Simplificando e juntando a recursividade com closures.

clojure.php

<?php

//mdc (PHP 5.3)
$mdc = function($x,$y) use (&$mdc){
		$a = max($x,$y);
		$b = min($x,$y);
		return ($a%$b == 0) ? ($b) : ($mdc($b,($a%$b)));
};

//mmc (PHP 5.3)	
$mmc = function($x,$y) use(&$mdc){
		return (($x*$y)/($mdc($x,$y)));
};

echo $mdc(48,30); //6
echo $mmc(4,6);	//12