Alternative.some and NonEmpty

[Tony Morris]

Ha!

I saw that a while back, was pleasantly surprised, then went ahead and
forgot about it. Thanks for the surprise again. Two for the price of one.


On Thu, Mar 9, 2017 at 2:19 PM, Edward Kmett <ekmett at gmail.com> wrote:

> Even better,
>
> http://hackage.haskell.org/package/base-4.9.1.0/docs/
> Data-List-NonEmpty.html#v:some1
>
> is already there in base! ;)
>
> On Tue, Mar 7, 2017 at 10:21 PM, Tony Morris <tmorris at tmorris.net> wrote:
>
>> Related: https://hackage.haskell.org/package/semigroups-0.18.1/docs/
>> src/Data.List.NonEmpty.html#some1
>>
>> On Wed, Mar 8, 2017 at 1:18 PM, Edward Kmett <ekmett at gmail.com> wrote:
>>
>>> I'm also in the "if we're going to do this, it should probably be a new
>>> function" camp. e.g. `some1`. I'm kinda neutral on adding it at all at this
>>> point, but if we do it, it should probably be done along these lines.
>>>
>>> As for using a semigroup based implementation, its performance is,
>>> sadly, rather awful for constructing `NonEmpty` lists, and more damning,
>>> you have no law relating the 'pure' or whatever you're using to create
>>> values and the Semigroup you're using to glue them together, so it only
>>> works for NonEmpty on a purely ad-hoc type-by-type basis. That signature
>>> isn't one we want as evidenced by the fact that if you pick m = Maybe you
>>> sure as heck won't get anything like what you expect! This is the pointed
>>> problem all over again. I'm very strongly -1 on that variant of the
>>> proposal.
>>>
>>> -Edward
>>>
>>>
>>> On Tue, Mar 7, 2017 at 2:02 PM, Sven Panne <svenpanne at gmail.com> wrote:
>>>
>>>> 2017-03-07 18:11 GMT+01:00 Henning Thielemann <
>>>> lemming at henning-thielemann.de>:
>>>>
>>>>>
>>>>> On Tue, 7 Mar 2017, Mario Blažević wrote:
>>>>>
>>>>>> [...]You're correct on both counts, sorry about that. It would have
>>>>>> to be
>>>>>>
>>>>>> genericMany, genericSome ::
>>>>>>  (Alternative f, Applicative m, Semigroup (m a)) => f a -> f (m a)
>>>>>>
>>>>>> once Semigroup is in base.
>>>>>>
>>>>>
>>>>> But then, for genericMany, Monoid would be appropriate, again. :-)
>>>>>
>>>>
>>>> I think this discussion alone is enough of a hint that there is a need
>>>> for a broader discussion to come up with coherent story regarding NonEmpty
>>>> in general. ;-) Focusing on one or two functions alone will probably do
>>>> more harm than improve the overall situation.
>>>>
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>>>>
>>>
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>>
>
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