[GHC] #13416: Unsolved Constraints (initTc)

[GHC]

#13416: Unsolved Constraints (initTc)
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           Reporter:  sgschlesinger  |             Owner:  (none)
               Type:  bug            |            Status:  new
           Priority:  normal         |         Milestone:
          Component:  Compiler       |           Version:  8.0.2
           Keywords:  constraint     |  Operating System:  Linux
       Architecture:  x86_64         |   Type of failure:  Compile-time
  (amd64)                            |  crash or panic
          Test Case:                 |        Blocked By:
           Blocking:                 |   Related Tickets:
Differential Rev(s):                 |         Wiki Page:
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 Another bug here:

 ghc: panic! (the 'impossible' happened)
   (GHC version 8.0.2 for x86_64-unknown-linux):
         initTc: unsolved constraints
   WC {wc_insol = [W] nub_a1U2 :: t_a1U1[tau:1] (CHoleCan: nub)}

 I've attached the relevant code.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13416>
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