[GHC] #13104: runRW# ruins join points

[GHC]

#13104: runRW# ruins join points
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        Reporter:  lukemaurer        |                Owner:
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler          |              Version:  8.1
      Resolution:                    |             Keywords:  JoinPoints
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by simonpj):

 What does the code for `loop` look like?  Why isn't it eta-expaned anyway?

 What's the source code for the example to reproduce this?  In #12781 you
 said that join points solved the example there...

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13104#comment:2>
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