@c the smallbook format.
@c @smallbook
-@c Set following if you have the new `shorttitlepage' command
-@c @clear shorttitlepage-enabled
-@c @set shorttitlepage-enabled
-
@c Set following if you want to document %default-prec and %no-default-prec.
@c This feature is experimental and may change in future Bison versions.
@c @set defaultprec
-@c ISPELL CHECK: done, 14 Jan 1993 --bob
-
-@c Check COPYRIGHT dates. should be updated in the titlepage, ifinfo
-@c titlepage; should NOT be changed in the GPL. --mew
-
-@c FIXME: I don't understand this `iftex'. Obsolete? --akim.
-@iftex
+@ifnotinfo
@syncodeindex fn cp
@syncodeindex vr cp
@syncodeindex tp cp
-@end iftex
+@end ifnotinfo
@ifinfo
@synindex fn cp
@synindex vr cp
@value{UPDATED}), the @acronym{GNU} parser generator.
Copyright @copyright{} 1988, 1989, 1990, 1991, 1992, 1993, 1995, 1998,
-1999, 2000, 2001, 2002, 2003, 2004, 2005 Free Software Foundation, Inc.
+1999, 2000, 2001, 2002, 2003, 2004, 2005, 2006 Free Software Foundation, Inc.
@quotation
Permission is granted to copy, distribute and/or modify this document
* bison: (bison). @acronym{GNU} parser generator (Yacc replacement).
@end direntry
-@ifset shorttitlepage-enabled
-@shorttitlepage Bison
-@end ifset
@titlepage
@title Bison
@subtitle The Yacc-compatible Parser Generator
Writing @acronym{GLR} Parsers
-* Simple GLR Parsers:: Using @acronym{GLR} parsers on unambiguous grammars
-* Merging GLR Parses:: Using @acronym{GLR} parsers to resolve ambiguities
-* Compiler Requirements:: @acronym{GLR} parsers require a modern C compiler
+* Simple GLR Parsers:: Using @acronym{GLR} parsers on unambiguous grammars.
+* Merging GLR Parses:: Using @acronym{GLR} parsers to resolve ambiguities.
+* GLR Semantic Actions:: Deferred semantic actions have special concerns.
+* Compiler Requirements:: @acronym{GLR} parsers require a modern C compiler.
Examples
* 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
Copying This Manual
@unnumbered Introduction
@cindex introduction
-@dfn{Bison} is a general-purpose parser generator that converts a
-grammar description for an @acronym{LALR}(1) context-free grammar into a C
-program to parse that grammar. Once you are proficient with Bison,
-you may use it to develop a wide range of language parsers, from those
+@dfn{Bison} is a general-purpose parser generator that converts a grammar
+description for an @acronym{LALR}(1) or @acronym{GLR} context-free grammar
+into a C or C++ program to parse that grammar. Once you are proficient with
+Bison, you can use it to develop a wide range of language parsers, from those
used in simple desk calculators to complex programming languages.
Bison is upward compatible with Yacc: all properly-written Yacc grammars
ought to work with Bison with no change. Anyone familiar with Yacc
should be able to use Bison with little trouble. You need to be fluent in
-C programming in order to use Bison or to understand this manual.
+C or C++ programming in order to use Bison or to understand this manual.
We begin with tutorial chapters that explain the basic concepts of using
Bison and show three explained examples, each building on the last. If you
square (int x) /* @r{identifier, open-paren, keyword `int',}
@r{identifier, close-paren} */
@{ /* @r{open-brace} */
- return x * x; /* @r{keyword `return', identifier, asterisk,
- identifier, semicolon} */
+ return x * x; /* @r{keyword `return', identifier, asterisk,}
+ @r{identifier, semicolon} */
@} /* @r{close-brace} */
@end example
@end ifinfo
merged result.
@menu
-* Simple GLR Parsers:: Using @acronym{GLR} parsers on unambiguous grammars
-* Merging GLR Parses:: Using @acronym{GLR} parsers to resolve ambiguities
-* Compiler Requirements:: @acronym{GLR} parsers require a modern C compiler
+* Simple GLR Parsers:: Using @acronym{GLR} parsers on unambiguous grammars.
+* Merging GLR Parses:: Using @acronym{GLR} parsers to resolve ambiguities.
+* GLR Semantic Actions:: Deferred semantic actions have special concerns.
+* Compiler Requirements:: @acronym{GLR} parsers require a modern C compiler.
@end menu
@node Simple GLR Parsers
and the parser will report an error during any parse that results in
the offending merge.
+@node GLR Semantic Actions
+@subsection GLR Semantic Actions
+
+@cindex deferred semantic actions
+By definition, a deferred semantic action is not performed at the same time as
+the associated reduction.
+This raises caveats for several Bison features you might use in a semantic
+action in a @acronym{GLR} parser.
+
+@vindex yychar
+@cindex @acronym{GLR} parsers and @code{yychar}
+@vindex yylval
+@cindex @acronym{GLR} parsers and @code{yylval}
+@vindex yylloc
+@cindex @acronym{GLR} parsers and @code{yylloc}
+In any semantic action, you can examine @code{yychar} to determine the type of
+the look-ahead token present at the time of the associated reduction.
+After checking that @code{yychar} is not set to @code{YYEMPTY} or @code{YYEOF},
+you can then examine @code{yylval} and @code{yylloc} to determine the
+look-ahead token's semantic value and location, if any.
+In a nondeferred semantic action, you can also modify any of these variables to
+influence syntax analysis.
+@xref{Look-Ahead, ,Look-Ahead Tokens}.
+
+@findex yyclearin
+@cindex @acronym{GLR} parsers and @code{yyclearin}
+In a deferred semantic action, it's too late to influence syntax analysis.
+In this case, @code{yychar}, @code{yylval}, and @code{yylloc} are set to
+shallow copies of the values they had at the time of the associated reduction.
+For this reason alone, modifying them is dangerous.
+Moreover, the result of modifying them is undefined and subject to change with
+future versions of Bison.
+For example, if a semantic action might be deferred, you should never write it
+to invoke @code{yyclearin} (@pxref{Action Features}) or to attempt to free
+memory referenced by @code{yylval}.
+
+@findex YYERROR
+@cindex @acronym{GLR} parsers and @code{YYERROR}
+Another Bison feature requiring special consideration is @code{YYERROR}
+(@pxref{Action Features}), which you can invoke in a semantic action to
+initiate error recovery.
+During deterministic @acronym{GLR} operation, the effect of @code{YYERROR} is
+the same as its effect in an @acronym{LALR}(1) parser.
+In a deferred semantic action, its effect is undefined.
+@c The effect is probably a syntax error at the split point.
+
+Also, see @ref{Location Default Action, ,Default Action for Locations}, which
+describes a special usage of @code{YYLLOC_DEFAULT} in @acronym{GLR} parsers.
+
@node Compiler Requirements
@subsection Considerations when Compiling @acronym{GLR} Parsers
@cindex @code{inline}
desk-top calculator.
These examples are simple, but Bison grammars for real programming
-languages are written the same way.
-@ifinfo
-You can copy these examples out of the Info file and into a source file
-to try them.
-@end ifinfo
+languages are written the same way. You can copy these examples into a
+source file to try them.
@menu
* RPN Calc:: Reverse polish notation calculator;
The groupings of the rpcalc ``language'' defined here are the expression
(given the name @code{exp}), the line of input (@code{line}), and the
complete input transcript (@code{input}). Each of these nonterminal
-symbols has several alternate rules, joined by the @samp{|} punctuator
+symbols has several alternate rules, joined by the vertical bar @samp{|}
which is read as ``or''. The following sections explain what these rules
mean.
don't need any C declarations, you may omit the @samp{%@{} and
@samp{%@}} delimiters that bracket this section.
+The @var{Prologue} section is terminated by the the first occurrence
+of @samp{%@}} that is outside a comment, a string literal, or a
+character constant.
+
You may have more than one @var{Prologue} section, intermixed with the
@var{Bison declarations}. This allows you to have C and Bison
declarations that refer to each other. For example, the @code{%union}
@end example
@noindent
+@cindex braced code
+This is an example of @dfn{braced code}, that is, C code surrounded by
+braces, much like a compound statement in C@. Braced code can contain
+any sequence of C tokens, so long as its braces are balanced. Bison
+does not check the braced code for correctness directly; it merely
+copies the code to the output file, where the C compiler can check it.
+
+Within braced code, the balanced-brace count is not affected by braces
+within comments, string literals, or character constants, but it is
+affected by the C digraphs @samp{<%} and @samp{%>} that represent
+braces. At the top level braced code must be terminated by @samp{@}}
+and not by a digraph. Bison does not look for trigraphs, so if braced
+code uses trigraphs you should ensure that they do not affect the
+nesting of braces or the boundaries of comments, string literals, or
+character constants.
+
Usually there is only one action and it follows the components.
@xref{Actions}.
Multiple rules for the same @var{result} can be written separately or can
be joined with the vertical-bar character @samp{|} as follows:
-@ifinfo
-@example
-@var{result}: @var{rule1-components}@dots{}
- | @var{rule2-components}@dots{}
- @dots{}
- ;
-@end example
-@end ifinfo
-@iftex
@example
@group
@var{result}: @var{rule1-components}@dots{}
;
@end group
@end example
-@end iftex
@noindent
They are still considered distinct rules even when joined in this way.
is to compute a semantic value for the grouping built by the rule from the
semantic values associated with tokens or smaller groupings.
-An action consists of C statements surrounded by braces, much like a
-compound statement in C@. An action can contain any sequence of C
-statements. Bison does not look for trigraphs, though, so if your C
-code uses trigraphs you should ensure that they do not affect the
-nesting of braces or the boundaries of comments, strings, or character
-literals.
-
-An action can be placed at any position in the rule;
+An action consists of braced code containing C statements, and can be
+placed at any position in the rule;
it is executed at that position. Most rules have just one action at the
end of the rule, following all the components. Actions in the middle of
a rule are tricky and used only for special purposes (@pxref{Mid-Rule
always refers to the @code{expr} which precedes @code{bar} in the
definition of @code{foo}.
+@vindex yylval
+It is also possible to access the semantic value of the look-ahead token, if
+any, from a semantic action.
+This semantic value is stored in @code{yylval}.
+@xref{Action Features, ,Special Features for Use in Actions}.
+
@node Action Types
@subsection Data Types of Values in Actions
@cindex action data types
removes the temporary @code{let}-variable from the list so that it won't
appear to exist while the rest of the program is parsed.
+@findex %destructor
+@cindex discarded symbols, mid-rule actions
+@cindex error recovery, mid-rule actions
+In the above example, if the parser initiates error recovery (@pxref{Error
+Recovery}) while parsing the tokens in the embedded statement @code{stmt},
+it might discard the previous semantic context @code{$<context>5} without
+restoring it.
+Thus, @code{$<context>5} needs a destructor (@pxref{Destructor Decl, , Freeing
+Discarded Symbols}).
+However, Bison currently provides no means to declare a destructor for a
+mid-rule action's semantic value.
+
+One solution is to bury the mid-rule action inside a nonterminal symbol and to
+declare a destructor for that symbol:
+
+@example
+@group
+%type <context> let
+%destructor @{ pop_context ($$); @} let
+
+%%
+
+stmt: let stmt
+ @{ $$ = $2;
+ pop_context ($1); @}
+ ;
+
+let: LET '(' var ')'
+ @{ $$ = push_context ();
+ declare_variable ($3); @}
+ ;
+
+@end group
+@end example
+
+@noindent
+Note that the action is now at the end of its rule.
+Any mid-rule action can be converted to an end-of-rule action in this way, and
+this is what Bison actually does to implement mid-rule actions.
+
Taking action before a rule is completely recognized often leads to
conflicts since the parser must commit to a parse in order to execute the
action. For example, the following two rules, without mid-rule actions,
@noindent
Now Bison can execute the action in the rule for @code{subroutine} without
-deciding which rule for @code{compound} it will eventually use. Note that
-the action is now at the end of its rule. Any mid-rule action can be
-converted to an end-of-rule action in this way, and this is what Bison
-actually does to implement mid-rule actions.
+deciding which rule for @code{compound} it will eventually use.
@node Locations
@section Tracking Locations
@end group
@end example
+@vindex yylloc
+It is also possible to access the location of the look-ahead token, if any,
+from a semantic action.
+This location is stored in @code{yylloc}.
+@xref{Action Features, ,Special Features for Use in Actions}.
+
@node Location Default Action
@subsection Default Action for Locations
@vindex YYLLOC_DEFAULT
+@cindex @acronym{GLR} parsers and @code{YYLLOC_DEFAULT}
Actually, actions are not the best place to compute locations. Since
locations are much more general than semantic values, there is room in
rule. The @code{YYLLOC_DEFAULT} macro is invoked each time a rule is
matched, before the associated action is run. It is also invoked
while processing a syntax error, to compute the error's location.
+Before reporting an unresolvable syntactic ambiguity, a @acronym{GLR}
+parser invokes @code{YYLLOC_DEFAULT} recursively to compute the location
+of that ambiguity.
Most of the time, this macro is general enough to suppress location
dedicated code from semantic actions.
the location of the grouping (the result of the computation). When a
rule is matched, the second parameter identifies locations of
all right hand side elements of the rule being matched, and the third
-parameter is the size of the rule's right hand side. When processing
-a syntax error, the second parameter identifies locations of
-the symbols that were discarded during error processing, and the third
+parameter is the size of the rule's right hand side.
+When a @acronym{GLR} parser reports an ambiguity, which of multiple candidate
+right hand sides it passes to @code{YYLLOC_DEFAULT} is undefined.
+When processing a syntax error, the second parameter identifies locations
+of the symbols that were discarded during error processing, and the third
parameter is the number of discarded symbols.
By default, @code{YYLLOC_DEFAULT} is defined this way:
@cindex value types, declaring
@findex %union
-The @code{%union} declaration specifies the entire collection of possible
-data types for semantic values. The keyword @code{%union} is followed by a
-pair of braces containing the same thing that goes inside a @code{union} in
-C.
+The @code{%union} declaration specifies the entire collection of
+possible data types for semantic values. The keyword @code{%union} is
+followed by braced code containing the same thing that goes inside a
+@code{union} in C@.
For example:
@end group
@end example
+@noindent
specifies the union tag @code{value}, so the corresponding C type is
@code{union value}. If you do not specify a tag, it defaults to
@code{YYSTYPE}.
+As another extension to @acronym{POSIX}, you may specify multiple
+@code{%union} declarations; their contents are concatenated. However,
+only the first @code{%union} declaration can specify a tag.
+
Note that, unlike making a @code{union} declaration in C, you need not write
a semicolon after the closing brace.
@deffn {Directive} %initial-action @{ @var{code} @}
@findex %initial-action
-Declare that the @var{code} must be invoked before parsing each time
+Declare that the braced @var{code} must be invoked before parsing each time
@code{yyparse} is called. The @var{code} may use @code{$$} and
@code{@@$} --- initial value and location of the look-ahead --- and the
@code{%parse-param}.
@deffn {Directive} %destructor @{ @var{code} @} @var{symbols}
@findex %destructor
-Invoke @var{code} whenever the parser discards one of the @var{symbols}.
+Invoke the braced @var{code} whenever the parser discards one of the
+@var{symbols}.
Within @var{code}, @code{$$} designates the semantic value associated
with the discarded symbol. The additional parser parameters are also
available (@pxref{Parser Function, , The Parser Function
@deffn {Directive} %name-prefix="@var{prefix}"
Rename the external symbols used in the parser so that they start with
@var{prefix} instead of @samp{yy}. The precise list of symbols renamed
+in C parsers
is @code{yyparse}, @code{yylex}, @code{yyerror}, @code{yynerrs},
-@code{yylval}, @code{yylloc}, @code{yychar}, @code{yydebug}, and
-possible @code{yylloc}. For example, if you use
+@code{yylval}, @code{yychar}, @code{yydebug}, and
+(if locations are used) @code{yylloc}. For example, if you use
@samp{%name-prefix="c_"}, the names become @code{c_parse}, @code{c_lex},
-and so on. @xref{Multiple Parsers, ,Multiple Parsers in the Same
-Program}.
+and so on. In C++ parsers, it is only the surrounding namespace which is
+named @var{prefix} instead of @samp{yy}.
+@xref{Multiple Parsers, ,Multiple Parsers in the Same Program}.
@end deffn
@ifset defaultprec
@deffn {Directive} %parse-param @{@var{argument-declaration}@}
@findex %parse-param
-Declare that an argument declared by @code{argument-declaration} is an
-additional @code{yyparse} argument.
+Declare that an argument declared by the braced-code
+@var{argument-declaration} is an additional @code{yyparse} argument.
The @var{argument-declaration} is used when declaring
functions or prototypes. The last identifier in
@var{argument-declaration} must be the argument name.
@deffn {Directive} lex-param @{@var{argument-declaration}@}
@findex %lex-param
-Declare that @code{argument-declaration} is an additional @code{yylex}
-argument declaration.
+Declare that the braced-code @var{argument-declaration} is an
+additional @code{yylex} argument declaration.
@end deffn
For instance:
Value stored in @code{yychar} when there is no look-ahead token.
@end deffn
+@deffn {Macro} YYEOF
+@vindex YYEOF
+Value stored in @code{yychar} when the look-ahead is the end of the input
+stream.
+@end deffn
+
@deffn {Macro} YYERROR;
@findex YYERROR
Cause an immediate syntax error. This statement initiates error
@end deffn
@deffn {Variable} yychar
-Variable containing the current look-ahead token. (In a pure parser,
-this is actually a local variable within @code{yyparse}.) When there is
-no look-ahead token, the value @code{YYEMPTY} is stored in the variable.
+Variable containing either the look-ahead token, or @code{YYEOF} when the
+look-ahead is the end of the input stream, or @code{YYEMPTY} when no look-ahead
+has been performed so the next token is not yet known.
+Do not modify @code{yychar} in a deferred semantic action (@pxref{GLR Semantic
+Actions}).
@xref{Look-Ahead, ,Look-Ahead Tokens}.
@end deffn
@deffn {Macro} yyclearin;
Discard the current look-ahead token. This is useful primarily in
-error rules. @xref{Error Recovery}.
+error rules.
+Do not invoke @code{yyclearin} in a deferred semantic action (@pxref{GLR
+Semantic Actions}).
+@xref{Error Recovery}.
@end deffn
@deffn {Macro} yyerrok;
@xref{Error Recovery}.
@end deffn
+@deffn {Variable} yylloc
+Variable containing the look-ahead token location when @code{yychar} is not set
+to @code{YYEMPTY} or @code{YYEOF}.
+Do not modify @code{yylloc} in a deferred semantic action (@pxref{GLR Semantic
+Actions}).
+@xref{Actions and Locations, ,Actions and Locations}.
+@end deffn
+
+@deffn {Variable} yylval
+Variable containing the look-ahead token semantic value when @code{yychar} is
+not set to @code{YYEMPTY} or @code{YYEOF}.
+Do not modify @code{yylval} in a deferred semantic action (@pxref{GLR Semantic
+Actions}).
+@xref{Actions, ,Actions}.
+@end deffn
+
@deffn {Value} @@$
@findex @@$
Acts like a structure variable containing information on the textual location
'!'}. No rule allows that sequence.
@vindex yychar
-The current look-ahead token is stored in the variable @code{yychar}.
+@vindex yylval
+@vindex yylloc
+The look-ahead token is stored in the variable @code{yychar}.
+Its semantic value and location, if any, are stored in the variables
+@code{yylval} and @code{yylloc}.
@xref{Action Features, ,Special Features for Use in Actions}.
@node Shift/Reduce
this is unacceptable, then the macro @code{yyclearin} may be used to clear
this token. Write the statement @samp{yyclearin;} in the error rule's
action.
+@xref{Action Features, ,Special Features for Use in Actions}.
For example, suppose that on a syntax error, an error handling routine is
called that advances the input stream to some point where parsing should
@item -b @var{file-prefix}
@itemx --file-prefix=@var{prefix}
-Pretend that @code{%verbose} was specified, i.e, specify prefix to use
+Pretend that @code{%file-prefix} was specified, i.e, specify prefix to use
for all Bison output file names. @xref{Decl Summary}.
@item -r @var{things}
the full set of items for each state, instead of its core only.
@end table
-For instance, on the following grammar
-
@item -v
@itemx --verbose
Pretend that @code{%verbose} was specified, i.e, write an extra output
@node Option Cross Key
@section Option Cross Key
+@c FIXME: How about putting the directives too?
Here is a list of options, alphabetized by long option, to help you find
the corresponding short option.
-@tex
-\def\leaderfill{\leaders\hbox to 1em{\hss.\hss}\hfill}
-
-{\tt
-\line{ --debug \leaderfill -t}
-\line{ --defines \leaderfill -d}
-\line{ --file-prefix \leaderfill -b}
-\line{ --graph \leaderfill -g}
-\line{ --help \leaderfill -h}
-\line{ --name-prefix \leaderfill -p}
-\line{ --no-lines \leaderfill -l}
-\line{ --no-parser \leaderfill -n}
-\line{ --output \leaderfill -o}
-\line{ --print-localedir}
-\line{ --token-table \leaderfill -k}
-\line{ --verbose \leaderfill -v}
-\line{ --version \leaderfill -V}
-\line{ --yacc \leaderfill -y}
-}
-@end tex
-
-@ifinfo
-@example
---debug -t
---defines=@var{defines-file} -d
---file-prefix=@var{prefix} -b @var{file-prefix}
---graph=@var{graph-file} -d
---help -h
---name-prefix=@var{prefix} -p @var{name-prefix}
---no-lines -l
---no-parser -n
---output=@var{outfile} -o @var{outfile}
---print-localedir
---token-table -k
---verbose -v
---version -V
---yacc -y
-@end example
-@end ifinfo
+@multitable {@option{--defines=@var{defines-file}}} {@option{-b @var{file-prefix}XXX}}
+@headitem Long Option @tab Short Option
+@item @option{--debug} @tab @option{-t}
+@item @option{--defines=@var{defines-file}} @tab @option{-d}
+@item @option{--file-prefix=@var{prefix}} @tab @option{-b @var{file-prefix}}
+@item @option{--graph=@var{graph-file}} @tab @option{-d}
+@item @option{--help} @tab @option{-h}
+@item @option{--name-prefix=@var{prefix}} @tab @option{-p @var{name-prefix}}
+@item @option{--no-lines} @tab @option{-l}
+@item @option{--no-parser} @tab @option{-n}
+@item @option{--output=@var{outfile}} @tab @option{-o @var{outfile}}
+@item @option{--print-localedir} @tab
+@item @option{--token-table} @tab @option{-k}
+@item @option{--verbose} @tab @option{-v}
+@item @option{--version} @tab @option{-V}
+@item @option{--yacc} @tab @option{-y}
+@end multitable
@node Yacc Library
@section Yacc Library
@c - Always pure
@c - initial action
-The C++ parser @acronym{LALR}(1) skeleton is named @file{lalr1.cc}. To select
-it, you may either pass the option @option{--skeleton=lalr1.cc} to
-Bison, or include the directive @samp{%skeleton "lalr1.cc"} in the
+The C++ parser @acronym{LALR}(1) skeleton is named @file{lalr1.cc}. To
+select it, you may either pass the option @option{--skeleton=lalr1.cc}
+to Bison, or include the directive @samp{%skeleton "lalr1.cc"} in the
grammar preamble. When run, @command{bison} will create several
-files:
+entities in the @samp{yy} namespace. Use the @samp{%name-prefix}
+directive to change the namespace name, see @ref{Decl Summary}. The
+various classes are generated in the following files:
+
@table @file
@item position.hh
@itemx location.hh
@comment file: calc++-driver.hh
@example
// Announce to Flex the prototype we want for lexing function, ...
-# define YY_DECL \
- int yylex (yy::calcxx_parser::semantic_type* yylval, \
- yy::calcxx_parser::location_type* yylloc, \
- calcxx_driver& driver)
+# define YY_DECL \
+ yy::calcxx_parser::token_type \
+ yylex (yy::calcxx_parser::semantic_type* yylval, \
+ yy::calcxx_parser::location_type* yylloc, \
+ calcxx_driver& driver)
// ... and declare it for the parser's sake.
YY_DECL;
@end example
To enable memory deallocation during error recovery, use
@code{%destructor}.
+@c FIXME: Document %printer, and mention that it takes a braced-code operand.
@comment file: calc++-parser.yy
@example
%printer @{ debug_stream () << *$$; @} "identifier"
# include <string>
# include "calc++-driver.hh"
# include "calc++-parser.hh"
+/* Work around a bug in flex 2.5.31. See Debian bug 333231
+ <http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=333231>. */
+# undef yywrap
+# define yywrap() 1
+/* By default yylex returns int, we use token_type.
+ Unfortunately yyterminate by default returns 0, which is
+ not of token_type. */
+#define yyterminate() return token::END
%@}
@end example
%@{
typedef yy::calcxx_parser::token token;
%@}
-
-[-+*/] return yytext[0];
+ /* Convert ints to the actual type of tokens. */
+[-+*/] return yy::calcxx_parser::token_type (yytext[0]);
":=" return token::ASSIGN;
@{int@} @{
errno = 0;
are addressed.
@menu
-* Memory Exhausted:: Breaking the Stack Limits
-* How Can I Reset the Parser:: @code{yyparse} Keeps some State
-* Strings are Destroyed:: @code{yylval} Loses Track of Strings
-* Implementing Gotos/Loops:: Control Flow in the Calculator
+* Memory Exhausted:: Breaking the Stack Limits
+* How Can I Reset the Parser:: @code{yyparse} Keeps some State
+* Strings are Destroyed:: @code{yylval} Loses Track of Strings
+* Implementing Gotos/Loops:: Control Flow in the Calculator
+* Multiple start-symbols:: Factoring closely related grammars
+* Secure? Conform?:: Is Bison @acronym{POSIX} safe?
+* I can't build Bison:: Troubleshooting
+* Where can I find help?:: Troubleshouting
+* Bug Reports:: Troublereporting
+* Other Languages:: Parsers in Java and others
+* Beta Testing:: Experimenting development versions
+* Mailing Lists:: Meeting other Bison users
@end menu
@node Memory Exhausted
This error is probably the single most frequent ``bug report'' sent to
Bison lists, but is only concerned with a misunderstanding of the role
-of scanner. Consider the following Lex code:
+of the scanner. Consider the following Lex code:
@verbatim
%{
invited to consult the dedicated literature.
+@node Multiple start-symbols
+@section Multiple start-symbols
+
+@display
+I have several closely related grammars, and I would like to share their
+implementations. In fact, I could use a single grammar but with
+multiple entry points.
+@end display
+
+Bison does not support multiple start-symbols, but there is a very
+simple means to simulate them. If @code{foo} and @code{bar} are the two
+pseudo start-symbols, then introduce two new tokens, say
+@code{START_FOO} and @code{START_BAR}, and use them as switches from the
+real start-symbol:
+
+@example
+%token START_FOO START_BAR;
+%start start;
+start: START_FOO foo
+ | START_BAR bar;
+@end example
+
+These tokens prevents the introduction of new conflicts. As far as the
+parser goes, that is all that is needed.
+
+Now the difficult part is ensuring that the scanner will send these
+tokens first. If your scanner is hand-written, that should be
+straightforward. If your scanner is generated by Lex, them there is
+simple means to do it: recall that anything between @samp{%@{ ... %@}}
+after the first @code{%%} is copied verbatim in the top of the generated
+@code{yylex} function. Make sure a variable @code{start_token} is
+available in the scanner (e.g., a global variable or using
+@code{%lex-param} etc.), and use the following:
+
+@example
+ /* @r{Prologue.} */
+%%
+%@{
+ if (start_token)
+ @{
+ int t = start_token;
+ start_token = 0;
+ return t;
+ @}
+%@}
+ /* @r{The rules.} */
+@end example
+
+
+@node Secure? Conform?
+@section Secure? Conform?
+
+@display
+Is Bison secure? Does it conform to POSIX?
+@end display
+
+If you're looking for a guarantee or certification, we don't provide it.
+However, Bison is intended to be a reliable program that conforms to the
+@acronym{POSIX} specification for Yacc. If you run into problems,
+please send us a bug report.
+
+@node I can't build Bison
+@section I can't build Bison
+
+@display
+I can't build Bison because @command{make} complains that
+@code{msgfmt} is not found.
+What should I do?
+@end display
+
+Like most GNU packages with internationalization support, that feature
+is turned on by default. If you have problems building in the @file{po}
+subdirectory, it indicates that your system's internationalization
+support is lacking. You can re-configure Bison with
+@option{--disable-nls} to turn off this support, or you can install GNU
+gettext from @url{ftp://ftp.gnu.org/gnu/gettext/} and re-configure
+Bison. See the file @file{ABOUT-NLS} for more information.
+
+
+@node Where can I find help?
+@section Where can I find help?
+
+@display
+I'm having trouble using Bison. Where can I find help?
+@end display
+
+First, read this fine manual. Beyond that, you can send mail to
+@email{help-bison@@gnu.org}. This mailing list is intended to be
+populated with people who are willing to answer questions about using
+and installing Bison. Please keep in mind that (most of) the people on
+the list have aspects of their lives which are not related to Bison (!),
+so you may not receive an answer to your question right away. This can
+be frustrating, but please try not to honk them off; remember that any
+help they provide is purely voluntary and out of the kindness of their
+hearts.
+
+@node Bug Reports
+@section Bug Reports
+
+@display
+I found a bug. What should I include in the bug report?
+@end display
+
+Before you send a bug report, make sure you are using the latest
+version. Check @url{ftp://ftp.gnu.org/pub/gnu/bison/} or one of its
+mirrors. Be sure to include the version number in your bug report. If
+the bug is present in the latest version but not in a previous version,
+try to determine the most recent version which did not contain the bug.
+
+If the bug is parser-related, you should include the smallest grammar
+you can which demonstrates the bug. The grammar file should also be
+complete (i.e., I should be able to run it through Bison without having
+to edit or add anything). The smaller and simpler the grammar, the
+easier it will be to fix the bug.
+
+Include information about your compilation environment, including your
+operating system's name and version and your compiler's name and
+version. If you have trouble compiling, you should also include a
+transcript of the build session, starting with the invocation of
+`configure'. Depending on the nature of the bug, you may be asked to
+send additional files as well (such as `config.h' or `config.cache').
+
+Patches are most welcome, but not required. That is, do not hesitate to
+send a bug report just because you can not provide a fix.
+
+Send bug reports to @email{bug-bison@@gnu.org}.
+
+@node Other Languages
+@section Other Languages
+
+@display
+Will Bison ever have C++ support? How about Java or @var{insert your
+favorite language here}?
+@end display
+
+C++ support is there now, and is documented. We'd love to add other
+languages; contributions are welcome.
+
+@node Beta Testing
+@section Beta Testing
+
+@display
+What is involved in being a beta tester?
+@end display
+
+It's not terribly involved. Basically, you would download a test
+release, compile it, and use it to build and run a parser or two. After
+that, you would submit either a bug report or a message saying that
+everything is okay. It is important to report successes as well as
+failures because test releases eventually become mainstream releases,
+but only if they are adequately tested. If no one tests, development is
+essentially halted.
+
+Beta testers are particularly needed for operating systems to which the
+developers do not have easy access. They currently have easy access to
+recent GNU/Linux and Solaris versions. Reports about other operating
+systems are especially welcome.
+
+@node Mailing Lists
+@section Mailing Lists
+
+@display
+How do I join the help-bison and bug-bison mailing lists?
+@end display
+
+See @url{http://lists.gnu.org/}.
@c ================================================= Table of Symbols
@end deffn
@deffn {Variable} yychar
-External integer variable that contains the integer value of the current
+External integer variable that contains the integer value of the
look-ahead token. (In a pure parser, it is a local variable within
@code{yyparse}.) Error-recovery rule actions may examine this variable.
@xref{Action Features, ,Special Features for Use in Actions}.
@deffn {Macro} YYLEX_PARAM
An obsolete macro for specifying an extra argument (or list of extra
-arguments) for @code{yyparse} to pass to @code{yylex}. he use of this
+arguments) for @code{yyparse} to pass to @code{yylex}. The use of this
macro is deprecated, and is supported only for Yacc like parsers.
@xref{Pure Calling,, Calling Conventions for Pure Parsers}.
@end deffn
External variable in which @code{yylex} should place the line and column
numbers associated with a token. (In a pure parser, it is a local
variable within @code{yyparse}, and its address is passed to
-@code{yylex}.) You can ignore this variable if you don't use the
-@samp{@@} feature in the grammar actions. @xref{Token Locations,
-,Textual Locations of Tokens}.
+@code{yylex}.)
+You can ignore this variable if you don't use the @samp{@@} feature in the
+grammar actions.
+@xref{Token Locations, ,Textual Locations of Tokens}.
+In semantic actions, it stores the location of the look-ahead token.
+@xref{Actions and Locations, ,Actions and Locations}.
@end deffn
@deffn {Type} YYLTYPE
External variable in which @code{yylex} should place the semantic
value associated with a token. (In a pure parser, it is a local
variable within @code{yyparse}, and its address is passed to
-@code{yylex}.) @xref{Token Values, ,Semantic Values of Tokens}.
+@code{yylex}.)
+@xref{Token Values, ,Semantic Values of Tokens}.
+In semantic actions, it stores the semantic value of the look-ahead token.
+@xref{Actions, ,Actions}.
@end deffn
@deffn {Macro} YYMAXDEPTH
@c LocalWords: yychar yydebug msg YYNTOKENS YYNNTS YYNRULES YYNSTATES
@c LocalWords: cparse clex deftypefun NE defmac YYACCEPT YYABORT param
@c LocalWords: strncmp intval tindex lvalp locp llocp typealt YYBACKUP
-@c LocalWords: YYEMPTY YYRECOVERING yyclearin GE def UMINUS maybeword
+@c LocalWords: YYEMPTY YYEOF YYRECOVERING yyclearin GE def UMINUS maybeword
@c LocalWords: Johnstone Shamsa Sadaf Hussain Tomita TR uref YYMAXDEPTH
@c LocalWords: YYINITDEPTH stmnts ref stmnt initdcl maybeasm VCG notype
@c LocalWords: hexflag STR exdent itemset asis DYYDEBUG YYFPRINTF args
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