anchor.diff:  
   get_subscriptions(_Module, _State) ->
       ok.
  -
  -always(_) -> true.
  
positive.code:     % this is an auxiliary connection.
      % XXX spawn connection handler
      {reply, {ok, self()}, State1};
  handle_call({message, _Connection, _Message}, _From, State) ->
      % switch sent us a message
      % XXX lookup message type in ets
      % XXX process message
      {reply, ok, State};
  handle_call({error, _Connection, _Reason}, _From, State) ->
      % error on the connection
      {reply, ok, State};
  
negative.code:     ok.
  
  subscribe(Module, in_packet, State) ->
      subscribe(Module, {in_packet, true}, State);
  subscribe(_Module, {in_packet, _FilterFn}, _State) ->
      % XXX store subscription in ets?
      ok;
  