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Today's Topics:
1. The Missing Arrow Function Strikes Back (Adrian May)
2. Re: The Missing Arrow Function Strikes Back (Ertugrul S?ylemez)
3. Re: The Missing Arrow Function Strikes Back (Adrian May)
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Message: 1
Date: Wed, 5 Jun 2013 12:30:26 +0800
From: Adrian May <[email protected]>
Subject: [Haskell-beginners] The Missing Arrow Function Strikes Back
To: "[email protected]" <[email protected]>
Message-ID:
<cad-ubzec8eypygwm6f9e0t3otu8wgsfzw_jnhetepxozza3...@mail.gmail.com>
Content-Type: text/plain; charset="utf-8"
Hi All,
I just banged up against this problem:
http://haskell.1045720.n5.nabble.com/The-case-of-the-missing-Arrow-function-td3125388.html
Was liftA2 (not the applicative one) a bad idea, or is there another way to
do it, or what?
TIA,
Adrian.
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Message: 2
Date: Wed, 5 Jun 2013 06:55:11 +0200
From: Ertugrul S?ylemez <[email protected]>
Subject: Re: [Haskell-beginners] The Missing Arrow Function Strikes
Back
To: [email protected]
Message-ID: <[email protected]>
Content-Type: text/plain; charset="us-ascii"
Adrian May <[email protected]> wrote:
> I just banged up against this problem:
>
> http://haskell.1045720.n5.nabble.com/The-case-of-the-missing-Arrow-function-td3125388.html
>
> Was liftA2 (not the applicative one) a bad idea, or is there another
> way to do it, or what?
That liftA2 (let me call it liftA2') likely has this type signature:
liftA2' :: (Arrow cat)
=> (b -> c -> d)
-> cat a b
-> cat a c
-> cat a d
Does this sound familiar? You can write this function in terms of the
arrow combinators:
liftA2' f c d = arr (uncurry f) . (c &&& d)
However, if your arrow is also a family of applicative functors
(i.e. pretty much always),
instance Applicative (MyArrow a)
then it's probably a bad idea, because you really want to use the
cleaner liftA2 instead:
liftA2 :: (Applicative f)
=> (a -> b -> c)
-> f a
-> f b
-> f c
Greets,
Ertugrul
--
Not to be or to be and (not to be or to be and (not to be or to be and
(not to be or to be and ... that is the list monad.
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Message: 3
Date: Wed, 5 Jun 2013 13:02:40 +0800
From: Adrian May <[email protected]>
Subject: Re: [Haskell-beginners] The Missing Arrow Function Strikes
Back
To: The Haskell-Beginners Mailing List - Discussion of primarily
beginner-level topics related to Haskell <[email protected]>
Message-ID:
<cad-ubzfgv-d2mojvbzt5wpc8bo1by8bix-tdchsuty-utbj...@mail.gmail.com>
Content-Type: text/plain; charset="utf-8"
Thanks Ertugrul. In the meantime I noticed that split and unsplit are also
missing. Is there a similar replacement for them?
Adrian.
On 5 Jun 2013 12:57, "Ertugrul S?ylemez" <[email protected]> wrote:
> Adrian May <[email protected]> wrote:
>
> > I just banged up against this problem:
> >
> >
> http://haskell.1045720.n5.nabble.com/The-case-of-the-missing-Arrow-function-td3125388.html
> >
> > Was liftA2 (not the applicative one) a bad idea, or is there another
> > way to do it, or what?
>
> That liftA2 (let me call it liftA2') likely has this type signature:
>
> liftA2' :: (Arrow cat)
> => (b -> c -> d)
> -> cat a b
> -> cat a c
> -> cat a d
>
> Does this sound familiar? You can write this function in terms of the
> arrow combinators:
>
> liftA2' f c d = arr (uncurry f) . (c &&& d)
>
> However, if your arrow is also a family of applicative functors
> (i.e. pretty much always),
>
> instance Applicative (MyArrow a)
>
> then it's probably a bad idea, because you really want to use the
> cleaner liftA2 instead:
>
> liftA2 :: (Applicative f)
> => (a -> b -> c)
> -> f a
> -> f b
> -> f c
>
>
> Greets,
> Ertugrul
>
> --
> Not to be or to be and (not to be or to be and (not to be or to be and
> (not to be or to be and ... that is the list monad.
>
> _______________________________________________
> Beginners mailing list
> [email protected]
> http://www.haskell.org/mailman/listinfo/beginners
>
>
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