Proposal: instance Alternative ZipList

[Edward Kmett]

Er.. I obviously meant

instance Alternative ZipList where
   empty = ZipList []
   ZipList xs <|> ZipList ys = ZipList (xs ++ drop (length xs) ys)

sorry for any confusion.

On Fri, Jul 17, 2015 at 11:37 AM, Edward Kmett <ekmett at gmail.com> wrote:

> The ZipList data type admits one legal Alternative instance
>
> instance Alternative ZipList where
>    pure = ZipList []
>    ZipList xs <|> ZipList ys = ZipList (xs ++ drop (length xs) ys)
>
> The legality of this instance was first noted in
> http://people.cs.kuleuven.be/~tom.schrijvers/Research/papers/ppdp2015.pdf
>
> I propose adding this instance, which acts like a generalized version of
> the Alternative for Maybe, choosing with a left bias.
>
> Discussion Period: 2 weeks
>
> -Edward
>
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