[GHC] #13520: instance Alternative ZipList
GHC
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Mon Apr 3 18:05:01 UTC 2017
#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?
--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13520>
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