Alternative.some and NonEmpty

[Vladislav Zavialov]

> that's solvable with CPP if needed

Note that it's possible to avoid CPP because one can use `fmap toList
. some` to achieve the old behavior. And the breakage is not silent,
so it won't be too hard for maintainers.

On Sun, Mar 5, 2017 at 2:49 PM, Ivan Lazar Miljenovic
<ivan.miljenovic at gmail.com> wrote:
> On 5 March 2017 at 21:51, Vladislav Zavialov <vlad.z.4096 at gmail.com> wrote:
>> Since 'Data.List.NonEmpty' is now in 'base', it makes sense to change
>> the type of 'some' from
>>
>> some :: Alternative f => f a -> f [a]
>>
>> to
>>
>> some :: Alternative f => f a -> f (NonEmpty a)
>>
>> as it's guaranteed to return a non-empty list.
>>
>> Currently, both users and implementors of 'Alternative' instances are
>> at a disadvantage. The users have to use the unsafe NonEmpty.fromList
>> function to take advantage of the fact that the result of 'some' is
>> indeed non-empty. The implementors have more space for error - it's
>> possible to accidentally return an empty list.
>
> The disadvantage is also for people trying to maintain a code base,
> though that's solvable with CPP if needed.
>
> However, this also affects the default instances.
>
> (As a user and implementor of Alternative instances, I've never found
> myself at a disadvantage for using the current type.)
>
>> I volunteer to implement. Does everyone agree it's a good idea?
>
> I'm -0.5.
>
> --
> Ivan Lazar Miljenovic
> Ivan.Miljenovic at gmail.com
> http://IvanMiljenovic.wordpress.com