.
+with @code{%define position_type "@var{class-name}"}. This class must
+be supplied by the user.
-@deftypemethod {Location} {Position} begin
-@deftypemethodx {Location} {Position} end
+@deftypeivar {Location} {Position} begin
+@deftypeivarx {Location} {Position} end
The first, inclusive, position of the range, and the first beyond.
-@end deftypemethod
+@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} {void} toString ()
+@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.
@c debug_stream.
@c - Reporting errors
-The output file defines the parser class in the package optionally
-indicated in the @code{%define package} section. The class name defaults
-to @code{YYParser}. The @code{YY} prefix may be changed using
-@samp{%name-prefix}; alternatively, you can use @samp{%define
-"parser_class_name" "@var{name}"} to give a custom name to the class.
-The interface of this class is detailed below. It can be extended using
-the @code{%parse-param} directive; each occurrence of the directive will
-add a field to the parser class, and an argument to its constructor.
+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.
+A single @code{%define annotations "@var{annotations}"} directive can
+be used to add any number of annotations to the parser class.
+
+The Java package name of the parser class can be specified using the
+@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.
-@deftypemethod {YYParser} {} YYParser (@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.
-@end deftypemethod
+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.
+
+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.
+
+@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.
+
+Use @code{%code init} for code added to the start of the constructor
+body. This is especially useful to initialize superclasses. Use
+@code{%define init_throws} to specify any uncatch exceptions.
+@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.
+
+Use @code{%code init} for code added to the start of the constructor
+body. This is especially useful to initialize superclasses. Use
+@code{%define init_throws} to specify any uncatch exceptions.
+@end deftypeop
@deftypemethod {YYParser} {boolean} parse ()
Run the syntactic analysis, and return @code{true} on success,
@code{false} otherwise.
@end deftypemethod
+@deftypemethod {YYParser} {boolean} getErrorVerbose ()
+@deftypemethodx {YYParser} {void} setErrorVerbose (boolean @var{verbose})
+Get or set the option to produce verbose error messages. These are only
+available with the @code{%define error-verbose} directive, which also turn on
+verbose error messages.
+@end deftypemethod
+
+@deftypemethod {YYParser} {void} yyerror (String @var{msg})
+@deftypemethodx {YYParser} {void} yyerror (Position @var{pos}, String @var{msg})
+@deftypemethodx {YYParser} {void} yyerror (Location @var{loc}, String @var{msg})
+Print an error message using the @code{yyerror} method of the scanner
+instance in use. The @code{Location} and @code{Position} parameters are
+available only if location tracking is active.
+@end deftypemethod
+
@deftypemethod {YYParser} {boolean} recovering ()
During the syntactic analysis, return @code{true} if recovering
-from a syntax error. @xref{Error Recovery}.
+from a syntax error.
+@xref{Error Recovery}.
@end deftypemethod
@deftypemethod {YYParser} {java.io.PrintStream} getDebugStream ()
or nonzero, full tracing.
@end deftypemethod
-@deftypemethod {YYParser} {void} error (Location @var{l}, String @var{m})
-The definition for this member function must be supplied by the user
-in the same way as the scanner interface (@pxref{Java Scanner
-Interface}); the parser uses it to report a parser error occurring at
-@var{l}, described by @var{m}.
-@end deftypemethod
+@deftypecv {Constant} {YYParser} {String} {bisonVersion}
+@deftypecvx {Constant} {YYParser} {String} {bisonSkeleton}
+Identify the Bison version and skeleton used to generate this parser.
+@end deftypecv
@node Java Scanner Interface
@c - %lex-param
@c - Lexer interface
-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}
-directive does not do anything when used in Java.
-@c FIXME: But a bit farther it is stated that
-@c If @code{%pure-parser} is not specified, the lexer interface
-@c resides in the same class (@code{YYParser}) as the Bison-generated
-@c parser. The fields and methods that are provided to
-@c this end are as follows.
-
-The scanner always resides in a separate class than the parser.
-Still, there are two possible ways to interface a Bison-generated Java
-parser with a scanner, that is, the scanner may reside in a separate file
-than the Bison grammar, or in the same file. The interface
-to the scanner is similar in the two cases.
-
-In the first case, where the scanner in the same file as the grammar, the
-scanner code has to be 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.
+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. This interface also
+contain constants for all user-defined token names and the predefined
+@code{EOF} token.
+
+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}).
In both cases, the scanner has to implement the following methods.
-@deftypemethod {Lexer} {void} yyerror (Location @var{l}, String @var{m})
-As explained in @pxref{Java Parser Interface}, 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
-@samp{%define "location_type" "@var{class-name}".}
+@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 (@var{type1} @var{arg1}, ...)
+@deftypemethod {Lexer} {int} yylex ()
Return the next token. Its type is the return value, its semantic
value and location are saved and returned by the ther methods in the
-interface. Invocations of @samp{%lex-param @{@var{type1}
-@var{arg1}@}} yield additional arguments.
+interface.
+
+Use @code{%define lex_throws} to specify any uncaught exceptions.
+Default is @code{java.io.IOException}.
@end deftypemethod
@deftypemethod {Lexer} {Position} getStartPos ()
@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 @samp{%define "position_type"
+The return type can be changed using @code{%define position_type
"@var{class-name}".}
@end deftypemethod
@deftypemethod {Lexer} {Object} getLVal ()
Return the semantical value of the last token that yylex returned.
-The return type can be changed using @samp{%define "stype"
+The return type can be changed using @code{%define stype
"@var{class-name}".}
@end deftypemethod
-The lexer interface resides in the same class (@code{YYParser}) as the
-Bison-generated parser.
-The fields and methods that are provided to this end are as follows.
+@node Java Action Features
+@subsection Special Features for Use in Java Actions
-@deftypemethod {YYParser} {void} error (Location @var{l}, String @var{m})
-As already explained (@pxref{Java Parser Interface}), this method is defined
-by the user to emit an error message. The first parameter is not used
-unless location tracking is active. Its type can be changed using
-@samp{%define "location_type" "@var{class-name}".}
-@end deftypemethod
+The following special constructs can be uses in Java actions.
+Other analogous C action features are currently unavailable for Java.
-@deftypemethod {YYParser} {int} yylex (@var{type1} @var{arg1}, ...)
-Return the next token. Its type is the return value, its semantic
-value and location are saved into @code{yylval}, @code{yystartpos},
-@code{yyendpos}. Invocations of @samp{%lex-param @{@var{type1}
-@var{arg1}@}} yield additional arguments.
-@end deftypemethod
+Use @code{%define throws} to specify any uncaught exceptions from parser
+actions, and initial actions specified by @code{%initial-action}.
-@deftypecv {Field} {YYParser} Position yystartpos
-@deftypecvx {Field} {YYParser} Position yyendpos
-Contain respectively the first position of the last token that yylex
-returned, and the first position beyond it. These methods are not
-needed unless location tracking is active.
+@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
-The field's type can be changed using @samp{%define "position_type"
-"@var{class-name}".}
-@end deftypecv
+@defvar $<@var{typealt}>@var{n}
+Like @code{$@var{n}} but specifies a alternative type @var{typealt}.
+@xref{Java Semantic Values}.
+@end defvar
-@deftypecv {Field} {YYParser} Object yylval
-Return respectively the first position of the last token that yylex
-returned, and the first position beyond it.
+@defvar $$
+The semantic value for the grouping made by the current rule. As a
+value, this is in the base type (@code{Object} or as specified by
+@code{%define stype}) as in not cast to the declared subtype because
+casts are not allowed on the left-hand side of Java assignments.
+Use an explicit Java cast if the correct subtype is needed.
+@xref{Java Semantic Values}.
+@end defvar
+
+@defvar $<@var{typealt}>$
+Same as @code{$$} since Java always allow assigning to the base type.
+Perhaps we should use this and @code{$<>$} for the value and @code{$$}
+for setting the value but there is currently no easy way to distinguish
+these constructs.
+@xref{Java Semantic Values}.
+@end defvar
+
+@defvar @@@var{n}
+The location information of the @var{n}th component of the current rule.
+This may not be assigned to.
+@xref{Java Location Values}.
+@end defvar
+
+@defvar @@$
+The location information of the grouping made by the current rule.
+@xref{Java Location Values}.
+@end defvar
+
+@deffn {Statement} {return YYABORT;}
+Return immediately from the parser, indicating failure.
+@xref{Java Parser Interface}.
+@end deffn
+
+@deffn {Statement} {return YYACCEPT;}
+Return immediately from the parser, indicating success.
+@xref{Java Parser Interface}.
+@end deffn
+
+@deffn {Statement} {return YYERROR;}
+Start error recovery without printing an error message.
+@xref{Error Recovery}.
+@end deffn
+
+@deffn {Statement} {return YYFAIL;}
+Print an error message and start error recovery.
+@xref{Error Recovery}.
+@end deffn
+
+@deftypefn {Function} {boolean} recovering ()
+Return whether error recovery is being done. In this state, the parser
+reads token until it reaches a known state, and then restarts normal
+operation.
+@xref{Error Recovery}.
+@end deftypefn
+
+@deftypefn {Function} {void} yyerror (String @var{msg})
+@deftypefnx {Function} {void} yyerror (Position @var{loc}, String @var{msg})
+@deftypefnx {Function} {void} yyerror (Location @var{loc}, String @var{msg})
+Print an error message using the @code{yyerror} method of the scanner
+instance in use. The @code{Location} and @code{Position} parameters are
+available only if location tracking is active.
+@end deftypefn
-The field's type can be changed using @samp{%define "stype"
-"@var{class-name}".}
-@end deftypecv
@node Java Differences
@subsection Differences between C/C++ and Java Grammars
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 than @code{yyparse} in order to have an intuitive syntax that
corresponds to these C macros.}.
+@item
+Java lacks unions, so @code{%union} has no effect. Instead, semantic
+values have a common base type: @code{Object} or as specified by
+@code{%define stype}. Angle backets on @code{%token}, @code{type},
+@code{$@var{n}} and @code{$$} specify subtypes rather than fields of
+an union. The type of @code{$$}, even with angle brackets, is the base
+type since Java casts are not allow on the left-hand side of assignments.
+Also, @code{$@var{n}} and @code{@@@var{n}} are not allowed on the
+left-hand side of assignments. See @pxref{Java Semantic Values} and
+@pxref{Java Action Features}.
+
@item
The prolog declarations have a different meaning than in C/C++ code.
@table @asis
@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.
+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 init} @{ @var{code} @dots{} @}
+Code inserted at the beginning of the parser constructor body.
+@xref{Java Parser Interface}.
+@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 imports} 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 annotations} "@var{annotations}"
+The Java annotations for the parser class. Default is none.
+@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 init_throws} "@var{exceptions}"
+The exceptions thrown by @code{%code init} from the parser class
+constructor. Default is none.
+@xref{Java Parser 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
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} %error-verbose
-Bison declaration to request verbose, specific error message strings
-when @code{yyerror} is called.
+An obsolete directive standing for @samp{%define error-verbose}.
@end deffn
@deffn {Directive} %file-prefix "@var{prefix}"
@end deffn
@deffn {Directive} %left
-Bison declaration to assign left associativity to token(s).
+Bison declaration to assign precedence and left associativity to token(s).
@xref{Precedence Decl, ,Operator Precedence}.
@end deffn
@end deffn
@deffn {Directive} %nonassoc
-Bison declaration to assign nonassociativity to token(s).
+Bison declaration to assign precedence and nonassociativity to token(s).
@xref{Precedence Decl, ,Operator Precedence}.
@end deffn
@xref{Contextual Precedence, ,Context-Dependent Precedence}.
@end deffn
+@deffn {Directive} %precedence
+Bison declaration to assign precedence to token(s), but no associativity
+@xref{Precedence Decl, ,Operator Precedence}.
+@end deffn
+
@deffn {Directive} %pure-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} %right
-Bison declaration to assign right associativity to token(s).
+Bison declaration to assign precedence and right associativity to token(s).
@xref{Precedence Decl, ,Operator Precedence}.
@end deffn
@deffn {Function} yyerror
User-supplied function to be called by @code{yyparse} on error.
-@xref{Error Reporting, ,The Error
-Reporting Function @code{yyerror}}.
+@xref{Error Reporting, ,The Error Reporting Function @code{yyerror}}.
@end deffn
@deffn {Macro} YYERROR_VERBOSE
-An obsolete macro that you define with @code{#define} in the prologue
-to request verbose, specific error message strings
-when @code{yyerror} is called. It doesn't matter what definition you
-use for @code{YYERROR_VERBOSE}, just whether you define it. Using
-@code{%error-verbose} is preferred.
+An obsolete macro used in the @file{yacc.c} skeleton, that you define
+with @code{#define} in the prologue to request verbose, specific error
+message strings when @code{yyerror} is called. It doesn't matter what
+definition you use for @code{YYERROR_VERBOSE}, just whether you define
+it. Using @code{%define error-verbose} is preferred (@pxref{Error
+Reporting, ,The Error Reporting Function @code{yyerror}}).
@end deffn
@deffn {Macro} YYINITDEPTH
@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_rules}.
+
@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 Rule
+The rule by which a parser should reduce if the current parser state
+contains no other action for the lookahead token.
+In permitted parser states, Bison declares the rule with the largest
+lookahead set to be the default rule and removes that lookahead set.
+@xref{Decl Summary,,lr.default_rules}.
+
@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 @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
@c LocalWords: akim fn cp syncodeindex vr tp synindex dircategory direntry
@c LocalWords: ifset vskip pt filll insertcopying sp ISBN Etienne Suvasa
@c LocalWords: ifnottex yyparse detailmenu GLR RPN Calc var Decls Rpcalc
-@c LocalWords: rpcalc Lexer Gen Comp Expr ltcalc mfcalc Decl Symtab yylex
+@c LocalWords: rpcalc Lexer Expr ltcalc mfcalc yylex
@c LocalWords: yyerror pxref LR yylval cindex dfn LALR samp gpl BNF xref
@c LocalWords: const int paren ifnotinfo AC noindent emph expr stmt findex
@c LocalWords: glr YYSTYPE TYPENAME prog dprec printf decl init stmtMerge
@c LocalWords: infile ypp yxx outfile itemx tex leaderfill
@c LocalWords: hbox hss hfill tt ly yyin fopen fclose ofirst gcc ll
@c LocalWords: nbar yytext fst snd osplit ntwo strdup AST
-@c LocalWords: YYSTACK DVI fdl printindex
+@c LocalWords: YYSTACK DVI fdl printindex IELR
projects / bison.git / blobdiff