oop.erl

foo() ->
    Object = spawn(?MODULE, bar, [42]),

    Object ! {add, 42},
    Object ! {get, self()},
    receive
        Num -> io:printf("~s~n", [Num]) % prints 84
    end.

bar(Num) ->
    receive
        {add, X} -> bar(Num + X);
        {sub, X} -> bar(Num - X);
        {mul, X} -> bar(Num * X);
        {get, Pid} -> Pid ! Num, bar(Num)
    end.