Hi, thanks for reporting this; sorry for taking so long to reply. The current version of Hugs now handles this error condition a little bit better: Prelude> :l Bug.hs Reading file "Bug.hs": ERROR "Bug.hs":3 - Undefined type variable "m" --sigbjorn ----- Original Message ----- From: Deling Ren To: hugs-bugs@haskell.org Sent: Friday, February 08, 2002 02:07 Subject: A bug in hugs Hugs version: Dec 2001. Platform: Windows. Both WinHugs and command line hugs have the same bug. start hugs with -98 option and try the following program: class Monad m => ExMonad where raise :: String-> m a instead of reporting an error, an internal error is raised: INTERNAL ERROR: inheritFundeps - predicate failed to match it's own head! Regards. Deling