Php rajout fonction comment puis-je

<?php
function listDirs($Current_Path = '.', $extension = 'pdf') {
	$dirs_in_dir = array();
	$files_in_dir = array();
	if ($handle = opendir($Current_Path)) {
		while (false !== ($file = readdir($handle))) {
			if ($file != "." && $file != "..") {
				$path = $Current_Path.'/'.$file;
				if (is_dir($path)) {
					$dirs_in_dir[]=$path;
				} else {
					$files_in_dir[]=$file;
				}
			}
		}
	}
	closedir($handle);
	$nb_files = count($files_in_dir) > 0;
	$nb_dirs  = count($dirs_in_dir) > 0;
	if($nb_files || $nb_dirs) {
		echo '<ul>'."\n";
		// Si des fichiers existent...
		if($nb_files) {
			foreach ($files_in_dir as $file) {
				$pathinfo = pathinfo($file);
				if ($pathinfo['extension'] == $extension) {
					$href = $Current_Path.'/'.$file;
					echo '<li><a href="'.$href.'">'.$file.'</a></li>'."\n";
				} else {
					echo '<li>'.$file.'</li>'."\n";
				}
			}
		}
		// Si des dossiers existent...
		if($nb_dirs) {
			// Tri inverse
			rsort($dirs_in_dir);
			foreach ($dirs_in_dir as $dir) {
				echo '<li><h2 class="title">'.substr(strrchr($dir, "/"), 1).'</h2>';
				listDirs($dir);
				echo '</li>'."\n";
			}
		}
		echo '</ul>'."\n";
	}
}

listDirs(); 
?>