[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:  closed          
  Priority:  normal              |      Milestone:  7.6.1           
 Component:  Compiler (Parser)   |        Version:  7.4.1           
Resolution:  fixed               |       Keywords:                  
        Os:  Windows             |   Architecture:  Unknown/Multiple
   Failure:  Compile-time crash  |     Difficulty:  Unknown         
  Testcase:                      |      Blockedby:                  
  Blocking:                      |        Related:                  
---------------------------------+------------------------------------------
Changes (by pcapriotti):

  * status:  new => closed
  * difficulty:  => Unknown
  * resolution:  => fixed
  * milestone:  => 7.6.1


Old description:

> 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

New description:

 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
 }}}

--

Comment:

 Thanks for the report. This is fixed in HEAD.

-- 
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/7094#comment:1>
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