Proposal: Add (&) to Data.Function

[Edward Kmett]

I'm a strong +1 for accepting this proposal as it stands.

I'm decidedly lukewarm / a weak -1 on switching it to (|>).

Another popular color of this bikeshed, (#) as is used in diagrams,
interacts very poorly with MagicHash and has a very high precedence that
ruins it for most dsl purposes.

We had it as (|>) in lens for a while and it didn't read well. It is often
used in long compositions and the extra character adds up when chained
several times.

-- >>> zipper ("hello","world") & down _1 & fromWithin traverse &
focus .~ 'J' & rightmost & focus .~ 'y' & rezip
-- ("Jelly","world")

isoRules = defaultRules
  & handleSingletons  .~ True
  & singletonRequired .~ True
  & singletonAndField .~ True


Both of those examples read much better with & than (|>).

We had switched to % from (|>) to be consistent with the other (+=) (*=)
operators where (%=) was being read as 'mod-equals' as a bit of a pun, and
could be seen as the application of the % operator to the target.

However this led to issues with a vocal minority who objected to it
changing the meaning of 4 % 3 on lambdabot when combined with NumInstances.

We converted to (&) because of its incredible terseness and general lack of
use across hackage. For DSL purposes, to me it is key that this operator be
as succinct as possible and (&) is remarkably underutilized in haskell
libraries today, due to the fact that (|) is taken by syntax, and our
C-inspired brains tend to pair them.

-Edward

On Tue, Nov 20, 2012 at 1:27 PM, Michael Sloan <mgsloan at gmail.com> wrote:

> And the results of the IRC discussion on lens:
> https://github.com/ekmett/lens/issues/100
>
> I do think that this looks nicer, for whatever reason.  While the mnemonic
> of "mod"ulus can suggest modify once you know that, (&) somewhat naturally
> suggests "and then" ... "and then".  I still prefer (#) for overall
> consistency and history, but other than its conjunction connotations, (&)
> is mnemonically better.
>
> It'll be funny to mix diagrams and lens code - (&) is used for sticking
> coordinates together for points / vectors - while (#) would stand in for
> (&).
>
>
>
> On Tue, Nov 20, 2012 at 10:17 AM, Michael Sloan <mgsloan at gmail.com> wrote:
>
>> (#) is also used by the diagrams library, mainly for using functions as
>> if they were "attributes".
>>
>> In the context of lens, this is discussed a bit here:
>> https://github.com/ekmett/lens/issues/17
>>
>>
>>
>> On Tue, Nov 20, 2012 at 9:31 AM, Stephen Tetley <stephen.tetley at gmail.com
>> > wrote:
>>
>>> "Haskell" called this operator (#) about 12 years ago - see Peter
>>> Thiemann's WASH and Eric Meijer and colleagues MS Agent scripting.
>>>
>>> I'd much prefer (#) if it didn't interfere with GHC's magic hash, I
>>> suspect the above authors were using Hugs...
>>>
>>> On 20 November 2012 17:19, Dan Burton <danburton.email at gmail.com> wrote:
>>> > Just to bring up some prior art, from what I've heard, F# calls this
>>> |>.
>>>
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>>
>>
>
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