In article <[EMAIL PROTECTED]>, "Tim Sweeney" <[EMAIL PROTECTED]> wrote:
> class Monad m => RefMonad m r | m -> r where > newRef :: a -> m (r a) > readRef :: r a -> m a > writeRef :: r a -> a -> m () > > Is it possible to actually implement a working instance of RefMonad in > Haskell, without making use of a built-in monad like IO or ST? If so, I'd > love any tips -- I've been making good use of monads for a while, but can't > figure this one out. You certainly wouldn't be able to do this for any monad M which had: performM :: forall a. M a -> a; ...because it wouldn't be type-safe: you'd be able to construct coerce :: a -> b just as you can with unsafePerformIO. -- Ashley Yakeley, Seattle WA _______________________________________________ Haskell mailing list [EMAIL PROTECTED] http://www.haskell.org/mailman/listinfo/haskell
