Idris 的“BorrowedType”背后的意图是什么？
What's the intention behind Idris' `BorrowedType`?
在 idris 中，有一个名为 UniqueType 的宇宙，类型的值只能在其中使用一次。据我所知，它可以用来编写高性能代码。
但是一个值只能使用一次的事实通常是太有限了，所以有一种方法可以借用一个值而不是使用它：
data Borrowed : UniqueType -> BorrowedType where ...
Borrowed 数据类型在 Idris 中定义如上。为什么它不简单 return Type 而是引入另一个类型域 (BorrowedType)？
As the documentation explains，对 BorrowedType 类型的 Borrowed 值有限制：
Unlike a unique value, a borrowed value may be referred to as many times as desired. However, there is a restriction on how a borrowed value can be used. After all, much like a library book or your neighbour’s lawnmower, if a function borrows a value it is expected to return it in exactly the condition in which it was received!
The restriction is that when a Borrowed type is matched, any pattern variables under the Read which have a unique type may not be referred to at all on the right hand side (unless they are themselves lent to another function).
此限制（以及 lend 的宽大处理）是通过类型检查器中的特殊类型规则实现的。这些规则需要适用于某些东西，这就是为什么 BorrowedType 必须是不同于常规 Type 的另一种类型（对于它们没有特殊的 lend/Read 键入规则).
在 idris 中，有一个名为 UniqueType 的宇宙，类型的值只能在其中使用一次。据我所知，它可以用来编写高性能代码。
但是一个值只能使用一次的事实通常是太有限了，所以有一种方法可以借用一个值而不是使用它：
data Borrowed : UniqueType -> BorrowedType where ...
Borrowed 数据类型在 Idris 中定义如上。为什么它不简单 return Type 而是引入另一个类型域 (BorrowedType)？
As the documentation explains，对 BorrowedType 类型的 Borrowed 值有限制：
Unlike a unique value, a borrowed value may be referred to as many times as desired. However, there is a restriction on how a borrowed value can be used. After all, much like a library book or your neighbour’s lawnmower, if a function borrows a value it is expected to return it in exactly the condition in which it was received!
The restriction is that when a
Borrowedtype is matched, any pattern variables under theReadwhich have a unique type may not be referred to at all on the right hand side (unless they are themselves lent to another function).
此限制（以及 lend 的宽大处理）是通过类型检查器中的特殊类型规则实现的。这些规则需要适用于某些东西，这就是为什么 BorrowedType 必须是不同于常规 Type 的另一种类型（对于它们没有特殊的 lend/Read 键入规则).