Process ring struggle

pr_ring.erl

-module(pr_ring).
-compile(export_all).


start(M, N, Message) ->
    io:format("Starting ~p processes and sending ~p ~p~n", [N,M,Message]),
    ProcessList = spawn_ring(M, N, []),
    io:format("Spawned ~p~n", [ProcessList]),
    hd(ProcessList) ! { Message, ProcessList }.

spawn_ring(_M, 0, ProcessList) ->
    ProcessList;

spawn_ring(M, N, ProcessList) ->
    Spawned = spawn(?MODULE, proc_loop, [M]),
    spawn_ring(M, N-1, [Spawned|ProcessList] ).

proc_loop(0) ->
    io:format("Done.~n"),
    ok;

proc_loop(M) ->
    io:format("Looping process (~p)~n", [M]),
    receive
        {Msg, [_|ProcessList]} ->
            io:format("~p Received message ~p (~p)~n", [self(), ProcessList, M]),
            io:format("Sending message from ~p to ~p~n", [self(),
                    hd(ProcessList)]),
            hd(ProcessList) ! {Msg, lists:append(ProcessList, [self()])},
            proc_loop(M-1)
    end.