[GHC] #7094: Irrefutable pattern failed for pattern Data.Maybe.Just

[GHC]

#7094: Irrefutable pattern failed for pattern Data.Maybe.Just
--------------------------------+-------------------------------------------
 Reporter:  pganelin            |          Owner:                   
     Type:  bug                 |         Status:  new              
 Priority:  normal              |      Component:  Compiler (Parser)
  Version:  7.4.1               |       Keywords:                   
       Os:  Windows             |   Architecture:  Unknown/Multiple 
  Failure:  Compile-time crash  |       Testcase:                   
Blockedby:                      |       Blocking:                   
  Related:                      |  
--------------------------------+-------------------------------------------
 The following invalid program causes ghc panic
 -----------------------
 --State-Monad.hs
 data Term =  Con Int
      | Div Term Term
      deriving (Show)

 type M a =  State -> (a,State)
 type State =Int

 instance Monad Int -> (a,Int) where
     g >>= f = undefined
     return = undefined
 -------------------------------


 D:\>"C:\Free\Haskell Platform\2012.2.0.0\bin\ghc.exe" D:\State-Monad.hs
 [1 of 1] Compiling Main             ( D:\State-Monad.hs, D:\State-Monad.o
 )
 ghc.exe: panic! (the 'impossible' happened)
   (GHC version 7.4.1 for i386-unknown-mingw32):
         compiler\rename\RnSource.lhs:429:14-81: Irrefutable pattern failed
 for pattern Data.Maybe.Just (inst_tyvars,
                                                         _,
                                                         SrcLoc.L _ cls,
                                                         _)


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

-- 
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/7094>
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