%{

/* compile: leg -o calc.c calc.leg
 *			cc -o calc calc.c
 *
 * run:		echo "2+3" | ./calc
 */

#define YYSTYPE int
YYSTYPE yylval = 0;

%}

start	=	e:exp					{ yylval = e }

exp		=	- s:sum					{ $$ = s }

sum		=	PLUS* l:prod
			( PLUS+ r:prod			{ l += r }
			| MINUS r:prod			{ l -= r }
			)*						{ $$ = l }

prod	=	l:neg
			( MULTI		r:neg		{ l *= r }
			| DIVIDE	r:neg		{ l /= r }
            | MODULO    r:neg       { l %= r }
			)*						{ $$ = l }

neg		=	MINUS n:neg				{ $$ = -n }
			| n:NUMBER				{ $$ = n }

-		=	[ \t]*
NUMBER	=	< [0-9]+ >	-			{ $$ = atoi(yytext) }
PLUS	=	'+'			-
MINUS	=	'-'			-
MULTI	=	'*'			-
DIVIDE	=	'/'			-
MODULO  =   '%'         -

%%

int main(int argc, char **argv)
{
	while (yyparse()) {
		printf("%d\n", yylval);
	}

	return 0;
}