// returns index of opening <
static int tok_leftScanTypeArgsOpt(LS tok, int i) {
  if (!eqGet(tok, i-2, ">")) ret i;
  int level = 0;
  while (i > 1) {
    S t = tok.get(i-2);
    if (eq(t, ">")) level++;
    else if (eq(t, "<")) {
      level--;
      if (level == 0) ret i-2;
    }
    i -= 2;
  }
  ret i;
}