[GHC] #13320: Unfortunate compiler loop when creating type loop (with UndecidableInstances)

[GHC]

#13320: Unfortunate compiler loop when creating type loop (with
UndecidableInstances)
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        Reporter:  Ptival            |                Owner:  dfeuer
            Type:  bug               |               Status:  new
        Priority:  low               |            Milestone:
       Component:  Compiler          |              Version:  8.0.1
      Resolution:                    |             Keywords:
                                     |  UndecidableInstances loop
Operating System:  Unknown/Multiple  |         Architecture:
 Type of failure:  Compile-time      |  Unknown/Multiple
  crash or panic                     |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by simonpj):

 Great!  Please add the test case though.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13320#comment:5>
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