Finding the factorial of a number, recursively

factorialFactorial.php

<?php
declare(strict_types = 1);

/**
 * factorialFactorial
 * Finding the factorial of a $number by recursion
 *
 * @author Er Galvão Abbott <galvao@php.net>
 */

function factorialFactorial(int $number, int $total = 0): int
{
    if ($number < 0) {
        throw new Exception('Negative Factorials are undefined.');
    }
   
    if ($number === 0) {
        $total = 1;
    }
   
    if ($total === 0) {
        $total = $number;
    }
   
    if ($number > 1) {
        $total *= --$number;
        $total = factorialfactorial($number, $total);
    }
   
    return $total;
}

// Example

try {
    echo factorialfactorial(8) . PHP_EOL;
} catch (Exception $e) {
    echo $e->getMessage() . PHP_EOL;
    exit();
}