static int indexOfMatches(S pat, L<S> l, Matches m default null) {
  ret indexOfMatches(pat, l, 0, m);
}

static int indexOfMatches(S pat, L<S> l, int i, Matches m default null) {
  for (int n = l(l); i < n; i++)
    if (match(pat, l.get(i), m))
      ret i;
  ret -1;
}