@Override
  public Boolean visit(Pos ast) {
    boolean checkArg = ast.getArg().accept(this);

    if (!checkArg) return false;

    Type argType = ast.getArg().typeOf(env);

    if (!argType.isCompatibleToNumeric()) {
      addToErrorList(
          ast,
          "the unary operator + can not be applied to instances of type " + argType.getClass());
      return false;
    }
    return true;
  }