Fwd: [Haskell-beginners] Applicative Composition

Forwarding to list - it looks like I forgot to reply-all. ---------- Forwarded message ---------- From: Antoine Latter Date: Thu, Sep 30, 2010 at 7:17 PM Subject: Re: [Haskell-beginners] Applicative Composition To: edgar klerks On Thu, Sep 30, 2010 at 6:47 PM, 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:

{-# 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