Creating a `newtype Maybe a`

Question

I created a newtype for Maybe Int:

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

But how can I create a generic newtype of Maybe a?

Answer 1

Add the a as a type parameter:

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