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%code top {
#include <assert.h>
#include <ctype.h> /* isdigit. */
#include <stdio.h> /* For printf, etc. */
#include <string.h> /* strcmp. */
}
%code {
int yylex (YYSTYPE *yylval);
void yyerror (char const *);
}
%define api.header.include {"calc.h"}
/* Generate YYSTYPE from the types used in %token and %type. */
%define api.value.type union
%token <double> NUM "number"
%type <double> expr term fact
/* Don't share global variables between the scanner and the parser. */
%define api.pure full
/* Generate a push parser. */
%define api.push-pull push
/* Nice error messages with details. */
%define parse.error detailed
/* Generate the parser description file (calc.output). */
%verbose
/* Enable run-time traces (yydebug). */
%define parse.trace
/* Formatting semantic values in debug traces. */
%printer { fprintf (yyo, "%g", $$); } <double>;
%% /* The grammar follows. */
input:
%empty
| input line
;
line:
'\n'
| expr '\n' { printf ("%.10g\n", $1); }
| error '\n' { yyerrok; }
;
expr:
expr '+' term { $$ = $1 + $3; }
| expr '-' term { $$ = $1 - $3; }
| term
;
term:
term '*' fact { $$ = $1 * $3; }
| term '/' fact { $$ = $1 / $3; }
| fact
;
fact:
"number"
| '(' expr ')' { $$ = $expr; }
;
%%
int
yylex (YYSTYPE *yylval)
{
int c;
/* Ignore white space, get first nonwhite character. */
while ((c = getchar ()) == ' ' || c == '\t')
continue;
if (c == EOF)
return 0;
/* Char starts a number => parse the number. */
if (c == '.' || isdigit (c))
{
ungetc (c, stdin);
int n = scanf ("%lf", &yylval->NUM);
assert (n == 1);
return NUM;
}
/* Any other character is a token by itself. */
return c;
}
/* Called by yyparse on error. */
void
yyerror (char const *s)
{
fprintf (stderr, "%s\n", s);
}
int
main (int argc, char const* argv[])
{
/* Enable parse traces on option -p. */
for (int i = 1; i < argc; ++i)
if (!strcmp (argv[i], "-p"))
yydebug = 1;
int status;
yypstate *ps = yypstate_new ();
do {
YYSTYPE lval;
status = yypush_parse (ps, yylex (&lval), &lval);
} while (status == YYPUSH_MORE);
yypstate_delete (ps);
return status;
}
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