[Template-haskell] type classes and template haskell (bug?)

[Jeremy Shaw]

Hello,

I have a file that contains the following, which I have loaded into
ghci 6.2:

module Main where

import Language.Haskell.THSyntax

class Test a where 
    test :: a -> a

instance Test (a,b,c) where
    test x = x

main = putStrLn "Hello, World!"

Now, the following works for me:

*Main> runQ [d| instance Test (Int,Int) |] >>= putStrLn . show
[InstanceD [] (AppT (ConT "Main:Test") (AppT (AppT (TupleT 2) (ConT "GHC.Base:Int")) (ConT "GHC.Base:Int"))) []]


But this doesn't:

*Main> runQ [d| instance Test (a,b) |] >>= putStrLn . show
ghc-6.2: panic! (the `impossible' happened, GHC version 6.2):
	Failed binder lookup: a {- tv a20x -}

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


Am I doing something wrong, or is this a bug? 

Thanks!  
Jeremy Shaw.  

ps. sorry if you get this message twice, I sent it once, but I had
signed up on the mailing list with the wrong email address. So, I
changed my account settings to have my correct email address, but now
I can't cancel the message that is awaiting moderator approval.