Y-Combinator in PHP

y-factorial.php

<?php
// Source: https://php100.wordpress.com/2009/04/13/php-y-combinator/
function Y($F)
{
    $func = function ($f) {
        return $f($f);
    };

    return $func(
        function ($f) use ($F) {
            return $F(
                function ($x) use ($f) {
                    $ff = $f($f);

                    return $ff($x);
                }
            );
        }
    );
}

$factorial = Y(
    function ($fact) {
        return function ($n) use ($fact) {
            return ($n <= 1)
                ? 1
                : $n * $fact($n - 1);
        };
    }
);

var_dump($factorial(6));