3v4l.org

run code in 300+ PHP versions simultaneously
<?php $arr = array('a', 'b', 'c', 'd', 'e', 'f'); $str = implode(array_walk(array_reverse($arr), function($v,&$k){if($k%3==0)$v.=';';})); echo $str;

preferences:
55.61 ms | 402 KiB | 5 Q