Online PHP editor | output for 4RRGV

<?php $radius = 2; $circumference = (fn($pi) => $pi * $radius ** 2)(pi()); var_export([ $pi ?? 'Not Declared', $radius, $circumference ]); echo "\n---\n"; $radius = 2; $circumference = (fn() => pi() * ++$radius ** 2)(); var_export([ $radius, // not 3 $circumference ]); echo "\n---\n"; $radius = 2; $circumference = (function() use (&$radius) { return pi() * ++$radius ** 2; })(); var_export([ $radius, // changed to 3 $circumference ]); echo "\n---\n"; $circumference = (fn($pi, $r, $pow) => $pi * $r ** $pow)(pi(), 2, 2); var_export($circumference);