My solution to the Erlang Process Ring Exercise 4-2 in Programming Erlang

ring.erl

-module(ring).
-export([start/3, loop/0]).

%%%
%%% An implementation of an Erlang process ring. This is probably the
%%% Erlang equivalent of breaking your first board in Karate class.
%%%

start(NumMsgs, NumProcs, Msg) ->
    UnlinkedRing = create_process([], NumProcs),
    LinkedRing = lists:append(UnlinkedRing, [hd(UnlinkedRing)]),
    send_message({Msg, NumMsgs}, LinkedRing).

create_process(Pids, 0) ->
    Pids;
create_process(Pids, Count) ->
    create_process([spawn(?MODULE, loop, [])|Pids], Count-1).

send_message({_, 0}, [Next|Pids]) ->
    Next ! {stop, Pids};
send_message({Msg, NumMsgs}, [Next|Pids]) ->
    Next ! {Msg, NumMsgs, Pids},
    send_message({Msg, NumMsgs-1}, [Next|Pids]).

loop() ->
    receive
        {stop, [Next|Pids]} ->
            io:format("~p -~p-> ~p~n", [self(), stop, Next]),
            Next ! {stop, Pids};
        {Msg, NumMsgs, [Next|Pids]} ->
            io:format("~p -~p-> ~p~n", [self(), NumMsgs, Next]),
            Next ! {Msg, NumMsgs, Pids},
            loop()
    end.