Rx\Observable\IteratorObservable::subscribe PHP Method

    public function subscribe(ObserverInterface $observer, SchedulerInterface $scheduler = null)
    {
        $scheduler = $scheduler ?: new ImmediateScheduler();
        $key = 0;
        $defaultFn = function ($reschedule) use(&$observer, &$key) {
            try {
                if (null === $key) {
                    $observer->onCompleted();
                    return;
                }
                $current = $this->items->current();
                $observer->onNext($current);
                $this->items->next();
                $key = $this->items->key();
                $reschedule();
            } catch (\Exception $e) {
                $observer->onError($e);
            }
        };
        $hhvmFn = function ($reschedule) use(&$observer, &$key) {
            try {
                //HHVM requires you to call next() before current()
                $this->items->next();
                $key = $this->items->key();
                if (null === $key) {
                    $observer->onCompleted();
                    return;
                }
                $current = $this->items->current();
                $observer->onNext($current);
                $reschedule();
            } catch (\Exception $e) {
                $observer->onError($e);
            }
        };
        return $scheduler->scheduleRecursive(defined('HHVM_VERSION') && version_compare(HHVM_VERSION, '3.11.0', 'lt') ? $hhvmFn : $defaultFn);
    }