Monoid Instance for ReaderT

[M Farkas-Dyck]

On 28/11/2017, Andrew Martin <andrew.thaddeus at gmail.com> wrote:
> This is also how the Monoid instance of basically everything with an
> Applicative instance is defined. The only one that I feel should differ
> from the others is Maybe, and that's getting fixed when Semigroup becomes a
> superclass of Monoid.

I also feel the `[]` instance ought to do the Cartesian product. (To
recover the free monoid one would write `Alt []` rather than `[]`
which is fine by me.)