<?php

use React\Async\Util as Async;

$loop = React\EventLoop\Factory::create();

Async::parallel(
    array(
        function ($callback, $errback) use ($loop) {
            $loop->addTimer(1, function () use ($callback) {
                $callback('Slept for a whole second');
            });
        },
        function ($callback, $errback) use ($loop) {
            $loop->addTimer(1, function () use ($callback) {
                $callback('Slept for another whole second');
            });
        },
        function ($callback, $errback) use ($loop) {
            $loop->addTimer(1, function () use ($callback) {
                $callback('Slept for yet another whole second');
            });
        },
    ),
    function (array $results) {
        foreach ($results as $result) {
            var_dump($result);
        }
    },
    function (\Exception $e) {
        throw $e;
    }
);

$loop->run();

<?php

use React\Async\Util as Async;

$loop = React\EventLoop\Factory::create();

$addOne = function ($prev, $callback = null) use ($loop) {
    if (!$callback) {
        $callback = $prev;
        $prev = 0;
    }

    $loop->addTimer(1, function () use ($prev, $callback) {
        $callback($prev + 1);
    });
};

Async::waterfall(array(
    $addOne,
    $addOne,
    $addOne,
    function ($prev, $callback) use ($loop) {
        echo "Final result is $prev\n";
        $callback();
    },
));

$loop->run();