+@item Default Value: @code{false}
+@end itemize
+@c api.pure
+
+
+
+@c ================================================== api.push-pull
+@item api.push-pull
+@findex %define api.push-pull
+
+@itemize @bullet
+@item Language(s): C (deterministic parsers only)
+
+@item Purpose: Requests a pull parser, a push parser, or both.
+@xref{Push Decl, ,A Push Parser}.
+(The current push parsing interface is experimental and may evolve.
+More user feedback will help to stabilize it.)
+
+@item Accepted Values: @code{pull}, @code{push}, @code{both}
+
+@item Default Value: @code{pull}
+@end itemize
+@c api.push-pull
+
+
+
+@c ================================================== api.tokens.prefix
+@item api.tokens.prefix
+@findex %define api.tokens.prefix
+
+@itemize
+@item Languages(s): all
+
+@item Purpose:
+Add a prefix to the token names when generating their definition in the
+target language. For instance
+
+@example
+%token FILE for ERROR
+%define api.tokens.prefix "TOK_"
+%%
+start: FILE for ERROR;
+@end example
+
+@noindent
+generates the definition of the symbols @code{TOK_FILE}, @code{TOK_for},
+and @code{TOK_ERROR} in the generated source files. In particular, the
+scanner must use these prefixed token names, while the grammar itself
+may still use the short names (as in the sample rule given above). The
+generated informational files (@file{*.output}, @file{*.xml},
+@file{*.dot}) are not modified by this prefix. See @ref{Calc++ Parser}
+and @ref{Calc++ Scanner}, for a complete example.
+
+@item Accepted Values:
+Any string. Should be a valid identifier prefix in the target language,
+in other words, it should typically be an identifier itself (sequence of
+letters, underscores, and ---not at the beginning--- digits).
+
+@item Default Value:
+empty
+@end itemize
+@c api.tokens.prefix
+
+
+@c ================================================== lex_symbol
+@item variant
+@findex %define lex_symbol
+
+@itemize @bullet
+@item Language(s):
+C++
+
+@item Purpose:
+When variant-based semantic values are enabled (@pxref{C++ Variants}),
+request that symbols be handled as a whole (type, value, and possibly
+location) in the scanner. @xref{Complete Symbols}, for details.
+
+@item Accepted Values:
+Boolean.
+
+@item Default Value:
+@code{false}
+@end itemize
+@c lex_symbol
+
+
+@c ================================================== lr.default-reductions
+
+@item lr.default-reductions
+@cindex default reductions
+@findex %define lr.default-reductions
+@cindex delayed syntax errors
+@cindex syntax errors delayed
+
+@itemize @bullet
+@item Language(s): all
+
+@item Purpose: Specifies the kind of states that are permitted to
+contain default reductions.
+That is, in such a state, Bison declares the reduction with the largest
+lookahead set to be the default reduction and then removes that
+lookahead set.
+The advantages of default reductions are discussed below.
+The disadvantage is that, when the generated parser encounters a
+syntactically unacceptable token, the parser might then perform
+unnecessary default reductions before it can detect the syntax error.
+
+(This feature is experimental.
+More user feedback will help to stabilize it.)
+
+@item Accepted Values:
+@itemize
+@item @code{all}.
+For @acronym{LALR} and @acronym{IELR} parsers (@pxref{Decl
+Summary,,lr.type}) by default, all states are permitted to contain
+default reductions.
+The advantage is that parser table sizes can be significantly reduced.
+The reason Bison does not by default attempt to address the disadvantage
+of delayed syntax error detection is that this disadvantage is already
+inherent in @acronym{LALR} and @acronym{IELR} parser tables.
+That is, unlike in a canonical @acronym{LR} state, the lookahead sets of
+reductions in an @acronym{LALR} or @acronym{IELR} state can contain
+tokens that are syntactically incorrect for some left contexts.
+
+@item @code{consistent}.
+@cindex consistent states
+A consistent state is a state that has only one possible action.
+If that action is a reduction, then the parser does not need to request
+a lookahead token from the scanner before performing that action.
+However, the parser only recognizes the ability to ignore the lookahead
+token when such a reduction is encoded as a default reduction.
+Thus, if default reductions are permitted in and only in consistent
+states, then a canonical @acronym{LR} parser reports a syntax error as
+soon as it @emph{needs} the syntactically unacceptable token from the
+scanner.
+
+@item @code{accepting}.
+@cindex accepting state
+By default, the only default reduction permitted in a canonical
+@acronym{LR} parser is the accept action in the accepting state, which
+the parser reaches only after reading all tokens from the input.
+Thus, the default canonical @acronym{LR} parser reports a syntax error
+as soon as it @emph{reaches} the syntactically unacceptable token
+without performing any extra reductions.
+@end itemize
+
+@item Default Value:
+@itemize
+@item @code{accepting} if @code{lr.type} is @code{canonical-lr}.
+@item @code{all} otherwise.
+@end itemize
+@end itemize
+
+@c ============================================ lr.keep-unreachable-states
+
+@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
+@c lr.keep-unreachable-states
+
+@c ================================================== lr.type
+
+@item lr.type
+@findex %define lr.type
+@cindex @acronym{LALR}
+@cindex @acronym{IELR}
+@cindex @acronym{LR}
+
+@itemize @bullet
+@item Language(s): all
+
+@item Purpose: Specifies the type of parser tables within the
+@acronym{LR}(1) family.
+(This feature is experimental.
+More user feedback will help to stabilize it.)
+
+@item Accepted Values:
+@itemize
+@item @code{lalr}.
+While Bison generates @acronym{LALR} parser tables by default for
+historical reasons, @acronym{IELR} or canonical @acronym{LR} is almost
+always preferable for deterministic parsers.
+The trouble is that @acronym{LALR} parser tables can suffer from
+mysterious conflicts and thus may not accept the full set of sentences
+that @acronym{IELR} and canonical @acronym{LR} accept.
+@xref{Mystery Conflicts}, for details.
+However, there are at least two scenarios where @acronym{LALR} may be
+worthwhile:
+@itemize
+@cindex @acronym{GLR} with @acronym{LALR}
+@item When employing @acronym{GLR} parsers (@pxref{GLR Parsers}), if you
+do not resolve any conflicts statically (for example, with @code{%left}
+or @code{%prec}), then the parser explores all potential parses of any
+given input.
+In this case, the use of @acronym{LALR} parser tables is guaranteed not
+to alter the language accepted by the parser.
+@acronym{LALR} parser tables are the smallest parser tables Bison can
+currently generate, so they may be preferable.
+
+@item Occasionally during development, an especially malformed grammar
+with a major recurring flaw may severely impede the @acronym{IELR} or
+canonical @acronym{LR} parser table generation algorithm.
+@acronym{LALR} can be a quick way to generate parser tables in order to
+investigate such problems while ignoring the more subtle differences
+from @acronym{IELR} and canonical @acronym{LR}.
+@end itemize
+
+@item @code{ielr}.
+@acronym{IELR} is a minimal @acronym{LR} algorithm.
+That is, given any grammar (@acronym{LR} or non-@acronym{LR}),
+@acronym{IELR} and canonical @acronym{LR} always accept exactly the same
+set of sentences.
+However, as for @acronym{LALR}, the number of parser states is often an
+order of magnitude less for @acronym{IELR} than for canonical
+@acronym{LR}.
+More importantly, because canonical @acronym{LR}'s extra parser states
+may contain duplicate conflicts in the case of non-@acronym{LR}
+grammars, the number of conflicts for @acronym{IELR} is often an order
+of magnitude less as well.
+This can significantly reduce the complexity of developing of a grammar.
+
+@item @code{canonical-lr}.
+@cindex delayed syntax errors
+@cindex syntax errors delayed
+The only advantage of canonical @acronym{LR} over @acronym{IELR} is
+that, for every left context of every canonical @acronym{LR} state, the
+set of tokens accepted by that state is the exact set of tokens that is
+syntactically acceptable in that left context.
+Thus, the only difference in parsing behavior is that the canonical
+@acronym{LR} parser can report a syntax error as soon as possible
+without performing any unnecessary reductions.
+@xref{Decl Summary,,lr.default-reductions}, for further details.
+Even when canonical @acronym{LR} behavior is ultimately desired,
+@acronym{IELR}'s elimination of duplicate conflicts should still
+facilitate the development of a grammar.
+@end itemize
+
+@item Default Value: @code{lalr}
+@end itemize
+
+
+@c ================================================== namespace
+@item namespace
+@findex %define namespace
+Obsoleted by @code{api.namespace}
+@c namespace
+
+
+@c ================================================== parse.assert
+@item parse.assert
+@findex %define parse.assert
+
+@itemize
+@item Languages(s): C++
+
+@item Purpose: Issue runtime assertions to catch invalid uses.
+In C++, when variants are used (@pxref{C++ Variants}), symbols must be
+constructed and
+destroyed properly. This option checks these constraints.
+
+@item Accepted Values: Boolean
+
+@item Default Value: @code{false}
+@end itemize
+@c parse.assert
+
+
+@c ================================================== parse.error
+@item parse.error
+@findex %define parse.error
+@itemize
+@item Languages(s):
+all.
+@item Purpose:
+Control the kind of error messages passed to the error reporting
+function. @xref{Error Reporting, ,The Error Reporting Function
+@code{yyerror}}.
+@item Accepted Values:
+@itemize
+@item @code{simple}
+Error messages passed to @code{yyerror} are simply @w{@code{"syntax
+error"}}.
+@item @code{verbose}
+Error messages report the unexpected token, and possibly the expected
+ones.
+@end itemize
+
+@item Default Value:
+@code{simple}
+@end itemize
+@c parse.error
+
+
+@c ================================================== parse.trace
+@item parse.trace
+@findex %define parse.trace
+
+@itemize
+@item Languages(s): C, C++
+
+@item Purpose: Require parser instrumentation for tracing.
+In C/C++, define the macro @code{YYDEBUG} to 1 in the parser file if it
+is not already defined, so that the debugging facilities are compiled.
+@xref{Tracing, ,Tracing Your Parser}.
+
+@item Accepted Values: Boolean
+
+@item Default Value: @code{false}
+@end itemize
+@c parse.trace
+
+@c ================================================== variant
+@item variant
+@findex %define variant
+
+@itemize @bullet
+@item Language(s):
+C++
+
+@item Purpose:
+Requests variant-based semantic values.
+@xref{C++ Variants}.
+
+@item Accepted Values:
+Boolean.
+
+@item Default Value:
+@code{false}
+@end itemize
+@c variant
+
+
+@end table
+@end deffn
+@c ---------------------------------------------------------- %define
+
+@deffn {Directive} %defines
+Write a header file containing macro definitions for the token type
+names defined in the grammar as well as a few other declarations.
+If the parser output file is named @file{@var{name}.c} then this file
+is named @file{@var{name}.h}.
+
+For C parsers, the output header declares @code{YYSTYPE} unless
+@code{YYSTYPE} is already defined as a macro or you have used a
+@code{<@var{type}>} tag without using @code{%union}.
+Therefore, if you are using a @code{%union}
+(@pxref{Multiple Types, ,More Than One Value Type}) with components that
+require other definitions, or if you have defined a @code{YYSTYPE} macro
+or type definition
+(@pxref{Value Type, ,Data Types of Semantic Values}), you need to
+arrange for these definitions to be propagated to all modules, e.g., by
+putting them in a prerequisite header that is included both by your
+parser and by any other module that needs @code{YYSTYPE}.
+
+Unless your parser is pure, the output header declares @code{yylval}
+as an external variable. @xref{Pure Decl, ,A Pure (Reentrant)
+Parser}.
+
+If you have also used locations, the output header declares
+@code{YYLTYPE} and @code{yylloc} using a protocol similar to that of
+the @code{YYSTYPE} macro and @code{yylval}. @xref{Locations, ,Tracking
+Locations}.
+
+This output file is normally essential if you wish to put the definition
+of @code{yylex} in a separate source file, because @code{yylex}
+typically needs to be able to refer to the above-mentioned declarations
+and to the token type codes. @xref{Token Values, ,Semantic Values of
+Tokens}.
+
+@findex %code requires
+@findex %code provides
+If you have declared @code{%code requires} or @code{%code provides}, the output
+header also contains their code.
+@xref{Decl Summary, ,%code}.
+@end deffn
+
+@deffn {Directive} %defines @var{defines-file}
+Same as above, but save in the file @var{defines-file}.
+@end deffn
+
+@deffn {Directive} %destructor
+Specify how the parser should reclaim the memory associated to
+discarded symbols. @xref{Destructor Decl, , Freeing Discarded Symbols}.
+@end deffn
+
+@deffn {Directive} %file-prefix "@var{prefix}"
+Specify a prefix to use for all Bison output file names. The names are
+chosen as if the input file were named @file{@var{prefix}.y}.
+@end deffn
+
+@deffn {Directive} %language "@var{language}"
+Specify the programming language for the generated parser. Currently
+supported languages include C, C++, and Java.
+@var{language} is case-insensitive.
+
+This directive is experimental and its effect may be modified in future
+releases.
+@end deffn
+
+@deffn {Directive} %locations
+Generate the code processing the locations (@pxref{Action Features,
+,Special Features for Use in Actions}). This mode is enabled as soon as
+the grammar uses the special @samp{@@@var{n}} tokens, but if your
+grammar does not use it, using @samp{%locations} allows for more
+accurate syntax error messages.
+@end deffn
+
+@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{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
+names become @code{c_parse}, @code{c_lex}, and so on.
+For C++ parsers, see the @samp{%define api.namespace} documentation in this
+section.
+@xref{Multiple Parsers, ,Multiple Parsers in the Same Program}.
+@end deffn
+
+@ifset defaultprec
+@deffn {Directive} %no-default-prec
+Do not assign a precedence to rules lacking an explicit @code{%prec}
+modifier (@pxref{Contextual Precedence, ,Context-Dependent
+Precedence}).
+@end deffn
+@end ifset
+
+@deffn {Directive} %no-lines
+Don't generate any @code{#line} preprocessor commands in the parser
+file. Ordinarily Bison writes these commands in the parser file so that
+the C compiler and debuggers will associate errors and object code with
+your source file (the grammar file). This directive causes them to
+associate errors with the parser file, treating it an independent source
+file in its own right.
+@end deffn
+
+@deffn {Directive} %output "@var{file}"
+Specify @var{file} for the parser file.
+@end deffn
+
+@deffn {Directive} %pure-parser
+Deprecated version of @samp{%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}"
+Require version @var{version} or higher of Bison. @xref{Require Decl, ,
+Require a Version of Bison}.
+@end deffn
+
+@deffn {Directive} %skeleton "@var{file}"
+Specify the skeleton to use.
+
+@c You probably don't need this option unless you are developing Bison.
+@c You should use @code{%language} if you want to specify the skeleton for a
+@c different language, because it is clearer and because it will always choose the
+@c correct skeleton for non-deterministic or push parsers.
+
+If @var{file} does not contain a @code{/}, @var{file} is the name of a skeleton
+file in the Bison installation directory.
+If it does, @var{file} is an absolute file name or a file name relative to the
+directory of the grammar file.
+This is similar to how most shells resolve commands.
+@end deffn
+
+@deffn {Directive} %token-table
+Generate an array of token names in the parser file. The name of the
+array is @code{yytname}; @code{yytname[@var{i}]} is the name of the
+token whose internal Bison token code number is @var{i}. The first
+three elements of @code{yytname} correspond to the predefined tokens
+@code{"$end"},
+@code{"error"}, and @code{"$undefined"}; after these come the symbols
+defined in the grammar file.
+
+The name in the table includes all the characters needed to represent
+the token in Bison. For single-character literals and literal
+strings, this includes the surrounding quoting characters and any
+escape sequences. For example, the Bison single-character literal
+@code{'+'} corresponds to a three-character name, represented in C as
+@code{"'+'"}; and the Bison two-character literal string @code{"\\/"}
+corresponds to a five-character name, represented in C as
+@code{"\"\\\\/\""}.
+
+When you specify @code{%token-table}, Bison also generates macro
+definitions for macros @code{YYNTOKENS}, @code{YYNNTS}, and
+@code{YYNRULES}, and @code{YYNSTATES}:
+
+@table @code
+@item YYNTOKENS
+The highest token number, plus one.
+@item YYNNTS
+The number of nonterminal symbols.
+@item YYNRULES
+The number of grammar rules,
+@item YYNSTATES
projects / bison.git / blobdiff