[Haskell-cafe] Re: Function composition

[Stuart Cook]

On 10/4/07, Dominic Steinitz <dominic.steinitz at blueyonder.co.uk> wrote:
> Look at the type of (.).(.).(.)

Indeed, this generalizes to functions of any arity on the "RHS":

  Prelude> :t (.)
  (.) :: (b -> c) -> (a -> b) -> a -> c

  Prelude> :t (.).(.)
  (.).(.) :: (b -> c) -> (a -> a1 -> b) -> a -> a1 -> c

  Prelude> :t (.).(.).(.)
  (.).(.).(.) :: (b -> c) -> (a -> a1 -> a2 -> b) -> a -> a1 -> a2 -> c

  Prelude> :t (.).(.).(.).(.)
  (.).(.).(.).(.) :: (b -> c) -> (a -> a1 -> a2 -> a3 -> b) -> a -> a1
-> a2 -> a3 -> c


Of course, if you want higher-arity functions anywhere *other* than
the head of your composition chain, you'll have to resort to tupling
and uncurrying.


Stuart