idklol.hs

{-# LANGUAGE TypeFamilies #-}
class Foo a where
	type I a t
	foo :: I a t -> t -> a

instance Foo () where
	type I () t = ()
	foo _ _ = ()

instance Foo b => Foo (a, b) where
	type I (a, b) t = (t -> a, I b t)
	foo (f, gs) t = (f t, foo gs t)

-- > foo ((+1), ((+2), ((+3), ()))) 0 :: (Int, (Int, (Int, ())))
-- (1,(2,(3,())))