Something

// load Smarty libraryrequire_once('Smarty.class.php');class Smarty_App extends Smarty {   function Smarty_App() {        $this->Smarty();        $this->template_dir = 'themes/' . $theme_dir . 'templates/';		$this->compile_dir  = 'templates_c/';		$this->config_dir   = 'configs/';		$this->cache_dir    = 'cache/';		$this->plugins_dir	= 'lib/smarty_plugins/';		        $this->assign('app_name', 'My App');		$theme_dir = (isset($theme_dir)) ? $theme_dir : 'default';		$this->assign('theme_dir', $theme_dir);   }}$smarty = new Smarty_App();