private function reversedBackwards()
{
$s = PersistentStack::createEmpty();
foreach ($this->backwards as $value) {
$s = $s->push($value);
}
return $s;
}
public function getIterator()
{
$stack = PersistentStack::createEmpty();
for ($current = $this; !$current->isEmpty() || !$stack->isEmpty(); $current = $current->right()) {
while (!$current->isEmpty()) {
$stack = $stack->push($current);
$current = $current->left();
}
$current = $stack->peek();
$stack = $stack->pop();
(yield $current->key() => $current->value());
}
}
public function enqueue($value)
{
return new PersistentQueue(PersistentStack::createEmpty()->push($value), PersistentStack::createEmpty(), 1);
}