type Debug m a = ErrorT (OutputT String m) a

debug  :: Monad m => String -> Debug m ()
debug s = lift $ output s

assert :: Monad m => Bool -> Debug m ()
assert True = return ()
assert False = wrong

runDebug :: Monad m => Debug m a -> m (Maybe a,[String])
runDebug dp = runOutputT $ runErrorT dp

fjas :: Debug IO ()
fjas = do debug "hej"
          q <- lift $ lift getLine
          debug q
	  assert (1<0)