anchor.diff:      code_change/3
   ]).
   
  --record(state,{eager,normal,defer}).
  +-record(state,{eager,normal,defer,caller}).
   -record(wf_action_queue,{
       pid     :: pid()
   }).
  
positive.code: 
  -spec start_link() -> {ok, action_queue()}.       
  start_link() ->
      {ok,Pid} = gen_server:start_link(?MODULE,self(),[]),
      {ok,#wf_action_queue{pid=Pid}}.
  
  -spec stop(action_queue()) -> ok.
  
negative.code:         defer=NewDefer
      },
      {reply, Reply, NewState};
  handle_call(clear, _Pid, State) ->
      {reply, ok, blank_state(State#state.caller)};
  handle_call(all, _Pid, State) ->
      AllActions = queue:to_list(State#state.eager) 
                   ++ queue:to_list(State#state.normal)
  