PHP实现无级递归分门别类（ThinkPHP框架）

/***   无级递归分类*   @param   int     $assortPid   要查询分类的父级id*   @param   mixed   $tag         上下级分类之间的分隔符*   @return  string  $tree        返回的分类树型结构结果 **/function recursiveAssort($assortPid, $tag = ''){       $assort = M('goods_class')->where("class_pid = $assortPid")->field('class_id, class_name')->select();    foreach ($assort as $value) {        $tree .= '$value['class_id'] . '">' . $tag . $value['class_name'] . '';        $tree .= recursiveAssort($value['class_id'], $tag . ' ');    }    return $tree;}