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haskellnewtype

Creating a `newtype Maybe a`

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?

Solution

  • Add the a as a type parameter:

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