Laravel 5.1 Singleton Always New Instance

Facing issues with Laravel's IoC and Singleton.

I have the following singleton class:

class ConcreteClass
{
    function __construct() {Log::info('I iz created...');}
}

And the following service provider:

class ConcreteClassServiceProvider extends ServiceProvider
{
    public function register()
    {
        $this->app->singleton('ConcreteClass', function () {
            return new ConcreteClass();
        });
    }
}

However with every App::make('ConcreteClass'), public function __construct(ConcreteClass $concrete) in a single request will cause the log to have a I iz created... which makes it highly doubtful the singleton thing works in Laravel. I am most probably wrong with the configuration. Please help me with it. Thank you.

via Chebli Mohamed