具有开放联合的类型定义
1）我有一个开放联合定义如下：
type 'a choice = [> `One | `Other ] as 'a
然后我尝试定义一个类型 choice_list：
type choice_list = choice list
这不起作用。如何定义其中一个或多个组件是开联合的类型？
2）如果我放弃创建 choice_list 类型，而只使用 选择列表，当我尝试使用选择列表编写接口/签名语句时，
val choice_handler : choice list -> int
编译器会抱怨type 'a choice = 'aconstraint 'a = [>; `一| `Other] 不包含在感染状态类型中。他们有不同的性质。
我的问题是，如何在接口/签名中编写选择列表的类型声明。
1) I have an open union defined as follows:
type 'a choice = [> `One | `Other ] as 'a
I then try to define a type choice_list:
type choice_list = choice list
which does not work. How does one define types where one or more of the components are open unions?
2) If instead I forgo creating the choice_list type, and just use a choice list, when I try writing an interface/signature statement using a choice list,
val choice_handler : choice list -> int
the compiler complains that type 'a choice = 'a constraint 'a = [> `One | `Other ] is not included in type infection_state. They have different arities.
My question is, how does one write the type declaration of choice list in the interface/signature.
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编译器试图告诉您
choice是一个参数化类型。在类型级别，它的元数为 1。换句话说，您需要提供一个类型参数。您已将参数限制为[`One|`Other]的子类型，但除此之外它可以是任何类型：如果您想定义选项列表，则额外类型必须来自某处。即，它必须是新类型的参数：（
根据我的经验，此类构造很快就会变得棘手。）
The compiler is trying to tell you that
choiceis a parameterized type. At the type level, it has an arity of 1. In other words, you need to supply one type parameter. You have constrained the parameter to be a subtype of[`One|`Other], but other than that it can be any type:If you want to define a list of choices, the extra type has to come from somewhere. I.e., it has to be a parameter to the new type:
(These sorts of constructions get tricky pretty fast, in my experience.)