$$->u.unary_expression.type = UNARY_SIGNED_CONSTANT;
$$->u.unary_expression.u.signed_constant =
-($$->u.unary_expression.u.unsigned_constant);
$$->u.unary_expression.type = UNARY_SIGNED_CONSTANT;
$$->u.unary_expression.u.signed_constant =
-($$->u.unary_expression.u.unsigned_constant);