/* Skip white space. */
while ((c = getchar ()) == ' ' || c == '\t')
- ;
+ continue;
@end group
@group
/* Process numbers. */
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:
found, a pointer to that symbol is returned; otherwise zero is returned.
@smallexample
+#include <stdlib.h> /* malloc. */
+#include <string.h> /* strlen. */
+
+@group
symrec *
putsym (char const *sym_name, int sym_type)
@{
sym_table = ptr;
return ptr;
@}
+@end group
+@group
symrec *
getsym (char const *sym_name)
@{
return ptr;
return 0;
@}
+@end group
@end smallexample
The function @code{yylex} must now recognize variables, numeric values, and
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;
Thus, they belong in one or more @code{%code requires}:
@smallexample
+@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
@code{%code} to a @code{%code provides}:
@smallexample
+@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
type:
@smallexample
+@group
%code requires @{ #include "type1.h" @}
%union @{ type1 field1; @}
%destructor @{ type1_free ($$); @} <field1>
%printer @{ type1_print ($$); @} <field1>
+@end group
+@group
%code requires @{ #include "type2.h" @}
%union @{ type2 field2; @}
%destructor @{ type2_free ($$); @} <field2>
%printer @{ type2_print ($$); @} <field2>
+@end group
@end smallexample
@noindent
of zero or more @code{word} groupings.
@example
+@group
sequence: /* empty */
@{ printf ("empty sequence\n"); @}
| maybeword
| sequence word
@{ printf ("added word %s\n", $2); @}
;
+@end group
+@group
maybeword: /* empty */
@{ printf ("empty maybeword\n"); @}
| word
@{ printf ("single word %s\n", $1); @}
;
+@end group
@end example
@noindent
from being empty:
@example
+@group
sequence: /* empty */
| sequence words
| sequence redirects
;
+@end group
+@group
words: word
| words word
;
+@end group
+@group
redirects:redirect
| redirects redirect
;
+@end group
@end example
@node Mysterious Conflicts
@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
;
+@end group
+@group
notype_initdcl:
notype_declarator maybeasm '='
init
| notype_declarator maybeasm
;
+@end group
@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
+@end group
+@group
Nonterminals, with rules where they appear
$accept (8)
on left: 0
exp (9)
on left: 1 2 3 4 5, on right: 0 1 2 3 4
+@end group
@end example
@noindent
The remaining states are similar:
@example
+@group
state 9
exp -> exp . '+' exp (rule 1)
'/' [reduce using rule 2 (exp)]
$default reduce using rule 2 (exp)
+@end group
+@group
state 10
exp -> exp . '+' exp (rule 1)
'/' [reduce using rule 3 (exp)]
$default reduce using rule 3 (exp)
+@end group
+@group
state 11
exp -> exp . '+' exp (rule 1)
'*' [reduce using rule 4 (exp)]
'/' [reduce using rule 4 (exp)]
$default reduce using rule 4 (exp)
+@end group
@end example
@noindent
@comment file: calc++-scanner.ll
@example
+@group
%@{
# define YY_USER_ACTION yylloc->columns (yyleng);
%@}
+@end group
%%
%@{
yylloc->step ();
@comment file: calc++-scanner.ll
@example
+@group
void
calcxx_driver::scan_begin ()
@{
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[])
@{
else if (!driver.parse (*argv))
std::cout << driver.result << std::endl;
@}
+@end group
@end example
@node Java Parsers
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)
- {
- perror ("fopen");
- exit (EXIT_FAILURE);
- }
+ @{
+ perror ("fopen");
+ exit (EXIT_FAILURE);
+ @}
+@end group
+@group
/* One token only. */
yylex ();
if (fclose (yyin) != 0)
- {
- perror ("fclose");
- exit (EXIT_FAILURE);
- }
+ @{
+ 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
of the scanner. Consider the following Lex code:
@verbatim
+@group
%{
#include <stdio.h>
char *yylval = NULL;
%}
+@end group
+@group
%%
.* yylval = yytext; return 1;
\n /* IGNORE */
%%
+@end group
+@group
int
main ()
{
printf ("\"%s\", \"%s\"\n", fst, snd);
return 0;
}
+@end group
@end verbatim
If you compile and run this code, you get:
projects / bison.git / commitdiff
