[GHC] #13520: instance Alternative ZipList

[GHC]

#13520: instance Alternative ZipList
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           Reporter:  Iceland_jack   |             Owner:  (none)
               Type:  bug            |            Status:  new
           Priority:  normal         |         Milestone:
          Component:                 |           Version:  8.0.1
  libraries/base                     |
           Keywords:                 |  Operating System:  Unknown/Multiple
       Architecture:                 |   Type of failure:  None/Unknown
  Unknown/Multiple                   |
          Test Case:                 |        Blocked By:
           Blocking:                 |   Related Tickets:
Differential Rev(s):                 |         Wiki Page:
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 The paper "From monoids to near-semirings:
 the essence of MonadPlus and Alternative`" mentions

 > Perhaps surprisingly, `ZipList`s have an `Alternative` instance.
 Like the `Alternative` instance for `Maybe`, the one for `ZipList` has
 a left bias.
 >
 > {{{#!hs
 > instance Alternative ZipList where
 >   empty :: ZipList a
 >   empty           = ZL []
 >
 >   (<|>) :: ZipList a -> ZipList a -> ZipList a
 >   ZL xs <|> ZL ys = ZL (xs ++ drop (length xs) ys)
 > }}}

 Has this been considered for base?

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13520>
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