static L<TokenAndRange> addRangesToTokenization(S text, LS tokens) {
  if (tokens == null) null;
  L<TokenAndRange> out = emptyList(tokens);
  int i = 0;
  for (S tok : tokens) {
    int j = i+l(tok);
    out.add(TokenAndRange(tok, intRange(i, j), text));
    i = j;
  }
  ret out;
}

static L<TokenAndRange> addRangesToTokenization(LS tokens) {
  ret addRangesToTokenization(join(tokens), tokens);
}