Functor
From HaskellWiki
import Data.Functor |
The Functor class is defined like this:
class Functor f where fmap :: (a -> b) -> f a -> f b
It is available in the Prelude, but defined in Data.Functor.
All instances of Functor should obey:
fmap id = id fmap (p . q) = (fmap p) . (fmap q)