record List(value:Int, next:UniqueValue[List]);

callbyname overload List(value:Int) = List(value, nullUniqueValue(List));
callbyname overload List(value:Int, next:List) = List(value, UniqueValue(next));

main() {
    var x = List(1, List(2, List(3)));
    x = move(x.next^.next^);
}