编写代码以反转Haskell程序

我编写了一个程序,将消息作为字符串,并根据需要用X填充消息,以返回一个字谜,这样字符串长度正好有4个因子,然后基本上重新排列消息,就像它是在网格中组织的一样,并向下读取而不是交叉读取。例如,输入“Haskell”将返回字符串“HealslkX”。我已经编写了一个程序来编码这个字谜,但我在编写一个程序来反转之前的程序并解码字谜时遇到了麻烦,尤其是使用removeX函数时,它应该删除X填充。以下是我所拥有的:

import Data.List

factors :: Int -> [Int]
factors n = [x | x <- [1..n], n `mod` x == 0]

split :: Int -> [a] -> [[a]]
split _ [] = []
split n xs =
    let (ys, zs) = splitAt n xs
    in  ys : split n zs

encode :: [Char] -> [Char]
encode (x:xs) = if (length (factors (length xs))) == 4 then concat 
(transpose (split ((factors (length xs))!!2) xs))
else encode (xs ++ ['X'])

解码:

import Data.List

factors :: Int -> [Int]
factors n = [x | x <- [1..n], n `mod` x == 0]

split :: Int -> [a] -> [[a]]
split _ [] = []
split n xs =
    let (ys, zs) = splitAt n xs
    in  ys : split n zs

removeX :: [a] -> [a]
removeX xs = if (last xs) == 'X' then ((init xs) && removeX xs)
 else xs

decode :: [Char] -> [Char]
decode (x:xs) = removeX (concat (transpose (split ((factors (length xs))!!1) xs)))