[GHC] #14898: Panic with repSplitAppTys

[GHC]

#14898: Panic with repSplitAppTys
-------------------------------------+-------------------------------------
           Reporter:  ryanreich      |             Owner:  (none)
               Type:  bug            |            Status:  new
           Priority:  normal         |         Milestone:
          Component:  Compiler       |           Version:  8.2.1
           Keywords:                 |  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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 I get a GHC panic while compiling a rather large module that contains a
 fairly simple function:

 {{{#!hs
 import Control.Monad.Reader
 usingReader ::
   (Monad m) =>
   r ->
   (a -> ReaderT r m b)
   (a -> m b)
 usingReader r f = flip runReaderT r . f
 }}}

 Unfortunately, that function alone in a module does not trigger the panic.
 The error message is:

 {{{
 ghc: panic! (the 'impossible' happened)
   (GHC version 8.2.1 for x86_64-unknown-linux):
         repSplitAppTys
   a_ahFs[sk:1]
   ReaderT r_ahFr[sk:1] m_ahFq[sk:1] b_ahFt[sk:1]
   []
   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:808:9 in ghc:Type
 }}}

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14898>
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