[GHC] #630: Found "ghc-6.4: panic!"

[GHC]

#630: Found "ghc-6.4: panic!"
-------------------------------+--------------------------------------------
 Reporter:  pupeno at pupeno.com  |          Owner:     
     Type:  bug                |         Status:  new
 Priority:  normal             |      Milestone:     
Component:  GHCi               |        Version:  6.4
 Severity:  normal             |       Keywords:     
       Os:  Unknown            |   Architecture:  x86
-------------------------------+--------------------------------------------
I have just gotten:
 {{{
 ghc-6.4: panic! (the `impossible' happened, GHC version 6.4):
         Unify.unifyTauTyLists: mismatched type lists!

 Please report it as a compiler bug to glasgow-haskell-bugs at haskell.org,
 or http://sourceforge.net/projects/ghc/.
 }}}
 from ghci.
 The code I loaded is:
 {{{
 module ProgramOptions
     where

 -- newtype Command n = Command [Option n]
 --                   deriving (Show)
 --
 -- data Option n = Option { keys :: [String],
 --                          value :: Value n,
 --                          description :: String }
 --               deriving (Show)
 data Option = Option [String] Value String

 data Num n => Value n = Boolean Bool
                       | Numeric n
                       | String String
 instance Num n => Show (Value n) where
     show (Boolean b) = show b
     show (Numeric n) = show n
     show (String s) = show s
 }}}
 and the whole session was:
 {{{
 $ ghci
    ___         ___ _
   / _ \ /\  /\/ __(_)
  / /_\// /_/ / /  | |      GHC Interactive, version 6.4, for Haskell 98.
 / /_\\/ __  / /___| |      http://www.haskell.org/ghc/
 \____/\/ /_/\____/|_|      Type :? for help.

 Loading package base-1.0 ... linking ... done.
 Prelude> :l ProgramOptions
 Compiling ProgramOptions   ( ProgramOptions.hs, interpreted )
 Ok, modules loaded: ProgramOptions.
 *ProgramOptions> Option ["n", "name"] (String "Pupeno") "Name"
 ghc-6.4: panic! (the `impossible' happened, GHC version 6.4):
         Unify.unifyTauTyLists: mismatched type lists!

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


 *ProgramOptions>
 }}}
 I am reporting mainly because the interpreter asked for it, I am very new
 to Haskell.

-- 
Ticket URL: <http://cvs.haskell.org/trac/ghc/ticket/630>
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