static synchronized S manageStringList(S s, S name, S varName, boolean canChange) {
  L<S> list = (L) get(main.class, varName);
  new Matches m;
  
  if (match("list " + plural(name), s))
    ret structure(list);
    
  if (match("how many " + plural(name), s))
    ret str(l(list));
    
  if (match("add " + name + " *", s, m)) {
    if (!canChange) ret "Sorry. Not authorized";
    S id = m.unq(0);
    list.add(id);
    save(varName);
    ret "OK, " + name + " " + quote(id) + " added. List size now: " + l(list);
  }
  
  if (match("remove " + name + " *", s, m)) {
    if (!canChange) ret "Sorry. Not authorized";
    S id = m.unq(0);
    int idx = list.indexOf(id);
    if (idx < 0) ret id + " is not a " + name;
    list.remove(idx);
    save(varName);
    ret "OK, " + name + " " + quote(id) + " removed. List size now: " + l(list);
  }
  
  ret null;
}