[Haskell-cafe] Trouble with types

Hi, I tried this code: ----------------------- f, g :: a -> a (f, g) = (id, id) ----------------------- Hugs: OK GHC: Couldn't match expected type `forall a. a -> a' against inferred type `a -> a' In the expression: id In the expression: (id, id) In a pattern binding: (f, g) = (id, id) What does mean this error message? And what of them (Hugs, GHC) is correct? Thanks Vladimir