Alternative.some and NonEmpty

[Tony Morris]

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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