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

6 Apr 2015

      #10248: GHC panic when used with deferred type errors, again
---------------------------------+-------------------------------------
        Reporter:  Iceland_jack  |                   Owner:
            Type:  bug           |                  Status:  new
        Priority:  normal        |               Milestone:
       Component:  GHCi          |                 Version:  7.10.1-rc3
      Resolution:                |                Keywords:
Operating System:  Linux         |            Architecture:  x86
 Type of failure:  Other         |               Test Case:
      Blocked By:                |                Blocking:
 Related Tickets:                |  Differential Revisions:
---------------------------------+-------------------------------------
Description changed by Iceland_jack:

Old description:
...
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>
}}}
New description:

 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
 GHCi, version 7.10.0.20150316: 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#comment:1
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