[GHC] #10248: GHC panic when used with deferred type errors, again

6 Apr 2015


      #10248: GHC panic when used with deferred type errors, again
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              Reporter:  Iceland_jack  |             Owner:
                  Type:  bug           |            Status:  new
              Priority:  normal        |         Milestone:
             Component:  GHCi          |           Version:  7.10.1-rc3
              Keywords:                |  Operating System:  Linux
          Architecture:  x86           |   Type of failure:  Other
             Test Case:                |        Blocked By:
              Blocking:                |   Related Tickets:
Differential Revisions:                |
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 Similar to previous report of mine #9834. Given `error.hs`
 {{{#!hs
 data I a = I a
 }}}

 I get the following result:
 {{{#!hs
 $ ghci -fdefer-type-errors -ignore-dot-ghci error.hs
 http://www.haskell.org/ghc/  :? for help
 [1 of 1] Compiling Main             ( error.hs, interpreted )
 Ok, modules loaded: Main.
 *Main> I <$> _
 I <$> _

 <interactive>:2:7: Warning:
     Found hole ‘_’ with type: IO a0
     Where: ‘a0’ is an ambiguous type variable
     In the second argument of ‘(<$>)’, namely ‘_’
     In the first argument of ‘GHC.GHCi.ghciStepIO ::
                                 IO a_auR -> IO a_auR’, namely
       ‘I <$> _’
     In a stmt of an interactive GHCi command:
       it <- GHC.GHCi.ghciStepIO :: IO a_auR -> IO a_auR (I <$> _)
 ghc: panic! (the 'impossible' happened)
   (GHC version 7.10.0.20150316 for i386-unknown-linux):
         nameModule $dShow_aIT

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

 *Main>
 }}}

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Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/10248
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