Proposal: add `on` to the Prelude

[Elliot Cameron]

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
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