package FunctorCrash where

class Functor f where
  map :: (a -> b) -> f a -> f b

interface Bar at bt =
  a :: at
  b :: bt

type Foo t = Bar t t

foo :: t -> t -> Foo t
foo a b = Foo { a = a; b = b; }

instance Functor Foo where
  map f x = foo (f x.a) (f x.b)