public Value append(List l2) {
Value[] elements = new Value[size() + l2.size()];
for (int i = 0; i < size(); i++) elements[i] = elementAt(i);
for (int i = 0; i < l2.size(); i++) elements[i + size()] = l2.elementAt(i);
return new List(elements);
}
public static List cons(Value head, List tail) {
Value[] values = new Value[tail.size() + 1];
values[0] = head;
for (int i = 0; i < tail.size(); i++) values[i + 1] = tail.elementAt(i);
return new List(values);
}