On 2/28/06, Johannes Waldmann <[EMAIL PROTECTED]> wrote:
> Malcolm Wallace wrote:
>
> > But if contexts-on-datatypes worked correctly,
> >
> > data Set a = Ord a => ....
> >
> > then even the "real" map from Data.Set:
> >
> > map :: (Ord a, Ord b) => (a -> b) -> Set a -> Set b
> >
> > could be an instance method of Functor.
>
> I'd love that. But I don't quite understand:
> do you think this is/should be possible with:
> current Haskell? Haskell-Prime? Current ghc (what extensions)?
as Oleg:
{-# OPTIONS -fglasgow-exts #-}
{-# OPTIONS -fallow-undecidable-instances #-}
module Map where
import qualified Data.Set
class MyMap f a b where
myMap :: (a -> b) -> f a -> f b
instance (Functor f) => MyMap f a b where
myMap = fmap
instance (Ord a, Ord b) => MyMap Data.Set.Set a b where
myMap = Data.Set.map
Jim
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