fac n = product [1..n]

##</code><code>##

fac n = if n<1 then 1 else n * (fac (n-1))

##</code><code>##

fac 0 = 1
fac n = n * fac (n-1)

##</code><code>##

fac n | n == 0 = 1
      | otherwise = n * (fac (n-1))

##</code><code>##

sub fac 
{
    $n = shift;
    if($n==0)
    {
        return 1;
    }
    else #otherwise
    {
        return $n*fac($n-1);
    }
}