Proposal: add `on` to the Prelude

[Carter Schonwald]

yeah, that pushes it to a hard -1 for me.

On Fri, Sep 13, 2019 at 9:33 AM Elliot Cameron <eacameron at gmail.com> wrote:

> > It's not only about top-level functions named 'on'. If I use 'on' as a
> local variable, then I get warnings about local redefinitions of the
> global Prelude.on.
>
> Oh heavens how did we not think of this point immediately? This frankly
> has me terrified of this proposal. This is such a cute name it's hard to
> imagine that it's not a local binding in numerous, invisible places.
>
> (Just last week I had to fix a package not on Hackage because it locally
> defined (<>)...)
>
> On Fri, Sep 13, 2019, 7:54 AM Henning Thielemann <
> lemming at henning-thielemann.de> wrote:
>
>>
>> On Tue, 10 Sep 2019, David Feuer wrote:
>>
>> > Every time I reach for Data.Function.on, I feel like a total dolt for
>> having to import a module to get a function
>> > whose implementation is barely longer than the import. And it's a
>> really good function too! Can we please add it
>> > to the Prelude?
>> >   on :: (b -> b -> c) -> (a -> b) -> a -> a -> c
>> >   (.*.) `on` f = \x y -> f x .*. f y
>>
>> Most of the time I would use this I can use the more specific 'equating'
>> and 'comparing'.
>>
>> I remember there was a lengthy discussion about the right name of 'on'
>> and
>> adding it to Data.Function. I had no need for that function because at
>> this point I already had:
>>
>> https://hackage.haskell.org/package/utility-ht-0.0.14/docs/Data-Function-HT.html#v:compose2
>>
>> If I am right the short name 'on' was only adopted because it was not
>> (automatically) exported by
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