static Lisp nlList(L list) {
  Lisp tree = lisp("[]");
  for (O s : list) {
    if (!tree.isEmpty()) tree.add(",");
    if (s instanceof Lisp)
      tree.add((Lisp) s);
    else if (s instanceof S)
      tree.add(quote((S) s));
    else
      tree.add("?");
  }
  ret tree;
}