[GHC] #974: Add isLeft, isRight, fromLeft, fromRight, and splitEithers to Data.Either

[Neil Mitchell]

Hi

> #974: Add isLeft, isRight, fromLeft, fromRight, and splitEithers to Data.Either

Woohoo! Finally!

> This proposal would add basic functionality to `Either` similar to that
>  for `Maybe`.  The `splitEithers` function of type `[Either a b] ->
>  ([a],[b])` is unique; however, it seems to be a widely useful function.

This (in my mind) is a parallel to unzip? unzipEithers to me gives a
much clearer picture of what is going on here.

Thanks

Neil