[GHC] #10602: ghc panic: Template variable unbound in rewrite rule when compiling with -O2

[GHC]

#10602: ghc panic: Template variable unbound in rewrite rule when compiling with
-O2
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        Reporter:  pacak             |                   Owner:  bgamari
            Type:  bug               |                  Status:  infoneeded
        Priority:  highest           |               Milestone:  7.10.2
       Component:  Compiler          |                 Version:  7.10.2-rc2
      Resolution:                    |                Keywords:
Operating System:  Unknown/Multiple  |            Architecture:
 Type of failure:  Compile-time      |  Unknown/Multiple
  crash                              |               Test Case:
      Blocked By:                    |                Blocking:
 Related Tickets:                    |  Differential Revisions:
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Comment (by thomie):

 I'm not sure what you're asking. For me, it fails with both `ghc-stage1`
 and `ghc-stage2` from a devel2 build of HEAD, as well as with
 `ghc-7.10.1.20150710` from hvr's ppa.

 If it wasn't clear: you need both `T10602.hs` and `T10602b.hs`.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10602#comment:18>
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