@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:: 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
+* 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
use Bison or Yacc, we suggest you start by reading this chapter carefully.
@menu
-* Language and Grammar:: Languages and context-free grammars,
- as mathematical ideas.
-* Grammar in Bison:: How we represent grammars for Bison's sake.
-* Semantic Values:: Each token or syntactic grouping can have
- a semantic value (the value of an integer,
- the name of an identifier, etc.).
-* Semantic Actions:: Each rule can have an action containing C code.
-* GLR Parsers:: Writing parsers for general context-free languages.
-* Locations Overview:: Tracking Locations.
-* Bison Parser:: What are Bison's input and output,
- how is the output used?
-* Stages:: Stages in writing and running Bison grammars.
-* Grammar Layout:: Overall structure of a Bison grammar file.
+* Language and Grammar:: Languages and context-free grammars,
+ as mathematical ideas.
+* Grammar in Bison:: How we represent grammars for Bison's sake.
+* Semantic Values:: Each token or syntactic grouping can have
+ a semantic value (the value of an integer,
+ the name of an identifier, etc.).
+* Semantic Actions:: Each rule can have an action containing C code.
+* GLR Parsers:: Writing parsers for general context-free languages.
+* Locations Overview:: Tracking Locations.
+* Bison Parser:: What are Bison's input and output,
+ how is the output used?
+* Stages:: Stages in writing and running Bison grammars.
+* Grammar Layout:: Overall structure of a Bison grammar file.
@end menu
@node Language and Grammar
merged result.
@menu
-* Simple GLR Parsers:: Using @acronym{GLR} parsers on unambiguous grammars.
-* Merging GLR Parses:: Using @acronym{GLR} parsers to resolve ambiguities.
-* GLR Semantic Actions:: Deferred semantic actions have special concerns.
-* Compiler Requirements:: @acronym{GLR} parsers require a modern C compiler.
+* Simple GLR Parsers:: Using @acronym{GLR} parsers on unambiguous grammars.
+* Merging GLR Parses:: Using @acronym{GLR} parsers to resolve ambiguities.
+* GLR Semantic Actions:: Deferred semantic actions have special concerns.
+* Compiler Requirements:: @acronym{GLR} parsers require a modern C compiler.
@end menu
@node Simple GLR Parsers
source file to try them.
@menu
-* RPN Calc:: Reverse polish notation calculator;
- a first example with no operator precedence.
-* Infix Calc:: Infix (algebraic) notation calculator.
- Operator precedence is introduced.
+* RPN Calc:: Reverse polish notation calculator;
+ a first example with no operator precedence.
+* Infix Calc:: Infix (algebraic) notation calculator.
+ Operator precedence is introduced.
* Simple Error Recovery:: Continuing after syntax errors.
* Location Tracking Calc:: Demonstrating the use of @@@var{n} and @@$.
-* Multi-function Calc:: Calculator with memory and trig functions.
- It uses multiple data-types for semantic values.
-* Exercises:: Ideas for improving the multi-function calculator.
+* Multi-function Calc:: Calculator with memory and trig functions.
+ It uses multiple data-types for semantic values.
+* Exercises:: Ideas for improving the multi-function calculator.
@end menu
@node RPN Calc
@samp{.y} extension is a convention used for Bison input files.
@menu
-* Decls: Rpcalc Decls. Prologue (declarations) for rpcalc.
-* Rules: Rpcalc Rules. Grammar Rules for rpcalc, with explanation.
-* Lexer: Rpcalc Lexer. The lexical analyzer.
-* Main: Rpcalc Main. The controlling function.
-* Error: Rpcalc Error. The error reporting function.
-* Gen: Rpcalc Gen. Running Bison on the grammar file.
-* Comp: Rpcalc Compile. Run the C compiler on the output code.
+* Rpcalc Declarations:: Prologue (declarations) for rpcalc.
+* Rpcalc Rules:: Grammar Rules for rpcalc, with explanation.
+* Rpcalc Lexer:: The lexical analyzer.
+* Rpcalc Main:: The controlling function.
+* Rpcalc Error:: The error reporting function.
+* Rpcalc Generate:: Running Bison on the grammar file.
+* Rpcalc Compile:: Run the C compiler on the output code.
@end menu
-@node Rpcalc Decls
+@node Rpcalc Declarations
@subsection Declarations for @code{rpcalc}
Here are the C and Bison declarations for the reverse polish notation
The semantic value of the token (if it has one) is stored into the
global variable @code{yylval}, which is where the Bison parser will look
for it. (The C data type of @code{yylval} is @code{YYSTYPE}, which was
-defined at the beginning of the grammar; @pxref{Rpcalc Decls,
+defined at the beginning of the grammar; @pxref{Rpcalc Declarations,
,Declarations for @code{rpcalc}}.)
A token type code of zero is returned if the end-of-input is encountered.
cause the calculator program to exit. This is not clean behavior for a
real calculator, but it is adequate for the first example.
-@node Rpcalc Gen
+@node Rpcalc Generate
@subsection Running Bison to Make the Parser
@cindex running Bison (introduction)
%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
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
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
* 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.
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
%@{
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
The other output files' names are constructed from @var{file} as
described under the @samp{-v} and @samp{-d} options.
-@item -g[@var{file}]
+@item -g [@var{file}]
@itemx --graph[=@var{file}]
Output a graphical representation of the @acronym{LALR}(1) grammar
automaton computed by Bison, in @uref{http://www.graphviz.org/, Graphviz}
If omitted and the grammar file is @file{foo.y}, the output file will be
@file{foo.dot}.
-@item -x[@var{file}]
+@item -x [@var{file}]
@itemx --xml[=@var{file}]
Output an XML report of the @acronym{LALR}(1) automaton computed by Bison.
@code{@var{file}} is optional.
@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
| 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:: 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
+* 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
@code{%defines} directive or the @option{-d}/@option{--defines} options.
@c FIXME: Possible code change.
-Currently, support for debugging and verbose errors are always compiled
+Currently, support for debugging is always compiled
in. Thus the @code{%debug} and @code{%token-table} directives and the
@option{-t}/@option{--debug} and @option{-k}/@option{--token-table}
options have no effect. This may change in the future to eliminate
-unused code in the generated parser, so use @code{%debug} and
-@code{%verbose-error} explicitly if needed. Also, in the future the
+unused code in the generated parser, so use @code{%debug} 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.
+
+
@node Java Semantic Values
@subsection Java Semantic Values
@c - No %union, specify type in %type/%token.
@end deftypeivar
@deftypeop {Constructor} {Location} {} Location (Position @var{loc})
-Create a @code{Location} denoting an empty range located at a given point.
+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})
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
below, all the other members and fields are preceded with a @code{yy} or
@code{YY} prefix to avoid clashes with user code.
-@c FIXME: The following constants and variables are still undocumented:
-@c @code{bisonVersion}, @code{bisonSkeleton} and @code{errorVerbose}.
-
The parser class can be extended using the @code{%parse-param}
directive. Each occurrence of the directive will add a @code{protected
final} field to the parser class, and an argument to its constructor,
which initialize them automatically.
-Token names defined by @code{%token} and the predefined @code{EOF} token
-name are added as constant fields to the parser class.
-
@deftypeop {Constructor} {YYParser} {} YYParser (@var{lex_param}, @dots{}, @var{parse_param}, @dots{})
Build a new parser object with embedded @code{%code lexer}. There are
no parameters, unless @code{%parse-param}s and/or @code{%lex-param}s are
used.
+
+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{})
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 ()
@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{%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.
or nonzero, full tracing.
@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
@subsection Java Scanner Interface
There are two possible ways to interface a Bison-generated Java parser
with a scanner: the scanner may be defined by @code{%code lexer}, or
defined elsewhere. In either case, the scanner has to implement the
-@code{Lexer} inner interface of the parser class.
+@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
@end deffn
@deffn {Statement} {return YYERROR;}
-Start error recovery without printing an error message.
+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.
+Print an error message and start error recovery.
@xref{Error Recovery}.
@end deffn
@xref{Error Recovery}.
@end deftypefn
-@deftypefn {Function} {protected void} yyerror (String msg)
-@deftypefnx {Function} {protected void} yyerror (Position pos, String msg)
-@deftypefnx {Function} {protected void} yyerror (Location loc, String msg)
+@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.
+instance in use. The @code{Location} and @code{Position} parameters are
+available only if location tracking is active.
@end deftypefn
@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{} %@}
-Not supported. Use @code{%code import} instead.
+Not supported. Use @code{%code imports} instead.
@xref{Java Differences}.
@end deffn
@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}.
@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}.
@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
@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
projects / bison.git / blobdiff