[GHC] #10565: GHC 7.10.2 RC: the impossible happened on hPDB-examples-1.2.0.2

[GHC]

#10565: GHC 7.10.2 RC: the impossible happened on hPDB-examples-1.2.0.2
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        Reporter:  snoyberg      |                   Owner:  bgamari
            Type:  bug           |                  Status:  new
        Priority:  normal        |               Milestone:  7.10.2
       Component:  Compiler      |                 Version:  7.10.2-rc1
      Resolution:                |                Keywords:
Operating System:  Linux         |            Architecture:  x86_64 (amd64)
 Type of failure:  None/Unknown  |               Test Case:
      Blocked By:                |                Blocking:
 Related Tickets:                |  Differential Revisions:
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Comment (by bgamari):

 I should note that the original testcase (found here
 https://github.com/bgamari/ghc-T10565/blob/master/Rg.hs) compiles with
 7.10.1 yet not with 7.10.2. It does, however, compile with 7.10.2 if one
 uses a more reasonable implementation of `guessElement`.

 It is do wonder what changed between 7.10.1 and 7.10.2, however.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10565#comment:3>
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