Proposal: add `on` to the Prelude

[Artyom Kazak]

I don't use `on` because my usecases are covered by `sortOn` and
`groupWith`; I can only recall a couple of cases when I had to resort to
`on`, and I don't often see it in others' code either, or if I do it's
often in conjuction  with `sort` anyway.

I have, however, seen people use `on` because it's /cute/, and it's
definitely not something I would want to encourage.

On the other hand, `for` and `when` and `and` and other common words are
taken already and it almost never creates any problems for me, so I would
not mind having `on` stolen either.

So, I'm -0.5 on the proposal.

On Thu, Sep 12, 2019, 18:20 Elliot Cameron <eacameron at gmail.com> wrote:

> Bleh. Now we have two functions that do the same thing, both in base... I
> don't want "on" in prelude but this seems far worse to me than the original
> proposal. Let's stick with that one for now and if it dies you can propose
> this separately? :D
>
> On Thu, Sep 12, 2019 at 11:15 AM David Feuer <david.feuer at gmail.com>
> wrote:
>
>> No, there's certainly no need to remove the existing function.
>>
>> On Thu, Sep 12, 2019, 10:57 AM Elliot Cameron <eacameron at gmail.com>
>> wrote:
>>
>>> You might be on2 something.
>>>
>>> But then you rename it in Data.Function too and break backward compat??
>>>
>>> On Thu, Sep 12, 2019 at 10:55 AM David Feuer <david.feuer at gmail.com>
>>> wrote:
>>>
>>>> For whatever it's worth, the unidiomatic but arguably more logical name
>>>> `on2` has no hits on Hoogle.
>>>>
>>>> On Tue, Sep 10, 2019, 6:59 PM David Feuer <david.feuer at gmail.com>
>>>> wrote:
>>>>
>>>>> Indeed, there are a lot more conflicts than I'd have expected.
>>>>> Ignoring functions with the same type, Hoogle shows this name in the below
>>>>> packages. I have no sense of the overall significance of the specific
>>>>> packages or (equally importantly) of the `on` function within each.
>>>>>
>>>>> haskell-gi-base:
>>>>> on :: forall object info m . (GObject object, MonadIO m, SignalInfo
>>>>> info) => object -> SignalProxy object info -> HaskellCallbackType info -> m
>>>>> SignalHandlerId
>>>>>
>>>>> brick:
>>>>> on :: Color -> Color -> Attr
>>>>>
>>>>> esqueletto:
>>>>> on :: SqlExpr (Value Bool) -> SqlQuery ()
>>>>>
>>>>> relational-query (both):
>>>>> on :: MonadQuery m => Predicate Flat -> m ()
>>>>> on :: MonadQuery m => QueryA m (Predicate Flat) ()
>>>>>
>>>>> threepenny-gui:
>>>>> on :: (element -> Event a) -> element -> (a -> UI void) -> UI ()
>>>>>
>>>>> miso:
>>>>> on :: MisoString -> Decoder r -> (r -> action) -> Attribute action
>>>>>
>>>>> wild-bind:
>>>>> on :: i -> v -> Binder i v ()
>>>>>
>>>>> massiv-io:
>>>>> on :: Pixel X Bit
>>>>>
>>>>> selda-postgresql:
>>>>> on :: Text -> Text -> PGConnectInfo
>>>>>
>>>>>
>>>>> On Tue, Sep 10, 2019, 6:42 PM Ryan Trinkle <ryan.trinkle at gmail.com>
>>>>> wrote:
>>>>>
>>>>>> One note: this does conflict with some other libraries, for instance
>>>>>> GTK2HS
>>>>>>
>>>>>> On Tue, Sep 10, 2019 at 6:26 PM chessai . <chessai1996 at gmail.com>
>>>>>> wrote:
>>>>>>
>>>>>>> +1
>>>>>>>
>>>>>>> On Tue, Sep 10, 2019, 5:53 PM David Feuer <david.feuer at gmail.com>
>>>>>>> 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
>>>>>>>> _______________________________________________
>>>>>>>> Libraries mailing list
>>>>>>>> Libraries at haskell.org
>>>>>>>> http://mail.haskell.org/cgi-bin/mailman/listinfo/libraries
>>>>>>>>
>>>>>>> _______________________________________________
>>>>>>> Libraries mailing list
>>>>>>> Libraries at haskell.org
>>>>>>> http://mail.haskell.org/cgi-bin/mailman/listinfo/libraries
>>>>>>>
>>>>>> _______________________________________________
>>>> Libraries mailing list
>>>> Libraries at haskell.org
>>>> http://mail.haskell.org/cgi-bin/mailman/listinfo/libraries
>>>>
>>> _______________________________________________
> Libraries mailing list
> Libraries at haskell.org
> http://mail.haskell.org/cgi-bin/mailman/listinfo/libraries
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://mail.haskell.org/pipermail/libraries/attachments/20190912/bc7b2760/attachment-0001.html>