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Today's Topics:
1. Code golf (Tilmann)
2. Re: Code golf (Imants Cekusins)
3. Re: Code golf (Tilmann)
4. Re: Code golf (Marcin Mrotek)
5. Re: Code golf (Tilmann)
6. Code golf (Silent Leaf)
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Message: 1
Date: Thu, 19 May 2016 15:12:26 +0200
From: Tilmann <t_g...@gmx.de>
To: Haskell Beginners <beginners@haskell.org>
Subject: [Haskell-beginners] Code golf
Message-ID: <875d19ea-7524-37ad-b475-68c7f4a36...@gmx.de>
Content-Type: text/plain; charset=utf-8; format=flowed
given:
inputA :: IO String
inputB :: IO String
update :: String -> String -> IO ()
Is there an elegant way to refactor / code golf this:
doIt :: IO ()
doIt = do
a <- inputA
b <- inputB
update a b
liftM2 doesn't work in this case..
Thank you!
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Message: 2
Date: Thu, 19 May 2016 15:22:10 +0200
From: Imants Cekusins <ima...@gmail.com>
To: The Haskell-Beginners Mailing List - Discussion of primarily
beginner-level topics related to Haskell <beginners@haskell.org>
Subject: Re: [Haskell-beginners] Code golf
Message-ID:
<CAP1qinZr16mhYih3VCmO_WH0_+Cgs7JMeBfTU5aO-FfXs=r...@mail.gmail.com>
Content-Type: text/plain; charset="utf-8"
if 'update' were changed to
update :: [String] -> IO ()
then you could do:
?doIt :: IO ()
doIt = sequence [inputA,inputB] >>= update
is this better?
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Message: 3
Date: Thu, 19 May 2016 15:34:17 +0200
From: Tilmann <t_g...@gmx.de>
To: The Haskell-Beginners Mailing List - Discussion of primarily
beginner-level topics related to Haskell <beginners@haskell.org>
Subject: Re: [Haskell-beginners] Code golf
Message-ID: <856d279c-1e01-228a-0dcc-451578f7e...@gmx.de>
Content-Type: text/plain; charset="utf-8"; Format="flowed"
this is nice, thanks! What if a and b are of different types? I
simplified my example to much..
Am 19.05.16 um 15:22 schrieb Imants Cekusins:
> if 'update' were changed to
> update :: [String] -> IO ()
>
> then you could do:
> ?doIt :: IO ()
> doIt = sequence [inputA,inputB] >>= update
>
> is this better?
>
>
> _______________________________________________
> Beginners mailing list
> Beginners@haskell.org
> http://mail.haskell.org/cgi-bin/mailman/listinfo/beginners
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Message: 4
Date: Thu, 19 May 2016 15:37:06 +0200
From: Marcin Mrotek <marcin.jan.mro...@gmail.com>
To: The Haskell-Beginners Mailing List - Discussion of primarily
beginner-level topics related to Haskell <beginners@haskell.org>
Subject: Re: [Haskell-beginners] Code golf
Message-ID:
<CAJcfPznFx3kcEJgnJEsmskA8fm+8WqRjoDB+NRd=jpyxuce...@mail.gmail.com>
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Hello,
What about "join $ update <$> a <*> b" ?
Best regards,
Marcin Mrotek
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Message: 5
Date: Thu, 19 May 2016 16:03:57 +0200
From: Tilmann <t_g...@gmx.de>
To: The Haskell-Beginners Mailing List - Discussion of primarily
beginner-level topics related to Haskell <beginners@haskell.org>
Subject: Re: [Haskell-beginners] Code golf
Message-ID: <1b168c3f-d5b6-208c-8862-d9749e11e...@gmx.de>
Content-Type: text/plain; charset="windows-1252"; Format="flowed"
That's what I was looking for! I didn't know about join! Thank you!
Am 19.05.16 um 15:37 schrieb Marcin Mrotek:
> Hello,
>
> What about "join $ update <$> a <*> b" ?
>
> Best regards,
> Marcin Mrotek
>
>
> _______________________________________________
> Beginners mailing list
> Beginners@haskell.org
> http://mail.haskell.org/cgi-bin/mailman/listinfo/beginners
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Message: 6
Date: Fri, 20 May 2016 04:50:28 +0200
From: Silent Leaf <silent.le...@gmail.com>
To: The Haskell-Beginners Mailing List - Discussion of primarily
beginner-level topics related to Haskell <beginners@haskell.org>
Subject: [Haskell-beginners] Code golf
Message-ID:
<cagfccjpx9cao9sry6rkfk8aq+te2dtxgfchykqeoykmso1x...@mail.gmail.com>
Content-Type: text/plain; charset="utf-8"
The interesting bit is, the following function
> \? ma mb -> join (pure ? <*> ma <*> mb)
which i like to write as follows using ((&) = flip ($)) [infixl 1]
> \? ma mb -> pure ? <*> ma <*> mb & join
(but it's just personal taste) is very similar to (=<<), aka (flip (>>=))
except the first argument (here ?) has type (a -> b -> m c) instead of (a
-> m b), and of course the lambda above takes an added argument too (mb).
Some could call it "bind2" (even if it's the flipped version of (>>=) that
is being generalized), and well, some do. For those interested, there are
several options are available to import it (along possibly with some of its
siblings), from several libraries. (List possibly non exhaustive.)
http://hackage.haskell.org/package/prelude-generalize-0.4/docs/Prelude-Generalize.html#v:bind2
http://hackage.haskell.org/package/SimpleH-1.2/docs/Algebra-Monad.html#v:bind2
http://hackage.haskell.org/package/definitive-base-2.3/docs/Algebra-Monad-Base.html#v:bind2
your problem become btw then:
> doIt = bind2 update a b
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