[GHC] #16211: Recompiling results in a missing instance

[GHC]

#16211: Recompiling results in a missing instance
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        Reporter:  crockeea          |                Owner:  (none)
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler          |              Version:  8.6.3
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
 Type of failure:  Incorrect         |  Unknown/Multiple
  error/warning at compile-time      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by simonpj):

 But you are getting further than me. I never got to compile your code even
 once, because I couldn't install `monad-classes`.  (Obviously you were.)
 Maybe someone can figure out why.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/16211#comment:3>
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