[GHC] #9918: GHC chooses an instance between two overlapping, but cannot resolve a clause within the similar closed type family

[GHC]

#9918: GHC chooses an instance between two overlapping, but cannot resolve a
clause within the similar closed type family
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              Reporter:  qnikst      |            Owner:
                  Type:  bug         |           Status:  new
              Priority:  normal      |        Milestone:
             Component:  Compiler    |          Version:  7.8.3
            Resolution:              |         Keywords:
      Operating System:              |     Architecture:  Unknown/Multiple
  Unknown/Multiple                   |       Difficulty:  Unknown
       Type of failure:              |       Blocked By:
  None/Unknown                       |  Related Tickets:
             Test Case:              |
              Blocking:              |
Differential Revisions:              |
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Comment (by simonpj):

 Can you be more explicit?

  * What, precisely, are the changes needed to do from "version that does
 work using overlapping instances" to "version that does not work using
 closed type families"?
  * What, as precisely as possible, does not work?
  * Why did you think it should work?

 I can't figure that out from the 50 lines of code you give.

 Thanks

 Simon

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9918#comment:1>
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