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
actions in nondeterministic mode, since the latter are deferred.
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
Here are the C and Bison declarations for the multi-function calculator.
@comment file: mfcalc.y
-@smallexample
+@example
@group
%@{
#include <stdio.h> /* For printf, etc. */
%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
those which mention @code{VAR} or @code{FNCT}, are new.
@comment file: mfcalc.y
-@smallexample
+@example
@group
input: /* empty */
| input line
@end group
/* End of grammar. */
%%
-@end smallexample
+@end example
@node Mfcalc Symbol Table
@subsection The @code{mfcalc} Symbol Table
provides for either functions or variables to be placed in the table.
@comment file: calc.h
-@smallexample
+@example
@group
/* Function type. */
typedef double (*func_t) (double);
symrec *putsym (char const *, int);
symrec *getsym (char const *);
@end group
-@end smallexample
+@end example
The new version of @code{main} will call @code{init_table} to initialize
the symbol table:
@comment file: mfcalc.y
-@smallexample
+@example
@group
struct init
@{
@}
@}
@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.
found, a pointer to that symbol is returned; otherwise zero is returned.
@comment file: mfcalc.y
-@smallexample
+@example
#include <stdlib.h> /* malloc. */
#include <string.h> /* strlen. */
return 0;
@}
@end group
-@end smallexample
+@end example
@node Mfcalc Lexer
@subsection The @code{mfcalc} Lexer
operators in @code{yylex}.
@comment file: mfcalc.y
-@smallexample
+@example
@group
#include <ctype.h>
@end group
return c;
@}
@end group
-@end smallexample
+@end example
@node Mfcalc Main
@subsection The @code{mfcalc} Main
@code{main} includes a call to @code{init_table}:
@comment file: mfcalc.y
-@smallexample
+@example
@group
/* Called by yyparse on error. */
void
return yyparse ();
@}
@end group
-@end smallexample
+@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
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
@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
@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 @{ type2_free ($$); @} <field2>
%printer @{ type2_print ($$); @} <field2>
@end group
-@end smallexample
+@end example
@noindent
You could even place each of the above directive groups in the rules section of
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
@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
@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
@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}.
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
@comment file: calc++-parser.yy
@example
-%skeleton "lalr1.cc" /* -*- C++ -*- */
+%skeleton "lalr1.cc" /* -*- C++ -*- */
%require "@value{VERSION}"
%defines
%define parser_class_name "calcxx_parser"
@comment file: calc++-scanner.ll
@example
-%@{ /* -*- C++ -*- */
+%@{ /* -*- C++ -*- */
# include <cerrno>
# include <climits>
# include <cstdlib>
@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
@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
projects / bison.git / commitdiff
