3v4l.org

run code in 200+ php & hhvm versions
Bugs & Features
<?php function ack($m, $n) { if (!$m) return ++$n; elseif (!$n) return ack($m-1, 1); return ack($m-1, ack($m, $n-1)); } echo ack(2, 5);
Output for 4.3.0 - 7.2.0
13