[GHC] #13846: GHC Panic: Visible type application + function type @(_ -> _)

[GHC]

#13846: GHC Panic: Visible type application + function type @(_ -> _)
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           Reporter:  Iceland_jack   |             Owner:  (none)
               Type:  bug            |            Status:  new
           Priority:  normal         |         Milestone:
          Component:  Compiler       |           Version:  8.3
           Keywords:                 |  Operating System:  Unknown/Multiple
  TypeApplications                   |
       Architecture:                 |   Type of failure:  None/Unknown
  Unknown/Multiple                   |
          Test Case:                 |        Blocked By:
           Blocking:                 |   Related Tickets:
Differential Rev(s):                 |         Wiki Page:
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 {{{
 $ ghci -XTypeApplications -ignore-dot-ghci
 GHCi, version 8.3.20170605: http://www.haskell.org/ghc/  :? for help
 Prelude> :t fmap @(_ -> _)
 ghc: panic! (the 'impossible' happened)
   (GHC version 8.3.20170605 for x86_64-unknown-linux):
         repSplitAppTys
   w0_a1pF[tau:2]
   w0_a1pH[tau:2]
   []
   Call stack:
       CallStack (from HasCallStack):
         prettyCurrentCallStack, called at
 compiler/utils/Outputable.hs:1133:58 in ghc:Outputable
         callStackDoc, called at compiler/utils/Outputable.hs:1137:37 in
 ghc:Outputable
         pprPanic, called at compiler/types/Type.hs:809:9 in ghc:Type

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

 Prelude>
 }}}

 Doesn't happen with other types it seems, probably something to do with
 levity polymorphism.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13846>
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