scope onUserUtterance_addHandler.

static TailFile #tailFile;
static L<VF1<S>> #handlers = synchroList();

// f : voidfunc(S) - gets only the utterance
static void onUserUtterance_addHandler(VF1<S> handler) {
  lock #lock;
  handlers.add(handler);
  if (tailFile == null) tailFile = onUserUtterance(vf1_distribute(handlers));
}

end scope