Add newtype for Alternative using QuantifiedConstraints in base-4.13

[George Wilson]

It'll have to use the underlying Functor and Applicative to get an Alternative.
Could you give some examples where you'd like to use this?

I don't like the name but don't have a better one off the top of my
head. AltMonoid or something?


On Sat, 16 Feb 2019 at 10:20, theindigamer <theindigamer15 at gmail.com> wrote:
>
> I'm not sure which implementation you have in mind - the newtype one?
> I suppose that it would be harmless to add it in, although I don't immediately
> see the use case.
>
>
> On Fri, Feb 15, 2019 at 7:11 PM Carter Schonwald <carter.schonwald at gmail.com> wrote:
>>
>> this looks quite pretty, though I must admit that im not the most savvy at quantified constraints yet
>>
>> wouldn't this newtype also benefit from a semigroup and monoid instance too? (or am I overlooking some reason why you can't do them too?)
>>
>> On Fri, Feb 15, 2019 at 7:05 PM theindigamer <theindigamer15 at gmail.com> wrote:
>>>
>>> Thoughts on adding a newtype with the following Alternative instance?
>>>
>>> (The name chosen is a placeholder, I don't have any particular preference).
>>>
>>> newtype Mon f a = Mon { unMon :: f a }
>>>
>>> instance (forall a. Monoid (f a)) => Alternative (Mon f) where
>>>   empty = Mon mempty
>>>   (<|>) (Mon m1) (Mon m2) = Mon (m1 <> m2)
>>>
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