To change it to produce instances of our case class AST hierarchy (Expr objects), the return type of the combinators has to be changed to be Parser[Expr].

要将它更改为生成 case 类 AST 层次结构的实例（Expr 对象），组合子的返回类型必须更改为 Parser[Expr]。

youdao

A command indicates a type of pattern to match, and a modifier can change the behavior that occurs in case of such a match.

命令显示欲匹配的此类模式，修饰符可以改变此类匹配中发生的行为。

youdao

Nevertheless, I am amazed (as I believe you are) at how infrequently executives take the opportunity to make an urgent case for any type of change including so-called flip-flops.

FORBES: Obama, Romney, and Mastery of the Flip-Flop