Hello haskell-cafe, In ghci, I tried to get info for Data.Stream.Stream: $ ghci GHCi, version 6.8.2: http://www.haskell.org/ghc/ :? for help Loading package base ... linking ... done. Prelude> :m Data.Stream Prelude Data.Stream> :i Stream data Stream a where Stream :: forall a s. (Data.Stream.Unlifted s) => !s -> Step a s -> !s -> Stream a -- Defined in Data.Stream instance Functor Stream -- Defined in Data.Stream This didn't seem right to me, so I asked tried this: Prelude Data.Stream> :t Stream Stream :: (Data.Stream.Unlifted s) => (s -> Step a s) -> s -> Stream a What's going on here? forall a s. (Data.Stream.Unlifted s) => !s -> Step a s -> !s -> Stream a and (Data.Stream.Unlifted s) => (s -> Step a s) -> s -> Stream a are completely different, right? And really, neither one makes much sense to me. I would have expected forall s. (Data.Stream.Unlifted s) => (s -> Step a s) -> s -> Stream a -- Chad