function multi_implode($glue, $array) {
    $ret = '';
    
    foreach ($array as $item) {
        if (is_array($item)) {
            $ret .= multi_implode($glue, $item) . $glue;
        } else {
            $ret .= $item . $glue;
        }
    }
    
    $ret = substr($ret, 0, 0-strlen($glue));
    
    return $ret;
}

// 使用示例
$multi_array = [
    'a',
    ['b', 'c'],
    'd' => ['e', 'f' => ['g', 'h']]
];
echo multi_implode(',', $multi_array); // 输出: a,b,c,e,g,h

function flatten_implode($glue, $array) {
    $result = [];
    array_walk_recursive($array, function($value) use (&$result) {
        $result[] = $value;
    });
    return implode($glue, $result);
}

// 使用示例
$multi_array = [
    'a',
    ['b', 'c'],
    'd' => ['e', 'f' => ['g', 'h']]
];
echo flatten_implode(',', $multi_array); // 输出: a,b,c,e,g,h