$seq = new class implements \ArrayAccess, \IteratorAggregate {
    public function offsetExists($offset): bool { return true; }
    public function offsetGet($offset): mixed { return 'val'; }
    public function offsetSet($offset, $value): void {}
    public function offsetUnset($offset): void {}
    public function getIterator(): \Traversable { yield 'odd'; yield 'even'; }
};

// Should return 'odd', currently returns the $seq object
$result = CoreExtension::cycle($seq, 0);