[GHC] #9337: Add `sortOn` function to Data.List

[GHC]

#9337: Add `sortOn` function to Data.List
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        Reporter:  JohnWiegley       |                   Owner:
            Type:  feature request   |                  Status:  closed
        Priority:  normal            |               Milestone:  7.10.1
       Component:  libraries/base    |                 Version:  7.8.3
      Resolution:  duplicate         |                Keywords:
Operating System:  Unknown/Multiple  |            Architecture:
 Type of failure:  None/Unknown      |  Unknown/Multiple
      Blocked By:                    |               Test Case:
 Related Tickets:  #9004             |                Blocking:
                                     |  Differential Revisions:
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Comment (by JohnWiegley):

 This is also a dupe of part of #2659, which was closed 5 years ago now as
 wontfix.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9337#comment:7>
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