[GHC] #13153: Several Traversable instances have an extra fmap

[GHC]

#13153: Several Traversable instances have an extra fmap
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        Reporter:  dfeuer            |                Owner:  dfeuer
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:  8.6.1
       Component:  Core Libraries    |              Version:  8.1
      Resolution:                    |             Keywords:
                                     |  QuantifiedConstraints
Operating System:  Unknown/Multiple  |         Architecture:
 Type of failure:  Runtime           |  Unknown/Multiple
  performance bug                    |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by dfeuer):

 If only we had `mapTraverse` instead of `traverse` as the class method,
 none of this mess would be necessary. That would obviously be a hard sell
 for backwards compatibility.

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13153#comment:14>
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