Contexts in Existential Types

14 Mar 2001

      Would it be appropriate for Haskell to be able to remember contexts in 
existential types? For instance, currently this does not work in Hugs:

--
class Charable a where
	obtainChar :: a -> Char

instance Charable Char where
	obtainChar c = c

data AnyCharable = forall c. (Charable c) => MkAnyCharable c

anyA = MkAnyCharable 'a'
recoverA = obtainChar ((\(MkAnyCharable c) -> c) anyA)
--

I believe allowing it to work would not amount to storing dynamic type 
information.

Is this an overlooked hole or would it break the spirit of the language?

-- 
Ashley Yakeley, Seattle WA