static FunctionCall parseFragmentExpressionToFunctionCall(O o) {
  if (!o instanceof L) null;
  L l = cast o;
  O first = first(l);
  if (!first instanceof Fragment) null;
  S first2 = first/Fragment.text;
  if (!isIdentifierPlusOpeningBracket(first2)) null;
  if (!eq(last(l), Fragment(")"))) null;
  int i = 1, n = l(l)-1;
  S fname = dropLast(first2);
  new L args;
  while (i < n) {
    args.add(get(l, i++));
    if (i >= n) break;
    if (!eq(get(l, i++), Fragment(","))) null;
  }
  ret FunctionCall(fname, toObjectArray(args));
}