Solr Sample

$closure = function (array $records, $callback) USE (&$set) {
    foreach ($records AS $key => $value)
    {
        $set[$key] = New SolrInputDocument();
        if (is_array($value)) {
            $set[$key]->addDocument($value, $callback);
        } else {
            $callback($value, $key);
        }
};