[GHC] #7437: peculiar behaviour with default instances and type variables

[GHC]

#7437: peculiar behaviour with default instances and type variables
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        Reporter:  bos               |                Owner:  simonpj
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Test Suite        |              Version:  7.6.1
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
 Type of failure:  GHC accepts       |  Unknown/Multiple
  invalid program                    |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:  #12151            |  Differential Rev(s):
       Wiki Page:                    |
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Changes (by thomie):

 * related:   => #12151


Comment:

 I wished I had added that test already, because now this issue has
 regressed. See #12151.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/7437#comment:9>
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