liftPass :: (Monad m) => Pass w m (Maybe a) -> Pass w (MaybeT m) a
liftPass pass = mapMaybeT $ \ m -> pass $ do
    a <- m
    return $! case a of
        Nothing     -> (Nothing, id)
        Just (v, f) -> (Just v, f)
liftPass :: (Monad m) => Pass w m (Maybe a) -> Pass w (MaybeT m) a
liftPass pass = mapMaybeT $ \ m -> pass $ do
    a <- m
    return $! case a of
        Nothing     -> (Nothing, id)
        Just (v, f) -> (Just v, f)
liftPass pass = mapMaybeT $ \ m -> pass $ do
    a <- m
    return $! case a of
        Nothing     -> (Nothing, id)
        Just (v, f) -> (Just v, f)