n = if n > 1
                        then helper (acc * n) (n - 1)
                        else acc
cube x = x * square x
  where
    square = (^2)

-- le
factorial'' n' = helper 1 n'
   where helper acc n = if n > 1
                        then helper (acc * n) (n - 1)
                        else acc
factorial'' n' = helper 1 n'
   where helper acc n = if n > 1
                        then helper (acc * n) (n - 1)
                        else acc