As a side note, I think a direct superclass of Functor for Monad is not a good idea, just sayin'
class Functor f where fmap :: (a -> b) -> f a -> f b class Functor f => Apply f where (<*>) :: f (a -> b) -> f a -> f b class Apply f => Bind f where (=<<) :: (a -> f b) -> f a -> f b class Apply f => Applicative f where unit :: a -> f a class (Applicative f, Bind f) => Monad f where Same goes for Comonad (e.g. [] has (=<<) but not counit) ... and again for Monoid, Category, I could go on... On 17/10/12 04:14, David Thomas wrote: > I think the version below (with a Functor or Applicative superclass) > is clearly the right answer if we were putting the prelude together > from a clean slate. You can implement whichever is easiest for the > particular monad, use whichever is most appropriate to the context > (and add optimized versions if you prove to need them). I see no > advantage in any other specific proposal, except the enormous > advantage held by the status quo that it is already written, already > documented, already distributed, and already coded to. > > Regarding mathematical "purity" of the solutions, "this is in every > way isomorphic to a monad, but we aren't calling it a monad because we > are describing it a little differently than the most common way to > describe a monad in category theory" strikes me as *less* > mathematically grounded than "we are calling this a monad because it > is in every way isomorphic to a monad." > > On Tue, Oct 16, 2012 at 7:03 AM, AUGER Cédric <sedri...@gmail.com> wrote: >> So I think that an implicit question was why wouldn't we have: >> >> class Monad m where >> return :: a -> m a >> kleisli :: (a -> m b) -> (b -> m c) -> (a -> m c) >> bind = \ x f -> ((const x) >=> f) () >> join = id>=>id :: (m (m a) -> m a) >> _______________________________________________ >> Haskell-Cafe mailing list >> Haskell-Cafe@haskell.org >> http://www.haskell.org/mailman/listinfo/haskell-cafe > _______________________________________________ > Haskell-Cafe mailing list > Haskell-Cafe@haskell.org > http://www.haskell.org/mailman/listinfo/haskell-cafe -- Tony Morris http://tmorris.net/ _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
