module Bug613 where
import Prelude (Either(Left, Right))
class Functor f where
fmap :: (a -> b) -> f a -> f b
instance Functor (Either a) where
fmap _ (Left x) = Left x
fmap f (Right y) = Right (f y)
-- | Phantom type a0 is added to block the first renaming from a to a0. This ensures that the renamer doesn't create a new conflict
data ThreeVars a0 a b = ThreeVars a b
instance Functor (ThreeVars a0 a) where
fmap f (ThreeVars a b) = ThreeVars a (f b)