[Haskell-beginners] Applicative Composition

[edgar klerks]

There was another small reason, I did ask it, because the applicative
interface isn't as rich as the monad interface. I have read, that is because
of historic reasons. They weren't in there at the beginning.

But I really like to use applicative functors, if possible and this one
seemed to be obvious, so I was a bit puzzeled, why it wasn't there.

Are there any plans to enrich the interface for applicative functors?

On Fri, Oct 1, 2010 at 11:03 AM, edgar klerks <edgar.klerks at gmail.com>wrote:

> Hi Brent and Antione,
>
> On Fri, Oct 1, 2010 at 3:41 AM, Brent Yorgey <byorgey at 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 at gmail.com> wrote:
>
>> Forwarding to list - it looks like I forgot to reply-all.
>>
>>
>> ---------- Forwarded message ----------
>> From: Antoine Latter <aslatter at gmail.com>
>> Date: Thu, Sep 30, 2010 at 7:17 PM
>> Subject: Re: [Haskell-beginners] Applicative Composition
>> To: edgar klerks <edgar.klerks at gmail.com>
>>
>>
>> On Thu, Sep 30, 2010 at 6:47 PM, edgar klerks <edgar.klerks at 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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>>
>
>
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