[GHC] #10990: Checking whether a default declaration is an instance of a defaultable typeclass is broken

[GHC]

#10990: Checking whether a default declaration is an instance of a defaultable
typeclass is broken
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        Reporter:  kanetw            |                Owner:
            Type:  bug               |               Status:  new
        Priority:  low               |            Milestone:
       Component:  Compiler (Type    |              Version:  7.10.2
  checker)                           |
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by thomie):

 Could you add sample code please (if you're not working on a fix already).

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10990#comment:1>
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