thenC :: FCode () -> FCode a -> FCode a
thenC (FCode m) (FCode k) =
        FCode $ \info_down state -> case m info_down state of
                                     (# _,new_state #) -> k info_down new_state
thenC :: FCode () -> FCode a -> FCode a
thenC (FCode m) (FCode k) =
        FCode $ \info_down state -> case m info_down state of
                                     (# _,new_state #) -> k info_down new_state
thenC (FCode m) (FCode k) =
        FCode $ \info_down state -> case m info_down state of
                                     (# _,new_state #) -> k info_down new_state