How to use the data type contains a function

Question

I have the following data type definition:

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

and then I can define the following:

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

My question is how to use f

?

+3

zero_coding Jun 28. 17 at 6:38 am

1 answer

Mark Seemann · Accepted Answer · 2017-06-28T06:54:47+0000

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