FlexBisonLab/eval.y

/*
Syntax analyser
for `bison`
*/
%{
#include <stdio.h>

/* Prototypes */
int yylex (void);
void yyerror (const char *);

/* Variable from lexical analysis */
extern char* yytext;

%}

%defines /* Geneates eval.tab.h */

%token  number

%start  EXPR_CALCS /* Axiom */

%%

EXPR_CALCS	: EXPR_CALC
		| EXPR_CALCS EXPR_CALC
		;

EXPR_CALC	: EXPR '=' 	{ printf("%d\n", $1); }
		;

EXPR	: EXPR '+' FACTOR	{$$ = $1 + $3;}
	| EXPR '-' FACTOR	{$$ = $1 - $3;}
        | FACTOR
	;

FACTOR	: FACTOR '*' ATOM	{$$ = $1 * $3;}
	| FACTOR '/' ATOM	{if ($3 == 0) $$ = $1; else $$ = $1 / $3;}
        | ATOM
	;

ATOM    : number                {$$ = $1;}
	| '(' EXPR ')'		{$$ = $2;}
        ;

%%
#include <stdio.h>
#include "eval.tab.h"

void yyerror (const char * error) 
{
    fprintf (stderr, "Error detected : %s\n for expression\n%s\n", error, yytext);
}

int main() {
    if ( yyparse() != 0 ) {
        fprintf(stderr, "Error detected : syntax error\n");
        return 1;
    }
    else
        return 0;
}