"Composition of Composition" (i.e.,
(.) . (.)) in Haskell), has type
(a -> b) -> (c -> d -> a) -> c -> d -> b. Apparently, this is an instance of
fmap, i.e. a functor between two categories.
The question is: what is the domain and the codomain of this functor? How do we interpret this functor in terms of functional programming?