Free MonadPlus and (another variant of) Alternative

[nponeccop]

There is From monoids to near-semirings: the essence of MonadPlus and Alternative article worth including in free.

[ElvishJerricco]

Your link is broken, but here's a working one.

[Zemyla]

I remember that, when I mathed it out and undid the innate right bias of the list based form, the Church style Free MonadPlus wound up being:

newtype FMP f a = FMP { runFMP :: forall r. Monoid r => (a -> r) -> (f r -> r) -> r }

In retrospect, it's just the crossbreed between FM and FreeMonoid, and the instances are all obvious.