Erlang programming ex4_2

ex4_2.erl

-module(ex4_2).
-export([start/3, stop/0, server/1]).

start(M, N, Message) ->
    register(first, spawn(?MODULE, server, [N-1])),
    send(M, N, Message).

stop() ->
    first ! stop,
    ok.

send(0, _, _) -> ok;
send(M, N, Message) ->
    first ! {N, Message},
    send(M-1, N, Message).

%%% server process
server(N) ->
    if
        N > 0 ->
            Next = spawn(?MODULE, server, [N-1]);
    true ->
        Next = first
    end,
    run(Next).

run(Pid) ->
    receive
        {0, _} ->
            run(Pid);
        {N, Message} ->
            io:format("~p~n", [Message]),
            Pid ! {N-1, Message},
            run(Pid);
        stop ->
            case Pid of
                first -> ok;
                _ -> Pid ! stop
            end,
            ok
    end.