How to use a data type contains function

Question

I have following data type definition:

newtype Combine a b = 
  Combine { unCombine :: a -> b }

and then I can defined as follow:

Prelude> let f = Combine $ \n -> Sum (n + 1)

My question is, how to use f?

Answer 1

Prelude Data.Monoid> unCombine f 1
Sum {getSum = 2}
Prelude Data.Monoid> unCombine f 42
Sum {getSum = 43}