ช่วยหาวิธีการส่งออกมาเป็น return แทน echo ของ function นี้หน่อยครับ

function category_menu($parent = '0') {
	$CI =& get_instance();
	$has_childs = FALSE; //this prevents printing 'ul' if we don't have subcategories for this category
	$categories = $CI->Menu_model->category_menu();
	$output = "";
	//print_r($categories);
	$i = 0;
	foreach($categories as $key => $value) {
		if ($value['parent'] == $parent)  {
			//if this is the first child print '<ul>'
			if ($has_childs === false) {
				//don't print '<ul>' multiple times
				$has_childs = true;
				echo "<ul id=\"child".$i."\">\n";
			}
			echo "<li><a href=\"/category/" . $value['name'] . "\">" . $value['name'] . "</a>";
			category_menu($key);
			//call function again to generate nested list for subcategories belonging to this category
                        echo "</li>\n";
		}
		$i++;
	}// endforeach
	if ($has_childs === true) echo "</ul>\n";
	//writecategory($output);
}// category_menu

function category_menu() {
		$sql = "select * from " . $this->db->dbprefix('categories') . " c";
		$sql .= " inner join " .  $this->db->dbprefix("category_lang") . " cl";
		$sql .= " on c.category_id = cl.category_id";
		$query = $this->db->query($sql);
		if ( $query->num_rows() > 0 ) {
			foreach ( $query->result() as $row ) {
				$output[$row->category_id] = array(
				    'name' => $this->Category_model->show_category_lang_info("category_name", $row->category_id),
				    'parent' => $row->category_parent,
				    'uri' => $this->Category_model->show_category_lang_info("category_uri", $row->category_id));
				/*
				$output[$i]['name'] = $this->Category_model->show_category_lang_info("category_name", $row->category_id);
				$output[$i]['depth'] = $row->category_depth;
				$output[$i]['uri'] = $this->Category_model->show_category_lang_info("category_uri", $row->category_id);*/
			}
		} else {
			return NULL;
		}
		return $output;
	}// category_menu