def p_expression_0(self, program):
        """
        expression : expression '*' expression
                    | expression '/' expression
                    | expression '+' expression
                    | expression '-' expression
                    | expression '^' expression
        """
        program[0] = node.BinaryOp([node.BinaryOperator(program[2]),
                                    program[1], program[3]])
expression : expression '*' expression
                    | expression '/' expression
                    | expression '+' expression
                    | expression '-' expression
                    | expression '^' expression