This manual (@value{UPDATED}) is for GNU Bison (version
@value{VERSION}), the GNU parser generator.
-Copyright @copyright{} 1988-1993, 1995, 1998-2011 Free Software
+Copyright @copyright{} 1988-1993, 1995, 1998-2012 Free Software
Foundation, Inc.
@quotation
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.
+* Locations:: Overview of location tracking.
* Bison Parser:: What are Bison's input and output,
how is the output used?
* Stages:: Stages in writing and running Bison grammars.
Bison Grammar Files
-* Grammar Outline:: Overall layout of the grammar file.
-* Symbols:: Terminal and nonterminal symbols.
-* Rules:: How to write grammar rules.
-* Recursion:: Writing recursive rules.
-* Semantics:: Semantic values and actions.
-* Locations:: Locations and actions.
-* Named References:: Using named references in actions.
-* Declarations:: All kinds of Bison declarations are described here.
-* Multiple Parsers:: Putting more than one Bison parser in one program.
+* Grammar Outline:: Overall layout of the grammar file.
+* Symbols:: Terminal and nonterminal symbols.
+* Rules:: How to write grammar rules.
+* Recursion:: Writing recursive rules.
+* Semantics:: Semantic values and actions.
+* Tracking Locations:: Locations and actions.
+* Named References:: Using named references in actions.
+* Declarations:: All kinds of Bison declarations are described here.
+* Multiple Parsers:: Putting more than one Bison parser in one program.
Outline of a Bison Grammar
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.
+* Locations:: Overview of location tracking.
* Bison Parser:: What are Bison's input and output,
how is the output used?
* Stages:: Stages in writing and running Bison grammars.
initiate error recovery.
During deterministic GLR operation, the effect of @code{YYERROR} is
the same as its effect in a deterministic parser.
-The effect in a deferred action is similar, but the precise point of the
-error is undefined; instead, the parser reverts to deterministic operation,
+The effect in a deferred action is similar, but the precise point of the
+error is undefined; instead, the parser reverts to deterministic operation,
selecting an unspecified stack on which to continue with a syntax error.
In a semantic predicate (see @ref{Semantic Predicates}) during nondeterministic
parsing, @code{YYERROR} silently prunes
@end smallexample
@noindent
-is one way to allow the same parser to handle two different syntaxes for
+is one way to allow the same parser to handle two different syntaxes for
widgets. The clause preceded by @code{%?} is treated like an ordinary
action, except that its text is treated as an expression and is always
-evaluated immediately (even when in nondeterministic mode). If the
+evaluated immediately (even when in nondeterministic mode). If the
expression yields 0 (false), the clause is treated as a syntax error,
-which, in a nondeterministic parser, causes the stack in which it is reduced
+which, in a nondeterministic parser, causes the stack in which it is reduced
to die. In a deterministic parser, it acts like YYERROR.
As the example shows, predicates otherwise look like semantic actions, and
There is a subtle difference between semantic predicates and ordinary
actions in nondeterministic mode, since the latter are deferred.
-For example, we could try to rewrite the previous example as
+For example, we could try to rewrite the previous example as
@smallexample
widget :
false). However, this
does @emph{not} have the same effect if @code{new_args} and @code{old_args}
have overlapping syntax.
-Since the mid-rule actions testing @code{new_syntax} are deferred,
+Since the mid-rule actions testing @code{new_syntax} are deferred,
a GLR parser first encounters the unresolved ambiguous reduction
for cases where @code{new_args} and @code{old_args} recognize the same string
@emph{before} performing the tests of @code{new_syntax}. It therefore
%@}
@end example
-@node Locations Overview
+@node Locations
@section Locations
@cindex location
@cindex textual location
Bison provides a mechanism for handling these locations.
Each token has a semantic value. In a similar fashion, each token has an
-associated location, but the type of locations is the same for all tokens and
-groupings. Moreover, the output parser is equipped with a default data
-structure for storing locations (@pxref{Locations}, for more details).
+associated location, but the type of locations is the same for all tokens
+and groupings. Moreover, the output parser is equipped with a default data
+structure for storing locations (@pxref{Tracking Locations}, for more
+details).
Like semantic values, locations can be reached in actions using a dedicated
set of constructs. In the example above, the location of the whole grouping
@xref{Invocation, ,Invoking Bison}.
@menu
-* Grammar Outline:: Overall layout of the grammar file.
-* Symbols:: Terminal and nonterminal symbols.
-* Rules:: How to write grammar rules.
-* Recursion:: Writing recursive rules.
-* Semantics:: Semantic values and actions.
-* Locations:: Locations and actions.
-* Named References:: Using named references in actions.
-* Declarations:: All kinds of Bison declarations are described here.
-* Multiple Parsers:: Putting more than one Bison parser in one program.
+* Grammar Outline:: Overall layout of the grammar file.
+* Symbols:: Terminal and nonterminal symbols.
+* Rules:: How to write grammar rules.
+* Recursion:: Writing recursive rules.
+* Semantics:: Semantic values and actions.
+* Tracking Locations:: Locations and actions.
+* Named References:: Using named references in actions.
+* Declarations:: All kinds of Bison declarations are described here.
+* Multiple Parsers:: Putting more than one Bison parser in one program.
@end menu
@node Grammar Outline
useful semantic value associated with the @samp{+} token, it could be
referred to as @code{$2}.
-@xref{Named References,,Using Named References}, for more information
-about using the named references construct.
+@xref{Named References}, for more information about using the named
+references construct.
Note that the vertical-bar character @samp{|} is really a rule
separator, and actions are attached to a single rule. This is a
Now Bison can execute the action in the rule for @code{subroutine} without
deciding which rule for @code{compound} it will eventually use.
-@node Locations
+@node Tracking Locations
@section Tracking Locations
@cindex location
@cindex textual location
In addition, the named references construct @code{@@@var{name}} and
@code{@@[@var{name}]} may also be used to address the symbol locations.
-@xref{Named References,,Using Named References}, for more information
-about using the named references construct.
+@xref{Named References}, for more information about using the named
+references construct.
Here is a basic example using the default data type for locations:
@end itemize
@node Named References
-@section Using Named References
+@section Named References
@cindex named references
As described in the preceding sections, the traditional way to refer to any
@end example
@noindent
-Explicit names may be declared for RHS and for LHS symbols as well. In order
-to access a semantic value generated by a mid-rule action, an explicit name
-may also be declared by putting a bracketed name after the closing brace of
-the mid-rule action code:
+In order to access a semantic value generated by a mid-rule action, an
+explicit name may also be declared by putting a bracketed name after the
+closing brace of the mid-rule action code:
@example
@group
exp[res]: exp[x] '+' @{$left = $x;@}[left] exp[right]
It often happens that named references are followed by a dot, dash or other
C punctuation marks and operators. By default, Bison will read
-@code{$name.suffix} as a reference to symbol value @code{$name} followed by
-@samp{.suffix}, i.e., an access to the @samp{suffix} field of the semantic
-value. In order to force Bison to recognize @code{name.suffix} in its entirety
-as the name of a semantic value, bracketed syntax @code{$[name.suffix]}
-must be used.
+@samp{$name.suffix} as a reference to symbol value @code{$name} followed by
+@samp{.suffix}, i.e., an access to the @code{suffix} field of the semantic
+value. In order to force Bison to recognize @samp{name.suffix} in its
+entirety as the name of a semantic value, the bracketed syntax
+@samp{$[name.suffix]} must be used.
+
+The named references feature is experimental. More user feedback will help
+to stabilize it.
@node Declarations
@section Bison Declarations
@cindex mid-rule actions
Finally, Bison will never invoke a @code{%destructor} for an unreferenced
mid-rule semantic value (@pxref{Mid-Rule Actions,,Actions in Mid-Rule}).
-That is, Bison does not consider a mid-rule to have a semantic value if you do
-not reference @code{$$} in the mid-rule's action or @code{$@var{n}} (where
-@var{n} is the RHS symbol position of the mid-rule) in any later action in that
-rule.
-However, if you do reference either, the Bison-generated parser will invoke the
-@code{<>} @code{%destructor} whenever it discards the mid-rule symbol.
+That is, Bison does not consider a mid-rule to have a semantic value if you
+do not reference @code{$$} in the mid-rule's action or @code{$@var{n}}
+(where @var{n} is the right-hand side symbol position of the mid-rule) in
+any later action in that rule. However, if you do reference either, the
+Bison-generated parser will invoke the @code{<>} @code{%destructor} whenever
+it discards the mid-rule symbol.
@ignore
@noindent
(Reentrant) Parser}.
If you have also used locations, the parser header file declares
-@code{YYLTYPE} and @code{yylloc} using a protocol similar to that of
-the @code{YYSTYPE} macro and @code{yylval}. @xref{Locations,
-,Tracking Locations}.
+@code{YYLTYPE} and @code{yylloc} using a protocol similar to that of the
+@code{YYSTYPE} macro and @code{yylval}. @xref{Tracking Locations}.
This parser header file is normally essential if you wish to put the
definition of @code{yylex} in a separate source file, because
@subsection Textual Locations of Tokens
@vindex yylloc
-If you are using the @samp{@@@var{n}}-feature (@pxref{Locations, ,
-Tracking Locations}) in actions to keep track of the textual locations
-of tokens and groupings, then you must provide this information in
-@code{yylex}. The function @code{yyparse} expects to find the textual
-location of a token just parsed in the global variable @code{yylloc}.
-So @code{yylex} must store the proper data in that variable.
+If you are using the @samp{@@@var{n}}-feature (@pxref{Tracking Locations})
+in actions to keep track of the textual locations of tokens and groupings,
+then you must provide this information in @code{yylex}. The function
+@code{yyparse} expects to find the textual location of a token just parsed
+in the global variable @code{yylloc}. So @code{yylex} must store the proper
+data in that variable.
By default, the value of @code{yylloc} is a structure and you need only
initialize the members that are going to be used by the actions. The
@deffn {Value} @@$
@findex @@$
-Acts like a structure variable containing information on the textual location
-of the grouping made by the current rule. @xref{Locations, ,
-Tracking Locations}.
+Acts like a structure variable containing information on the textual
+location of the grouping made by the current rule. @xref{Tracking
+Locations}.
@c Check if those paragraphs are still useful or not.
@deffn {Value} @@@var{n}
@findex @@@var{n}
-Acts like a structure variable containing information on the textual location
-of the @var{n}th component of the current rule. @xref{Locations, ,
-Tracking Locations}.
+Acts like a structure variable containing information on the textual
+location of the @var{n}th component of the current rule. @xref{Tracking
+Locations}.
@end deffn
@node Internationalization
Do not allow @code{YYINITDEPTH} to be greater than @code{YYMAXDEPTH}.
You can generate a deterministic parser containing C++ user code from
-the default (C) skeleton, as well as from the C++ skeleton
+the default (C) skeleton, as well as from the C++ skeleton
(@pxref{C++ Parsers}). However, if you do use the default skeleton
and want to allow the parsing stack to grow,
be careful not to use semantic types or location types that require
@c - %define filename_type "const symbol::Symbol"
When the directive @code{%locations} is used, the C++ parser supports
-location tracking, see @ref{Locations, , Locations Overview}. Two
-auxiliary classes define a @code{position}, a single point in a file,
-and a @code{location}, a range composed of a pair of
-@code{position}s (possibly spanning several files).
+location tracking, see @ref{Tracking Locations}. Two auxiliary classes
+define a @code{position}, a single point in a file, and a @code{location}, a
+range composed of a pair of @code{position}s (possibly spanning several
+files).
@deftypemethod {position} {std::string*} file
The name of the file. It will always be handled as a pointer, the
@c - class Position
@c - class Location
-When the directive @code{%locations} is used, the Java parser
-supports location tracking, see @ref{Locations, , Locations Overview}.
-An auxiliary user-defined class defines a @dfn{position}, a single point
-in a file; Bison itself defines a class representing a @dfn{location},
-a range composed of a pair of positions (possibly spanning several
-files). The location class is an inner class of the parser; the name
-is @code{Location} by default, and may also be renamed using
-@samp{%define location_type "@var{class-name}"}.
+When the directive @code{%locations} is used, the Java parser supports
+location tracking, see @ref{Tracking Locations}. An auxiliary user-defined
+class defines a @dfn{position}, a single point in a file; Bison itself
+defines a class representing a @dfn{location}, a range composed of a pair of
+positions (possibly spanning several files). The location class is an inner
+class of the parser; the name is @code{Location} by default, and may also be
+renamed using @samp{%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
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 a bug report just because you cannot provide a fix.
Send bug reports to @email{bug-bison@@gnu.org}.
@deffn {Variable} @@$
In an action, the location of the left-hand side of the rule.
-@xref{Locations, , Locations Overview}.
+@xref{Tracking Locations}.
@end deffn
@deffn {Variable} @@@var{n}
-In an action, the location of the @var{n}-th symbol of the right-hand
-side of the rule. @xref{Locations, , Locations Overview}.
+In an action, the location of the @var{n}-th symbol of the right-hand side
+of the rule. @xref{Tracking Locations}.
@end deffn
@deffn {Variable} @@@var{name}
-In an action, the location of a symbol addressed by name.
-@xref{Locations, , Locations Overview}.
+In an action, the location of a symbol addressed by name. @xref{Tracking
+Locations}.
@end deffn
@deffn {Variable} @@[@var{name}]
-In an action, the location of a symbol addressed by name.
-@xref{Locations, , Locations Overview}.
+In an action, the location of a symbol addressed by name. @xref{Tracking
+Locations}.
@end deffn
@deffn {Variable} $$
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