Exercise 1 of Chapter 12, Programming Erlang 2nd Edition

gistfile1.erl

start(AnAtom, Fun) when is_atom(AnAtom), is_function(Fun, 0) ->
  Sender = self(),
  Run = fun() ->
    case catch register(AnAtom, self()) of
      true ->
        Sender ! {started, self()},
        Fun();
      _ ->
        Sender ! {already_running, self()}
      end
    end,
  Pid = spawn(Run),
  receive
    {started, Pid} ->
      {ok, Pid};
    {already_running, Pid} ->
      already_running
  end.