proposal #4095: add Applicative instance for Either

[Ross Paterson]

Ashley Yakeley <ashley at semantic.org> writes:
> I currently have my own implementations for these:

>      instance Foldable Identity
>      instance Traversable Identity
>      instance Applicative Identity

The transformers package has such instances (but currently for a different
Identity type).

>      instance Foldable (Either p)
>      instance Traversable (Either p)
>      instance Applicative (Either p)

>      instance Foldable ((,) p)
>      instance Traversable ((,) p)

The Applicative one is proposed here.  The others should also be added.