static SS matchDollarVarsIC_plusBrackets(S pat, S s) {
  if (pat == null || s == null) null;
  new L<S> vars;
  S pat2 = dollarVarsToStars(pat, vars);
  new Matches m;
  if (!match3_plusBrackets(pat2, s, m)) null;
  new SS map;
  for (int i = 0; i < l(m.m); i++) {
    S var = vars.get(i);
    S value = m.get(i);
    if (startsWith(var, "$_q_")) {
      if (!isQuoted(value)) null;
      var = "$" + substring(var, 4);
      value = unquote(value);
    }
    if (!strictPutIC(map, var, value)) null;
  }
  ret map;
}