PHP Factorial without using a loop

factorial.php

<?php declare(strict_types=1);

/**
* Calculate factorial using recursive function call
*
* @see https://3v4l.org/oeZp9
*
* @param int $n
* 
* @throws InvalidArguemntException 
* @return int $factorial
*/
function factorial(int $n): int {
    if ($n < 0) {
        throw new InvalidArgumentException('The factorial function is defined for non-negative integers only.');
    }
    
    if ($n === 0 || $n === 1) {
        return 1;
    }
    
    return $n * factorial($n-1);
}