// +var => "var", +var
static void tok_expandVarCopies(L<S> tok) {
  for (int i = 3; i+2 < l(tok); i += 2) {
    if (!eq(tok.get(i), "+")) continue;
    if (!eqOneOf(tok.get(i-2), "(", ",", "{")) continue;
    S s = tok.get(i+2);
    if (!isIdentifier(s)) continue;
    tok.set(i, quote(s) + ", ");
    reTok(tok, i, i+1);
  }
}