[Haskell-cafe] RankNTypes question

Marcin Mrotek marcin.jan.mrotek at gmail.com
Thu Feb 26 18:53:41 UTC 2015

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


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

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