[GHC] #11815: Data.List: Add a function to get consecutive elements (mapConsecutives)

[GHC]

#11815: Data.List: Add a function to get consecutive elements (mapConsecutives)
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           Reporter:  holmisen       |             Owner:
               Type:  feature        |            Status:  new
  request                            |
           Priority:  low            |         Milestone:
          Component:                 |           Version:
  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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 A recurring pattern is to get a list of all consecutive elements of a
 list, for further processing.

 I propose adding the following function to `Data.List` for this:

 {{{
 mapConsecutives :: (a -> a -> b) -> [a] -> [b]
 mapConsecutives _ [] = []
 mapConsecutives f xs = zipWith f xs (tail xs)
 }}}

 Since it requires pattern matching, to separate the empty case, it is not
 practical to inline at each use site.

 Sidenote: A similar function `mapAdjacent` is available in the `utility-
 ht` library (with a partial implementation(!)) [1].

 I realise that `Data.List` is often imported unqualified and hence
 additions may cause trouble. I would have raised this on the libraries
 mailing list first, but the guidelines for proposals pointed me here.

 [1] http://hackage.haskell.org/package/utility-ht-0.0.11/docs/Data-List-
 HT.html#v:mapAdjacent

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11815>
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