simple_gen_server.erl

-module(gs1).
-export([start/0, loop/1]).

% simple gen server with state

start() ->
    % io:format("Start ~p~n", [self()]),
    % spawn(fun loop/0).
    InitialState = [],
    spawn(?MODULE, loop, [InitialState]).

loop(State) ->
    % io:format("~p enters loop ~n", [self()]),
    % receive
    %     stop -> io:format("~p stops now ~n", [self()]);
    %     Msg -> io:format("~p receive ~p~n", [self(), Msg]),
    %         loop()
    % end.
    receive
        {add, Item} -> io:format("~p adds ~p its state~n", [self(), Item]),
            NewState = [Item | State],
            loop(NewState);
        {remove, Item} -> NewState = case lists:member(Item, State) of
                true -> lists:delete(Item, State);
                false -> io:format("I have no ~p~n)", [Item]),
                    State
            end
            loop(NewState);
        show_items -> io:format("my items is ~p~n", [State]),
            loop(State);
        stop -> io:format("~p stops now ~n", [self()]);
        _Any -> loop(State)
    end.


-module(gs3).
-export([start/0, loop/1]).

% simple gen server with hot code reload
start() ->
    InitialState = [],
    spawn(?MODULE, loop, [InitialState]).

loop(State) ->
    receive
        {add, Item} -> io:format("~p adds ~p to its state ~n", [self(), Item]),
            NewState = [Item|State],
            ?MODULE:loop(NewState);
        {remove, Item} -> NewState = case lists:member(Item, State) of
                true -> lists:delete(Item, State);
                false -> io:format("I have no ~p~n)", [Item]),
                    State
            end
            ?MODULE:loop(NewState);
        show_items -> op:format("My items is ~p ~n", [State]),
            ?MODULE:loop(State);
        stop -> io:format("~p stops now ~n", [self()]);
        _Any -> ?MODULE:loop(State)
    end.