Re: [Haskell-cafe] nested maybes

On 2/4/07, Udo Stenzel wrote:

J. Garrett Morris wrote:

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On 2/4/07, Udo Stenzel wrote: Well, depends on whether we are allowed to define new combinators. I sometimes use

-- Kleisli composition infixl 1 @@ (@@) :: Monad m => (a -> m b) -> (b -> m c) -> (a -> m c) f @@ g = join . liftM g . f

I was responding to this, but Dons beat me to it. Personally, I use this combinator quite a bit. (As much as I would rather use >>>, the Kleisli arrow is a bit verbose to use for my taste.)

and the resulting

...

exists s = Map.lookup (sort s) @@ find (== s) . snd >>> isJust

isn't all that bad. (To be read as: one can get used to it.) I also think, (@@) and (>>>) belong in the Prelude and (>>>) at type ((a->b) -> (b->c) -> (b->c)) should be known under a shorter name. Unfortunately, everything short but (?) is already taken...

Presumably you mean (a -> b) -> (b -> c) -> (a -> c)? I would personally be fine with Arrows being in the prelude (and, for instance, (.) defined as flip (>>>)). I'd support your shorter name idea if I could think of one... /g -- It is myself I have never met, whose face is pasted on the underside of my mind.