[Haskell-cafe] explicit type for "local" functions

[Tom Ellis]

On Wed, Jan 27, 2021 at 11:48:10AM +0100, Jean-Marc Alliot wrote:
> Let's consider the following function:
> collatz n =
>   let coll (n,cpt)
>         | n==1 = (1,cpt)
>         | even n = coll (div n 2,cpt+1)
>         | odd n = coll (div (n*3+1) 2,cpt+1) in
>     snd (coll (n,0))
[..]
> But can I set explicitly the type of the "local" function "coll" ?

Do you mean this?


collatz :: Integer -> Int
collatz n =
  let coll :: (Integer, Int) -> (Integer, Int)
      coll (n,cpt)
        | n==1 = (1,cpt)
        | even n = coll (div n 2,cpt+1)
        | odd n = coll (div (n*3+1) 2,cpt+1) in
    snd (coll (n,0))