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

[Donald Bruce Stewart]

ndmitchell:
> 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.

yeah, if its an unzip, then unzipEithers makes more sense.

-- Don