Hi Brent and Antione,
On Fri, Oct 1, 2010 at 3:41 AM, Brent Yorgey <byorgey@seas.upenn.edu> wrote:On Fri, Oct 01, 2010 at 01:47:09AM +0200, edgar klerks wrote:
> Hi All,
>
> I was wondering, why there isn't a composition operator for applicative
> functors. Of course it is rather trivial to implement, but it is a useful
> feature:
I think you've answered your own question: it's rather trivial to
implement. If we added every single useful function to the standard
libraries, we'd be up to our necks.
Ah yes I understand that. '
> {-# LANGUAGE FlexibleInstances, UndecidableInstances #-}
> module ApplicativeComposition where
> import Control.Applicative
>
> class (Applicative f) => ApplicativeComposition f where
> (<.>) :: f (b -> c) -> f (a -> b) -> f (a -> c)
>
> instance (Applicative f) => ApplicativeComposition f where
> (<.>) f g = pure (.) <*> f <*> g
>
> Can this be added to later versions of haskell?
You can always make a formal proposal [1], although judging by past
discussions of similar sorts of things I doubt it would be accepted,
for the reasons I wrote above.
Nopes I will refrain from that, I had to search first, before ask. My apologies for that, it was a bit late, when I posted it.
And another thing is, that there are different implementations for such a operator. Better let the user create it themself.Thnx for the reply.
Greets,
Edgar
On Fri, Oct 1, 2010 at 7:15 AM, Antoine Latter <aslatter@gmail.com> wrote:
Forwarding to list - it looks like I forgot to reply-all.
---------- Forwarded message ----------
From: Antoine Latter <aslatter@gmail.com>
Date: Thu, Sep 30, 2010 at 7:17 PM
Subject: Re: [Haskell-beginners] Applicative Composition
To: edgar klerks <edgar.klerks@gmail.com>
On Thu, Sep 30, 2010 at 6:47 PM, edgar klerks <edgar.klerks@gmail.com> wrote:
> Hi All,
>
> I was wondering, why there isn't a composition operator for applicative
> functors. Of course it is rather trivial to implement, but it is a useful
> feature:
>
> {-# LANGUAGE FlexibleInstances, UndecidableInstances #-}
> module ApplicativeComposition where
> import Control.Applicative
>
> class (Applicative f) => ApplicativeComposition f where
> (<.>) :: f (b -> c) -> f (a -> b) -> f (a -> c)
>
> instance (Applicative f) => ApplicativeComposition f where
> (<.>) f g = pure (.) <*> f <*> g
>
> Can this be added to later versions of haskell?
>
Here's the last time this topic came up on the lists:
http://www.haskell.org/pipermail/libraries/2010-August/013992.html
Here's the corresponding library proposal ticket:
http://hackage.haskell.org/trac/ghc/ticket/4189
There were a few folks against it for a few different reasons.
Antoine
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