On Sun, 2006-10-29 at 14:46 +0000, Jon Fairbairn wrote:
On 2006-10-29 at 09:30EST kahl@cas.mcmaster.ca wrote:
Speaking of small functions, Kleisli composition should at least be in Control.Monad. It's a simple thing, and not commonly explicitly used at the moment, but rather important conceptually.
(@@) :: (Monad m) => (b -> m c) -> (a -> m b) -> (a -> m c) g @@ f = \x -> f x >>= g
I support this strongly.
My notation is (=>>=), to go with (>>=).
That's a better symbol for it. (@@) could be just about anything, while (=>>=) is suggestive. Though I think what it suggests might be with the arguments in a different order?
Yes, we already have =<< for reverse >>= which is nice sometimes when you want to emphasise the similarity to (.) rather than imperative order, eg: return . foldr h z . map f . filter p =<< getContents So it'd be: (=<<=) :: (Monad m) => (b -> m c) -> (a -> m b) -> (a -> m c) (g =<<= f) x = g =<< f x (or should it really be written with a lambda?) and if there's demand for (=>>=) too then that's obviously easy to add. Duncan