static L<ParsedWithTokens<S>> pwt_fromTokenization(LS tok) {
  int iChar = 0;
  new L<ParsedWithTokens<S>> out;
  for i over tok: {
    S t = tok.get(i);
    int iNext = iChar+l(t);
    out.add(ParsedWithTokens(t, iChar, iNext));
    iChar = iNext;
  }
  ret out;
}