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.
Grammar Rules for @code{rpcalc}
-* Rpcalc Input::
-* Rpcalc Line::
-* Rpcalc Expr::
+* Rpcalc Input:: Explanation of the @code{input} nonterminal
+* Rpcalc Line:: Explanation of the @code{line} nonterminal
+* Rpcalc Expr:: Explanation of the @code{expr} nonterminal
Location Tracking Calculator: @code{ltcalc}
* Mfcalc Declarations:: Bison declarations for multi-function calculator.
* Mfcalc Rules:: Grammar rules for the calculator.
* Mfcalc Symbol Table:: Symbol table management subroutines.
+* Mfcalc Lexer:: The lexical analyzer.
+* Mfcalc Main:: The controlling function.
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
Here are the C and Bison declarations for the reverse polish notation
calculator. As in C, comments are placed between @samp{/*@dots{}*/}.
+@comment file: rpcalc.y
@example
/* Reverse polish notation calculator. */
%@{
#define YYSTYPE double
+ #include <stdio.h>
#include <math.h>
int yylex (void);
void yyerror (char const *);
Here are the grammar rules for the reverse polish notation calculator.
+@comment file: rpcalc.y
@example
input: /* empty */
| input line
;
line: '\n'
- | exp '\n' @{ printf ("\t%.10g\n", $1); @}
+ | exp '\n' @{ printf ("%.10g\n", $1); @}
;
exp: NUM @{ $$ = $1; @}
rule are referred to as @code{$1}, @code{$2}, and so on.
@menu
-* Rpcalc Input::
-* Rpcalc Line::
-* Rpcalc Expr::
+* Rpcalc Input:: Explanation of the @code{input} nonterminal
+* Rpcalc Line:: Explanation of the @code{line} nonterminal
+* Rpcalc Expr:: Explanation of the @code{expr} nonterminal
@end menu
@node Rpcalc Input
@example
line: '\n'
- | exp '\n' @{ printf ("\t%.10g\n", $1); @}
+ | exp '\n' @{ printf ("%.10g\n", $1); @}
;
@end example
Here is the code for the lexical analyzer:
+@comment file: rpcalc.y
@example
@group
/* The lexical analyzer returns a double floating point
kept to the bare minimum. The only requirement is that it call
@code{yyparse} to start the process of parsing.
+@comment file: rpcalc.y
@example
@group
int
@code{yyerror} (@pxref{Interface, ,Parser C-Language Interface}), so
here is the definition we will use:
+@comment file: rpcalc.y
@example
@group
#include <stdio.h>
@example
$ @kbd{rpcalc}
@kbd{4 9 +}
-13
+@result{} 13
@kbd{3 7 + 3 4 5 *+-}
--13
+@result{} -13
@kbd{3 7 + 3 4 5 * + - n} @r{Note the unary minus, @samp{n}}
-13
+@result{} 13
@kbd{5 6 / 4 n +}
--3.166666667
+@result{} -3.166666667
@kbd{3 4 ^} @r{Exponentiation}
-81
+@result{} 81
@kbd{^D} @r{End-of-file indicator}
$
@end example
@example
$ @kbd{mfcalc}
@kbd{pi = 3.141592653589}
-3.1415926536
+@result{} 3.1415926536
@kbd{sin(pi)}
-0.0000000000
+@result{} 0.0000000000
@kbd{alpha = beta1 = 2.3}
-2.3000000000
+@result{} 2.3000000000
@kbd{alpha}
-2.3000000000
+@result{} 2.3000000000
@kbd{ln(alpha)}
-0.8329091229
+@result{} 0.8329091229
@kbd{exp(ln(beta1))}
-2.3000000000
+@result{} 2.3000000000
$
@end example
* Mfcalc Declarations:: Bison declarations for multi-function calculator.
* Mfcalc Rules:: Grammar rules for the calculator.
* Mfcalc Symbol Table:: Symbol table management subroutines.
+* Mfcalc Lexer:: The lexical analyzer.
+* Mfcalc Main:: The controlling function.
@end menu
@node Mfcalc Declarations
Here are the C and Bison declarations for the multi-function calculator.
+@comment file: mfcalc.y
@smallexample
@group
%@{
- #include <math.h> /* For math functions, cos(), sin(), etc. */
- #include "calc.h" /* Contains definition of `symrec'. */
+ #include <stdio.h> /* For printf, etc. */
+ #include <math.h> /* For pow, used in the grammar. */
+ #include "calc.h" /* Contains definition of `symrec'. */
int yylex (void);
void yyerror (char const *);
%@}
Most of them are copied directly from @code{calc}; three rules,
those which mention @code{VAR} or @code{FNCT}, are new.
+@comment file: mfcalc.y
@smallexample
@group
input: /* empty */
@group
line:
'\n'
- | exp '\n' @{ printf ("\t%.10g\n", $1); @}
- | error '\n' @{ yyerrok; @}
+ | exp '\n' @{ printf ("%.10g\n", $1); @}
+ | error '\n' @{ yyerrok; @}
;
@end group
definition, which is kept in the header @file{calc.h}, is as follows. It
provides for either functions or variables to be placed in the table.
+@comment file: calc.h
@smallexample
@group
/* Function type. */
@end group
@end smallexample
-The new version of @code{main} includes a call to @code{init_table}, a
-function that initializes the symbol table. Here it is, and
-@code{init_table} as well:
+The new version of @code{main} will call @code{init_table} to initialize
+the symbol table:
+@comment file: mfcalc.y
@smallexample
-#include <stdio.h>
-
-@group
-/* Called by yyparse on error. */
-void
-yyerror (char const *s)
-@{
- printf ("%s\n", s);
-@}
-@end group
-
@group
struct init
@{
@group
struct init const arith_fncts[] =
@{
- "sin", sin,
- "cos", cos,
- "atan", atan,
- "ln", log,
- "exp", exp,
- "sqrt", sqrt,
- 0, 0
+ @{ "atan", atan @},
+ @{ "cos", cos @},
+ @{ "exp", exp @},
+ @{ "ln", log @},
+ @{ "sin", sin @},
+ @{ "sqrt", sqrt @},
+ @{ 0, 0 @},
@};
@end group
@group
/* Put arithmetic functions in table. */
+static
void
init_table (void)
@{
@}
@}
@end group
-
-@group
-int
-main (void)
-@{
- init_table ();
- return yyparse ();
-@}
-@end group
@end smallexample
By simply editing the initialization list and adding the necessary include
The function @code{getsym} is passed the name of the symbol to look up. If
found, a pointer to that symbol is returned; otherwise zero is returned.
+@comment file: mfcalc.y
@smallexample
+#include <stdlib.h> /* malloc. */
+#include <string.h> /* strlen. */
+
symrec *
putsym (char const *sym_name, int sym_type)
@{
@}
@end smallexample
+@node Mfcalc Lexer
+@subsection The @code{mfcalc} Lexer
+
The function @code{yylex} must now recognize variables, numeric values, and
the single-character arithmetic operators. Strings of alphanumeric
characters with a leading letter are recognized as either variables or
No change is needed in the handling of numeric values and arithmetic
operators in @code{yylex}.
+@comment file: mfcalc.y
@smallexample
@group
#include <ctype.h>
/* Initially make the buffer long enough
for a 40-character symbol name. */
if (length == 0)
- length = 40, symbuf = (char *)malloc (length + 1);
+ @{
+ length = 40;
+ symbuf = (char *) malloc (length + 1);
+ @}
i = 0;
do
@end group
@end smallexample
+@node Mfcalc Main
+@subsection The @code{mfcalc} Main
+
+The error reporting function is unchanged, and the new version of
+@code{main} includes a call to @code{init_table}:
+
+@comment file: mfcalc.y
+@smallexample
+
+@group
+@group
+/* Called by yyparse on error. */
+void
+yyerror (char const *s)
+@{
+ fprintf (stderr, "%s\n", s);
+@}
+@end group
+
+int
+main (int argc, char const* argv[])
+@{
+ init_table ();
+ return yyparse ();
+@}
+@end group
+@end smallexample
+
This program is both powerful and flexible. You may easily add new
functions, and it is a simple job to modify this code to install
predefined variables such as @code{pi} or @code{e} as well.
@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
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
bracketed syntax @code{$[name]} and @code{@@[name]} must be used:
@example
@group
-if-stmt: IF '(' expr ')' THEN then.stmt ';'
+if-stmt: "if" '(' expr ')' "then" then.stmt ';'
@{ $[if-stmt] = new_if_stmt ($expr, $[then.stmt]); @}
@end group
@end example
(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
@defcv {Type} {parser} {syntax_error}
This class derives from @code{std::runtime_error}. Throw instances of it
-from user actions to raise parse errors. This is equivalent with first
+from the scanner or from the user actions to raise parse errors. This is
+equivalent with first
invoking @code{error} to report the location and message of the syntax
error, and then to invoke @code{YYERROR} to enter the error-recovery mode.
But contrary to @code{YYERROR} which can only be invoked from user actions
else if (!(yyin = fopen (file.c_str (), "r")))
@{
error (std::string ("cannot open ") + file + ": " + strerror(errno));
- exit (1);
+ exit (EXIT_FAILURE);
@}
@}
@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
{
yyin = fopen (file, "r");
if (!yyin)
- exit (2);
+ {
+ perror ("fopen");
+ exit (EXIT_FAILURE);
+ }
/* One token only. */
yylex ();
if (fclose (yyin) != 0)
- exit (3);
+ {
+ perror ("fclose");
+ exit (EXIT_FAILURE);
+ }
return 0;
}
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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