static L<S> regexpGetGroups(Matcher matcher) {
  int n = matcher.groupCount();
  new L<S> l;
  for (int i = 1; i <= n; i++)
    l.add(matcher.group(i));
  ret l;
}

// performs find()
static L<S> regexpGetGroups(S pat, S s) {
  Matcher m = regexpMatcher(pat, s);
  if (m.find())
    ret regexpGetGroups(m);
  null;
}