gistfile1.php

<?php

namespace Acme\DemoBundle\Controller;

use Symfony\Bundle\FrameworkBundle\Controller\Controller;
use Symfony\Component\HttpFoundation\RedirectResponse;
use Acme\DemoBundle\Form\ContactType;

// these import the "@Route" and "@Template" annotations
use Sensio\Bundle\FrameworkExtraBundle\Configuration\Route;
use Sensio\Bundle\FrameworkExtraBundle\Configuration\Template;

class DemoController extends Controller
{
    /**
     * @Route("/", name="_demo")
     * @Template()
     */
    public function indexAction()
    {
        return array();
    }

    /**
     * @Route("/hello/{name}", name="_demo_hello")
     * @Template()
     */
    public function helloAction($name)
    {
        $x = '';
        $obj = new \stdClass;
        $obj->x = '';

        $first = function() use ($obj) {

            $obj->x .= ' 1 ';

            yield ControlFlow::NEXT;

            $obj->x .= ' 2 ';
        };

        $second = function() use ($obj){

            $obj->x .= ' 3 ';

            yield ControlFlow::NEXT;

            $obj->x .= ' 4 ';
        };

        $third = function() use ($obj){

            $obj->x .= ' 5 ';

            return ControlFlow::NEXT;
        };

        $fourth = function() use ($obj){

            $obj->x .= ' 6 ';

            return ControlFlow::NEXT;
        };

        $flow = new ControlFlow;
        $flow->queue($first())
             ->queue($second())
             ->queue($third)
             ->queue($fourth);

        $flow->run();

        return array('name' => $name, 'x' => $obj->x);
    }

    /**
     * @Route("/contact", name="_demo_contact")
     * @Template()
     *
    public function contactAction()
    {
        $form = $this->get('form.factory')->create(new ContactType());

        $request = $this->get('request');
        if ($request->isMethod('POST')) {
            $form->submit($request);
            if ($form->isValid()) {
                $mailer = $this->get('mailer');
                // .. setup a message and send it
                // http://symfony.com/doc/current/cookbook/email.html

                $this->get('session')->getFlashBag()->set('notice', 'Message sent!');

                return new RedirectResponse($this->generateUrl('_demo'));
            }
        }

        return array('form' => $form->createView());
    }
    */
}

class ControlFlow
{
    const NEXT = 'NEXT';

    /**
     * @var array
     */
    protected $queued = [];

    /**
     * @var array
     */
    protected $initiated = [];

    /**
     * Add to the ControlFlow
     *
     * @param \Closure|\Generator $item
     * @return $this
     * @throws \InvalidArgumentException
     */
    public function queue($item)
    {
        if ( ! $item instanceof \Closure && ! $item instanceof \Generator) {
            throw new \InvalidArgumentException('Queued item must be a \Closure or \Generator');
        }

        $this->queued[] = $item;
        return $this;
    }

    /**
     * Run all queued
     *
     * @return void
     */
    public function run()
    {
        foreach ($this->queued as $queued) {
            $this->runQueued($queued);
        }

        $this->flush();
    }

    /**
     * Run a queued \Closure or \Generator
     *
     * @param \Closure|\Generator $queued
     * @return void
     */
    private function runQueued($queued)
    {
        if (in_array($queued, $this->initiated, true)) return;

        $this->initiated[] = $queued;

        if ($queued instanceof \Generator) {
            $this->runGenerator($queued);
        } elseif ($queued instanceof \Closure) {
            $this->runClosure($queued);
        }
    }

    /**
     * Run a queued closure
     *
     * @param \Closure $closure
     * @return void
     */
    private function runClosure(\Closure $closure)
    {
        if ($closure() === self::NEXT) {
            $this->initiateNext();
        }
    }

    /**
     * Run a queued Generator
     *
     * @param \Generator $generator
     * @return void
     */
    private function runGenerator(\Generator $generator)
    {
        foreach ($generator as $result) {

            if ($result === self::NEXT) {
                $this->initiateNext();
            }
        }
    }

    /**
     * Initiate the next queued
     *
     * @return void
     */
    private function initiateNext()
    {
        $next = current($this->queued);
        next($this->queued);
        $this->runQueued($next);
    }

    /**
     * Empty the ControlFlow
     *
     * @return void
     */
    public function flush()
    {
        $this->queued = [];
        $this->initiated = [];
    }
}