[GHC] #974: Add unzipEithers, lefts, rights to Data.Either

[Ross Paterson]

On Sun, Nov 12, 2006 at 11:40:19AM -0500, roconnor at theorem.ca wrote:
> Everyone seems satified with the name unzipEithers.  There have been 
> suggestions for
> 
>  partitionEither :: (a -> Either b c) -> [a] -> ([b], [c])
> 
> but I suggest they be pursued in a different trac.

I think it makes sense to consider them together, as these functions are
closely related, the only concerns anyone has raised about them relate
to names, and they're competing for the same part of the namespace.

Apropos of that, I'm convinced by Henning's argument against the name
mapEither (that you can't compose them).  I'm not sure about unzip,
but I agree there are too many split's.