@function ballistic-factorial($number) {
  @if not ballistic-is-int($number) or $number < 0 {
    @return ballistic-warn("Argument for `factorial()` must be a positive integer. Returning `null`.");
  }

  $index:  1;
  $result: 1;

  @while $index <= $number {
    $result: $result * $index;
    $index: $index + 1;
  }

  @return $result;
}