F#类型定义语法 [英] F# type definition syntax

问题描述

我正在研究'99 F#问题'，看到了 NestedList 的以下定义:

I'm working on the '99 problems of F#', and saw the following definition of NestedList:

type 'a NestedList = List of 'a NestedList list | Elem of 'a

我对这里的语法有些困惑，因为通常在 type 之后只有一个类型名称.有人可以澄清吗?谢谢！

I'm a little confused by the syntax here, as normally there is only a type name after the type. Can someone clarify it? Thanks!

推荐答案

这是简明的联盟.您也可以将其编写为:

This is a discriminated union in a condensed syntax. You can also write it as:

type 'a NestedList =
    | List of 'a NestedList list
    | Elem of 'a

或

type NestedList<'a> =
    | List of NestedList<'a> list
    | Elem of 'a

这是使用泛型，其中类型本身正在将另一种类型用作参数.

This is using generics, where the type itself is taking another type as an argument.

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