foralls in class assertions

16 Feb 2002

      It would be nice to be able to put foralls in class assertions. For 
instance:

    class HasIdentity a where
        {
        identity :: a;
        };

    class Composable a b ab | a b -> ab where
        {
        compose :: a -> b -> ab;
        };

    class
        (
        forall a. HasIdentity (m a a),
        forall a b c. Composable (m b c) (m a b) (m a c)
        ) =>
     Category m;

    instance
        (
        forall a. HasIdentity (m a a),
        forall a b c. Composable (m b c) (m a b) (m a c)
        ) =>
     Category m;

Or even allow the foralls their own context:

    foo :: (forall a. (C a b) => D a c) => T b c;

Does this make sense? Would it have unpleasant consequences?

-- 
Ashley Yakeley, Seattle WA