Add newtype for Alternative using QuantifiedConstraints in base-4.13

[theindigamer]

Thoughts on adding a newtype with the following Alternative instance?

(The name chosen is a placeholder, I don't have any particular preference).

newtype Mon f a = Mon { unMon :: f a }

instance (forall a. Monoid (f a)) => Alternative (Mon f) where
  empty = Mon mempty
  (<|>) (Mon m1) (Mon m2) = Mon (m1 <> m2)
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