@value{UPDATED}), the @acronym{GNU} parser generator.
Copyright @copyright{} 1988, 1989, 1990, 1991, 1992, 1993, 1995, 1998,
-1999, 2000, 2001, 2002, 2003, 2004, 2005, 2006, 2007 Free Software Foundation, Inc.
+1999, 2000, 2001, 2002, 2003, 2004, 2005, 2006, 2007, 2008 Free Software
+Foundation, Inc.
@quotation
Permission is granted to copy, distribute and/or modify this document
(a) below. A copy of the license is included in the section entitled
``@acronym{GNU} Free Documentation License.''
-(a) The @acronym{FSF}'s Back-Cover Text is: ``You have freedom to copy
-and modify this @acronym{GNU} Manual, like @acronym{GNU} software.
-Copies published by the Free Software Foundation raise funds for
-@acronym{GNU} development.''
+(a) The FSF's Back-Cover Text is: ``You have the freedom to copy and
+modify this @acronym{GNU} manual. Buying copies from the @acronym{FSF}
+supports it in developing @acronym{GNU} and promoting software
+freedom.''
@end quotation
@end copying
@xref{Precedence, ,Operator Precedence}, for general information on
operator precedence.
-The syntax of a precedence declaration is the same as that of
+The syntax of a precedence declaration is nearly the same as that of
@code{%token}: either
@example
the one declared later has the higher precedence and is grouped first.
@end itemize
+For backward compatibility, there is a confusing difference between the
+argument lists of @code{%token} and precedence declarations.
+Only a @code{%token} can associate a literal string with a token type name.
+A precedence declaration always interprets a literal string as a reference to a
+separate token.
+For example:
+
+@example
+%left OR "<=" // Does not declare an alias.
+%left OR 134 "<=" 135 // Declares 134 for OR and 135 for "<=".
+@end example
+
@node Union Decl
@subsection The Collection of Value Types
@cindex declaring value types
@subsection A Pure (Reentrant) Parser
@cindex reentrant parser
@cindex pure parser
-@findex %pure-parser
+@findex %define api.pure
A @dfn{reentrant} program is one which does not alter in the course of
execution; in other words, it consists entirely of @dfn{pure} (read-only)
including @code{yylval} and @code{yylloc}.)
Alternatively, you can generate a pure, reentrant parser. The Bison
-declaration @code{%pure-parser} says that you want the parser to be
+declaration @code{%define api.pure} says that you want the parser to be
reentrant. It looks like this:
@example
-%pure-parser
+%define api.pure
@end example
The result is that the communication variables @code{yylval} and
@code{yylloc} become local variables in @code{yyparse}, and a different
calling convention is used for the lexical analyzer function
@code{yylex}. @xref{Pure Calling, ,Calling Conventions for Pure
-Parsers}, for the details of this. The variable @code{yynerrs}
-becomes local in @code{yyparse} in pull mode but it becomes a member
+Parsers}, for the details of this. The variable @code{yynerrs}
+becomes local in @code{yyparse} in pull mode but it becomes a member
of yypstate in push mode. (@pxref{Error Reporting, ,The Error
Reporting Function @code{yyerror}}). The convention for calling
@code{yyparse} itself is unchanged.
@subsection A Push Parser
@cindex push parser
@cindex push parser
-@findex %define push_pull
+@findex %define api.push_pull
-A pull parser is called once and it takes control until all its input
-is completely parsed. A push parser, on the other hand, is called
+A pull parser is called once and it takes control until all its input
+is completely parsed. A push parser, on the other hand, is called
each time a new token is made available.
-A push parser is typically useful when the parser is part of a
+A push parser is typically useful when the parser is part of a
main event loop in the client's application. This is typically
-a requirement of a GUI, when the main event loop needs to be triggered
-within a certain time period.
+a requirement of a GUI, when the main event loop needs to be triggered
+within a certain time period.
Normally, Bison generates a pull parser.
The following Bison declaration says that you want the parser to be a push
-parser (@pxref{Decl Summary,,%define push_pull}):
+parser (@pxref{Decl Summary,,%define api.push_pull}):
@example
-%define push_pull "push"
+%define api.push_pull "push"
@end example
In almost all cases, you want to ensure that your push parser is also
a pure parser (@pxref{Pure Decl, ,A Pure (Reentrant) Parser}). The only
-time you should create an impure push parser is to have backwards
+time you should create an impure push parser is to have backwards
compatibility with the impure Yacc pull mode interface. Unless you know
what you are doing, your declarations should look like this:
@example
-%pure-parser
-%define push_pull "push"
+%define api.pure
+%define api.push_pull "push"
@end example
-There is a major notable functional difference between the pure push parser
-and the impure push parser. It is acceptable for a pure push parser to have
+There is a major notable functional difference between the pure push parser
+and the impure push parser. It is acceptable for a pure push parser to have
many parser instances, of the same type of parser, in memory at the same time.
An impure push parser should only use one parser at a time.
When a push parser is selected, Bison will generate some new symbols in
-the generated parser. @code{yypstate} is a structure that the generated
-parser uses to store the parser's state. @code{yypstate_new} is the
+the generated parser. @code{yypstate} is a structure that the generated
+parser uses to store the parser's state. @code{yypstate_new} is the
function that will create a new parser instance. @code{yypstate_delete}
will free the resources associated with the corresponding parser instance.
-Finally, @code{yypush_parse} is the function that should be called whenever a
+Finally, @code{yypush_parse} is the function that should be called whenever a
token is available to provide the parser. A trivial example
of using a pure push parser would look like this:
@end example
If the user decided to use an impure push parser, a few things about
-the generated parser will change. The @code{yychar} variable becomes
+the generated parser will change. The @code{yychar} variable becomes
a global variable instead of a variable in the @code{yypush_parse} function.
For this reason, the signature of the @code{yypush_parse} function is
-changed to remove the token as a parameter. A nonreentrant push parser
+changed to remove the token as a parameter. A nonreentrant push parser
example would thus look like this:
@example
yypstate_delete (ps);
@end example
-That's it. Notice the next token is put into the global variable @code{yychar}
+That's it. Notice the next token is put into the global variable @code{yychar}
for use by the next invocation of the @code{yypush_parse} function.
-Bison also supports both the push parser interface along with the pull parser
+Bison also supports both the push parser interface along with the pull parser
interface in the same generated parser. In order to get this functionality,
-you should replace the @code{%define push_pull "push"} declaration with the
-@code{%define push_pull "both"} declaration. Doing this will create all of the
-symbols mentioned earlier along with the two extra symbols, @code{yyparse}
-and @code{yypull_parse}. @code{yyparse} can be used exactly as it normally
-would be used. However, the user should note that it is implemented in the
+you should replace the @code{%define api.push_pull "push"} declaration with the
+@code{%define api.push_pull "both"} declaration. Doing this will create all of
+the symbols mentioned earlier along with the two extra symbols, @code{yyparse}
+and @code{yypull_parse}. @code{yyparse} can be used exactly as it normally
+would be used. However, the user should note that it is implemented in the
generated parser by calling @code{yypull_parse}.
This makes the @code{yyparse} function that is generated with the
-@code{%define push_pull "both"} declaration slower than the normal
+@code{%define api.push_pull "both"} declaration slower than the normal
@code{yyparse} function. If the user
calls the @code{yypull_parse} function it will parse the rest of the input
-stream. It is possible to @code{yypush_parse} tokens to select a subgrammar
-and then @code{yypull_parse} the rest of the input stream. If you would like
-to switch back and forth between between parsing styles, you would have to
-write your own @code{yypull_parse} function that knows when to quit looking
-for input. An example of using the @code{yypull_parse} function would look
+stream. It is possible to @code{yypush_parse} tokens to select a subgrammar
+and then @code{yypull_parse} the rest of the input stream. If you would like
+to switch back and forth between between parsing styles, you would have to
+write your own @code{yypull_parse} function that knows when to quit looking
+for input. An example of using the @code{yypull_parse} function would look
like this:
@example
yypstate_delete (ps);
@end example
-Adding the @code{%pure-parser} declaration does exactly the same thing to the
-generated parser with @code{%define push_pull "both"} as it did for
-@code{%define push_pull "push"}.
+Adding the @code{%define api.pure} declaration does exactly the same thing to
+the generated parser with @code{%define api.push_pull "both"} as it did for
+@code{%define api.push_pull "push"}.
@node Decl Summary
@subsection Bison Declaration Summary
Some of the accepted @var{variable}s are:
@itemize @bullet
-@item push_pull
-@findex %define push_pull
+@item api.pure
+@findex %define api.pure
+
+@itemize @bullet
+@item Language(s): C
+
+@item Purpose: Request a pure (reentrant) parser program.
+@xref{Pure Decl, ,A Pure (Reentrant) Parser}.
+
+@item Accepted Values: Boolean
+
+@item Default Value: @code{"false"}
+@end itemize
+
+@item api.push_pull
+@findex %define api.push_pull
@itemize @bullet
@item Language(s): C (LALR(1) only)
@item Default Value: @code{"pull"}
@end itemize
+@item lr.keep_unreachable_states
+@findex %define lr.keep_unreachable_states
+
+@itemize @bullet
+@item Language(s): all
+
+@item Purpose: Requests that Bison allow unreachable parser states to remain in
+the parser tables.
+Bison considers a state to be unreachable if there exists no sequence of
+transitions from the start state to that state.
+A state can become unreachable during conflict resolution if Bison disables a
+shift action leading to it from a predecessor state.
+Keeping unreachable states is sometimes useful for analysis purposes, but they
+are useless in the generated parser.
+
+@item Accepted Values: Boolean
+
+@item Default Value: @code{"false"}
+
+@item Caveats:
+
+@itemize @bullet
+
+@item Unreachable states may contain conflicts and may use rules not used in
+any other state.
+Thus, keeping unreachable states may induce warnings that are irrelevant to
+your parser's behavior, and it may eliminate warnings that are relevant.
+Of course, the change in warnings may actually be relevant to a parser table
+analysis that wants to keep unreachable states, so this behavior will likely
+remain in future Bison releases.
+
+@item While Bison is able to remove unreachable states, it is not guaranteed to
+remove other kinds of useless states.
+Specifically, when Bison disables reduce actions during conflict resolution,
+some goto actions may become useless, and thus some additional states may
+become useless.
+If Bison were to compute which goto actions were useless and then disable those
+actions, it could identify such states as unreachable and then remove those
+states.
+However, Bison does not compute which goto actions are useless.
+@end itemize
+@end itemize
+
@item namespace
@findex %define namespace
in C parsers
is @code{yyparse}, @code{yylex}, @code{yyerror}, @code{yynerrs},
@code{yylval}, @code{yychar}, @code{yydebug}, and
-(if locations are used) @code{yylloc}. If you use a push parser,
-@code{yypush_parse}, @code{yypull_parse}, @code{yypstate},
-@code{yypstate_new} and @code{yypstate_delete} will
-also be renamed. For example, if you use @samp{%name-prefix "c_"}, the
+(if locations are used) @code{yylloc}. If you use a push parser,
+@code{yypush_parse}, @code{yypull_parse}, @code{yypstate},
+@code{yypstate_new} and @code{yypstate_delete} will
+also be renamed. For example, if you use @samp{%name-prefix "c_"}, the
names become @code{c_parse}, @code{c_lex}, and so on.
For C++ parsers, see the @code{%define namespace} documentation in this
section.
@end deffn
@deffn {Directive} %pure-parser
-Request a pure (reentrant) parser program (@pxref{Pure Decl, ,A Pure
-(Reentrant) Parser}).
+Deprecated version of @code{%define api.pure} (@pxref{Decl Summary, ,%define}),
+for which Bison is more careful to warn about unreasonable usage.
@end deffn
@deffn {Directive} %require "@var{version}"
The precise list of symbols renamed is @code{yyparse}, @code{yylex},
@code{yyerror}, @code{yynerrs}, @code{yylval}, @code{yylloc},
-@code{yychar} and @code{yydebug}. If you use a push parser,
-@code{yypush_parse}, @code{yypull_parse}, @code{yypstate},
+@code{yychar} and @code{yydebug}. If you use a push parser,
+@code{yypush_parse}, @code{yypull_parse}, @code{yypstate},
@code{yypstate_new} and @code{yypstate_delete} will also be renamed.
-For example, if you use @samp{-p c}, the names become @code{cparse},
+For example, if you use @samp{-p c}, the names become @code{cparse},
@code{clex}, and so on.
@strong{All the other variables and macros associated with Bison are not
* 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
+* 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
+* Parser Delete Function:: How to call @code{yypstate_delete} and what it
returns.
* Lexical:: You must supply a function @code{yylex}
which reads tokens.
@section The Push Parser Function @code{yypush_parse}
@findex yypush_parse
-You call the function @code{yypush_parse} to parse a single token. This
-function is available if either the @code{%define push_pull "push"} or
-@code{%define push_pull "both"} declaration is used.
+You call the function @code{yypush_parse} to parse a single token. This
+function is available if either the @code{%define api.push_pull "push"} or
+@code{%define api.push_pull "both"} declaration is used.
@xref{Push Decl, ,A Push Parser}.
@deftypefun int yypush_parse (yypstate *yyps)
-The value returned by @code{yypush_parse} is the same as for yyparse with the
+The value returned by @code{yypush_parse} is the same as for yyparse with the
following exception. @code{yypush_parse} will return YYPUSH_MORE if more input
is required to finish parsing the grammar.
@end deftypefun
@section The Pull Parser Function @code{yypull_parse}
@findex yypull_parse
-You call the function @code{yypull_parse} to parse the rest of the input
-stream. This function is available if the @code{%define push_pull "both"}
-declaration is used.
+You call the function @code{yypull_parse} to parse the rest of the input
+stream. This function is available if the @code{%define api.push_pull "both"}
+declaration is used.
@xref{Push Decl, ,A Push Parser}.
@deftypefun int yypull_parse (yypstate *yyps)
@section The Parser Create Function @code{yystate_new}
@findex yypstate_new
-You call the function @code{yypstate_new} to create a new parser instance.
-This function is available if either the @code{%define push_pull "push"} or
-@code{%define push_pull "both"} declaration is used.
+You call the function @code{yypstate_new} to create a new parser instance.
+This function is available if either the @code{%define api.push_pull "push"} or
+@code{%define api.push_pull "both"} declaration is used.
@xref{Push Decl, ,A Push Parser}.
@deftypefun yypstate *yypstate_new (void)
@findex yypstate_delete
You call the function @code{yypstate_delete} to delete a parser instance.
-function is available if either the @code{%define push_pull "push"} or
-@code{%define push_pull "both"} declaration is used.
+function is available if either the @code{%define api.push_pull "push"} or
+@code{%define api.push_pull "both"} declaration is used.
@xref{Push Decl, ,A Push Parser}.
@deftypefun void yypstate_delete (yypstate *yyps)
@node Pure Calling
@subsection Calling Conventions for Pure Parsers
-When you use the Bison declaration @code{%pure-parser} to request a
+When you use the Bison declaration @code{%define api.pure} to request a
pure, reentrant parser, the global communication variables @code{yylval}
and @code{yylloc} cannot be used. (@xref{Pure Decl, ,A Pure (Reentrant)
Parser}.) In such parsers the two global variables are replaced by
int yyparse (int *nastiness, int *randomness);
@end example
-If @code{%pure-parser} is added:
+If @code{%define api.pure} is added:
@example
int yylex (YYSTYPE *lvalp, int *nastiness);
@end example
@noindent
-and finally, if both @code{%pure-parser} and @code{%locations} are used:
+and finally, if both @code{%define api.pure} and @code{%locations} are used:
@example
int yylex (YYSTYPE *lvalp, YYLTYPE *llocp, int *nastiness);
an access to the current location.
This is indeed the case for the @acronym{GLR}
parsers, but not for the Yacc parser, for historical reasons. I.e., if
-@samp{%locations %pure-parser} is passed then the prototypes for
+@samp{%locations %define api.pure} is passed then the prototypes for
@code{yyerror} are:
@example
Finally, @acronym{GLR} and Yacc parsers share the same @code{yyerror} calling
convention for absolutely pure parsers, i.e., when the calling
convention of @code{yylex} @emph{and} the calling convention of
-@code{%pure-parser} are pure. I.e.:
+@code{%define api.pure} are pure.
+I.e.:
@example
/* Location tracking. */
%locations
/* Pure yylex. */
-%pure-parser
+%define api.pure
%lex-param @{int *nastiness@}
/* Pure yyparse. */
%parse-param @{int *nastiness@}
@command{bison} reports:
@example
-calc.y: warning: 1 useless nonterminal and 1 useless rule
-calc.y:11.1-7: warning: useless nonterminal: useless
-calc.y:11.10-12: warning: useless rule: useless: STR
+calc.y: warning: 1 nonterminal and 1 rule useless in grammar
+calc.y:11.1-7: warning: nonterminal useless in grammar: useless
+calc.y:11.10-12: warning: rule useless in grammar: useless: STR
calc.y: conflicts: 7 shift/reduce
@end example
The next section reports useless tokens, nonterminal and rules. Useless
nonterminals and rules are removed in order to produce a smaller parser,
but useless tokens are preserved, since they might be used by the
-scanner (note the difference between ``useless'' and ``not used''
+scanner (note the difference between ``useless'' and ``unused''
below):
@example
-Useless nonterminals:
+Nonterminals useless in grammar:
useless
-Terminals which are not used:
+Terminals unused in grammar:
STR
-Useless rules:
+Rules useless in grammar:
#6 useless: STR;
@end example
@example
state 8
- exp -> exp . '+' exp [$, '+', '-', '/'] (rule 1)
+ exp -> exp . '+' exp (rule 1)
exp -> exp '+' exp . [$, '+', '-', '/'] (rule 1)
exp -> exp . '-' exp (rule 2)
exp -> exp . '*' exp (rule 3)
@item --print-localedir
Print the name of the directory containing locale-dependent data.
+@item --print-datadir
+Print the name of the directory containing skeletons and XSLT.
+
@item -y
@itemx --yacc
Act more like the traditional Yacc command. This can cause
the full set of items for each state, instead of its core only.
@end table
+@item --report-file=@var{file}
+Specify the @var{file} for the verbose description.
+
@item -v
@itemx --verbose
Pretend that @code{%verbose} was specified, i.e., write an extra output
@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{--output=@var{outfile}} @tab @option{-o @var{outfile}}
-@item @option{--print-localedir} @tab
-@item @option{--token-table} @tab @option{-k}
-@item @option{--verbose} @tab @option{-v}
-@item @option{--version} @tab @option{-V}
-@item @option{--yacc} @tab @option{-y}
+@include cross-options.texi
@end multitable
@node Yacc Library
The parser invokes the scanner by calling @code{yylex}. Contrary to C
parsers, C++ parsers are always pure: there is no point in using the
-@code{%pure-parser} directive. Therefore the interface is as follows.
+@code{%define api.pure} directive. Therefore the interface is as follows.
@deftypemethod {parser} {int} yylex (semantic_value_type& @var{yylval}, location_type& @var{yylloc}, @var{type1} @var{arg1}, ...)
Return the next token. Its type is the return value, its semantic
@end deftypemethod
-If @code{%pure-parser} is not specified, the lexer interface
-resides in the same class (@code{YYParser}) as the Bison-generated
-parser. The fields and methods that are provided to
-this end are as follows.
+The lexer interface resides in the same class (@code{YYParser}) as the
+Bison-generated parser.
+The fields and methods that are provided to this end are as follows.
@deftypemethod {YYParser} {void} error (Location @var{l}, String @var{m})
As explained in @pxref{Java Parser Interface}, this method is defined
@display
My parser includes support for an @samp{#include}-like feature, in
which case I run @code{yyparse} from @code{yyparse}. This fails
-although I did specify I needed a @code{%pure-parser}.
+although I did specify @code{%define api.pure}.
@end display
These problems typically come not from Bison itself, but from
@end deffn
@deffn {Directive} %pure-parser
-Bison declaration to request a pure (reentrant) parser.
-@xref{Pure Decl, ,A Pure (Reentrant) Parser}.
+Deprecated version of @code{%define api.pure} (@pxref{Decl Summary, ,%define}),
+for which Bison is more careful to warn about unreasonable usage.
@end deffn
@deffn {Directive} %require "@var{version}"
@deffn {Variable} yynerrs
Global variable which Bison increments each time it reports a syntax error.
-(In a pure parser, it is a local variable within @code{yyparse}. In a
+(In a pure parser, it is a local variable within @code{yyparse}. In a
pure push parser, it is a member of yypstate.)
@xref{Error Reporting, ,The Error Reporting Function @code{yyerror}}.
@end deffn
@end deffn
@deffn {Function} yypstate_delete
-The function to delete a parser instance, produced by Bison in push mode;
+The function to delete a parser instance, produced by Bison in push mode;
call this function to delete the memory associated with a parser.
-@xref{Parser Delete Function, ,The Parser Delete Function
+@xref{Parser Delete Function, ,The Parser Delete Function
@code{yypstate_delete}}.
@end deffn
@deffn {Function} yypstate_new
-The function to create a parser instance, produced by Bison in push mode;
+The function to create a parser instance, produced by Bison in push mode;
call this function to create a new parser.
-@xref{Parser Create Function, ,The Parser Create Function
+@xref{Parser Create Function, ,The Parser Create Function
@code{yypstate_new}}.
@end deffn
@deffn {Function} yypull_parse
-The parser function produced by Bison in push mode; call this function to
-parse the rest of the input stream.
-@xref{Pull Parser Function, ,The Pull Parser Function
+The parser function produced by Bison in push mode; call this function to
+parse the rest of the input stream.
+@xref{Pull Parser Function, ,The Pull Parser Function
@code{yypull_parse}}.
@end deffn
@deffn {Function} yypush_parse
-The parser function produced by Bison in push mode; call this function to
-parse a single token. @xref{Push Parser Function, ,The Push Parser Function
+The parser function produced by Bison in push mode; call this function to
+parse a single token. @xref{Push Parser Function, ,The Push Parser Function
@code{yypush_parse}}.
@end deffn
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