gistfile1.hs

data (:|:) f g a = L (f a)
                 | R (g a)

instance (Functor f, Functor g) => Functor (f :|: g) where
  fmap = undefined

instance (Monad f, Monad g) => Monad (f :|: g) where
  return = undefined
  (>>=)  = undefined

class (Functor f, Functor e) => Liftable f e  where
  liftEff :: f a -> e a

class (Monad f, Monad e) => LiftableM f e  where
  liftEffM :: f a -> e a

data Foo a = Foo a deriving Functor
data Bar a = Bar a deriving Functor
data Baz a = Baz a deriving Functor

type MyEff = Foo :|: Bar :|: Baz

instance Liftable Foo MyEff where

instance Liftable Bar MyEff where

instance Liftable Baz MyEff where