[ ghc-Bugs-1050406 ] compiler panic with show (?)

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Bugs item #1050406, was opened at 2004-10-19 19:03
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Category: Compiler
Group: None
Status: Open
Resolution: None
Priority: 5
Submitted By: Andrew Pimlott (pimlott)
Assigned to: Nobody/Anonymous (nobody)
Summary: compiler panic with show (?)

Initial Comment:
This code is is based upon a post by Oleg at
http://www.haskell.org/pipermail/haskell-cafe/2004-October/007160.html.

{-# OPTIONS -fglasgow-exts #-}
import Control.Monad.Trans

data Bar m = forall t. (MonadTrans t, Monad (t m)) =>
               Bar (t m () -> m ()) (t m Int)

data Foo = Foo (forall m. Monad m => Bar m)

runProg (Foo (Bar run op)) = run $ prog op

prog op = do
          lift $ putStrLn "Running prog"
          return ()
                                   
data ABC = A 
instance Show ABC where
  show A = "A"

main = putStrLn $ show A

It seems to be nearly minimal, though I have no idea
why.  When I compile with ghc 6.2.1 from Debian
unstable, I get

% ghc try.hs
ghc-6.2.1: panic! (the `impossible' happened, GHC
version 6.2.1):
        cgPanic
    zddMonad {- v aGa -}
    static binds for:
    local binds for:
    Main.prog {- v rz -}
    show {- v rJG -}
    SRT labelghc-6.2.1: panic! (the `impossible'
happened, GHC version 6.2.1):
        initC: srt


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