Proposal: Add a wrapped applicative type to Data.Monoid

[Ryan Scott]

One thing that is not clear to me: is this Ap type intended to be a
catch-all for defining instances that are "lifted" through an
Applicative? Or are you deliberately restricting that to the Semigroup
and Monoid instances? For instance, I noticed that you currently
derive Ap's Eq, Ord, Read, and Show instances, which would give:

    instance Eq (f a) => Eq (Ap f a)
    instance Ord (f a) => Ord (Ap f a)
    instance Read (f a) => Read (Ap f a)
    instance Show (f a) => Show (Ap f a)

Would you not want this instead, to be in line with the Semigroup and
Monoid instances?

    instance (Applicative f, Eq a) => Eq (Ap f a)
    instance (Applicative f, Ord a) => Ord (Ap f a)
    instance (Applicative f, Read a) => Read (Ap f a)
    instance (Applicative f, Show a) => Show (Ap f a)

I would be fine with either option, but if we should be clear about
Ap's intentions when we end up documenting it.

Ryan S.