docs: function(left, right, exp) {
                      this.callBase();
                      this.setFlag("Brackets");
                      // 参数整理
                      if (arguments.length === 2) {
                          exp = right;
                          right = left;
                      }
                      this.leftSymbol = left;
                      this.rightSymbol = right;
                      this.setOperator(new BracketsOperator());
                      this.setOperand(exp, 0);
                  }