I sometimes do this -< class (Show c) => C c where foo = show c data CObj= forall c. (C c, Show c) => CObj c instance C Cobj where -- my existantial type should also implement class C foo (CObj c) = foo c -> Would it be a nice idea to just write -< data CObj= forall c. (C c, Show c) => CObj c deriving (C) ? -> ? Or is this already possible? Marc Weber