Applicative ((,) a)

[Conal Elliott]

What was the motivation for providing the following Applicative instance?

instance Monoid a => Applicative ((,) a) where
    pure x = (mempty, x)
    (u, f) <*> (v, x) = (u `mappend` v, f x)

Is this instance described in "Applicative Programming with
Effects<http://www.soi.city.ac.uk/%7Eross/papers/Applicative.html>"?
I didn't spot  a mention.

Thanks,  - Conal
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