[GHC] #13381: "opt_univ fell into a hole" panic from rewrite rule

[GHC]

#13381: "opt_univ fell into a hole" panic from rewrite rule
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        Reporter:  dfeuer            |                Owner:  (none)
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:  8.2.1
       Component:  Compiler          |              Version:  8.1
      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 RyanGlScott):

 To make things even more interesting, this error does not occur on GHC 7.8
 or 7.10. Here's the error you get with 7.10.3:

 {{{
 GHCi, version 7.10.3: http://www.haskell.org/ghc/  :? for help
 [1 of 1] Compiling Crash            ( Bug.hs, interpreted )

 Bug.hs:25:23:
     Couldn't match type ‘Exp Int’ with ‘Int’
     Expected type: Exp Int -> Iter (Exp Int) (Exp Char)
       Actual type: Int -> Iter (Exp Int) (Exp Char)
     In the first argument of ‘iterLoop’, namely ‘f’
     In the first argument of ‘fromExp’, namely ‘(iterLoop f init)’

 Bug.hs:25:25:
     Couldn't match expected type ‘Exp Int’ with actual type ‘Int’
     In the second argument of ‘iterLoop’, namely ‘init’
     In the first argument of ‘fromExp’, namely ‘(iterLoop f init)’
 }}}

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13381#comment:1>
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