Renaming instance method right-hand sides is probably not right (add tests)

[osa1]

When renaming we want to give class methods and the methods in the instances different ids. Example:

class Functor f where
  fmap :: ...                    -- (1)

instance Functor Maybe where
  fmap = ...                     -- (2)

f x y z = ... fmap ...           -- (3)

Here the fmaps in (1) and (3) should have the same id, but (2) should have a different id.

This is to be able to type check (2) against a different type than the fmap in (1). Type of (1) is Functor f => (a -> b) -> f a -> f b, while type of (2) is (a -> b) -> Maybe a -> Maybe b.

This much should be working fine and we have some tests. However the right-hand sides of instance methods are probably not renamed correctly. For example:

class Show a where
  show :: a -> String                                   -- (1)

instance Show a => Show [a] where
  show l = "[" ++ intercalate "," (map show l) ++ "]"   -- (2)

Here I think the show in the right-hand side will have the id (2), but it should have the id (1) otherwise we can't type check map show l.

We should start by adding a test.