sS charRange(char first, char last) {
  new StringBuilder buf;
  while (first <= last) buf.append(first++);
  ret str(buf);
}

sS charRange(int first, int last) {
  ret charRange((char) first, (char) last);
}

static L<Char> charRange() {
  ret lazyMap_noSave(i -> (char) i, countIterator(0x10000));
}