It really seems to me that the error message you've got explains everything quite clear.
Отправлено с iPad 31.07.2012, в 22:59, Shayan Najd Javadipour <[email protected]> написал(а): > 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 > _______________________________________________ > Haskell-Cafe mailing list > [email protected] > http://www.haskell.org/mailman/listinfo/haskell-cafe
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