On 2006-08-15 at 16:25CDT Taral wrote: > On 8/15/06, Bulat Ziganshin <[EMAIL PROTECTED]> wrote: > > in this case we lose "class Functor a => Monad a" base class > > declaration. so what will be the meaning of this: > > I don't see why that is the case. > > class Functor m => Monad m where > return :: a -> m a > (>>=) :: m a -> (a -> m b) -> m b > instance Functor m where > fmap f = (>>= return . f) > > What's wrong with this? All Monads are Functors. If you don't provide > a Functor, it gets defined for you. The problem is working out whether > to use the default Functor or an external Functor.
It seems obvious to me that we always use an external definition if one exists, so I suppose the problem is knowing whether an external instance exists -- so this proposal would rely on doing something about scoping for instances, I suppose. -- Jón Fairbairn Jon.Fairbairn at cl.cam.ac.uk _______________________________________________ Haskell-prime mailing list Haskell-prime@haskell.org http://www.haskell.org/mailman/listinfo/haskell-prime
