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
* Type Decl:: Declaring the choice of type for a nonterminal symbol.
* Initial Action Decl:: Code run before parsing starts.
* Destructor Decl:: Declaring how symbols are freed.
+* Printer Decl:: Declaring how symbol values are displayed.
* Expect Decl:: Suppressing warnings about parsing conflicts.
* Start Decl:: Specifying the start symbol.
* Pure Decl:: Requesting a reentrant parser.
* Understanding:: Understanding the structure of your parser.
* Tracing:: Tracing the execution of your parser.
+Tracing Your Parser
+
+* Enabling Traces:: Activating run-time trace support
+* Mfcalc Traces:: Extending @code{mfcalc} to support traces
+* The YYPRINT Macro:: Obsolete interface for semantic value reports
+
Invoking Bison
* Bison Options:: All the options described in detail,
* C++ Scanner Interface:: Exchanges between yylex and parse
* A Complete C++ Example:: Demonstrating their use
+C++ Location Values
+
+* C++ position:: One point in the source file
+* C++ location:: Two points in the source file
+
A Complete C++ Example
* Calc++ --- C++ Calculator:: The specifications
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.
Here is a simple C function subdivided into tokens:
-@ifinfo
@example
int /* @r{keyword `int'} */
square (int x) /* @r{identifier, open-paren, keyword `int',}
@r{identifier, semicolon} */
@} /* @r{close-brace} */
@end example
-@end ifinfo
-@ifnotinfo
-@example
-int /* @r{keyword `int'} */
-square (int x) /* @r{identifier, open-paren, keyword `int', identifier, close-paren} */
-@{ /* @r{open-brace} */
- return x * x; /* @r{keyword `return', identifier, asterisk, identifier, semicolon} */
-@} /* @r{close-brace} */
-@end example
-@end ifnotinfo
The syntactic groupings of C include the expression, the statement, the
declaration, and the function definition. These are represented in the
used in every rule.
@example
-stmt: RETURN expr ';'
- ;
+stmt: RETURN expr ';' ;
@end example
@noindent
two subexpressions:
@example
-expr: expr '+' expr @{ $$ = $1 + $3; @}
- ;
+expr: expr '+' expr @{ $$ = $1 + $3; @} ;
@end example
@noindent
%%
@group
-type_decl : TYPE ID '=' type ';'
- ;
+type_decl: TYPE ID '=' type ';' ;
@end group
@group
-type : '(' id_list ')'
- | expr DOTDOT expr
- ;
+type:
+ '(' id_list ')'
+| expr DOTDOT expr
+;
@end group
@group
-id_list : ID
- | id_list ',' ID
- ;
+id_list:
+ ID
+| id_list ',' ID
+;
@end group
@group
-expr : '(' expr ')'
- | expr '+' expr
- | expr '-' expr
- | expr '*' expr
- | expr '/' expr
- | ID
- ;
+expr:
+ '(' expr ')'
+| expr '+' expr
+| expr '-' expr
+| expr '*' expr
+| expr '/' expr
+| ID
+;
@end group
@end example
%%
-prog :
- | prog stmt @{ printf ("\n"); @}
- ;
+prog:
+ /* Nothing. */
+| prog stmt @{ printf ("\n"); @}
+;
-stmt : expr ';' %dprec 1
- | decl %dprec 2
- ;
+stmt:
+ expr ';' %dprec 1
+| decl %dprec 2
+;
-expr : ID @{ printf ("%s ", $$); @}
- | TYPENAME '(' expr ')'
- @{ printf ("%s <cast> ", $1); @}
- | expr '+' expr @{ printf ("+ "); @}
- | expr '=' expr @{ printf ("= "); @}
- ;
+expr:
+ ID @{ printf ("%s ", $$); @}
+| TYPENAME '(' expr ')'
+ @{ printf ("%s <cast> ", $1); @}
+| expr '+' expr @{ printf ("+ "); @}
+| expr '=' expr @{ printf ("= "); @}
+;
-decl : TYPENAME declarator ';'
- @{ printf ("%s <declare> ", $1); @}
- | TYPENAME declarator '=' expr ';'
- @{ printf ("%s <init-declare> ", $1); @}
- ;
+decl:
+ TYPENAME declarator ';'
+ @{ printf ("%s <declare> ", $1); @}
+| TYPENAME declarator '=' expr ';'
+ @{ printf ("%s <init-declare> ", $1); @}
+;
-declarator : ID @{ printf ("\"%s\" ", $1); @}
- | '(' declarator ')'
- ;
+declarator:
+ ID @{ printf ("\"%s\" ", $1); @}
+| '(' declarator ')'
+;
@end example
@noindent
follows:
@example
-stmt : expr ';' %merge <stmtMerge>
- | decl %merge <stmtMerge>
- ;
+stmt:
+ expr ';' %merge <stmtMerge>
+| decl %merge <stmtMerge>
+;
@end example
@noindent
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
if there are alternative parses. (This feature is experimental and may
evolve. We welcome user feedback.) For example,
-@smallexample
-widget :
- %?@{ new_syntax @} "widget" id new_args @{ $$ = f($3, $4); @}
- | %?@{ !new_syntax @} "widget" id old_args @{ $$ = f($3, $4); @}
- ;
-@end smallexample
+@example
+widget:
+ %?@{ new_syntax @} "widget" id new_args @{ $$ = f($3, $4); @}
+| %?@{ !new_syntax @} "widget" id old_args @{ $$ = f($3, $4); @}
+;
+@end example
@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 :
- @{ if (!new_syntax) YYERROR; @} "widget" id new_args @{ $$ = f($3, $4); @}
- | @{ if (new_syntax) YYERROR; @} "widget" id old_args @{ $$ = f($3, $4); @}
- ;
-@end smallexample
+@example
+widget:
+ @{ if (!new_syntax) YYERROR; @}
+ "widget" id new_args @{ $$ = f($3, $4); @}
+| @{ if (new_syntax) YYERROR; @}
+ "widget" id old_args @{ $$ = f($3, $4); @}
+;
+@end example
@noindent
(reversing the sense of the predicate tests to cause an error when they are
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
@example
%@{
- #if __STDC_VERSION__ < 199901 && ! defined __GNUC__ && ! defined inline
- #define inline
+ #if (__STDC_VERSION__ < 199901 && ! defined __GNUC__ \
+ && ! defined inline)
+ # define inline
#endif
%@}
@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
@cindex simple examples
@cindex examples, simple
-Now we show and explain three sample programs written using Bison: a
+Now we show and explain several sample programs written using Bison: a
reverse polish notation calculator, an algebraic (infix) notation
-calculator, and a multi-function calculator. All three have been tested
-under BSD Unix 4.3; each produces a usable, though limited, interactive
-desk-top calculator.
+calculator --- later extended to track ``locations'' ---
+and a multi-function calculator. All
+produce usable, though limited, interactive desk-top calculators.
These examples are simple, but Bison grammars for real programming
languages are written the same way. You can copy these examples into a
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
+@group
+input:
+ /* empty */
+| input line
;
+@end group
-line: '\n'
- | exp '\n' @{ printf ("\t%.10g\n", $1); @}
+@group
+line:
+ '\n'
+| exp '\n' @{ printf ("%.10g\n", $1); @}
;
+@end group
-exp: NUM @{ $$ = $1; @}
- | exp exp '+' @{ $$ = $1 + $2; @}
- | exp exp '-' @{ $$ = $1 - $2; @}
- | exp exp '*' @{ $$ = $1 * $2; @}
- | exp exp '/' @{ $$ = $1 / $2; @}
- /* Exponentiation */
- | exp exp '^' @{ $$ = pow ($1, $2); @}
- /* Unary minus */
- | exp 'n' @{ $$ = -$1; @}
+@group
+exp:
+ NUM @{ $$ = $1; @}
+| exp exp '+' @{ $$ = $1 + $2; @}
+| exp exp '-' @{ $$ = $1 - $2; @}
+| exp exp '*' @{ $$ = $1 * $2; @}
+| exp exp '/' @{ $$ = $1 / $2; @}
+| exp exp '^' @{ $$ = pow ($1, $2); @} /* Exponentiation */
+| exp 'n' @{ $$ = -$1; @} /* Unary minus */
;
+@end group
%%
@end example
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
Consider the definition of @code{input}:
@example
-input: /* empty */
- | input line
+input:
+ /* empty */
+| input line
;
@end example
Now consider the definition of @code{line}:
@example
-line: '\n'
- | exp '\n' @{ printf ("\t%.10g\n", $1); @}
+line:
+ '\n'
+| exp '\n' @{ printf ("%.10g\n", $1); @}
;
@end example
followed by a plus-sign. The third handles subtraction, and so on.
@example
-exp: NUM
- | exp exp '+' @{ $$ = $1 + $2; @}
- | exp exp '-' @{ $$ = $1 - $2; @}
- @dots{}
- ;
+exp:
+ NUM
+| exp exp '+' @{ $$ = $1 + $2; @}
+| exp exp '-' @{ $$ = $1 - $2; @}
+@dots{}
+;
@end example
We have used @samp{|} to join all the rules for @code{exp}, but we could
equally well have written them separately:
@example
-exp: NUM ;
-exp: exp exp '+' @{ $$ = $1 + $2; @} ;
-exp: exp exp '-' @{ $$ = $1 - $2; @} ;
- @dots{}
+exp: NUM ;
+exp: exp exp '+' @{ $$ = $1 + $2; @};
+exp: exp exp '-' @{ $$ = $1 - $2; @};
+@dots{}
@end example
Most of the rules have actions that compute the value of the expression in
For example, this:
@example
-exp : NUM | exp exp '+' @{$$ = $1 + $2; @} | @dots{} ;
+exp: NUM | exp exp '+' @{$$ = $1 + $2; @} | @dots{} ;
@end example
@noindent
means the same thing as this:
@example
-exp: NUM
- | exp exp '+' @{ $$ = $1 + $2; @}
- | @dots{}
+exp:
+ NUM
+| exp exp '+' @{ $$ = $1 + $2; @}
+| @dots{}
;
@end example
Here is the code for the lexical analyzer:
+@comment file: rpcalc.y
@example
@group
/* The lexical analyzer returns a double floating point
/* Skip white space. */
while ((c = getchar ()) == ' ' || c == '\t')
- ;
+ continue;
@end group
@group
/* Process numbers. */
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>
+@end group
+@group
/* Called by yyparse on error. */
void
yyerror (char const *s)
@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
/* Infix notation calculator. */
+@group
%@{
#define YYSTYPE double
#include <math.h>
int yylex (void);
void yyerror (char const *);
%@}
+@end group
+@group
/* Bison declarations. */
%token NUM
%left '-' '+'
%left '*' '/'
%precedence NEG /* negation--unary minus */
%right '^' /* exponentiation */
+@end group
%% /* The grammar follows. */
-input: /* empty */
- | input line
+@group
+input:
+ /* empty */
+| input line
;
+@end group
-line: '\n'
- | exp '\n' @{ printf ("\t%.10g\n", $1); @}
+@group
+line:
+ '\n'
+| exp '\n' @{ printf ("\t%.10g\n", $1); @}
;
+@end group
-exp: NUM @{ $$ = $1; @}
- | exp '+' exp @{ $$ = $1 + $3; @}
- | exp '-' exp @{ $$ = $1 - $3; @}
- | exp '*' exp @{ $$ = $1 * $3; @}
- | exp '/' exp @{ $$ = $1 / $3; @}
- | '-' exp %prec NEG @{ $$ = -$2; @}
- | exp '^' exp @{ $$ = pow ($1, $3); @}
- | '(' exp ')' @{ $$ = $2; @}
+@group
+exp:
+ NUM @{ $$ = $1; @}
+| exp '+' exp @{ $$ = $1 + $3; @}
+| exp '-' exp @{ $$ = $1 - $3; @}
+| exp '*' exp @{ $$ = $1 * $3; @}
+| exp '/' exp @{ $$ = $1 / $3; @}
+| '-' exp %prec NEG @{ $$ = -$2; @}
+| exp '^' exp @{ $$ = pow ($1, $3); @}
+| '(' exp ')' @{ $$ = $2; @}
;
+@end group
%%
@end example
@example
@group
-line: '\n'
- | exp '\n' @{ printf ("\t%.10g\n", $1); @}
- | error '\n' @{ yyerrok; @}
+line:
+ '\n'
+| exp '\n' @{ printf ("\t%.10g\n", $1); @}
+| error '\n' @{ yyerrok; @}
;
@end group
@end example
@example
@group
-input : /* empty */
- | input line
+input:
+ /* empty */
+| input line
;
@end group
@group
-line : '\n'
- | exp '\n' @{ printf ("%d\n", $1); @}
+line:
+ '\n'
+| exp '\n' @{ printf ("%d\n", $1); @}
;
@end group
@group
-exp : NUM @{ $$ = $1; @}
- | exp '+' exp @{ $$ = $1 + $3; @}
- | exp '-' exp @{ $$ = $1 - $3; @}
- | exp '*' exp @{ $$ = $1 * $3; @}
+exp:
+ NUM @{ $$ = $1; @}
+| exp '+' exp @{ $$ = $1 + $3; @}
+| exp '-' exp @{ $$ = $1 - $3; @}
+| exp '*' exp @{ $$ = $1 * $3; @}
@end group
@group
- | exp '/' exp
- @{
- if ($3)
- $$ = $1 / $3;
- else
- @{
- $$ = 1;
- fprintf (stderr, "%d.%d-%d.%d: division by zero",
- @@3.first_line, @@3.first_column,
- @@3.last_line, @@3.last_column);
- @}
- @}
+| exp '/' exp
+ @{
+ if ($3)
+ $$ = $1 / $3;
+ else
+ @{
+ $$ = 1;
+ fprintf (stderr, "%d.%d-%d.%d: division by zero",
+ @@3.first_line, @@3.first_column,
+ @@3.last_line, @@3.last_column);
+ @}
+ @}
@end group
@group
- | '-' exp %prec NEG @{ $$ = -$2; @}
- | exp '^' exp @{ $$ = pow ($1, $3); @}
- | '(' exp ')' @{ $$ = $2; @}
+| '-' exp %prec NEG @{ $$ = -$2; @}
+| exp '^' exp @{ $$ = pow ($1, $3); @}
+| '(' exp ')' @{ $$ = $2; @}
@end group
@end example
if (c == EOF)
return 0;
+@group
/* Return a single char, and update location. */
if (c == '\n')
@{
++yylloc.last_column;
return c;
@}
+@end group
@end example
Basically, the lexical analyzer performs the same processing as before:
Here is a sample session with the multi-function calculator:
@example
+@group
$ @kbd{mfcalc}
@kbd{pi = 3.141592653589}
-3.1415926536
+@result{} 3.1415926536
+@end group
+@group
@kbd{sin(pi)}
-0.0000000000
+@result{} 0.0000000000
+@end group
@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.
-@smallexample
+@comment file: mfcalc.y: 1
+@example
@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 *);
%@}
@end group
+
@group
%union @{
double val; /* For returning numbers. */
@}
@end group
%token <val> NUM /* Simple double precision number. */
-%token <tptr> VAR FNCT /* Variable and Function. */
+%token <tptr> VAR FNCT /* Variable and function. */
%type <val> exp
@group
%precedence NEG /* negation--unary minus */
%right '^' /* exponentiation */
@end group
-%% /* The grammar follows. */
-@end smallexample
+@end example
The above grammar introduces only two new features of the Bison language.
These features allow semantic values to have various data types
Most of them are copied directly from @code{calc}; three rules,
those which mention @code{VAR} or @code{FNCT}, are new.
-@smallexample
+@comment file: mfcalc.y: 3
+@example
+%% /* The grammar follows. */
@group
-input: /* empty */
- | input line
+input:
+ /* empty */
+| input line
;
@end group
@group
line:
- '\n'
- | exp '\n' @{ printf ("\t%.10g\n", $1); @}
- | error '\n' @{ yyerrok; @}
+ '\n'
+| exp '\n' @{ printf ("%.10g\n", $1); @}
+| error '\n' @{ yyerrok; @}
;
@end group
@group
-exp: NUM @{ $$ = $1; @}
- | VAR @{ $$ = $1->value.var; @}
- | VAR '=' exp @{ $$ = $3; $1->value.var = $3; @}
- | FNCT '(' exp ')' @{ $$ = (*($1->value.fnctptr))($3); @}
- | exp '+' exp @{ $$ = $1 + $3; @}
- | exp '-' exp @{ $$ = $1 - $3; @}
- | exp '*' exp @{ $$ = $1 * $3; @}
- | exp '/' exp @{ $$ = $1 / $3; @}
- | '-' exp %prec NEG @{ $$ = -$2; @}
- | exp '^' exp @{ $$ = pow ($1, $3); @}
- | '(' exp ')' @{ $$ = $2; @}
+exp:
+ NUM @{ $$ = $1; @}
+| VAR @{ $$ = $1->value.var; @}
+| VAR '=' exp @{ $$ = $3; $1->value.var = $3; @}
+| FNCT '(' exp ')' @{ $$ = (*($1->value.fnctptr))($3); @}
+| exp '+' exp @{ $$ = $1 + $3; @}
+| exp '-' exp @{ $$ = $1 - $3; @}
+| exp '*' exp @{ $$ = $1 * $3; @}
+| exp '/' exp @{ $$ = $1 / $3; @}
+| '-' exp %prec NEG @{ $$ = -$2; @}
+| exp '^' exp @{ $$ = pow ($1, $3); @}
+| '(' exp ')' @{ $$ = $2; @}
;
@end group
/* End of grammar. */
%%
-@end smallexample
+@end example
@node Mfcalc Symbol Table
@subsection The @code{mfcalc} Symbol Table
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.
-@smallexample
+@comment file: calc.h
+@example
@group
/* Function type. */
typedef double (*func_t) (double);
symrec *putsym (char const *, int);
symrec *getsym (char const *);
@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:
+@end example
-@smallexample
-#include <stdio.h>
-
-@group
-/* Called by yyparse on error. */
-void
-yyerror (char const *s)
-@{
- printf ("%s\n", s);
-@}
-@end group
+The new version of @code{main} will call @code{init_table} to initialize
+the symbol table:
+@comment file: mfcalc.y: 3
+@example
@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)
@{
int i;
- symrec *ptr;
for (i = 0; arith_fncts[i].fname != 0; i++)
@{
- ptr = putsym (arith_fncts[i].fname, FNCT);
+ symrec *ptr = putsym (arith_fncts[i].fname, FNCT);
ptr->value.fnctptr = arith_fncts[i].fnct;
@}
@}
@end group
-
-@group
-int
-main (void)
-@{
- init_table ();
- return yyparse ();
-@}
-@end group
-@end smallexample
+@end example
By simply editing the initialization list and adding the necessary include
files, you can add additional functions to the calculator.
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.
-@smallexample
+@comment file: mfcalc.y: 3
+@example
+#include <stdlib.h> /* malloc. */
+#include <string.h> /* strlen. */
+
+@group
symrec *
putsym (char const *sym_name, int sym_type)
@{
- symrec *ptr;
- ptr = (symrec *) malloc (sizeof (symrec));
+ symrec *ptr = (symrec *) malloc (sizeof (symrec));
ptr->name = (char *) malloc (strlen (sym_name) + 1);
strcpy (ptr->name,sym_name);
ptr->type = sym_type;
sym_table = ptr;
return ptr;
@}
+@end group
+@group
symrec *
getsym (char const *sym_name)
@{
symrec *ptr;
for (ptr = sym_table; ptr != (symrec *) 0;
ptr = (symrec *)ptr->next)
- if (strcmp (ptr->name,sym_name) == 0)
+ if (strcmp (ptr->name, sym_name) == 0)
return ptr;
return 0;
@}
-@end smallexample
+@end group
+@end example
+
+@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
No change is needed in the handling of numeric values and arithmetic
operators in @code{yylex}.
-@smallexample
+@comment file: mfcalc.y: 3
+@example
@group
#include <ctype.h>
@end group
int c;
/* Ignore white space, get first nonwhite character. */
- while ((c = getchar ()) == ' ' || c == '\t');
+ while ((c = getchar ()) == ' ' || c == '\t')
+ continue;
if (c == EOF)
return 0;
/* Char starts an identifier => read the name. */
if (isalpha (c))
@{
- symrec *s;
+ /* Initially make the buffer long enough
+ for a 40-character symbol name. */
+ static size_t length = 40;
static char *symbuf = 0;
- static int length = 0;
+ symrec *s;
int i;
@end group
-
-@group
- /* Initially make the buffer long enough
- for a 40-character symbol name. */
- if (length == 0)
- length = 40, symbuf = (char *)malloc (length + 1);
+ if (!symbuf)
+ symbuf = (char *) malloc (length + 1);
i = 0;
do
-@end group
@group
@{
/* If buffer is full, make it bigger. */
return c;
@}
@end group
-@end smallexample
+@end example
+
+@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} and sets the @code{yydebug}
+on user demand (@xref{Tracing, , Tracing Your Parser}, for details):
+
+@comment file: mfcalc.y: 3
+@example
+@group
+/* Called by yyparse on error. */
+void
+yyerror (char const *s)
+@{
+ fprintf (stderr, "%s\n", s);
+@}
+@end group
+
+@group
+int
+main (int argc, char const* argv[])
+@{
+ int i;
+ /* Enable parse traces on option -p. */
+ for (i = 1; i < argc; ++i)
+ if (!strcmp(argv[i], "-p"))
+ yydebug = 1;
+ init_table ();
+ return yyparse ();
+@}
+@end group
+@end example
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
@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
can be done with two @var{Prologue} blocks, one before and one after the
@code{%union} declaration.
-@smallexample
+@example
%@{
#define _GNU_SOURCE
#include <stdio.h>
%@}
@dots{}
-@end smallexample
+@end example
When in doubt, it is usually safer to put prologue code before all
Bison declarations, rather than after. For example, any definitions
Look again at the example of the previous section:
-@smallexample
+@example
%@{
#define _GNU_SOURCE
#include <stdio.h>
%@}
@dots{}
-@end smallexample
+@end example
@noindent
Notice that there are two @var{Prologue} sections here, but there's a
Let's go ahead and add the new @code{YYLTYPE} definition and the
@code{trace_token} prototype at the same time:
-@smallexample
+@example
%code top @{
#define _GNU_SOURCE
#include <stdio.h>
@}
@dots{}
-@end smallexample
+@end example
@noindent
In this way, @code{%code top} and the unqualified @code{%code} achieve the same
definitions.
Thus, they belong in one or more @code{%code requires}:
-@smallexample
+@example
+@group
%code top @{
#define _GNU_SOURCE
#include <stdio.h>
@}
+@end group
+@group
%code requires @{
#include "ptypes.h"
@}
+@end group
+@group
%union @{
long int n;
tree t; /* @r{@code{tree} is defined in @file{ptypes.h}.} */
@}
+@end group
+@group
%code requires @{
#define YYLTYPE YYLTYPE
typedef struct YYLTYPE
char *filename;
@} YYLTYPE;
@}
+@end group
+@group
%code @{
static void print_token_value (FILE *, int, YYSTYPE);
#define YYPRINT(F, N, L) print_token_value (F, N, L)
static void trace_token (enum yytokentype token, YYLTYPE loc);
@}
+@end group
@dots{}
-@end smallexample
+@end example
@noindent
Now Bison will insert @code{#include "ptypes.h"} and the new
sufficient. Instead, move its prototype from the unqualified
@code{%code} to a @code{%code provides}:
-@smallexample
+@example
+@group
%code top @{
#define _GNU_SOURCE
#include <stdio.h>
@}
+@end group
+@group
%code requires @{
#include "ptypes.h"
@}
+@end group
+@group
%union @{
long int n;
tree t; /* @r{@code{tree} is defined in @file{ptypes.h}.} */
@}
+@end group
+@group
%code requires @{
#define YYLTYPE YYLTYPE
typedef struct YYLTYPE
char *filename;
@} YYLTYPE;
@}
+@end group
+@group
%code provides @{
void trace_token (enum yytokentype token, YYLTYPE loc);
@}
+@end group
+@group
%code @{
static void print_token_value (FILE *, int, YYSTYPE);
#define YYPRINT(F, N, L) print_token_value (F, N, L)
@}
+@end group
@dots{}
-@end smallexample
+@end example
@noindent
Bison will insert the @code{trace_token} prototype into both the
For example, you may organize semantic-type-related directives by semantic
type:
-@smallexample
+@example
+@group
%code requires @{ #include "type1.h" @}
%union @{ type1 field1; @}
%destructor @{ type1_free ($$); @} <field1>
-%printer @{ type1_print ($$); @} <field1>
+%printer @{ type1_print (yyoutput, $$); @} <field1>
+@end group
+@group
%code requires @{ #include "type2.h" @}
%union @{ type2 field2; @}
%destructor @{ type2_free ($$); @} <field2>
-%printer @{ type2_print ($$); @} <field2>
-@end smallexample
+%printer @{ type2_print (yyoutput, $$); @} <field2>
+@end group
+@end example
@noindent
You could even place each of the above directive groups in the rules section of
@example
@group
-@var{result}: @var{components}@dots{}
- ;
+@var{result}: @var{components}@dots{};
@end group
@end example
@example
@group
-exp: exp '+' exp
- ;
+exp: exp '+' exp;
@end group
@end example
@example
@group
-@var{result}: @var{rule1-components}@dots{}
- | @var{rule2-components}@dots{}
- @dots{}
- ;
+@var{result}:
+ @var{rule1-components}@dots{}
+| @var{rule2-components}@dots{}
+@dots{}
+;
@end group
@end example
@example
@group
-expseq: /* empty */
- | expseq1
- ;
+expseq:
+ /* empty */
+| expseq1
+;
@end group
@group
-expseq1: exp
- | expseq1 ',' exp
- ;
+expseq1:
+ exp
+| expseq1 ',' exp
+;
@end group
@end example
@example
@group
-expseq1: exp
- | expseq1 ',' exp
- ;
+expseq1:
+ exp
+| expseq1 ',' exp
+;
@end group
@end example
@example
@group
-expseq1: exp
- | exp ',' expseq1
- ;
+expseq1:
+ exp
+| exp ',' expseq1
+;
@end group
@end example
@example
@group
-expr: primary
- | primary '+' primary
- ;
+expr:
+ primary
+| primary '+' primary
+;
@end group
@group
-primary: constant
- | '(' expr ')'
- ;
+primary:
+ constant
+| '(' expr ')'
+;
@end group
@end example
@example
@group
-exp: @dots{}
- | exp '+' exp
- @{ $$ = $1 + $3; @}
+exp:
+@dots{}
+| exp '+' exp @{ $$ = $1 + $3; @}
@end group
@end example
@example
@group
-exp[result]: @dots{}
- | exp[left] '+' exp[right]
- @{ $result = $left + $right; @}
+exp[result]:
+@dots{}
+| exp[left] '+' exp[right] @{ $result = $left + $right; @}
@end group
@end example
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
@example
@group
-foo: expr bar '+' expr @{ @dots{} @}
- | expr bar '-' expr @{ @dots{} @}
- ;
+foo:
+ expr bar '+' expr @{ @dots{} @}
+| expr bar '-' expr @{ @dots{} @}
+;
@end group
@group
-bar: /* empty */
- @{ previous_expr = $0; @}
- ;
+bar:
+ /* empty */ @{ previous_expr = $0; @}
+;
@end group
@end example
@example
@group
-exp: @dots{}
- | exp '+' exp
- @{ $$ = $1 + $3; @}
+exp:
+ @dots{}
+| exp '+' exp @{ $$ = $1 + $3; @}
@end group
@end example
@example
@group
-stmt: LET '(' var ')'
- @{ $<context>$ = push_context ();
- declare_variable ($3); @}
- stmt @{ $$ = $6;
- pop_context ($<context>5); @}
+stmt:
+ LET '(' var ')'
+ @{ $<context>$ = push_context (); declare_variable ($3); @}
+ stmt
+ @{ $$ = $6; pop_context ($<context>5); @}
@end group
@end example
%%
-stmt: let stmt
- @{ $$ = $2;
- pop_context ($1); @}
- ;
+stmt:
+ let stmt
+ @{
+ $$ = $2;
+ pop_context ($1);
+ @};
-let: LET '(' var ')'
- @{ $$ = push_context ();
- declare_variable ($3); @}
- ;
+let:
+ LET '(' var ')'
+ @{
+ $$ = push_context ();
+ declare_variable ($3);
+ @};
@end group
@end example
@example
@group
-compound: '@{' declarations statements '@}'
- | '@{' statements '@}'
- ;
+compound:
+ '@{' declarations statements '@}'
+| '@{' statements '@}'
+;
@end group
@end example
@example
@group
-compound: @{ prepare_for_local_variables (); @}
- '@{' declarations statements '@}'
+compound:
+ @{ prepare_for_local_variables (); @}
+ '@{' declarations statements '@}'
@end group
@group
- | '@{' statements '@}'
- ;
+| '@{' statements '@}'
+;
@end group
@end example
@example
@group
-compound: @{ prepare_for_local_variables (); @}
- '@{' declarations statements '@}'
- | @{ prepare_for_local_variables (); @}
- '@{' statements '@}'
- ;
+compound:
+ @{ prepare_for_local_variables (); @}
+ '@{' declarations statements '@}'
+| @{ prepare_for_local_variables (); @}
+ '@{' statements '@}'
+;
@end group
@end example
@example
@group
-compound: '@{' @{ prepare_for_local_variables (); @}
- declarations statements '@}'
- | '@{' statements '@}'
- ;
+compound:
+ '@{' @{ prepare_for_local_variables (); @}
+ declarations statements '@}'
+| '@{' statements '@}'
+;
@end group
@end example
@example
@group
-subroutine: /* empty */
- @{ prepare_for_local_variables (); @}
- ;
-
+subroutine:
+ /* empty */ @{ prepare_for_local_variables (); @}
+;
@end group
@group
-compound: subroutine
- '@{' declarations statements '@}'
- | subroutine
- '@{' statements '@}'
- ;
+compound:
+ subroutine '@{' declarations statements '@}'
+| subroutine '@{' statements '@}'
+;
@end group
@end example
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:
@example
@group
-exp: @dots{}
- | exp '/' exp
- @{
- @@$.first_column = @@1.first_column;
- @@$.first_line = @@1.first_line;
- @@$.last_column = @@3.last_column;
- @@$.last_line = @@3.last_line;
- if ($3)
- $$ = $1 / $3;
- else
- @{
- $$ = 1;
- fprintf (stderr,
- "Division by zero, l%d,c%d-l%d,c%d",
- @@3.first_line, @@3.first_column,
- @@3.last_line, @@3.last_column);
- @}
- @}
+exp:
+ @dots{}
+| exp '/' exp
+ @{
+ @@$.first_column = @@1.first_column;
+ @@$.first_line = @@1.first_line;
+ @@$.last_column = @@3.last_column;
+ @@$.last_line = @@3.last_line;
+ if ($3)
+ $$ = $1 / $3;
+ else
+ @{
+ $$ = 1;
+ fprintf (stderr,
+ "Division by zero, l%d,c%d-l%d,c%d",
+ @@3.first_line, @@3.first_column,
+ @@3.last_line, @@3.last_column);
+ @}
+ @}
@end group
@end example
@example
@group
-exp: @dots{}
- | exp '/' exp
- @{
- if ($3)
- $$ = $1 / $3;
- else
- @{
- $$ = 1;
- fprintf (stderr,
- "Division by zero, l%d,c%d-l%d,c%d",
- @@3.first_line, @@3.first_column,
- @@3.last_line, @@3.last_column);
- @}
- @}
+exp:
+ @dots{}
+| exp '/' exp
+ @{
+ if ($3)
+ $$ = $1 / $3;
+ else
+ @{
+ $$ = 1;
+ fprintf (stderr,
+ "Division by zero, l%d,c%d-l%d,c%d",
+ @@3.first_line, @@3.first_column,
+ @@3.last_line, @@3.last_column);
+ @}
+ @}
@end group
@end example
By default, @code{YYLLOC_DEFAULT} is defined this way:
-@smallexample
-@group
-# define YYLLOC_DEFAULT(Current, Rhs, N) \
- do \
- if (N) \
- @{ \
- (Current).first_line = YYRHSLOC(Rhs, 1).first_line; \
- (Current).first_column = YYRHSLOC(Rhs, 1).first_column; \
- (Current).last_line = YYRHSLOC(Rhs, N).last_line; \
- (Current).last_column = YYRHSLOC(Rhs, N).last_column; \
- @} \
- else \
- @{ \
- (Current).first_line = (Current).last_line = \
- YYRHSLOC(Rhs, 0).last_line; \
- (Current).first_column = (Current).last_column = \
- YYRHSLOC(Rhs, 0).last_column; \
- @} \
- while (0)
-@end group
-@end smallexample
+@example
+@group
+# define YYLLOC_DEFAULT(Cur, Rhs, N) \
+do \
+ if (N) \
+ @{ \
+ (Cur).first_line = YYRHSLOC(Rhs, 1).first_line; \
+ (Cur).first_column = YYRHSLOC(Rhs, 1).first_column; \
+ (Cur).last_line = YYRHSLOC(Rhs, N).last_line; \
+ (Cur).last_column = YYRHSLOC(Rhs, N).last_column; \
+ @} \
+ else \
+ @{ \
+ (Cur).first_line = (Cur).last_line = \
+ YYRHSLOC(Rhs, 0).last_line; \
+ (Cur).first_column = (Cur).last_column = \
+ YYRHSLOC(Rhs, 0).last_column; \
+ @} \
+while (0)
+@end group
+@end example
+@noindent
where @code{YYRHSLOC (rhs, k)} is the location of the @var{k}th symbol
in @var{rhs} when @var{k} is positive, and the location of the symbol
just before the reduction when @var{k} and @var{n} are both zero.
@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 = $x;@}[left] exp[right]
bracketed syntax @code{$[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, $[then.stmt]); @}
@end group
@end example
It often happens that named references are followed by a dot, dash or other
C punctuation marks and operators. By default, Bison will read
-@code{$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
* Type Decl:: Declaring the choice of type for a nonterminal symbol.
* Initial Action Decl:: Code run before parsing starts.
* Destructor Decl:: Declaring how symbols are freed.
+* Printer Decl:: Declaring how symbol values are displayed.
* Expect Decl:: Suppressing warnings about parsing conflicts.
* Start Decl:: Specifying the start symbol.
* Pure Decl:: Requesting a reentrant parser.
@noindent
For example:
-@smallexample
+@example
%union @{ char *string; @}
%token <string> STRING1
%token <string> STRING2
%destructor @{ free ($$); @} <*>
%destructor @{ free ($$); printf ("%d", @@$.first_line); @} STRING1 string1
%destructor @{ printf ("Discarding tagless symbol.\n"); @} <>
-@end smallexample
+@end example
@noindent
guarantees that, when the parser discards any user-defined symbol that has a
However, it may invoke one of them for the end token (token 0) if you
redefine it from @code{$end} to, for example, @code{END}:
-@smallexample
+@example
%token END 0
-@end smallexample
+@end example
@cindex actions in mid-rule
@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
of thumb, destructors are invoked only when user actions cannot manage
the memory.
+@node Printer Decl
+@subsection Printing Semantic Values
+@cindex printing semantic values
+@findex %printer
+@findex <*>
+@findex <>
+When run-time traces are enabled (@pxref{Tracing, ,Tracing Your Parser}),
+the parser reports its actions, such as reductions. When a symbol involved
+in an action is reported, only its kind is displayed, as the parser cannot
+know how semantic values should be formatted.
+
+The @code{%printer} directive defines code that is called when a symbol is
+reported. Its syntax is the same as @code{%destructor} (@pxref{Destructor
+Decl, , Freeing Discarded Symbols}).
+
+@deffn {Directive} %printer @{ @var{code} @} @var{symbols}
+@findex %printer
+@vindex yyoutput
+@c This is the same text as for %destructor.
+Invoke the braced @var{code} whenever the parser displays one of the
+@var{symbols}. Within @var{code}, @code{yyoutput} denotes the output stream
+(a @code{FILE*} in C, and an @code{std::ostream&} in C++),
+@code{$$} designates the semantic value associated with the symbol, and
+@code{@@$} its location. The additional parser parameters are also
+available (@pxref{Parser Function, , The Parser Function @code{yyparse}}).
+
+The @var{symbols} are defined as for @code{%destructor} (@pxref{Destructor
+Decl, , Freeing Discarded Symbols}.): they can be per-type (e.g.,
+@samp{<ival>}), per-symbol (e.g., @samp{exp}, @samp{NUM}, @samp{"float"}),
+typed per-default (i.e., @samp{<*>}, or untyped per-default (i.e.,
+@samp{<>}).
+@end deffn
+
+@noindent
+For example:
+
+@example
+%union @{ char *string; @}
+%token <string> STRING1
+%token <string> STRING2
+%type <string> string1
+%type <string> string2
+%union @{ char character; @}
+%token <character> CHR
+%type <character> chr
+%token TAGLESS
+
+%printer @{ fprintf (yyoutput, "'%c'", $$); @} <character>
+%printer @{ fprintf (yyoutput, "&%p", $$); @} <*>
+%printer @{ fprintf (yyoutput, "\"%s\"", $$); @} STRING1 string1
+%printer @{ fprintf (yyoutput, "<>"); @} <>
+@end example
+
+@noindent
+guarantees that, when the parser print any symbol that has a semantic type
+tag other than @code{<character>}, it display the address of the semantic
+value by default. However, when the parser displays a @code{STRING1} or a
+@code{string1}, it formats it as a string in double quotes. It performs
+only the second @code{%printer} in this case, so it prints only once.
+Finally, the parser print @samp{<>} for any symbol, such as @code{TAGLESS},
+that has no semantic type tag. See also
+
+
@node Expect Decl
@subsection Suppressing Conflict Warnings
@cindex suppressing conflict warnings
(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
@item Purpose: Specify the namespace for the parser class.
For example, if you specify:
-@smallexample
+@example
%define api.namespace "foo::bar"
-@end smallexample
+@end example
Bison uses @code{foo::bar} verbatim in references such as:
-@smallexample
+@example
foo::bar::parser::semantic_type
-@end smallexample
+@end example
However, to open a namespace, Bison removes any leading @code{::} and then
splits on any remaining occurrences:
-@smallexample
+@example
namespace foo @{ namespace bar @{
class position;
class location;
@} @}
-@end smallexample
+@end example
@item Accepted Values:
Any absolute or relative C++ namespace reference without a trailing
api.namespace} so that @code{%name-prefix} @emph{only} affects the
lexical analyzer function. For example, if you specify:
-@smallexample
+@example
%define api.namespace "foo"
%name-prefix "bar::"
-@end smallexample
+@end example
The parser namespace is @code{foo} and @code{yylex} is referenced as
@code{bar::lex}.
occasionally it is necessary to insert code much nearer the top of the
parser implementation file. For example:
-@smallexample
+@example
%code top @{
#define _GNU_SOURCE
#include <stdio.h>
@}
-@end smallexample
+@end example
@item Location(s): Near the top of the parser implementation file.
@end itemize
@samp{%define api.push-pull both} declaration is used.
@xref{Push Decl, ,A Push Parser}.
-@deftypefun yypstate *yypstate_new (void)
+@deftypefun {yypstate*} yypstate_new (void)
The function will return a valid parser instance if there was memory available
or 0 if no memory was available.
In impure mode, it will also return 0 if a parser instance is currently
@code{token_buffer}, and assuming that the token does not contain any
characters like @samp{"} that require escaping.
-@smallexample
+@example
for (i = 0; i < YYNTOKENS; i++)
@{
if (yytname[i] != 0
&& yytname[i][strlen (token_buffer) + 2] == 0)
break;
@}
-@end smallexample
+@end example
The @code{yytname} table is generated only if you use the
@code{%token-table} declaration. @xref{Decl Summary}.
@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
@end example
@noindent
-results in the following signature:
+results in the following signatures:
@example
int yylex (scanner_mode *mode, environment_type *env);
@xref{Action Types, ,Data Types of Values in Actions}.
@end deffn
-@deffn {Macro} YYABORT;
+@deffn {Macro} YYABORT @code{;}
Return immediately from @code{yyparse}, indicating failure.
@xref{Parser Function, ,The Parser Function @code{yyparse}}.
@end deffn
-@deffn {Macro} YYACCEPT;
+@deffn {Macro} YYACCEPT @code{;}
Return immediately from @code{yyparse}, indicating success.
@xref{Parser Function, ,The Parser Function @code{yyparse}}.
@end deffn
-@deffn {Macro} YYBACKUP (@var{token}, @var{value});
+@deffn {Macro} YYBACKUP (@var{token}, @var{value})@code{;}
@findex YYBACKUP
Unshift a token. This macro is allowed only for rules that reduce
a single value, and only when there is no lookahead token.
@end deffn
@deffn {Macro} YYEMPTY
-@vindex YYEMPTY
Value stored in @code{yychar} when there is no lookahead token.
@end deffn
@deffn {Macro} YYEOF
-@vindex YYEOF
Value stored in @code{yychar} when the lookahead is the end of the input
stream.
@end deffn
-@deffn {Macro} YYERROR;
-@findex YYERROR
+@deffn {Macro} YYERROR @code{;}
Cause an immediate syntax error. This statement initiates error
recovery just as if the parser itself had detected an error; however, it
does not call @code{yyerror}, and does not print any message. If you
@xref{Lookahead, ,Lookahead Tokens}.
@end deffn
-@deffn {Macro} yyclearin;
+@deffn {Macro} yyclearin @code{;}
Discard the current lookahead token. This is useful primarily in
error rules.
Do not invoke @code{yyclearin} in a deferred semantic action (@pxref{GLR
@xref{Error Recovery}.
@end deffn
-@deffn {Macro} yyerrok;
+@deffn {Macro} yyerrok @code{;}
Resume generating error messages immediately for subsequent syntax
errors. This is useful primarily in error rules.
@xref{Error Recovery}.
@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
@example
@group
-expr: term '+' expr
- | term
- ;
+expr:
+ term '+' expr
+| term
+;
@end group
@group
-term: '(' expr ')'
- | term '!'
- | NUMBER
- ;
+term:
+ '(' expr ')'
+| term '!'
+| NUMBER
+;
@end group
@end example
@example
@group
if_stmt:
- IF expr THEN stmt
- | IF expr THEN stmt ELSE stmt
- ;
+ IF expr THEN stmt
+| IF expr THEN stmt ELSE stmt
+;
@end group
@end example
%%
@end group
@group
-stmt: expr
- | if_stmt
- ;
+stmt:
+ expr
+| if_stmt
+;
@end group
@group
if_stmt:
- IF expr THEN stmt
- | IF expr THEN stmt ELSE stmt
- ;
+ IF expr THEN stmt
+| IF expr THEN stmt ELSE stmt
+;
@end group
-expr: variable
- ;
+expr:
+ variable
+;
@end example
@node Precedence
@example
@group
-expr: expr '-' expr
- | expr '*' expr
- | expr '<' expr
- | '(' expr ')'
- @dots{}
- ;
+expr:
+ expr '-' expr
+| expr '*' expr
+| expr '<' expr
+| '(' expr ')'
+@dots{}
+;
@end group
@end example
@example
@group
-exp: @dots{}
- | exp '-' exp
- @dots{}
- | '-' exp %prec UMINUS
+exp:
+ @dots{}
+| exp '-' exp
+ @dots{}
+| '-' exp %prec UMINUS
@end group
@end example
of zero or more @code{word} groupings.
@example
-sequence: /* empty */
- @{ printf ("empty sequence\n"); @}
- | maybeword
- | sequence word
- @{ printf ("added word %s\n", $2); @}
- ;
+@group
+sequence:
+ /* empty */ @{ printf ("empty sequence\n"); @}
+| maybeword
+| sequence word @{ printf ("added word %s\n", $2); @}
+;
+@end group
-maybeword: /* empty */
- @{ printf ("empty maybeword\n"); @}
- | word
- @{ printf ("single word %s\n", $1); @}
- ;
+@group
+maybeword:
+ /* empty */ @{ printf ("empty maybeword\n"); @}
+| word @{ printf ("single word %s\n", $1); @}
+;
+@end group
@end example
@noindent
proper way to define @code{sequence}:
@example
-sequence: /* empty */
- @{ printf ("empty sequence\n"); @}
- | sequence word
- @{ printf ("added word %s\n", $2); @}
- ;
+sequence:
+ /* empty */ @{ printf ("empty sequence\n"); @}
+| sequence word @{ printf ("added word %s\n", $2); @}
+;
@end example
Here is another common error that yields a reduce/reduce conflict:
@example
-sequence: /* empty */
- | sequence words
- | sequence redirects
- ;
+sequence:
+ /* empty */
+| sequence words
+| sequence redirects
+;
-words: /* empty */
- | words word
- ;
+words:
+ /* empty */
+| words word
+;
-redirects:/* empty */
- | redirects redirect
- ;
+redirects:
+ /* empty */
+| redirects redirect
+;
@end example
@noindent
of sequence:
@example
-sequence: /* empty */
- | sequence word
- | sequence redirect
- ;
+sequence:
+ /* empty */
+| sequence word
+| sequence redirect
+;
@end example
Second, to prevent either a @code{words} or a @code{redirects}
from being empty:
@example
-sequence: /* empty */
- | sequence words
- | sequence redirects
- ;
+@group
+sequence:
+ /* empty */
+| sequence words
+| sequence redirects
+;
+@end group
-words: word
- | words word
- ;
+@group
+words:
+ word
+| words word
+;
+@end group
-redirects:redirect
- | redirects redirect
- ;
+@group
+redirects:
+ redirect
+| redirects redirect
+;
+@end group
@end example
@node Mysterious Conflicts
%token ID
%%
-def: param_spec return_spec ','
- ;
+def: param_spec return_spec ',';
param_spec:
- type
- | name_list ':' type
- ;
+ type
+| name_list ':' type
+;
@end group
@group
return_spec:
- type
- | name ':' type
- ;
+ type
+| name ':' type
+;
@end group
@group
-type: ID
- ;
+type: ID;
@end group
@group
-name: ID
- ;
+name: ID;
name_list:
- name
- | name ',' name_list
- ;
+ name
+| name ',' name_list
+;
@end group
@end example
%%
@dots{}
return_spec:
- type
- | name ':' type
- /* This rule is never used. */
- | ID BOGUS
- ;
+ type
+| name ':' type
+| ID BOGUS /* This rule is never used. */
+;
@end group
@end example
@example
param_spec:
- type
- | name_list ':' type
- ;
+ type
+| name_list ':' type
+;
return_spec:
- type
- | ID ':' type
- ;
+ type
+| ID ':' type
+;
@end example
For a more detailed exposition of LALR(1) parsers and parser
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.
+has proved insignificant for practical grammars.
@end itemize
While the LAC algorithm shares techniques that have been recognized in the
Because Bison parsers have growing stacks, hitting the upper limit
usually results from using a right recursion instead of a left
-recursion, @xref{Recursion, ,Recursive Rules}.
+recursion, see @ref{Recursion, ,Recursive Rules}.
@vindex YYMAXDEPTH
By defining the macro @code{YYMAXDEPTH}, you can control how deep the
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
For example:
@example
-stmnts: /* empty string */
- | stmnts '\n'
- | stmnts exp '\n'
- | stmnts error '\n'
+stmts:
+ /* empty string */
+| stmts '\n'
+| stmts exp '\n'
+| stmts error '\n'
@end example
The fourth rule in this example says that an error followed by a newline
-makes a valid addition to any @code{stmnts}.
+makes a valid addition to any @code{stmts}.
What happens if a syntax error occurs in the middle of an @code{exp}? The
error recovery rule, interpreted strictly, applies to the precise sequence
-of a @code{stmnts}, an @code{error} and a newline. If an error occurs in
+of a @code{stmts}, an @code{error} and a newline. If an error occurs in
the middle of an @code{exp}, there will probably be some additional tokens
-and subexpressions on the stack after the last @code{stmnts}, and there
+and subexpressions on the stack after the last @code{stmts}, and there
will be tokens to read before the next newline. So the rule is not
applicable in the ordinary way.
the semantic context and part of the input. First it discards states
and objects from the stack until it gets back to a state in which the
@code{error} token is acceptable. (This means that the subexpressions
-already parsed are discarded, back to the last complete @code{stmnts}.)
+already parsed are discarded, back to the last complete @code{stmts}.)
At this point the @code{error} token can be shifted. Then, if the old
lookahead token is not acceptable to be shifted next, the parser reads
tokens and discards them until it finds a token which is acceptable. In
the current input line or current statement if an error is detected:
@example
-stmnt: error ';' /* On error, skip until ';' is read. */
+stmt: error ';' /* On error, skip until ';' is read. */
@end example
It is also useful to recover to the matching close-delimiter of an
spurious error message:
@example
-primary: '(' expr ')'
- | '(' error ')'
- @dots{}
- ;
+primary:
+ '(' expr ')'
+| '(' error ')'
+@dots{}
+;
@end example
Error recovery strategies are necessarily guesses. When they guess wrong,
one syntax error often leads to another. In the above example, the error
recovery rule guesses that an error is due to bad input within one
-@code{stmnt}. Suppose that instead a spurious semicolon is inserted in the
-middle of a valid @code{stmnt}. After the error recovery rule recovers
+@code{stmt}. Suppose that instead a spurious semicolon is inserted in the
+middle of a valid @code{stmt}. After the error recovery rule recovers
from the first error, another syntax error will be found straightaway,
since the text following the spurious semicolon is also an invalid
-@code{stmnt}.
+@code{stmt}.
To prevent an outpouring of error messages, the parser will output no error
message for another syntax error that happens shortly after the first; only
@example
typedef int foo, bar;
int baz (void)
+@group
@{
static bar (bar); /* @r{redeclare @code{bar} as static variable} */
extern foo foo (foo); /* @r{redeclare @code{foo} as function} */
return foo (bar);
@}
+@end group
@end example
Unfortunately, the name being declared is separated from the declaration
duplication, with actions omitted for brevity:
@example
+@group
initdcl:
- declarator maybeasm '='
- init
- | declarator maybeasm
- ;
+ declarator maybeasm '=' init
+| declarator maybeasm
+;
+@end group
+@group
notype_initdcl:
- notype_declarator maybeasm '='
- init
- | notype_declarator maybeasm
- ;
+ notype_declarator maybeasm '=' init
+| notype_declarator maybeasm
+;
+@end group
@end example
@noindent
@dots{}
@end group
@group
-expr: IDENTIFIER
- | constant
- | HEX '('
- @{ hexflag = 1; @}
- expr ')'
- @{ hexflag = 0;
- $$ = $4; @}
- | expr '+' expr
- @{ $$ = make_sum ($1, $3); @}
- @dots{}
- ;
+expr:
+ IDENTIFIER
+| constant
+| HEX '(' @{ hexflag = 1; @}
+ expr ')' @{ hexflag = 0; $$ = $4; @}
+| expr '+' expr @{ $$ = make_sum ($1, $3); @}
+@dots{}
+;
@end group
@group
constant:
- INTEGER
- | STRING
- ;
+ INTEGER
+| STRING
+;
@end group
@end example
tokens until the next semicolon, and then start a new statement, like this:
@example
-stmt: expr ';'
- | IF '(' expr ')' stmt @{ @dots{} @}
- @dots{}
- error ';'
- @{ hexflag = 0; @}
- ;
+stmt:
+ expr ';'
+| IF '(' expr ')' stmt @{ @dots{} @}
+@dots{}
+| error ';' @{ hexflag = 0; @}
+;
@end example
If there is a syntax error in the middle of a @samp{hex (@var{expr})}
@example
@group
-expr: @dots{}
- | '(' expr ')'
- @{ $$ = $2; @}
- | '(' error ')'
- @dots{}
+expr:
+ @dots{}
+| '(' expr ')' @{ $$ = $2; @}
+| '(' error ')'
+@dots{}
@end group
@end example
@node Debugging
@chapter Debugging Your Parser
-Developing a parser can be a challenge, especially if you don't
-understand the algorithm (@pxref{Algorithm, ,The Bison Parser
-Algorithm}). Even so, sometimes a detailed description of the automaton
-can help (@pxref{Understanding, , Understanding Your Parser}), or
-tracing the execution of the parser can give some insight on why it
-behaves improperly (@pxref{Tracing, , Tracing Your Parser}).
+Developing a parser can be a challenge, especially if you don't understand
+the algorithm (@pxref{Algorithm, ,The Bison Parser Algorithm}). This
+chapter explains how to generate and read the detailed description of the
+automaton, and how to enable and understand the parser run-time traces.
@menu
* Understanding:: Understanding the structure of your parser.
representation of it, either textually or graphically (as a DOT file).
The textual file is generated when the options @option{--report} or
-@option{--verbose} are specified, see @xref{Invocation, , Invoking
+@option{--verbose} are specified, see @ref{Invocation, , Invoking
Bison}. Its name is made by removing @samp{.tab.c} or @samp{.c} from
the parser implementation file name, and adding @samp{.output}
instead. Therefore, if the grammar file is @file{foo.y}, then the
%left '+' '-'
%left '*'
%%
-exp: exp '+' exp
- | exp '-' exp
- | exp '*' exp
- | exp '/' exp
- | NUM
- ;
+exp:
+ exp '+' exp
+| exp '-' exp
+| exp '*' exp
+| exp '/' exp
+| NUM
+;
useless: STR;
%%
@end example
order of the output and the exact presentation might vary, but the
interpretation is the same.
-The first section includes details on conflicts that were solved thanks
-to precedence and/or associativity:
-
-@example
-Conflict in state 8 between rule 2 and token '+' resolved as reduce.
-Conflict in state 8 between rule 2 and token '-' resolved as reduce.
-Conflict in state 8 between rule 2 and token '*' resolved as shift.
-@exdent @dots{}
-@end example
-
-@noindent
-The next section lists states that still have conflicts.
-
-@example
-State 8 conflicts: 1 shift/reduce
-State 9 conflicts: 1 shift/reduce
-State 10 conflicts: 1 shift/reduce
-State 11 conflicts: 4 shift/reduce
-@end example
-
@noindent
@cindex token, useless
@cindex useless token
@cindex useless nonterminal
@cindex rule, useless
@cindex useless rule
-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 ``unused''
-below):
+The first section reports useless tokens, nonterminals 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 ``unused'' below):
@example
-Nonterminals useless in grammar:
+Nonterminals useless in grammar
useless
-Terminals unused in grammar:
+Terminals unused in grammar
STR
-Rules useless in grammar:
-#6 useless: STR;
+Rules useless in grammar
+ 6 useless: STR
+@end example
+
+@noindent
+The next section lists states that still have conflicts.
+
+@example
+State 8 conflicts: 1 shift/reduce
+State 9 conflicts: 1 shift/reduce
+State 10 conflicts: 1 shift/reduce
+State 11 conflicts: 4 shift/reduce
@end example
@noindent
-The next section reproduces the exact grammar that Bison used:
+Then Bison reproduces the exact grammar it used:
@example
Grammar
- Number, Line, Rule
- 0 5 $accept -> exp $end
- 1 5 exp -> exp '+' exp
- 2 6 exp -> exp '-' exp
- 3 7 exp -> exp '*' exp
- 4 8 exp -> exp '/' exp
- 5 9 exp -> NUM
+ 0 $accept: exp $end
+
+ 1 exp: exp '+' exp
+ 2 | exp '-' exp
+ 3 | exp '*' exp
+ 4 | exp '/' exp
+ 5 | NUM
@end example
@noindent
and reports the uses of the symbols:
@example
+@group
Terminals, with rules where they appear
$end (0) 0
'/' (47) 4
error (256)
NUM (258) 5
+STR (259)
+@end group
+@group
Nonterminals, with rules where they appear
-$accept (8)
+$accept (9)
on left: 0
-exp (9)
+exp (10)
on left: 1 2 3 4 5, on right: 0 1 2 3 4
+@end group
@end example
@noindent
@cindex pointed rule
@cindex rule, pointed
Bison then proceeds onto the automaton itself, describing each state
-with it set of @dfn{items}, also known as @dfn{pointed rules}. Each
-item is a production rule together with a point (marked by @samp{.})
-that the input cursor.
+with its set of @dfn{items}, also known as @dfn{pointed rules}. Each
+item is a production rule together with a point (@samp{.}) marking
+the location of the input cursor.
@example
state 0
- $accept -> . exp $ (rule 0)
+ 0 $accept: . exp $end
- NUM shift, and go to state 1
+ NUM shift, and go to state 1
- exp go to state 2
+ exp go to state 2
@end example
This reads as follows: ``state 0 corresponds to being at the very
symbol (here, @code{exp}). When the parser returns to this state right
after having reduced a rule that produced an @code{exp}, the control
flow jumps to state 2. If there is no such transition on a nonterminal
-symbol, and the lookahead is a @code{NUM}, then this token is shifted on
+symbol, and the lookahead is a @code{NUM}, then this token is shifted onto
the parse stack, and the control flow jumps to state 1. Any other
lookahead triggers a syntax error.''
at the beginning of any rule deriving an @code{exp}. By default Bison
reports the so-called @dfn{core} or @dfn{kernel} of the item set, but if
you want to see more detail you can invoke @command{bison} with
-@option{--report=itemset} to list all the items, include those that can
-be derived:
+@option{--report=itemset} to list the derived items as well:
@example
state 0
- $accept -> . exp $ (rule 0)
- exp -> . exp '+' exp (rule 1)
- exp -> . exp '-' exp (rule 2)
- exp -> . exp '*' exp (rule 3)
- exp -> . exp '/' exp (rule 4)
- exp -> . NUM (rule 5)
+ 0 $accept: . exp $end
+ 1 exp: . exp '+' exp
+ 2 | . exp '-' exp
+ 3 | . exp '*' exp
+ 4 | . exp '/' exp
+ 5 | . NUM
- NUM shift, and go to state 1
+ NUM shift, and go to state 1
- exp go to state 2
+ exp go to state 2
@end example
@noindent
-In the state 1...
+In the state 1@dots{}
@example
state 1
- exp -> NUM . (rule 5)
+ 5 exp: NUM .
- $default reduce using rule 5 (exp)
+ $default reduce using rule 5 (exp)
@end example
@noindent
@example
state 2
- $accept -> exp . $ (rule 0)
- exp -> exp . '+' exp (rule 1)
- exp -> exp . '-' exp (rule 2)
- exp -> exp . '*' exp (rule 3)
- exp -> exp . '/' exp (rule 4)
+ 0 $accept: exp . $end
+ 1 exp: exp . '+' exp
+ 2 | exp . '-' exp
+ 3 | exp . '*' exp
+ 4 | exp . '/' exp
- $ shift, and go to state 3
- '+' shift, and go to state 4
- '-' shift, and go to state 5
- '*' shift, and go to state 6
- '/' shift, and go to state 7
+ $end shift, and go to state 3
+ '+' shift, and go to state 4
+ '-' shift, and go to state 5
+ '*' shift, and go to state 6
+ '/' shift, and go to state 7
@end example
@noindent
In state 2, the automaton can only shift a symbol. For instance,
-because of the item @samp{exp -> exp . '+' exp}, if the lookahead if
-@samp{+}, it will be shifted on the parse stack, and the automaton
-control will jump to state 4, corresponding to the item @samp{exp -> exp
-'+' . exp}. Since there is no default action, any other token than
-those listed above will trigger a syntax error.
+because of the item @samp{exp: exp . '+' exp}, if the lookahead is
+@samp{+} it is shifted onto the parse stack, and the automaton
+jumps to state 4, corresponding to the item @samp{exp: exp '+' . exp}.
+Since there is no default action, any lookahead not listed triggers a syntax
+error.
@cindex accepting state
The state 3 is named the @dfn{final state}, or the @dfn{accepting
@example
state 3
- $accept -> exp $ . (rule 0)
+ 0 $accept: exp $end .
- $default accept
+ $default accept
@end example
@noindent
-the initial rule is completed (the start symbol and the end
-of input were read), the parsing exits successfully.
+the initial rule is completed (the start symbol and the end-of-input were
+read), the parsing exits successfully.
The interpretation of states 4 to 7 is straightforward, and is left to
the reader.
@example
state 4
- exp -> exp '+' . exp (rule 1)
+ 1 exp: exp '+' . exp
- NUM shift, and go to state 1
+ NUM shift, and go to state 1
+
+ exp go to state 8
- exp go to state 8
state 5
- exp -> exp '-' . exp (rule 2)
+ 2 exp: exp '-' . exp
+
+ NUM shift, and go to state 1
- NUM shift, and go to state 1
+ exp go to state 9
- exp go to state 9
state 6
- exp -> exp '*' . exp (rule 3)
+ 3 exp: exp '*' . exp
- NUM shift, and go to state 1
+ NUM shift, and go to state 1
+
+ exp go to state 10
- exp go to state 10
state 7
- exp -> exp '/' . exp (rule 4)
+ 4 exp: exp '/' . exp
- NUM shift, and go to state 1
+ NUM shift, and go to state 1
- exp go to state 11
+ exp go to state 11
@end example
As was announced in beginning of the report, @samp{State 8 conflicts:
@example
state 8
- exp -> exp . '+' exp (rule 1)
- exp -> exp '+' exp . (rule 1)
- exp -> exp . '-' exp (rule 2)
- exp -> exp . '*' exp (rule 3)
- exp -> exp . '/' exp (rule 4)
+ 1 exp: exp . '+' exp
+ 1 | exp '+' exp .
+ 2 | exp . '-' exp
+ 3 | exp . '*' exp
+ 4 | exp . '/' exp
- '*' shift, and go to state 6
- '/' shift, and go to state 7
+ '*' shift, and go to state 6
+ '/' shift, and go to state 7
- '/' [reduce using rule 1 (exp)]
- $default reduce using rule 1 (exp)
+ '/' [reduce using rule 1 (exp)]
+ $default reduce using rule 1 (exp)
@end example
Indeed, there are two actions associated to the lookahead @samp{/}:
Because in deterministic parsing a single decision can be made, Bison
arbitrarily chose to disable the reduction, see @ref{Shift/Reduce, ,
-Shift/Reduce Conflicts}. Discarded actions are reported in between
+Shift/Reduce Conflicts}. Discarded actions are reported between
square brackets.
Note that all the previous states had a single possible action: either
@example
state 8
- exp -> exp . '+' exp (rule 1)
- exp -> exp '+' exp . [$, '+', '-', '/'] (rule 1)
- exp -> exp . '-' exp (rule 2)
- exp -> exp . '*' exp (rule 3)
- exp -> exp . '/' exp (rule 4)
+ 1 exp: exp . '+' exp
+ 1 | exp '+' exp . [$end, '+', '-', '/']
+ 2 | exp . '-' exp
+ 3 | exp . '*' exp
+ 4 | exp . '/' exp
+
+ '*' shift, and go to state 6
+ '/' shift, and go to state 7
- '*' shift, and go to state 6
- '/' shift, and go to state 7
+ '/' [reduce using rule 1 (exp)]
+ $default reduce using rule 1 (exp)
+@end example
+
+Note however that while @samp{NUM + NUM / NUM} is ambiguous (which results in
+the conflicts on @samp{/}), @samp{NUM + NUM * NUM} is not: the conflict was
+solved thanks to associativity and precedence directives. If invoked with
+@option{--report=solved}, Bison includes information about the solved
+conflicts in the report:
- '/' [reduce using rule 1 (exp)]
- $default reduce using rule 1 (exp)
+@example
+Conflict between rule 1 and token '+' resolved as reduce (%left '+').
+Conflict between rule 1 and token '-' resolved as reduce (%left '-').
+Conflict between rule 1 and token '*' resolved as shift ('+' < '*').
@end example
+
The remaining states are similar:
@example
+@group
state 9
- exp -> exp . '+' exp (rule 1)
- exp -> exp . '-' exp (rule 2)
- exp -> exp '-' exp . (rule 2)
- exp -> exp . '*' exp (rule 3)
- exp -> exp . '/' exp (rule 4)
+ 1 exp: exp . '+' exp
+ 2 | exp . '-' exp
+ 2 | exp '-' exp .
+ 3 | exp . '*' exp
+ 4 | exp . '/' exp
- '*' shift, and go to state 6
- '/' shift, and go to state 7
+ '*' shift, and go to state 6
+ '/' shift, and go to state 7
- '/' [reduce using rule 2 (exp)]
- $default reduce using rule 2 (exp)
+ '/' [reduce using rule 2 (exp)]
+ $default reduce using rule 2 (exp)
+@end group
+@group
state 10
- exp -> exp . '+' exp (rule 1)
- exp -> exp . '-' exp (rule 2)
- exp -> exp . '*' exp (rule 3)
- exp -> exp '*' exp . (rule 3)
- exp -> exp . '/' exp (rule 4)
+ 1 exp: exp . '+' exp
+ 2 | exp . '-' exp
+ 3 | exp . '*' exp
+ 3 | exp '*' exp .
+ 4 | exp . '/' exp
- '/' shift, and go to state 7
+ '/' shift, and go to state 7
- '/' [reduce using rule 3 (exp)]
- $default reduce using rule 3 (exp)
+ '/' [reduce using rule 3 (exp)]
+ $default reduce using rule 3 (exp)
+@end group
+@group
state 11
- exp -> exp . '+' exp (rule 1)
- exp -> exp . '-' exp (rule 2)
- exp -> exp . '*' exp (rule 3)
- exp -> exp . '/' exp (rule 4)
- exp -> exp '/' exp . (rule 4)
-
- '+' shift, and go to state 4
- '-' shift, and go to state 5
- '*' shift, and go to state 6
- '/' shift, and go to state 7
-
- '+' [reduce using rule 4 (exp)]
- '-' [reduce using rule 4 (exp)]
- '*' [reduce using rule 4 (exp)]
- '/' [reduce using rule 4 (exp)]
- $default reduce using rule 4 (exp)
+ 1 exp: exp . '+' exp
+ 2 | exp . '-' exp
+ 3 | exp . '*' exp
+ 4 | exp . '/' exp
+ 4 | exp '/' exp .
+
+ '+' shift, and go to state 4
+ '-' shift, and go to state 5
+ '*' shift, and go to state 6
+ '/' shift, and go to state 7
+
+ '+' [reduce using rule 4 (exp)]
+ '-' [reduce using rule 4 (exp)]
+ '*' [reduce using rule 4 (exp)]
+ '/' [reduce using rule 4 (exp)]
+ $default reduce using rule 4 (exp)
+@end group
@end example
@noindent
@cindex debugging
@cindex tracing the parser
-If a Bison grammar compiles properly but doesn't do what you want when it
-runs, the @code{yydebug} parser-trace feature can help you figure out why.
+When a Bison grammar compiles properly but parses ``incorrectly'', the
+@code{yydebug} parser-trace feature helps figuring out why.
+@menu
+* Enabling Traces:: Activating run-time trace support
+* Mfcalc Traces:: Extending @code{mfcalc} to support traces
+* The YYPRINT Macro:: Obsolete interface for semantic value reports
+@end menu
+
+@node Enabling Traces
+@subsection Enabling Traces
There are several means to enable compilation of trace facilities:
@table @asis
We suggest that you always enable the trace option so that debugging is
always possible.
+@findex YYFPRINTF
The trace facility outputs messages with macro calls of the form
@code{YYFPRINTF (stderr, @var{format}, @var{args})} where
@var{format} and @var{args} are the usual @code{printf} format and variadic
of the state stack afterward.
@end itemize
-To make sense of this information, it helps to refer to the listing file
-produced by the Bison @samp{-v} option (@pxref{Invocation, ,Invoking
-Bison}). This file shows the meaning of each state in terms of
+To make sense of this information, it helps to refer to the automaton
+description file (@pxref{Understanding, ,Understanding Your Parser}).
+This file shows the meaning of each state in terms of
positions in various rules, and also what each state will do with each
possible input token. As you read the successive trace messages, you
can see that the parser is functioning according to its specification in
something undesirable happens, and you will see which parts of the
grammar are to blame.
-The parser implementation file is a C program and you can use C
+The parser implementation file is a C/C++/Java program and you can use
debuggers on it, but it's not easy to interpret what it is doing. The
parser function is a finite-state machine interpreter, and aside from
the actions it executes the same code over and over. Only the values
of variables show where in the grammar it is working.
+@node Mfcalc Traces
+@subsection Enabling Debug Traces for @code{mfcalc}
+
+The debugging information normally gives the token type of each token read,
+but not its semantic value. The @code{%printer} directive allows specify
+how semantic values are reported, see @ref{Printer Decl, , Printing
+Semantic Values}. For backward compatibility, Yacc like C parsers may also
+use the @code{YYPRINT} (@pxref{The YYPRINT Macro, , The @code{YYPRINT}
+Macro}), but its use is discouraged.
+
+As a demonstration of @code{%printer}, consider the multi-function
+calculator, @code{mfcalc} (@pxref{Multi-function Calc}). To enable run-time
+traces, and semantic value reports, insert the following directives in its
+prologue:
+
+@comment file: mfcalc.y: 2
+@example
+/* Generate the parser description file. */
+%verbose
+/* Enable run-time traces (yydebug). */
+%define parse.trace
+
+/* Formatting semantic values. */
+%printer @{ fprintf (yyoutput, "%s", $$->name); @} VAR;
+%printer @{ fprintf (yyoutput, "%s()", $$->name); @} FNCT;
+%printer @{ fprintf (yyoutput, "%g", $$); @} <val>;
+@end example
+
+The @code{%define} directive instructs Bison to generate run-time trace
+support. Then, activation of these traces is controlled at run-time by the
+@code{yydebug} variable, which is disabled by default. Because these traces
+will refer to the ``states'' of the parser, it is helpful to ask for the
+creation of a description of that parser; this is the purpose of (admittedly
+ill-named) @code{%verbose} directive.
+
+The set of @code{%printer} directives demonstrates how to format the
+semantic value in the traces. Note that the specification can be done
+either on the symbol type (e.g., @code{VAR} or @code{FNCT}), or on the type
+tag: since @code{<val>} is the type for both @code{NUM} and @code{exp}, this
+printer will be used for them.
+
+Here is a sample of the information provided by run-time traces. The traces
+are sent onto standard error.
+
+@example
+$ @kbd{echo 'sin(1-1)' | ./mfcalc -p}
+Starting parse
+Entering state 0
+Reducing stack by rule 1 (line 34):
+-> $$ = nterm input ()
+Stack now 0
+Entering state 1
+@end example
+
+@noindent
+This first batch shows a specific feature of this grammar: the first rule
+(which is in line 34 of @file{mfcalc.y} can be reduced without even having
+to look for the first token. The resulting left-hand symbol (@code{$$}) is
+a valueless (@samp{()}) @code{input} non terminal (@code{nterm}).
+
+Then the parser calls the scanner.
+@example
+Reading a token: Next token is token FNCT (sin())
+Shifting token FNCT (sin())
+Entering state 6
+@end example
+
+@noindent
+That token (@code{token}) is a function (@code{FNCT}) whose value is
+@samp{sin} as formatted per our @code{%printer} specification: @samp{sin()}.
+The parser stores (@code{Shifting}) that token, and others, until it can do
+something about it.
+
+@example
+Reading a token: Next token is token '(' ()
+Shifting token '(' ()
+Entering state 14
+Reading a token: Next token is token NUM (1.000000)
+Shifting token NUM (1.000000)
+Entering state 4
+Reducing stack by rule 6 (line 44):
+ $1 = token NUM (1.000000)
+-> $$ = nterm exp (1.000000)
+Stack now 0 1 6 14
+Entering state 24
+@end example
+
+@noindent
+The previous reduction demonstrates the @code{%printer} directive for
+@code{<val>}: both the token @code{NUM} and the resulting non-terminal
+@code{exp} have @samp{1} as value.
+
+@example
+Reading a token: Next token is token '-' ()
+Shifting token '-' ()
+Entering state 17
+Reading a token: Next token is token NUM (1.000000)
+Shifting token NUM (1.000000)
+Entering state 4
+Reducing stack by rule 6 (line 44):
+ $1 = token NUM (1.000000)
+-> $$ = nterm exp (1.000000)
+Stack now 0 1 6 14 24 17
+Entering state 26
+Reading a token: Next token is token ')' ()
+Reducing stack by rule 11 (line 49):
+ $1 = nterm exp (1.000000)
+ $2 = token '-' ()
+ $3 = nterm exp (1.000000)
+-> $$ = nterm exp (0.000000)
+Stack now 0 1 6 14
+Entering state 24
+@end example
+
+@noindent
+The rule for the subtraction was just reduced. The parser is about to
+discover the end of the call to @code{sin}.
+
+@example
+Next token is token ')' ()
+Shifting token ')' ()
+Entering state 31
+Reducing stack by rule 9 (line 47):
+ $1 = token FNCT (sin())
+ $2 = token '(' ()
+ $3 = nterm exp (0.000000)
+ $4 = token ')' ()
+-> $$ = nterm exp (0.000000)
+Stack now 0 1
+Entering state 11
+@end example
+
+@noindent
+Finally, the end-of-line allow the parser to complete the computation, and
+display its result.
+
+@example
+Reading a token: Next token is token '\n' ()
+Shifting token '\n' ()
+Entering state 22
+Reducing stack by rule 4 (line 40):
+ $1 = nterm exp (0.000000)
+ $2 = token '\n' ()
+@result{} 0
+-> $$ = nterm line ()
+Stack now 0 1
+Entering state 10
+Reducing stack by rule 2 (line 35):
+ $1 = nterm input ()
+ $2 = nterm line ()
+-> $$ = nterm input ()
+Stack now 0
+Entering state 1
+@end example
+
+The parser has returned into state 1, in which it is waiting for the next
+expression to evaluate, or for the end-of-file token, which causes the
+completion of the parsing.
+
+@example
+Reading a token: Now at end of input.
+Shifting token $end ()
+Entering state 2
+Stack now 0 1 2
+Cleanup: popping token $end ()
+Cleanup: popping nterm input ()
+@end example
+
+
+@node The YYPRINT Macro
+@subsection The @code{YYPRINT} Macro
+
+@findex YYPRINT
+Before @code{%printer} support, semantic values could be displayed using the
+@code{YYPRINT} macro, which works only for terminal symbols and only with
+the @file{yacc.c} skeleton.
+
+@deffn {Macro} YYPRINT (@var{stream}, @var{token}, @var{value});
@findex YYPRINT
-The debugging information normally gives the token type of each token
-read, but not its semantic value. You can optionally define a macro
-named @code{YYPRINT} to provide a way to print the value. If you define
-@code{YYPRINT}, it should take three arguments. The parser will pass a
-standard I/O stream, the numeric code for the token type, and the token
-value (from @code{yylval}).
+If you define @code{YYPRINT}, it should take three arguments. The parser
+will pass a standard I/O stream, the numeric code for the token type, and
+the token value (from @code{yylval}).
+
+For @file{yacc.c} only. Obsoleted by @code{%printer}.
+@end deffn
Here is an example of @code{YYPRINT} suitable for the multi-function
calculator (@pxref{Mfcalc Declarations, ,Declarations for @code{mfcalc}}):
-@smallexample
+@example
%@{
static void print_token_value (FILE *, int, YYSTYPE);
- #define YYPRINT(file, type, value) print_token_value (file, type, value)
+ #define YYPRINT(File, Type, Value) \
+ print_token_value (File, Type, Value)
%@}
@dots{} %% @dots{} %% @dots{}
else if (type == NUM)
fprintf (file, "%d", value.val);
@}
-@end smallexample
+@end example
@c ================================================= Invoking Bison
For example, warn about unset @code{$$} in the mid-rule action in:
@example
- exp: '1' @{ $1 = 1; @} '+' exp @{ $$ = $2 + $4; @};
+exp: '1' @{ $1 = 1; @} '+' exp @{ $$ = $2 + $4; @};
@end example
These warnings are not enabled by default since they sometimes prove to
@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).
+
+@tindex uint
+In this section @code{uint} is an abbreviation for @code{unsigned int}: in
+genuine code only the latter is used.
+
+@menu
+* C++ position:: One point in the source file
+* C++ location:: Two points in the source file
+@end menu
+
+@node C++ position
+@subsubsection C++ @code{position}
+
+@deftypeop {Constructor} {position} {} position (std::string* @var{file} = 0, uint @var{line} = 1, uint @var{col} = 1)
+Create a @code{position} denoting a given point. Note that @code{file} is
+not reclaimed when the @code{position} is destroyed: memory managed must be
+handled elsewhere.
+@end deftypeop
+
+@deftypemethod {position} {void} initialize (std::string* @var{file} = 0, uint @var{line} = 1, uint @var{col} = 1)
+Reset the position to the given values.
+@end deftypemethod
-@deftypemethod {position} {std::string*} file
+@deftypeivar {position} {std::string*} file
The name of the file. It will always be handled as a pointer, the
parser will never duplicate nor deallocate it. As an experimental
feature you may change it to @samp{@var{type}*} using @samp{%define
filename_type "@var{type}"}.
-@end deftypemethod
+@end deftypeivar
-@deftypemethod {position} {unsigned int} line
+@deftypeivar {position} {uint} line
The line, starting at 1.
-@end deftypemethod
+@end deftypeivar
-@deftypemethod {position} {unsigned int} lines (int @var{height} = 1)
+@deftypemethod {position} {uint} lines (int @var{height} = 1)
Advance by @var{height} lines, resetting the column number.
@end deftypemethod
-@deftypemethod {position} {unsigned int} column
-The column, starting at 0.
-@end deftypemethod
+@deftypeivar {position} {uint} column
+The column, starting at 1.
+@end deftypeivar
-@deftypemethod {position} {unsigned int} columns (int @var{width} = 1)
+@deftypemethod {position} {uint} columns (int @var{width} = 1)
Advance by @var{width} columns, without changing the line number.
@end deftypemethod
-@deftypemethod {position} {position&} operator+= (position& @var{pos}, int @var{width})
-@deftypemethodx {position} {position} operator+ (const position& @var{pos}, int @var{width})
-@deftypemethodx {position} {position&} operator-= (const position& @var{pos}, int @var{width})
-@deftypemethodx {position} {position} operator- (position& @var{pos}, int @var{width})
+@deftypemethod {position} {position&} operator+= (int @var{width})
+@deftypemethodx {position} {position} operator+ (int @var{width})
+@deftypemethodx {position} {position&} operator-= (int @var{width})
+@deftypemethodx {position} {position} operator- (int @var{width})
Various forms of syntactic sugar for @code{columns}.
@end deftypemethod
-@deftypemethod {position} {position} operator<< (std::ostream @var{o}, const position& @var{p})
+@deftypemethod {position} {bool} operator== (const position& @var{that})
+@deftypemethodx {position} {bool} operator!= (const position& @var{that})
+Whether @code{*this} and @code{that} denote equal/different positions.
+@end deftypemethod
+
+@deftypefun {std::ostream&} operator<< (std::ostream& @var{o}, const position& @var{p})
Report @var{p} on @var{o} like this:
@samp{@var{file}:@var{line}.@var{column}}, or
@samp{@var{line}.@var{column}} if @var{file} is null.
+@end deftypefun
+
+@node C++ location
+@subsubsection C++ @code{location}
+
+@deftypeop {Constructor} {location} {} location (const position& @var{begin}, const position& @var{end})
+Create a @code{Location} from the endpoints of the range.
+@end deftypeop
+
+@deftypeop {Constructor} {location} {} location (const position& @var{pos} = position())
+@deftypeopx {Constructor} {location} {} location (std::string* @var{file}, uint @var{line}, uint @var{col})
+Create a @code{Location} denoting an empty range located at a given point.
+@end deftypeop
+
+@deftypemethod {location} {void} initialize (std::string* @var{file} = 0, uint @var{line} = 1, uint @var{col} = 1)
+Reset the location to an empty range at the given values.
@end deftypemethod
-@deftypemethod {location} {position} begin
-@deftypemethodx {location} {position} end
+@deftypeivar {location} {position} begin
+@deftypeivarx {location} {position} end
The first, inclusive, position of the range, and the first beyond.
-@end deftypemethod
+@end deftypeivar
-@deftypemethod {location} {unsigned int} columns (int @var{width} = 1)
-@deftypemethodx {location} {unsigned int} lines (int @var{height} = 1)
+@deftypemethod {location} {uint} columns (int @var{width} = 1)
+@deftypemethodx {location} {uint} lines (int @var{height} = 1)
Advance the @code{end} position.
@end deftypemethod
-@deftypemethod {location} {location} operator+ (const location& @var{begin}, const location& @var{end})
-@deftypemethodx {location} {location} operator+ (const location& @var{begin}, int @var{width})
-@deftypemethodx {location} {location} operator+= (const location& @var{loc}, int @var{width})
+@deftypemethod {location} {location} operator+ (const location& @var{end})
+@deftypemethodx {location} {location} operator+ (int @var{width})
+@deftypemethodx {location} {location} operator+= (int @var{width})
Various forms of syntactic sugar.
@end deftypemethod
Move @code{begin} onto @code{end}.
@end deftypemethod
+@deftypemethod {location} {bool} operator== (const location& @var{that})
+@deftypemethodx {location} {bool} operator!= (const location& @var{that})
+Whether @code{*this} and @code{that} denote equal/different ranges of
+positions.
+@end deftypemethod
+
+@deftypefun {std::ostream&} operator<< (std::ostream& @var{o}, const location& @var{p})
+Report @var{p} on @var{o}, taking care of special cases such as: no
+@code{filename} defined, or equal filename/line or column.
+@end deftypefun
@node C++ Parser Interface
@subsection C++ Parser Interface
@end defcv
@defcv {Type} {parser} {token}
-A structure that contains (only) the definition of the tokens as the
-@code{yytokentype} enumeration. To refer to the token @code{FOO}, the
-scanner should use @code{yy::parser::token::FOO}. The scanner can use
+A structure that contains (only) the @code{yytokentype} enumeration, which
+defines the tokens. To refer to the token @code{FOO},
+use @code{yy::parser::token::FOO}. The scanner can use
@samp{typedef yy::parser::token token;} to ``import'' the token enumeration
(@pxref{Calc++ Scanner}).
@end defcv
@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
@comment file: calc++-parser.yy
@example
-%skeleton "lalr1.cc" /* -*- C++ -*- */
+%skeleton "lalr1.cc" /* -*- C++ -*- */
%require "@value{VERSION}"
%defines
%define parser_class_name "calcxx_parser"
@c FIXME: Document %printer, and mention that it takes a braced-code operand.
@comment file: calc++-parser.yy
@example
-%printer @{ debug_stream () << $$; @} <*>;
+%printer @{ yyoutput << $$; @} <*>;
@end example
@noindent
unit: assignments exp @{ driver.result = $2; @};
assignments:
- assignments assignment @{@}
-| /* Nothing. */ @{@};
+ /* Nothing. */ @{@}
+| assignments assignment @{@};
assignment:
"identifier" ":=" exp @{ driver.variables[$1] = $3; @};
@comment file: calc++-scanner.ll
@example
-%@{ /* -*- C++ -*- */
+%@{ /* -*- C++ -*- */
# include <cerrno>
# include <climits>
# include <cstdlib>
@comment file: calc++-scanner.ll
@example
+@group
%@{
// Code run each time a pattern is matched.
# define YY_USER_ACTION loc.columns (yyleng);
%@}
+@end group
%%
+@group
%@{
// Code run each time yylex is called.
loc.step ();
%@}
+@end group
@{blank@}+ loc.step ();
[\n]+ loc.lines (yyleng); loc.step ();
@end example
")" return yy::calcxx_parser::make_RPAREN(loc);
":=" return yy::calcxx_parser::make_ASSIGN(loc);
+@group
@{int@} @{
errno = 0;
long n = strtol (yytext, NULL, 10);
driver.error (loc, "integer is out of range");
return yy::calcxx_parser::make_NUMBER(n, loc);
@}
+@end group
@{id@} return yy::calcxx_parser::make_IDENTIFIER(yytext, loc);
. driver.error (loc, "invalid character");
<<EOF>> return yy::calcxx_parser::make_END(loc);
@comment file: calc++-scanner.ll
@example
+@group
void
calcxx_driver::scan_begin ()
@{
yy_flex_debug = trace_scanning;
- if (file == "-")
+ if (file.empty () || file == "-")
yyin = stdin;
else if (!(yyin = fopen (file.c_str (), "r")))
@{
- error (std::string ("cannot open ") + file + ": " + strerror(errno));
- exit (1);
+ error ("cannot open " + file + ": " + strerror(errno));
+ exit (EXIT_FAILURE);
@}
@}
+@end group
+@group
void
calcxx_driver::scan_end ()
@{
fclose (yyin);
@}
+@end group
@end example
@node Calc++ Top Level
#include <iostream>
#include "calc++-driver.hh"
+@group
int
main (int argc, char *argv[])
@{
int res = 0;
calcxx_driver driver;
- for (++argv; argv[0]; ++argv)
- if (*argv == std::string ("-p"))
+ for (int i = 1; i < argc; ++i)
+ if (argv[i] == std::string ("-p"))
driver.trace_parsing = true;
- else if (*argv == std::string ("-s"))
+ else if (argv[i] == std::string ("-s"))
driver.trace_scanning = true;
- else if (!driver.parse (*argv))
+ else if (!driver.parse (argv[i]))
std::cout << driver.result << std::endl;
else
res = 1;
return res;
@}
+@end group
@end example
@node Java Parsers
@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
Use @code{%code init} for code added to the start of the constructor
body. This is especially useful to initialize superclasses. Use
-@samp{%define init_throws} to specify any uncatch exceptions.
+@samp{%define init_throws} to specify any uncaught exceptions.
@end deftypeop
@deftypemethod {YYParser} {boolean} parse ()
@xref{Java Location Values}.
@end defvar
-@deffn {Statement} {return YYABORT;}
+@deftypefn {Statement} return YYABORT @code{;}
Return immediately from the parser, indicating failure.
@xref{Java Parser Interface}.
-@end deffn
+@end deftypefn
-@deffn {Statement} {return YYACCEPT;}
+@deftypefn {Statement} return YYACCEPT @code{;}
Return immediately from the parser, indicating success.
@xref{Java Parser Interface}.
-@end deffn
+@end deftypefn
-@deffn {Statement} {return YYERROR;}
-Start error recovery without printing an error message.
+@deftypefn {Statement} {return} YYERROR @code{;}
+Start error recovery (without printing an error message).
@xref{Error Recovery}.
-@end deffn
+@end deftypefn
@deftypefn {Function} {boolean} recovering ()
Return whether error recovery is being done. In this state, the parser
appear in an action. The actual definition of these symbols is
opaque to the Bison grammar, and it might change in the future. The
only meaningful operation that you can do, is to return them.
-See @pxref{Java Action Features}.
+@xref{Java Action Features}.
Note that of these three symbols, only @code{YYACCEPT} and
@code{YYABORT} will cause a return from the @code{yyparse}
an union. The type of @code{$$}, even with angle brackets, is the base
type since Java casts are not allow on the left-hand side of assignments.
Also, @code{$@var{n}} and @code{@@@var{n}} are not allowed on the
-left-hand side of assignments. See @pxref{Java Semantic Values} and
-@pxref{Java Action Features}.
+left-hand side of assignments. @xref{Java Semantic Values}, and
+@ref{Java Action Features}.
@item
The prologue declarations have a different meaning than in C/C++ code.
@item @code{%code lexer}
blocks, if specified, should include the implementation of the
scanner. If there is no such block, the scanner can be any class
-that implements the appropriate interface (see @pxref{Java Scanner
+that implements the appropriate interface (@pxref{Java Scanner
Interface}).
@end table
@node Memory Exhausted
@section Memory Exhausted
-@display
+@quotation
My parser returns with error with a @samp{memory exhausted}
message. What can I do?
-@end display
+@end quotation
-This question is already addressed elsewhere, @xref{Recursion,
-,Recursive Rules}.
+This question is already addressed elsewhere, see @ref{Recursion, ,Recursive
+Rules}.
@node How Can I Reset the Parser
@section How Can I Reset the Parser
The following phenomenon has several symptoms, resulting in the
following typical questions:
-@display
+@quotation
I invoke @code{yyparse} several times, and on correct input it works
properly; but when a parse error is found, all the other calls fail
too. How can I reset the error flag of @code{yyparse}?
-@end display
+@end quotation
@noindent
or
-@display
+@quotation
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 @samp{%define api.pure}.
-@end display
+@end quotation
These problems typically come not from Bison itself, but from
Lex-generated scanners. Because these scanners use large buffers for
demonstration, consider the following source file,
@file{first-line.l}:
-@verbatim
-%{
+@example
+@group
+%@{
#include <stdio.h>
#include <stdlib.h>
-%}
+%@}
+@end group
%%
.*\n ECHO; return 1;
%%
+@group
int
yyparse (char const *file)
-{
+@{
yyin = fopen (file, "r");
if (!yyin)
- exit (2);
+ @{
+ perror ("fopen");
+ exit (EXIT_FAILURE);
+ @}
+@end group
+@group
/* One token only. */
yylex ();
if (fclose (yyin) != 0)
- exit (3);
+ @{
+ perror ("fclose");
+ exit (EXIT_FAILURE);
+ @}
return 0;
-}
+@}
+@end group
+@group
int
main (void)
-{
+@{
yyparse ("input");
yyparse ("input");
return 0;
-}
-@end verbatim
+@}
+@end group
+@end example
@noindent
If the file @file{input} contains
-@verbatim
+@example
input:1: Hello,
input:2: World!
-@end verbatim
+@end example
@noindent
then instead of getting the first line twice, you get:
@node Strings are Destroyed
@section Strings are Destroyed
-@display
+@quotation
My parser seems to destroy old strings, or maybe it loses track of
them. Instead of reporting @samp{"foo", "bar"}, it reports
@samp{"bar", "bar"}, or even @samp{"foo\nbar", "bar"}.
-@end display
+@end quotation
This error is probably the single most frequent ``bug report'' sent to
Bison lists, but is only concerned with a misunderstanding of the role
of the scanner. Consider the following Lex code:
-@verbatim
-%{
+@example
+@group
+%@{
#include <stdio.h>
char *yylval = NULL;
-%}
+%@}
+@end group
+@group
%%
.* yylval = yytext; return 1;
\n /* IGNORE */
%%
+@end group
+@group
int
main ()
-{
+@{
/* Similar to using $1, $2 in a Bison action. */
char *fst = (yylex (), yylval);
char *snd = (yylex (), yylval);
printf ("\"%s\", \"%s\"\n", fst, snd);
return 0;
-}
-@end verbatim
+@}
+@end group
+@end example
If you compile and run this code, you get:
@node Implementing Gotos/Loops
@section Implementing Gotos/Loops
-@display
+@quotation
My simple calculator supports variables, assignments, and functions,
but how can I implement gotos, or loops?
-@end display
+@end quotation
Although very pedagogical, the examples included in the document blur
the distinction to make between the parser---whose job is to recover
@node Multiple start-symbols
@section Multiple start-symbols
-@display
+@quotation
I have several closely related grammars, and I would like to share their
implementations. In fact, I could use a single grammar but with
multiple entry points.
-@end display
+@end quotation
Bison does not support multiple start-symbols, but there is a very
simple means to simulate them. If @code{foo} and @code{bar} are the two
@example
%token START_FOO START_BAR;
%start start;
-start: START_FOO foo
- | START_BAR bar;
+start:
+ START_FOO foo
+| START_BAR bar;
@end example
These tokens prevents the introduction of new conflicts. As far as the
@node Secure? Conform?
@section Secure? Conform?
-@display
+@quotation
Is Bison secure? Does it conform to POSIX?
-@end display
+@end quotation
If you're looking for a guarantee or certification, we don't provide it.
However, Bison is intended to be a reliable program that conforms to the
@node I can't build Bison
@section I can't build Bison
-@display
+@quotation
I can't build Bison because @command{make} complains that
@code{msgfmt} is not found.
What should I do?
-@end display
+@end quotation
Like most GNU packages with internationalization support, that feature
is turned on by default. If you have problems building in the @file{po}
@node Where can I find help?
@section Where can I find help?
-@display
+@quotation
I'm having trouble using Bison. Where can I find help?
-@end display
+@end quotation
First, read this fine manual. Beyond that, you can send mail to
@email{help-bison@@gnu.org}. This mailing list is intended to be
@node Bug Reports
@section Bug Reports
-@display
+@quotation
I found a bug. What should I include in the bug report?
-@end display
+@end quotation
Before you send a bug report, make sure you are using the latest
version. Check @url{ftp://ftp.gnu.org/pub/gnu/bison/} or one of its
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}.
@node More Languages
@section More Languages
-@display
+@quotation
Will Bison ever have C++ and Java support? How about @var{insert your
favorite language here}?
-@end display
+@end quotation
C++ and Java support is there now, and is documented. We'd love to add other
languages; contributions are welcome.
@node Beta Testing
@section Beta Testing
-@display
+@quotation
What is involved in being a beta tester?
-@end display
+@end quotation
It's not terribly involved. Basically, you would download a test
release, compile it, and use it to build and run a parser or two. After
@node Mailing Lists
@section Mailing Lists
-@display
+@quotation
How do I join the help-bison and bug-bison mailing lists?
-@end display
+@end quotation
See @url{http://lists.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} $$
@end deffn
@deffn {Macro} YYERROR
-Macro to pretend that a syntax error has just been detected: call
-@code{yyerror} and then perform normal error recovery if possible
-(@pxref{Error Recovery}), or (if recovery is impossible) make
-@code{yyparse} return 1. @xref{Error Recovery}.
+Cause an immediate syntax error. This statement initiates error
+recovery just as if the parser itself had detected an error; however, it
+does not call @code{yyerror}, and does not print any message. If you
+want to print an error message, call @code{yyerror} explicitly before
+the @samp{YYERROR;} statement. @xref{Error Recovery}.
For Java parsers, this functionality is invoked using @code{return YYERROR;}
instead.
(@pxref{Error Reporting, ,The Error Reporting Function @code{yyerror}}).
@end deffn
+@deffn {Macro} YYFPRINTF
+Macro used to output run-time traces.
+@xref{Enabling Traces}.
+@end deffn
+
@deffn {Macro} YYINITDEPTH
Macro for specifying the initial size of the parser stack.
@xref{Memory Management}.
parsing. @xref{Parser Function, ,The Parser Function @code{yyparse}}.
@end deffn
+@deffn {Macro} YYPRINT
+Macro used to output token semantic values. For @file{yacc.c} only.
+Obsoleted by @code{%printer}.
+@xref{The YYPRINT Macro, , The @code{YYPRINT} Macro}.
+@end deffn
+
@deffn {Function} yypstate_delete
The function to delete a parser instance, produced by Bison in push mode;
call this function to delete the memory associated with a parser.
@c LocalWords: NUM exp subsubsection kbd Ctrl ctype EOF getchar isdigit nonfree
@c LocalWords: ungetc stdin scanf sc calc ulator ls lm cc NEG prec yyerrok rr
@c LocalWords: longjmp fprintf stderr yylloc YYLTYPE cos ln Stallman Destructor
-@c LocalWords: smallexample symrec val tptr FNCT fnctptr func struct sym enum
+@c LocalWords: symrec val tptr FNCT fnctptr func struct sym enum IEC syntaxes
@c LocalWords: fnct putsym getsym fname arith fncts atan ptr malloc sizeof Lex
@c LocalWords: strlen strcpy fctn strcmp isalpha symbuf realloc isalnum DOTDOT
@c LocalWords: ptypes itype YYPRINT trigraphs yytname expseq vindex dtype Unary
@c LocalWords: strncmp intval tindex lvalp locp llocp typealt YYBACKUP subrange
@c LocalWords: YYEMPTY YYEOF YYRECOVERING yyclearin GE def UMINUS maybeword loc
@c LocalWords: Johnstone Shamsa Sadaf Hussain Tomita TR uref YYMAXDEPTH inline
-@c LocalWords: YYINITDEPTH stmnts ref stmnt initdcl maybeasm notype Lookahead
+@c LocalWords: YYINITDEPTH stmts ref initdcl maybeasm notype Lookahead yyoutput
@c LocalWords: hexflag STR exdent itemset asis DYYDEBUG YYFPRINTF args Autoconf
@c LocalWords: infile ypp yxx outfile itemx tex leaderfill Troubleshouting sqrt
@c LocalWords: hbox hss hfill tt ly yyin fopen fclose ofirst gcc ll lookahead
@c LocalWords: nbar yytext fst snd osplit ntwo strdup AST Troublereporting th
@c LocalWords: YYSTACK DVI fdl printindex IELR nondeterministic nonterminals ps
@c LocalWords: subexpressions declarator nondeferred config libintl postfix LAC
-@c LocalWords: preprocessor nonpositive unary nonnumeric typedef extern rhs
-@c LocalWords: yytokentype destructor multicharacter nonnull EBCDIC
+@c LocalWords: preprocessor nonpositive unary nonnumeric typedef extern rhs sr
+@c LocalWords: yytokentype destructor multicharacter nonnull EBCDIC nterm LR's
@c LocalWords: lvalue nonnegative XNUM CHR chr TAGLESS tagless stdout api TOK
-@c LocalWords: destructors Reentrancy nonreentrant subgrammar nonassociative
+@c LocalWords: destructors Reentrancy nonreentrant subgrammar nonassociative Ph
@c LocalWords: deffnx namespace xml goto lalr ielr runtime lex yacc yyps env
@c LocalWords: yystate variadic Unshift NLS gettext po UTF Automake LOCALEDIR
@c LocalWords: YYENABLE bindtextdomain Makefile DEFS CPPFLAGS DBISON DeRemer
-@c LocalWords: autoreconf Pennello multisets nondeterminism Generalised baz
+@c LocalWords: autoreconf Pennello multisets nondeterminism Generalised baz ACM
@c LocalWords: redeclare automata Dparse localedir datadir XSLT midrule Wno
-@c LocalWords: Graphviz multitable headitem hh basename Doxygen fno
+@c LocalWords: Graphviz multitable headitem hh basename Doxygen fno filename
@c LocalWords: doxygen ival sval deftypemethod deallocate pos deftypemethodx
@c LocalWords: Ctor defcv defcvx arg accessors arithmetics CPP ifndef CALCXX
@c LocalWords: lexer's calcxx bool LPAREN RPAREN deallocation cerrno climits
@c LocalWords: cstdlib Debian undef yywrap unput noyywrap nounput zA yyleng
-@c LocalWords: errno strtol ERANGE str strerror iostream argc argv Javadoc
+@c LocalWords: errno strtol ERANGE str strerror iostream argc argv Javadoc PSLR
@c LocalWords: bytecode initializers superclass stype ASTNode autoboxing nls
@c LocalWords: toString deftypeivar deftypeivarx deftypeop YYParser strictfp
@c LocalWords: superclasses boolean getErrorVerbose setErrorVerbose deftypecv
@c LocalWords: getDebugStream setDebugStream getDebugLevel setDebugLevel url
@c LocalWords: bisonVersion deftypecvx bisonSkeleton getStartPos getEndPos
-@c LocalWords: getLVal defvar deftypefn deftypefnx gotos msgfmt Corbett
-@c LocalWords: subdirectory Solaris nonassociativity
+@c LocalWords: getLVal defvar deftypefn deftypefnx gotos msgfmt Corbett LALR's
+@c LocalWords: subdirectory Solaris nonassociativity perror schemas Malloy
+@c LocalWords: Scannerless ispell american
@c Local Variables:
@c ispell-dictionary: "american"
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