+@item Purpose: Specify the namespace for the parser class.
+For example, if you specify:
+
+@smallexample
+%define api.namespace "foo::bar"
+@end smallexample
+
+Bison uses @code{foo::bar} verbatim in references such as:
+
+@smallexample
+foo::bar::parser::semantic_type
+@end smallexample
+
+However, to open a namespace, Bison removes any leading @code{::} and then
+splits on any remaining occurrences:
+
+@smallexample
+namespace foo @{ namespace bar @{
+ class position;
+ class location;
+@} @}
+@end smallexample
+
+@item Accepted Values:
+Any absolute or relative C++ namespace reference without a trailing
+@code{"::"}. For example, @code{"foo"} or @code{"::foo::bar"}.
+
+@item Default Value:
+The value specified by @code{%name-prefix}, which defaults to @code{yy}.
+This usage of @code{%name-prefix} is for backward compatibility and can
+be confusing since @code{%name-prefix} also specifies the textual prefix
+for the lexical analyzer function. Thus, if you specify
+@code{%name-prefix}, it is best to also specify @samp{%define
+api.namespace} so that @code{%name-prefix} @emph{only} affects the
+lexical analyzer function. For example, if you specify:
+
+@smallexample
+%define api.namespace "foo"
+%name-prefix "bar::"
+@end smallexample
+
+The parser namespace is @code{foo} and @code{yylex} is referenced as
+@code{bar::lex}.
+@end itemize
+@c namespace
+
+
+
+@c ================================================== api.pure
+@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
+@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: Request 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 lex_symbol
+@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
+@cindex LAC
+@findex %nonassoc
+
+@itemize @bullet
+@item Language(s): all
+
+@item Purpose: Specify the kind of states that are permitted to
+contain default reductions.
+That is, in such a state, Bison selects the reduction with the largest
+lookahead set to be the default parser action and then removes that
+lookahead set.
+(The ability to specify where default reductions should be used is
+experimental.
+More user feedback will help to stabilize it.)
+
+@item Accepted Values:
+@itemize
+@item @code{all}.
+This is the traditional Bison behavior. The main advantage is a
+significant decrease in the size of the parser tables. 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.
+Such delayed syntax error detection is usually inherent in LALR and
+IELR parser tables anyway due to LR state merging (@pxref{%define
+Summary,,lr.type}). Furthermore, the use of @code{%nonassoc} can
+contribute to delayed syntax error detection even in the case of
+canonical LR. As an experimental feature, delayed syntax error
+detection can be overcome in all cases by enabling LAC (@pxref{%define
+Summary,,parse.lac}, for details, including a discussion of the
+effects of delayed syntax error detection).
+
+@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 recognizes the ability to ignore the lookahead token
+in this way only when such a reduction is encoded as a default
+reduction.
+Thus, if default reductions are permitted only in consistent states,
+then a canonical LR parser that does not employ
+@code{%nonassoc} detects a syntax error as soon as it @emph{needs} the
+syntactically unacceptable token from the scanner.
+
+@item @code{accepting}.
+@cindex accepting state
+In the accepting state, the default reduction is actually the accept
+action.
+In this case, a canonical LR parser that does not employ
+@code{%nonassoc} detects a syntax error as soon as it @emph{reaches} the
+syntactically unacceptable token in the input.
+That is, it does not perform 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: Request 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 LALR
+@cindex IELR
+@cindex LR
+
+@itemize @bullet
+@item Language(s): all
+
+@item Purpose: Specify the type of parser tables within the
+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 LALR parser tables by default for
+historical reasons, IELR or canonical LR is almost
+always preferable for deterministic parsers.
+The trouble is that LALR parser tables can suffer from
+mysterious conflicts and thus may not accept the full set of sentences
+that IELR and canonical LR accept.
+@xref{Mystery Conflicts}, for details.
+However, there are at least two scenarios where LALR may be
+worthwhile:
+@itemize
+@cindex GLR with LALR
+@item When employing 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 LALR parser tables is guaranteed not
+to alter the language accepted by the parser.
+LALR parser tables are the smallest parser tables Bison can
+currently generate, so they may be preferable.
+Nevertheless, once you begin to resolve conflicts statically,
+GLR begins to behave more like a deterministic parser, and so
+IELR and canonical LR can be helpful to avoid
+LALR's mysterious behavior.
+
+@item Occasionally during development, an especially malformed grammar
+with a major recurring flaw may severely impede the IELR or
+canonical LR parser table generation algorithm.
+LALR can be a quick way to generate parser tables in order to
+investigate such problems while ignoring the more subtle differences
+from IELR and canonical LR.
+@end itemize
+
+@item @code{ielr}.
+IELR is a minimal LR algorithm.
+That is, given any grammar (LR or non-LR),
+IELR and canonical LR always accept exactly the same
+set of sentences.
+However, as for LALR, the number of parser states is often an
+order of magnitude less for IELR than for canonical
+LR.
+More importantly, because canonical LR's extra parser states
+may contain duplicate conflicts in the case of non-LR
+grammars, the number of conflicts for 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
+@cindex LAC
+@findex %nonassoc
+While inefficient, canonical LR parser tables can be an interesting
+means to explore a grammar because they have a property that IELR and
+LALR tables do not. That is, if @code{%nonassoc} is not used and
+default reductions are left disabled (@pxref{%define
+Summary,,lr.default-reductions}), then, for every left context of
+every canonical LR state, the set of tokens accepted by that state is
+guaranteed to be the exact set of tokens that is syntactically
+acceptable in that left context. It might then seem that an advantage
+of canonical LR parsers in production is that, under the above
+constraints, they are guaranteed to detect a syntax error as soon as
+possible without performing any unnecessary reductions. However, IELR
+parsers using LAC (@pxref{%define Summary,,parse.lac}) are also able
+to achieve this behavior without sacrificing @code{%nonassoc} or
+default reductions.
+@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.lac
+@item parse.lac
+@findex %define parse.lac
+@cindex LAC
+@cindex lookahead correction
+
+@itemize
+@item Languages(s): C
+
+@item Purpose: Enable LAC (lookahead correction) to improve
+syntax error handling.
+
+Canonical LR, IELR, and LALR can suffer
+from a couple of problems upon encountering a syntax error. First, the
+parser might perform additional parser stack reductions before
+discovering the syntax error. Such reductions perform user semantic
+actions that are unexpected because they are based on an invalid token,
+and they cause error recovery to begin in a different syntactic context
+than the one in which the invalid token was encountered. Second, when
+verbose error messages are enabled (with @code{%error-verbose} or
+@code{#define YYERROR_VERBOSE}), the expected token list in the syntax
+error message can both contain invalid tokens and omit valid tokens.
+
+The culprits for the above problems are @code{%nonassoc}, default
+reductions in inconsistent states, and parser state merging. Thus,
+IELR and LALR suffer the most. Canonical
+LR can suffer only if @code{%nonassoc} is used or if default
+reductions are enabled for inconsistent states.
+
+LAC is a new mechanism within the parsing algorithm that
+completely solves these problems for canonical LR,
+IELR, and LALR without sacrificing @code{%nonassoc},
+default reductions, or state mering. Conceptually, the mechanism is
+straight-forward. Whenever the parser fetches a new token from the
+scanner so that it can determine the next parser action, it immediately
+suspends normal parsing and performs an exploratory parse using a
+temporary copy of the normal parser state stack. During this
+exploratory parse, the parser does not perform user semantic actions.
+If the exploratory parse reaches a shift action, normal parsing then
+resumes on the normal parser stacks. If the exploratory parse reaches
+an error instead, the parser reports a syntax error. If verbose syntax
+error messages are enabled, the parser must then discover the list of
+expected tokens, so it performs a separate exploratory parse for each
+token in the grammar.
+
+There is one subtlety about the use of LAC. That is, when in a
+consistent parser state with a default reduction, the parser will not
+attempt to fetch a token from the scanner because no lookahead is
+needed to determine the next parser action. Thus, whether default
+reductions are enabled in consistent states (@pxref{%define
+Summary,,lr.default-reductions}) affects how soon the parser detects a
+syntax error: when it @emph{reaches} an erroneous token or when it
+eventually @emph{needs} that token as a lookahead. The latter
+behavior is probably more intuitive, so Bison currently provides no
+way to achieve the former behavior while default reductions are fully
+enabled.
+
+Thus, when LAC is in use, for some fixed decision of whether
+to enable default reductions in consistent states, canonical
+LR and IELR behave exactly the same for both
+syntactically acceptable and syntactically unacceptable input. While
+LALR still does not support the full language-recognition
+power of canonical LR and IELR, LAC at
+least enables LALR's syntax error handling to correctly
+reflect LALR's language-recognition power.
+
+Because LAC requires many parse actions to be performed twice,
+it can have a performance penalty. However, not all parse actions must
+be performed twice. Specifically, during a series of default reductions
+in consistent states and shift actions, the parser never has to initiate
+an exploratory parse. Moreover, the most time-consuming tasks in a
+parse are often the file I/O, the lexical analysis performed by the
+scanner, and the user's semantic actions, but none of these are
+performed during the exploratory parse. Finally, the base of the
+temporary stack used during an exploratory parse is a pointer into the
+normal parser state stack so that the stack is never physically copied.
+In our experience, the performance penalty of LAC has proven
+insignificant for practical grammars.
+
+@item Accepted Values: @code{none}, @code{full}
+
+@item Default Value: @code{none}
+@end itemize
+@c parse.lac
+
+@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 implementation
+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:
+Request variant-based semantic values.
+@xref{C++ Variants}.
+
+@item Accepted Values:
+Boolean.
+
+@item Default Value:
+@code{false}
+@end itemize
+@c variant
+@end table
+
+
+@node %code Summary
+@subsection %code Summary
+@findex %code
+@cindex Prologue
+
+The @code{%code} directive inserts code verbatim into the output
+parser source at any of a predefined set of locations. It thus serves
+as a flexible and user-friendly alternative to the traditional Yacc
+prologue, @code{%@{@var{code}%@}}. This section summarizes the
+functionality of @code{%code} for the various target languages
+supported by Bison. For a detailed discussion of how to use
+@code{%code} in place of @code{%@{@var{code}%@}} for C/C++ and why it
+is advantageous to do so, @pxref{Prologue Alternatives}.
+
+@deffn {Directive} %code @{@var{code}@}
+This is the unqualified form of the @code{%code} directive. It
+inserts @var{code} verbatim at a language-dependent default location
+in the parser implementation.
+
+For C/C++, the default location is the parser implementation file
+after the usual contents of the parser header file. Thus, the
+unqualified form replaces @code{%@{@var{code}%@}} for most purposes.
+
+For Java, the default location is inside the parser class.
+@end deffn
+
+@deffn {Directive} %code @var{qualifier} @{@var{code}@}
+This is the qualified form of the @code{%code} directive.
+@var{qualifier} identifies the purpose of @var{code} and thus the
+location(s) where Bison should insert it. That is, if you need to
+specify location-sensitive @var{code} that does not belong at the
+default location selected by the unqualified @code{%code} form, use
+this form instead.
+@end deffn
+
+For any particular qualifier or for the unqualified form, if there are
+multiple occurrences of the @code{%code} directive, Bison concatenates
+the specified code in the order in which it appears in the grammar
+file.
+
+Not all qualifiers are accepted for all target languages. Unaccepted
+qualifiers produce an error. Some of the accepted qualifiers are:
+
+@table @code
+@item requires
+@findex %code requires
+
+@itemize @bullet
+@item Language(s): C, C++
+
+@item Purpose: This is the best place to write dependency code required for
+@code{YYSTYPE} and @code{YYLTYPE}.
+In other words, it's the best place to define types referenced in @code{%union}
+directives, and it's the best place to override Bison's default @code{YYSTYPE}
+and @code{YYLTYPE} definitions.
+
+@item Location(s): The parser header file and the parser implementation file
+before the Bison-generated @code{YYSTYPE} and @code{YYLTYPE}
+definitions.
+@end itemize
+
+@item provides
+@findex %code provides
+
+@itemize @bullet
+@item Language(s): C, C++
+
+@item Purpose: This is the best place to write additional definitions and
+declarations that should be provided to other modules.
+
+@item Location(s): The parser header file and the parser implementation
+file after the Bison-generated @code{YYSTYPE}, @code{YYLTYPE}, and
+token definitions.
+@end itemize
+
+@item top
+@findex %code top
+
+@itemize @bullet
+@item Language(s): C, C++
+
+@item Purpose: The unqualified @code{%code} or @code{%code requires}
+should usually be more appropriate than @code{%code top}. However,
+occasionally it is necessary to insert code much nearer the top of the
+parser implementation file. For example:
+
+@smallexample
+%code top @{
+ #define _GNU_SOURCE
+ #include <stdio.h>
+@}
+@end smallexample
+
+@item Location(s): Near the top of the parser implementation file.
+@end itemize
+
+@item imports
+@findex %code imports
+
+@itemize @bullet
+@item Language(s): Java
+
+@item Purpose: This is the best place to write Java import directives.
+
+@item Location(s): The parser Java file after any Java package directive and
+before any class definitions.
+@end itemize
+@end table
+
+Though we say the insertion locations are language-dependent, they are
+technically skeleton-dependent. Writers of non-standard skeletons
+however should choose their locations consistently with the behavior
+of the standard Bison skeletons.
+
+
+@node Multiple Parsers
+@section Multiple Parsers in the Same Program
+
+Most programs that use Bison parse only one language and therefore contain
+only one Bison parser. But what if you want to parse more than one
+language with the same program? Then you need to avoid a name conflict
+between different definitions of @code{yyparse}, @code{yylval}, and so on.
+
+The easy way to do this is to use the option @samp{-p @var{prefix}}
+(@pxref{Invocation, ,Invoking Bison}). This renames the interface
+functions and variables of the Bison parser to start with @var{prefix}
+instead of @samp{yy}. You can use this to give each parser distinct
+names that do not conflict.
+
+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{yypstate_new} and @code{yypstate_delete} will also be renamed.
+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
+renamed.} These others are not global; there is no conflict if the same
+name is used in different parsers. For example, @code{YYSTYPE} is not
+renamed, but defining this in different ways in different parsers causes
+no trouble (@pxref{Value Type, ,Data Types of Semantic Values}).
+
+The @samp{-p} option works by adding macro definitions to the
+beginning of the parser implementation file, defining @code{yyparse}
+as @code{@var{prefix}parse}, and so on. This effectively substitutes
+one name for the other in the entire parser implementation file.
+
+@node Interface
+@chapter Parser C-Language Interface
+@cindex C-language interface
+@cindex interface
+
+The Bison parser is actually a C function named @code{yyparse}. Here we
+describe the interface conventions of @code{yyparse} and the other
+functions that it needs to use.
+
+Keep in mind that the parser uses many C identifiers starting with
+@samp{yy} and @samp{YY} for internal purposes. If you use such an
+identifier (aside from those in this manual) in an action or in epilogue
+in the grammar file, you are likely to run into trouble.
+
+@menu
+* Parser Function:: How to call @code{yyparse} and what it returns.
+* Push Parser Function:: How to call @code{yypush_parse} and what it returns.
+* Pull Parser Function:: How to call @code{yypull_parse} and what it returns.
+* Parser Create Function:: How to call @code{yypstate_new} and what it returns.
+* Parser Delete Function:: How to call @code{yypstate_delete} and what it returns.
+* Lexical:: You must supply a function @code{yylex}
+ which reads tokens.
+* Error Reporting:: You must supply a function @code{yyerror}.
+* Action Features:: Special features for use in actions.
+* Internationalization:: How to let the parser speak in the user's
+ native language.
+@end menu
+
+@node Parser Function
+@section The Parser Function @code{yyparse}
+@findex yyparse
+
+You call the function @code{yyparse} to cause parsing to occur. This
+function reads tokens, executes actions, and ultimately returns when it
+encounters end-of-input or an unrecoverable syntax error. You can also
+write an action which directs @code{yyparse} to return immediately
+without reading further.
+
+
+@deftypefun int yyparse (void)
projects / bison.git / blobdiff