/**
* Register a provider.
*
* @param string $root root
* @param Provider $provider provider
* @param closure|null configuration closure
*/
public function registerProvider($root, Provider $provider, $config = null)
{
$provider->setContainer($this);
$provider->setRoot($root);
if ($config) {
$config($provider);
}
$provider->provide($this);
$this->providers[$root] = $provider;
return $this;
}