delete :: Char -> [Char] -> [Char]
delete a as = [ x | x <- as, x /= a]

convertToInt n
    | n == 'X'    = 10
    | otherwise   = read [n] :: Integer

isbnToList n = do
    let simplify = delete '-' n
    return [convertToInt a | a <- simplify ]


BUT!!!!


*Main> isbnToList "3-598-21508-8"
[3,5,9,8,2,1,5,0,8,8]

*Main> zipWith (*) [10,9,8,7,6,5,4,3,2,1] [3,5,9,8,2,1,5,0,8,8]
[30,45,72,56,12,5,20,0,16,8]

*Main> zipWith (*) [10,9,8,7,6,5,4,3,2,1] $ isbnToList "3-598-21508-8"

<interactive>:140:9: error:
    • No instance for (Num [Integer]) arising from a use of ‘*’
    • In the first argument of ‘zipWith’, namely ‘(*)’
      In the expression: zipWith (*) [10, 9, 8, 7, ....]
      In the expression:
        zipWith (*) [10, 9, 8, 7, ....] $ isbnToList "3-598-21508-8"