int parser(char expr [])
{/*parser for parethesis language
  if left paren, bracket or brace, push
  if right paren, bracket, or brace pop and compare
  if not a match return false. */
   int i;
   char ch;
   stack_ptr top = NULL;
   for (i = 0; i < strlen(expr); i++)
       switch (expr[i]) {
	   case '[': case  '{': case '(': push(&top, expr[i]);
	           break;
	   case ']': if (IS_EMPTY(top))
	               return FALSE;
	              ch = pop(&top);
				  if (ch != '[') return FALSE;
				  break;
		case '}': if (IS_EMPTY(top))
	               return FALSE;
	              ch = pop(&top);
				  if (ch != '{') return FALSE;
				  break;	
		case ')': if (IS_EMPTY(top))
	               return FALSE;
	              ch = pop(&top);
				  if (ch != '(') return FALSE;
	   }
    if (IS_EMPTY(top)) /*string is finished, stack contains items */
        return TRUE;
    return FALSE;
}