anchor.diff:  
   shutdown(Server) ->
       gen_server:call(Server, shutdown).
  +
  +listen(Server, Port) ->
  +    gen_server:call(Server, {listen, Port}).
   
   %%====================================================================
   %% gen_server callbacks
  
positive.code: %% @doc Call message handler callbacks
  %% @end
  %%--------------------------------------------------------------------
  handle_call(Call, _From, State) ->
      ?WARN("Unexpected call ~p.", [Call]),
      {noreply, State}.
  
negative.code: %% API
  -export([start_link/2
           ,shutdown/1
           ,gproc_name/1
           ,listen/2]).
  
  %% gen_server callbacks
  -export([init/1, handle_call/3, handle_cast/2, handle_info/2,
           terminate/2, code_change/3]).
  
  -record(state, {net, name, users = [], channels = [], listener}).
  -record(user, {nick, pid, ref}).
  -record(chan, {name, pid, ref}).
  -define(SERVER, ?MODULE).
  