Re: Contexts in Existential Types

14 Mar 2001

      At 2001-03-13 19:36, I wrote:
...
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)
--
Whoops, my error. It is possible to do this:

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

Sorry...

-- 
Ashley Yakeley, Seattle WA