[Haskell-cafe] RankNTypes question

[Marcin Mrotek]

Ah sorry, I think I responded only to you, not to the whole list. If
anyone else is interested, my answer was:

test :: (forall a. a -> a) -> Int -> Int
test f a = f a

Also consider this:

foo :: Maybe a -> Maybe b
foo Nothing = Nothing

vs.

foo :: Maybe a -> Maybe b
fooo a at Nothing = a

You don't actually need RankNTypes to bump into this. Don't feel
stupid, I remember running into this kind of things frequently when I
was trying to define Prisms (from lens) by hand ;)

Kind regards,
Marcin Mrotek