Re: Proposal: instance Alternative ZipList

17 Jul 2015


      +1. It obeys laws. It feels zippy. LGTM.

On Friday, July 17, 2015, Edward Kmett  wrote:
...
Er.. I obviously meant
instance Alternative ZipList where
   empty = ZipList []
   ZipList xs <|> ZipList ys = ZipList (xs ++ drop (length xs) ys)
sorry for any confusion.
On Fri, Jul 17, 2015 at 11:37 AM, Edward Kmett javascript:_e(%7B%7D,'cvml','ekmett@gmail.com');> wrote:
...
The ZipList data type admits one legal Alternative instance
instance Alternative ZipList where
   pure = ZipList []
   ZipList xs <|> ZipList ys = ZipList (xs ++ drop (length xs) ys)
The legality of this instance was first noted in
http://people.cs.kuleuven.be/~tom.schrijvers/Research/papers/ppdp2015.pdf
I propose adding this instance, which acts like a generalized version of
the Alternative for Maybe, choosing with a left bias.
Discussion Period: 2 weeks
-Edward
-- 
-- Dan Burton