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

13 Nov 2006

      Aaron Denney wrote:
...
On 2006-11-13, roconnor@theorem.ca  wrote:
...
On Mon, 13 Nov 2006, Bulat Ziganshin wrote:
...
i prefer name splitEithers. [...]
[...]
Unzip is reversible though.  The order is preserved, and
(uncurry zip) . unzip = id = unzip . (uncurry zip)
There is no "zipEithers" that is any sort of reverse.
Only one-sided, of course:

splitEithers . (\ (xs, ys) -> map Left xs ++ map Right ys) = id
...
Hmm.  (,) is the generic product, and Either is the generic coproduct.
counzip?
Or, better even, ``cozip'' ;-)       (I couldn't resist...)

(uncurry zip) :: ([a],[b]) -> [a * b]
                                /
                               /
                              /
                             /
                            /
                           /
                          /
                         /
                        /
                       /
cozip         ::   [a + b] -> ([a],[b])

;-)

Wolfram

P.S.:  I currently have:

eitherList :: [Either a b] -> ([a], [b])

eitherPair2 :: (a, Either b c) -> Either (a,b) (a,c)

eitherMap :: (a -> c) -> (b -> d) -> Either a b -> Either c d

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

kahl＠cas.mcmaster.ca