fp.fact = ($n) -> {
	if($n < 0) {
		throw fn.withErrorMessage($LANG_ERROR_INVALID_ARGUMENTS, n must be >= 0)
	}
	
	$ret = 1L
	
	$i = 2
	while($i <= $n) {
		$ret *= $i
		
		$i += 1
	}
	
	return $ret
}