On 24 September 2011 09:20, Antoine Latter
From what I understand (I haven't tried the extension yet) you would still need an instance declaration, even if it had no body:
Yes you would indeed. While I already said I liked this idea, I do see one complication: as also explained in the DefaulSuperclassInstances[1] proposal there can be multiple ways of defining fmap: default fmap :: Applicative f => (a -> b) -> f a -> f b fmap = Control.Applicative.liftA default fmap :: Traversable f => (a -> b) -> f a -> f b fmap = Data.Traversable.fmapDefault Which do we choose? I'm happy with liftA but others might disagree. With regard to [1], is there already a plan to implement them? And if so, when is it expected to be finished? If it takes some time, this might be a temporary solution. Regards, Bas [1] http://hackage.haskell.org/trac/ghc/wiki/DefaultSuperclassInstances