Type variables from instances and class functions are conflated

[endgame]

GHC Version: 8.0.2
Haddock Version: 2.17.3
Minimal Example:

import Prelude hiding (Functor)

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

instance Functor (Either a) where
    fmap _ (Left x) = Left x
    fmap f (Right a) = Right $ f a

Expand the instance declaration for Either and note that it's conflated the a from the instance with the a from the type signature of fmap, which makes it look like a more restrictive type than it really is.

[RyanGlScott]

I believe this is a duplicate of #613.

[alexbiehl]

Yes, you are right, closing this in favour of #613 .