[GHC] #14828: panic! when using :print on some functions with class constraints?

[GHC]

#14828: panic! when using :print on some functions with class constraints?
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        Reporter:  jol               |                Owner:  (none)
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  GHCi              |              Version:  8.2.2
      Resolution:                    |             Keywords:  debugger
Operating System:  Linux             |         Architecture:  x86_64
 Type of failure:  Compile-time      |  (amd64)
  crash or panic                     |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by olligobber):

 Note this is still an issue in 8.6.2

 {{{
 GHCi, version 8.6.2: http://www.haskell.org/ghc/  :? for help
 Prelude> :print fmap
 ghc: panic! (the 'impossible' happened)
   (GHC version 8.6.2 for x86_64-unknown-linux):
         isUnliftedType
   t1_a1x6[rt] :: TYPE t_a1x5[rt]
   Call stack:
       CallStack (from HasCallStack):
         callStackDoc, called at compiler/utils/Outputable.hs:1160:37 in
 ghc:Outputable
         pprPanic, called at compiler/types/Type.hs:2021:10 in ghc:Type

 Please report this as a GHC bug:  http://www.haskell.org/ghc/reportabug
 }}}

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14828#comment:2>
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