sclass WithComment<A> extends Var<A> {
  S comment;
  
  *() {}
  *(A value) { super(value); }
  *(S *comment, A value) { super(value); }
  
  toString {
    if (empty(comment)) ret super.toString();
    ret super.toString() + " [" + comment + "]";
  }
}

Began life as a copy of #1026688