Hello, I have loaded the following from a file 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!" This 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@haskell.org, or http://sourceforge.net/projects/ghc/. Am I doing something wrong, or is this a bug? Thanks! Jeremy Shaw.