Factorial Haskell v PHP

factorial.hs

factorial :: Integer -> Integer
factorial 0 = 1
factorial n = n * factorial (n-1)

factorial.php

<?php

if (! is_numeric($argv[1])) {
  die('Expecting number to be passed');
}

function factorial($n, $factorial = 1)
{
    if ($n === 0) {
        return $factorial;
    }

    $factorial = $n * $factorial;

    return factorial(--$n, $factorial);
}

$factorialResult = factorial($argv[1]);
printf($factorialResult);