[GHC] #12549: Panic on ":t datatypeName"

[GHC]

#12549: Panic on ":t datatypeName"
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        Reporter:  johnleo       |                Owner:  johnleo
            Type:  bug           |               Status:  new
        Priority:  normal        |            Milestone:
       Component:  Compiler      |              Version:  8.1
      Resolution:                |             Keywords:
Operating System:  MacOS X       |         Architecture:  x86_64 (amd64)
 Type of failure:  None/Unknown  |            Test Case:
      Blocked By:                |             Blocking:
 Related Tickets:                |  Differential Rev(s):
       Wiki Page:                |
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Comment (by johnleo):

 Replying to [comment:9 goldfire]:
 > Looks to me that you're hot on the case. Let me know if I can be of
 help.

 If you have any insight as to why some of the universally quantified
 variables are moved past the class constraint in 8.1 that would be very
 helpful.  Was this on purpose to fix some bug (it's not clear to me if the
 semantics are different or not), or might it just have been an unintended
 side-effect of some other change?

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12549#comment:10>
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