Proposal: Add missing Monoid for ZipList

[M Farkas-Dyck]

On 26/07/2015 at 08:30:33 +0200, Henning Thielemann wrote:
> 
> On Sun, 26 Jul 2015, Oleg Grenrus wrote:
> 
> >>On 26 Jul 2015, at 06:43, M Farkas-Dyck <strake888 at gmail.com> wrote:
> >>
> >>On 26/07/2015 at 12:23:13 +0900, Fumiaki Kinoshita wrote:
> >>>There is another possible instance:
> >>>
> >>>instance Semigroup a => Monoid (ZipList a) where
> >>> mempty = ZipList []
> >>> mappend (ZipList xs0) (ZipList ys0) = ZipList (mappend xs0 ys0) where
> >>>   go (x:xs) (y:ys) = x <> y : go xs ys
> >>>   go xs [] = xs
> >>>   go [] ys = ys
> >>
> >>This breaks the identity law.
> 
> I don't see, how it breaks the identity law. :-(

Derp. I misread the code, sorry.