[GHC] #708: Error: Data.Generics / Cast

[Ralf Lammel]

Hi,
I have at least simplified your test case; could you resubmit?
Regards,
Ralf

module Test where

  class C a where
    mycast :: (C b) => a -> Maybe b 
    mycast = undefined
    equals :: (C b) => a -> b -> Bool
    equals = undefined
    
  instance C Int

  data T1 = N11 Int

  instance C T1 where
    mycast (N11 x) = undefined
    x `equals` y = (mycast x :: Maybe Int) == undefined

{-

*Test> mycast (1::Int) :: Maybe Int
ghc.exe: panic! (the `impossible' happened, GHC version 6.4):
        nameModule mycast{v ah3m}

Please report it as a compiler bug to glasgow-haskell-bugs at haskell.org,
or http://sourceforge.net/projects/ghc/.

-}




> -----Original Message-----
> From: glasgow-haskell-bugs-bounces at haskell.org
[mailto:glasgow-haskell-
> bugs-bounces at haskell.org] On Behalf Of GHC
> Sent: Thursday, March 02, 2006 1:24 AM
> To: glasgow-haskell-bugs at haskell.org
> Subject: [GHC] #708: Error: Data.Generics / Cast
> 
> #708: Error: Data.Generics / Cast
>
----------------------------------------------+-------------------------
--
> --
>     Reporter:  r.j.rorije at student.utwente.nl  |        Owner:
>         Type:  bug                            |       Status:  new
>     Priority:  normal                         |    Milestone:
>    Component:  Compiler                       |      Version:  6.4.1
>     Severity:  normal                         |     Keywords:
>           Os:  Windows                        |   Difficulty:  Unknown
> Architecture:  x86                            |
>
----------------------------------------------+-------------------------
--
> --
> Hi,
> 
>  I am using Data.Generics and type classes to be able to compare
values on
>  their most inner type. Doing this a compiler bug occurred. I have
tried
> to
>  find a minimum example that crashed. The example I found may be not
as
>  minimal as you would like, though. I can not track down the exact
source
>  of the error, but the error occurs only when using the function
mycast.
>  when '''both''' implementations of mycast are removed no error
occurs.
> 
>  I hope I made the problem clear enough, otherwise, feel free to
contact
>  me.
> 
>  source of the bug-example:
>  [http://wwwhome.cs.utwente.nl/~rorijerj/Test.hs]
> 
> --
> Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/708>
> GHC <http://www.haskell.org/ghc/>
> The Glasgow Haskell Compiler