At 2002-04-09 20:02, I wrote:

Does anyone even know of a workaround? Given this, find an implementation of 'f' that retrieves the contents of its 'D' argument:

class C a b | a -> b

data D a = forall b. (C a b) => MkD b

f :: (C a b) => D a -> b -- f (MkD b) = b won't compile

It's very annoying if it can't be done.

Oh, I suppose I can always do this: data D a b = MkD b ...so perhaps in all fairness it's not quite so annoying. -- Ashley Yakeley, Seattle WA