code: @SuppressWarnings("unchecked")
      private List<Object> fetchParam(){
          List<Object> rvals = new ArrayList<Object>();
          if(right != null){
              if(right instanceof CommaOpt){
                  rvals = (List<Object>) ((CommaOpt) right).calculate();
              } else {
                  rvals.add(calculateItem(right));
              }
          }
          if(!rvals.isEmpty()){
              for(int i = 0; i < rvals.size(); i ++){
                  if(rvals.get(i) instanceof Operator){
                      rvals.set(i, ((Operator)rvals.get(i)).calculate());
                  }
              }
          }
          return rvals;
      }
docs: 取得方法执行的参数
  @return