[Haskell-cafe] Proposal: (.:) operator in base.

[Mike Ledger]

(Forgot reply all)
---------- Forwarded message ----------
From: "Mike Ledger" <eleventynine at gmail.com>
Date: 18 Aug 2016 7:52 AM
Subject: Re: [Haskell-cafe] Proposal: (.:) operator in base.
To: "Csongor Kiss" <kiss.csongor.kiss at gmail.com>
Cc:

IMO: I've never seen a compelling use of this; I think it decreases
clarity, and barely shaves off any characters from equivalent "pointful"
expressions.

On Thu, Aug 18, 2016 at 7:45 AM, Csongor Kiss <kiss.csongor.kiss at gmail.com>
wrote:

> Of course I meant to write ((->) e)
>
> On 17 August 2016 at 22:39:36, Csongor Kiss (kiss.csongor.kiss at gmail.com)
> wrote:
>
> Can you provide a bit more detail on why you think (fmap . fmap) captures
> the concept behind (.) . (.) ?
> It certainly does generalise it in one way - and I do get how, but is it
> the *right* generalisation?
>
> Or does it just coincide with (-> e)’s fmap being defined as (.), and in
> fact we would prefer to
> generalise the composition aspect, in which case Category would be a more
> ‘obvious’ place to look?
>
> On 17 August 2016 at 22:15:56, Tony Morris (tonymorris at gmail.com) wrote:
>
> You'd generalise it to:
>
> fmap . fmap :: (Functor f, Functor g) => (a -> b) -> f (g a) -> f (g b)
>
> And then, would you do the same for Traversable, Foldable and Applicative?
>
> On 18/08/16 03:43, Alex Belanger wrote:
>
> Hi,
>
> Some of you might be familiar with (.:) = (.) . (.).
>
> It has type :: (c -> d) -> (a -> b -> c) -> a -> b -> d
>
> It allows the composition of two functions, the first one, accepting one
> operand, and the second, two operands.
>
> This appears to be a very common pattern, referenced a bit everywhere,
> almost always defined on lambdabot and found in multiple codebases in the
> wild.
>
> I'd like the know the general sentiment about this operator, as well as
> how its inclusion in base, probably Data.Function, would be perceived
> before I actually try to make it happen.
>
> Cheers,
> Alex (nitrix).
>
>
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