gistfile1.php

<?php

// Regular recursion
function factorial ($n)
{
    if ($n == 1 ) {
        return 1;
    }
    return $n * factorial($n-1);
}

// Tail recursion
function tail_factorial($n)
{
    function loop($acc, $n)
    {
        if ($n == 0) {
            return $acc;
        } else {
            return loop($acc * $n, $n - 1);
        }
    }
    return loop(1, $n);
}



echo factorial(100), "\n";
echo tail_factorial(100), "\n";