[GHC] #9623: Use Data.List.dropWhileEnd

[GHC]

#9623: Use Data.List.dropWhileEnd
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       Reporter:  dfeuer             |                   Owner:
           Type:  task               |                  Status:  new
       Priority:  normal             |               Milestone:  7.10.1
      Component:  Compiler           |                 Version:  7.8.3
       Keywords:                     |        Operating System:
   Architecture:  Unknown/Multiple   |  Unknown/Multiple
     Difficulty:  Easy (less than 1  |         Type of failure:
  hour)                              |  None/Unknown
     Blocked By:                     |               Test Case:
Related Tickets:                     |                Blocking:
                                     |  Differential Revisions:
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 The GHC tree has many instances of `reverse . dropWhile ... . reverse`. As
 well as being harder to read and work with (searching for those forms led
 me to discover #9616) this approach is less efficient than `dropWhileEnd`.
 I think I've found all the places this is used, and I'll submit a patch to
 fix all the instances except for tests and nofib.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9623>
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