Proposal: Make Semigroup and Monoid instances for Data.Functor.Compose

[Keith]

With the Monoid 'First' and 'Last' newtypes going away, it would be nice to have equivalent Functor and Applicative instances.

This works if Compose uses its components' instances:

instance Semigroup (m (n a)) ⇒ Semigroup (Compose m n a) where
  Compose mnx <> Compose mny = Compose (mnx <> mny)

instance Monoid (m (n a)) ⇒ Monoid (Compose m n a) where
  mempty = Compose mempty

–Keith
-- 
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