ghc-6.4: panic!

[Simon Marlow]

Thurston Hou Yeen Dang wrote:
> Hello,
> 
> The following code:
> -----
> data Tree a = Leaf | Node a Tree Tree
> 
> double :: Tree Int -> Tree Int
> double Leaf
>     = Node 1 Leaf Leaf
> double (Node myKey leftTree rightTree)
>     = Node myKey (double leftTree) (double rightTree)
> -----
> caused an error message:
> -----
> ghc-6.4: panic! (the `impossible' happened, GHC version 6.4):
>         Unify.unifyTauTyLists: mismatched type lists!

This was fixed in version 6.4.1:

   http://hackage.haskell.org/trac/ghc/ticket/456

Cheers,
	Simon