[GHC] #15436: Compile-time panic, Prelude.!!: negative index

[GHC]

#15436: Compile-time panic, Prelude.!!: negative index
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        Reporter:  pbrisbin          |                Owner:  (none)
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:  8.6.1
       Component:  Compiler          |              Version:  8.5
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
 Type of failure:  Compile-time      |  Unknown/Multiple
  crash or panic                     |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by hsyl20):

 `-fno-case-folding` makes the panic disappear

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/15436#comment:3>
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