[prev in list] [next in list] [prev in thread] [next in thread] 

List:       haskell-cafe
Subject:    Re: [Haskell-cafe] Re: new Haskell hacker seeking peer review
From:       "Andreas Farre" <d00farre () dtek ! chalmers ! se>
Date:       2005-02-23 14:56:45
Message-ID: 61705.129.16.30.109.1109170605.squirrel () webmail ! chalmers ! se
[Download RAW message or body]


Bjorn Bringert said:
>
> Or why not the two characters shorter, but much less readable:
>
> pointsFreeCat' = getArgs >>= mapM_ ((>>= putStr) . readFile)
>
> or maybe:
>
> pointsFreeCat'' = getArgs >>= mapM_ (putStr >>. readFile)
>
> (>>.) :: (b -> IO c) -> (a -> IO b) -> a -> IO c
> (>>.) = (.) . flip (>>=)
>
> Is (>>.) in the standard libs? If not, should it be? I'm sure there is a
> shorter definition of (>>.) that I haven't thought of.
>
> /Bjorn

Or even:

k :: Monad m => (a -> m b) -> Kleisli m a b
k = Kleisli

runKleisli :: Monad m => Kleisli m a b -> (a -> m b)
runKleisli (Kleisli f) = f

cat :: IO ()
cat = getArgs >>= (runKleisli $ (k $ mapM readFile) >>> (k $ mapM_ putStr))

after noticing that (>>.) is pretty similar to (<<<) when we lift (a -> IO
b) to (Kleisli IO a b). It is pretty disappointing that runKleisli isn't
defined so that I can be cool and completely point free too ;)

/Andreas

-- 
some cannot be created more equal than others


[prev in list] [next in list] [prev in thread] [next in thread]