The point is that someone can write

instance Monoid Thingy where
  mempty = <something>
  mappend a b = <something else>
  mconcat ls = <another thing>

deriving instance Semigroup Thingy via (WrappedMonoid Thingy)

Most of the benefit is not having to look up "stimesMonoid" over and over again.

On Sat, Sep 14, 2019 at 3:36 PM John Villarreal via Libraries
<libraries@haskell.org> wrote:
>
> Hello Georgi,
>
>
> I'm confused about WrappedMonoid. How can something have a Monoid instance already without having a Semigroup instance in the first place?
>
> But also what is the benefit of WrappedMonoid over the standard way of defining Semigroups and Monoids for your example
>
> data List a = Nil | Cons a (List a)
>
> instance Semigroup (List a) where
>   Nil       <> ys = ys
>   Cons x xs <> ys = Cons x (xs <> ys)
>
> instance Monoid (List a) where mempty = Nil
>
> ?
>
> Cheers,
> John
>
>
> On Saturday, 14 September 2019, 19:18:01 UTC, Georgi Lyubenov <godzbanebane@gmail.com> wrote:
>
>
> Hello!
>
> Sorry if this is not the right place to ask!
>
> As of right now (14.09.2019) Data.Semigroup.WrappedMonoid is slated to be deprecated.
>
> I believe that this newtype is actually useful in tandem with DerivingVia, as it allows you to derive the Semigroup instance for something that has a Monoid instance already, as discussed in this twitter thread.
>
> Would it be possible to *not* deprecate it in the future, and instead keep it around for exactly this purpose?
>
> Cheers,
> Georgi
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