The Haskell 98 Report says that fail in instance Monad IO invokes error. The Library Report says that fail in instance Monad IO raises a user error. I would let it raise a user error, to be able to use fail in exception monads where strings suffice as the error type. -- __("< Marcin Kowalczyk * qrczak@knm.org.pl http://qrczak.ids.net.pl/ \__/ ^^ SYGNATURA ZASTÊPCZA QRCZAK