import Data.List

abc = ["C", "C#/Db", "D", "D#/Eb", "E", "F", "F#/Gb", "G", "G#/Ab", "A", "A#/Bb", "B"]

transpose' :: [[Char]] -> [Char] -> Maybe [[Char]]
transpose' scale = fmap (\x -> concat [(drop x scale), (take x scale)]).(`elemIndex` scale)

major :: [Char] -> Maybe [[Char]]
major key = let rslt = transpose' abc key in
    case rslt of
        Just lst -> Just [s | s <- lst, idx <- [0, 2, 4, 5, 7, 9, 11], Just idx == elemIndex s lst]
        Nothing -> Nothing

foo :: Int -> [Char] -> Maybe [[Char]]
foo shift = (>>= major).fmap (!!shift).major

ionic = foo 0
dorian = foo 1
frigian = foo 2
lidian = foo 3
mixolidian = foo 4
eolian = foo 5
locrian = foo 6