sclass WithMakingOf<A> extends Var<A> {
  O makingOf;
  
  *() {}
  *(A value) { super(value); }
  *(A value, O *makingOf) { super(value); }
  
  toString {
    if (makingOf == null) ret super.toString();
    ret super.toString() + "\n" +
      indentx("[made with " + makingOf + "]");
  }
}