protected function registerMarkdownPhpEngine($resolver)
    {
        $app = $this->app;

        $app->singleton('markdown.php.compiler', function ($app) {
            $cache = $app['config']['view.compiled'];

            return new MarkdownPhpCompiler($app['files'], $cache);
        });

        $resolver->register('markdown.php', function () use ($app) {
            return new MarkdownEngine($app['markdown.php.compiler'], $app['files']);
        });

        $app['view']->addExtension('md.php', 'markdown.php');
    }