anchor.diff:  %% @end
   %%--------------------------------------------------------------------
   handle_call({add, TaskName, Schedule, Detail}, _From, State) ->
  -    Task = {TaskName, Schedule, Detail},
       %% TODO: receive a message from task worker
  -    NewTasks = [Task|State#state.tasks],
  -    io:format("adds a task: ~p", [Task]),
  +    NewTasks = dict:append(TaskName, {Schedule, Detail}, State#state.tasks),
  +    io:format("adds a task: {~p, ~p, ~p}", [TaskName, Schedule, Detail]),
       {reply, ok, State#state{ tasks = NewTasks }};
   handle_call({cancel, _Task}, _From, State) ->
       Reply = ok,
       {reply, Reply, State};
   handle_call({show, all}, _From, State) ->
  -    Reply = ok,
  -    {reply, Reply, State};
  -handle_call({show, _Task}, _From, State) ->
  -    Reply = ok,
  -    {reply, Reply, State};
  +    {reply, dict:to_list(State#state.tasks), State};
  +handle_call({show, TaskName}, _From, State) ->
  +    Task = dict:find(TaskName, State#state.tasks),
  +    %% TODO: formats output.
  +    {reply, {TaskName, Task}, State};
   handle_call({members}, _From, State) ->
       Reply = ok,
       {reply, Reply, State};
  
positive.code: %%% @spec add_task(task_name()) -> term()
  %%% @end
  -spec add_task(task_name(), schedule(), detail()) -> term().
  add_task(Task, Schedule, Detail) -> gen_server:call(?SERVER, {add, Task, Schedule, Detail}).
  
  %%% @doc
  %%% Cancels the task
  
negative.code: %%% @spec show_schedule(task_name()) -> term().
  %%% @end
  -spec show_schedule(binary()) -> term().
  show_schedule(Task) -> 
      gen_server:call(?SERVER, {show, Task}).
  
  %%% @doc
  %%% Shows schedules of all tasks.
  