void expression(expr_rec *result)
{
	/* <expression>		-> <primary> {<add op> <primary> #gen_infix} */
	expr_rec left_operand, right_operand;
	op_rec op;

	primary(&left_operand);
	while (next_token() == PLUSOP || next_token() == MINUSOP) {
		add_op(&op);
		primary(&right_operand);
		left_operand = gen_infix(left_operand, op, right_operand);
	}
	*result = left_operand;
}