class HelloMiddleware implements MiddlewareInterface
{

    public function __invoke(
        ServerRequestInterface $request,
        ResponseInterface $response,
        callable $next
    )
    {
        $response->getBody()->write('Hello ');

        return $next($request, $response);
    }
}

class WorldMiddleware implements MiddlewareInterface
{

    public function __invoke(
        ServerRequestInterface $request,
        ResponseInterface $response,
        callable $next
    )
    {
        $response = $next($request, $response);
        $response->getBody()->write('World!');
        return $response;
    }
}

class FuckingMiddleware implements MiddlewareInterface
{

    public function __invoke(
        ServerRequestInterface $request,
        ResponseInterface $response,
        callable $next
    )
    {
        $response->getBody()->write('fucking ');
        return $next($request, $response);
    }
}


$queue = new Queue();
$queue->append(new HelloMiddleware())
      ->append(new WorldMiddleware())
      ->append(new FuckingMiddleware());

Runtime::emit($queue); //(Output) "Hello fucking World!"