WhyCan Forum(哇酷开发者社区)

%{
#include <string.h>
#include "cal.tab.h"

#define YY_SKIP_YYWRAP

extern int yylval;
int yylex(void);
%}

numbers ([0-9])+
plus "+"
minus "-"
times "*"
divide "/"
lp "("
rp ")"
delim [ \n\t]
ws {delim}*

%%
{numbers} {
	sscanf(yytext, "%d", &yylval);
	return INTEGER;
}

{plus} {
	return PLUS;
}

{minus} {
	return MINUS;
}

{times} {
	return TIMES;
}

{divide} {
	return DIVIDE;
}

{lp} {
	return LP;
}

{rp} {
	return RP;
}

{ws} {
}

. {
}
%%

%{
#include <stdio.h>
#include "lex.yy.c"
#define YYSTYPE int
int yyparse(void);
void yyerror(char* s);
%}

%token PLUS MINUS TIMES DIVIDE INTEGER LP RP

%%
command: exp {printf("%d\n", $1);}

exp: exp PLUS term {$$ = $1 + $3;}
   | exp MINUS term {$$ = $1 - $3;}
   | term {$$ = $1;}
   ;

term: term TIMES factor {$$ = $1 * $3;}
    | term DIVIDE factor {$$ = $1 / $3;}
    | factor {$$ = $1;}
	;

factor: INTEGER {$$ = $1;}
      | LP exp RP {$$ = $2;}
	  ;
%%

int main(int argc, char *argv[]) {
	return yyparse();
}

int yywrap() {
	return 1;
}

void yyerror(char* s) {
	printf("error: %s\n", s);
}