sS replaceDollarVarsWithAngleBracketed(S s) {
  LS tok = javaTok(s);
  for (int i = 1; i < l(tok); i += 2) {
    S t = tok.get(i);
    if (isDollarVar(t))
      tok.set(i, angleBracketed(dropDollarPrefix(t)));
  }
  ret join(tok);
}