Hi, 

I wonder why the following code doesn't typecheck in GHC 7.4.1:

{-# LANGUAGE GADTs,RankNTypes #-}
data T a where T1 :: (forall b. b -> b) -> (forall a. Int -> T a)

{- Error:
Data constructor `T1' returns type `forall a. Int -> T a'
      instead of an instance of its parent type `T a'
    In the definition of data constructor `T1'
    In the data type declaration for `T'
Failed, modules loaded: none. -}

While:


{-# LANGUAGE GADTs,RankNTypes #-}

f :: (forall b. b -> b) -> (forall a. Int -> Maybe a)
f = undefined

{- 
ghci> :t f
f :: (forall b. b -> b) -> Int -> Maybe a
-} 

Thanks, 
 Shayan