chat_client.erl

-module(chat_client).
-compile(export_all).

register_nickname(Nickname) ->
  message_router:register_nick(Nickname, fun(Msg) -> chat_client:print_message(Nickname, Msg) end).

unregister_nickname(Nickname) ->
  message_router:unregister_nick(Nickname).

send_message(Addressee, MessageBody) ->
  message_router:send_chat_message(Addressee, MessageBody).

print_message(Who, MessageBody) ->
  io:format("~p received: ~p~n", [Who, MessageBody]).

start_router() ->
  message_router:start().

message_router.erl

-module(message_router).

-define(SERVER, message_router).

-compile(export_all).

start() ->
  Pid = spawn(message_router, route_messages, [dict:new()]),
  erlang:register(?SERVER, Pid).

stop() ->
  ?SERVER ! shutdown.

send_chat_message(Addressee, MessageBody) ->
  ?SERVER ! {send_chat_msg, Addressee, MessageBody}.

register_nick(ClientName, PrintFun) ->
  ?SERVER ! {register_nick, ClientName, PrintFun}.

unregister_nick(ClientName) ->
  ?SERVER ! {unregister_nick, ClientName}.

route_messages(Clients) ->
  receive
    {send_chat_msg, ClientName, MessageBody} ->
      ?SERVER ! {recv_chat_msg, ClientName, MessageBody},
      route_messages(Clients);
    {recv_chat_msg, ClientName, MessageBody} ->
      case dict:find(ClientName, Clients) of
        {ok, PrintFun} ->
          PrintFun(MessageBody);
        error ->
          io:format("Unknown client~n")
      end,
      route_messages(Clients);
    {register_nick, ClientName, PrintFun} ->
      route_messages(dict:store(ClientName, PrintFun, Clients));
    {unregister_nick, ClientName} ->
      route_messages(dict:erase(ClientName, Clients));
    shutdown ->
      io:format("Shutting down~n");
    Oops ->
      io:format("Warning! Received: ~p~n", [Oops]),
      route_messages(Clients)
  end.

https://gist.github.com/1427880#file_test.erlsh If you're curious what i was using for testing the the shell.

Thanks.

I just posted my v3 code, as well, and merged it (biasing towards your whitespace for as long as I could).