[GHC] #15772: Strange constraint error that disappears when adding another top-level declaration

[GHC]

#15772: Strange constraint error that disappears when adding another top-level
declaration
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        Reporter:  kosmikus          |                Owner:  (none)
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler (Type    |              Version:  8.6.1
  checker)                           |
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
 Type of failure:  GHC rejects       |  Unknown/Multiple
  valid program                      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by kosmikus):

 Thanks Ryan. I can confirm that my original test case works as expected
 with GHC 8.0. In addition, it also seems to typecheck ''much'' faster.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/15772#comment:6>
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