static S[] match2x(L<S> pat, L<S> tok) {
  new ArrayList<S> result;
  if (pat.size() != tok.size()) null;
  for (int i = 1; i < pat.size(); i += 2) {
    S p = pat.get(i), t = tok.get(i);
    bool match;
    if (eq(p, "*")) match = true;
    else if (eq(p, "<quoted>")) match = isQuoted(t);
    else if (eq(p, "<id>")) match = isIdentifier(t);
    else if (eq(p, "<int>")) match = isInteger(t);
    else { if (!eq(p, t)) null; continue; }
    if (!match) null;
    result.add(t);
  }
  return result.toArray(new S[result.size()]);
}