[GHC] #9160: Panic: Template variable unbound in rewrite rule

[GHC]

#9160: Panic: Template variable unbound in rewrite rule
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        Reporter:  mietek              |            Owner:
            Type:  bug                 |           Status:  new
        Priority:  normal              |        Milestone:
       Component:  Compiler            |          Version:  7.8.2
      Resolution:                      |         Keywords:
Operating System:  Unknown/Multiple    |     Architecture:  x86_64 (amd64)
 Type of failure:  Compile-time crash  |       Difficulty:  Unknown
       Test Case:                      |       Blocked By:
        Blocking:                      |  Related Tickets:  #4524
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Description changed by mietek:

Old description:

> Installing `singletons-1.0` with GHC 7.8.2 on OS X 10.9.2 fails:
>
> {{{
> ghc: panic! (the 'impossible' happened)
>   (GHC version 7.8.2 for x86_64-apple-darwin):
>         Template variable unbound in rewrite rule
> }}}
>
> See also [https://github.com/goldfirere/singletons/issues/83
> goldfirere/singletons#83]

New description:

 Installing `singletons-1.0` with GHC 7.8.2 on both OS X 10.9.2 and Ubuntu
 2014.04 fails:

 {{{
 ghc: panic! (the 'impossible' happened)
   (GHC version 7.8.2 for x86_64-apple-darwin):
         Template variable unbound in rewrite rule
 }}}

 This seems to be an issue with the optimizer, as the bug only appears with
 optimization level 2, using the following line in `~/.cabal/config`:

 {{{
 optimization: 2
 }}}

 See also [https://github.com/goldfirere/singletons/issues/83
 goldfirere/singletons#83]

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9160#comment:5>
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