sS indentStructureString(S s) {
  if (s == null) null;
  LS tok = javaTok(s);
  new StringBuilder buf;
  int indent = 0;
  for i over tok: {
    S t = tok.get(i);
    if (eqOneOf(t, "(", "{", "["))
      buf.append(t).append("\n").append(spaces(indent += 2));
    else if (eqOneOf(t, ")", "}", "]"))
      buf.append("\n").append(spaces(indent -= 2)).append(t);
    else if (eq(t, ",")) {
      buf.append(t).append("\n").append(spaces(indent));
      i++;
    } else
      buf.append(t);
  }
  ret str(buf);
}