sS substringFromCharArray(char[] s, int x) {
  ret substringFromCharArray(s, x, l(s));
}

sS substringFromCharArray(char[] s, int x, int y) {
  if (s == null) null;
  if (x < 0) x = 0;
  if (x >= s.length) ret "";
  if (y < x) y = x;
  if (y > s.length) y = s.length;
  ret new S(s, x, y-x);
}