static Object clone(Object o) {

  return clone(o, new IdentityHashMap);

}

static Object clone(Object o, IdentityHashMap seen) ctex {

  if (o == null)

    return o;

  Object y = seen.get(o);

  if (y != null) return y;

  if (o instanceof List) {

    print("Cloning list: " + o);

    List l = new ArrayList();

    seen.put(o, l);

    for (Object x : (List) o)

      l.add(clone(x, seen));

    return l;

  }

  if (o instanceof Map) {

    Map m = o instanceof TreeMap ? new TreeMap() : new HashMap();

    seen.put(o, m);

    for (O entry : ((Map) o).entrySet()) {

      Map.Entry e = (Map.Entry) entry;

      m.put(clone(e.getKey(), seen), clone(e.getValue(), seen));

    }

    return m;

  }

  if (o instanceof String || o instanceof Number || o instanceof Boolean)

    return o;

  if (o instanceof Object[]) {

    Object[] l = (Object[]) o;

    Object[] l2 = l.clone();

    seen.put(o, l2);

    for (int i = 0; i < l.length; i++)

      l2[i] = clone(l[i], seen);

    return l2;

  }

  // clone an arbitrary custom object

  // TODO: use Constructor object and setAccessible

  print("Cloning custom: " + o);

  Object clone = o.getClass().newInstance();

  seen.put(o, clone);

  Class c = o.getClass();

  while (c != Object.class) {

    Field[] fields = c.getDeclaredFields();

    for (Field field : fields) {

      if ((field.getModifiers() & Modifier.STATIC) != 0)

        continue;

      Object value;

      field.setAccessible(true);

      value = field.get(o);

      field.set(clone, clone(value, seen));

    }

    c = c.getSuperclass();

  }

  return clone;

}