[GHC] #8747: GHC 7.4.1 ghc: panic! (the 'impossible' happened)

[GHC]

#8747: GHC 7.4.1 ghc: panic! (the 'impossible' happened)
----------------------------------+-------------------------------
       Reporter:  codygman        |             Owner:
           Type:  bug             |            Status:  new
       Priority:  normal          |         Milestone:
      Component:  GHCi            |           Version:  7.4.1
       Keywords:                  |  Operating System:  Linux
   Architecture:  x86_64 (amd64)  |   Type of failure:  GHCi crash
     Difficulty:  Unknown         |         Test Case:
     Blocked By:                  |          Blocking:
Related Tickets:                  |
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 I was just trying to create the records in the all about monads tutorial
 and after changing my code to:

 {{{

 import Data.Maybe (Maybe(Nothing,Just))

 data Gender = M | F
 data Sheep = Sheep (Gender) (Maybe Sheep) (Maybe Sheep) deriving (show)
 main = undefined

 }}}

 I got the following error:


 {{{
 *Main> :r
 [1 of 1] Compiling Main             ( Main.hs, interpreted )
 ghc: panic! (the 'impossible' happened)
   (GHC version 7.4.1 for x86_64-unknown-linux):
         nameModule show{tv aD4}
 }}}


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


 I've attached my entire ghci log for completeness sake. I'm using debian
 stable and kernel 3.11-0.bpo.2-amd64.

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8747>
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