Speaking of small functions
duncan.coutts at worc.ox.ac.uk
Sun Oct 29 10:19:10 EST 2006
On Sun, 2006-10-29 at 14:46 +0000, Jon Fairbairn wrote:
> On 2006-10-29 at 09:30EST kahl at 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
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.
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