Just a fun Show instance for functions

import Data.List
import Data.Maybe
import Control.Monad
import Control.Arrow

(*) `on` f = \x y -> f x * f y

class Inhabitants a where inhabitants :: [a]
instance Inhabitants () where inhabitants = [()]
instance Inhabitants Bool where inhabitants = [True,False]
instance (Inhabitants x, Inhabitants y) => Inhabitants (x,y) where inhabitants = liftM2 (,) inhabitants inhabitants
instance Inhabitants x => Inhabitants (Maybe x) where inhabitants = Nothing : map Just inhabitants

instance (Inhabitants p, Show p, Show q) => Show (p -> q) where
  show f = "(fromJust . flip lookup " ++ show (map (id &&& f) inhabitants) ++ ")"


-- > not
-- (fromJust . flip lookup [(True,False),(False,True)])
-- > (fromJust . flip lookup [(True,False),(False,True)]) True
-- False
-- > \x -> Just Nothing
-- (fromJust . flip lookup [((),Just Nothing)])
-- > id
-- (fromJust . flip lookup [((),())])
-- > maybe not (&&)
-- (fromJust . flip lookup [(Nothing,(fromJust . flip lookup [(True,False),(False,True)])),(Just True,(fromJust . flip lookup [(True,True),(False,False)])),(Just False,(fromJust . flip lookup [(True,False),(False,False)]))])