gistfile1.php

<?php
$this->packages->to_xml(array('lamda' => function($key, $value){
				           switch($key) {
				             case 'user_id':
				               return array("username", User::find($value)->username);
				             break;
				             default:
				               return array($key, $value);
				             break;
				           }
				         }, 'append' => array('channel' => function($obj) {
                                                                             return $obj->user->pear_farm_url();
				                                           })));