创建一个`newtype也许a`

Question

我为newtype创建了Maybe Int：

Prelude> newtype MaybeTuple = MaybeTuple { getMaybe :: Maybe Int}
Prelude> let m = MaybeTuple (Just 5)
Prelude> getMaybe m
Just 5

但是如何创建newtype的通用Maybe a？

Answer 1

将a添加为类型参数：

newtype MaybeTuple a = MaybeTuple { getMaybe :: Maybe a }