[GHC] #13906: ApplicativeDo doesn't handle existentials as well as it could

[GHC]

#13906: ApplicativeDo doesn't handle existentials as well as it could
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        Reporter:  dfeuer            |                Owner:  (none)
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:  8.4.1
       Component:  Compiler          |              Version:  8.0.1
      Resolution:                    |             Keywords:  ApplicativeDo
Operating System:  Unknown/Multiple  |         Architecture:
 Type of failure:  GHC rejects       |  Unknown/Multiple
  valid program                      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by simonmar):

 Well ok, but we're a bit down in the weeds here!  Some other more
 important improvements we could make to ApplicativeDo are e.g. #10892 and
 #10976.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13906#comment:1>
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