第18回オフラインリアルタイムどう書くの参考問題をHaskellで解いた

invert [] = []
invert xs = map invert' $ reverse xs
    where
        invert' 'm' = 'V'
        invert' 'V' = 'm'

j [] = "V"
j xs = xs ++ "V" ++ (invert xs)

l [] = "V"
l xs = (invert xs) ++ "V" ++ xs

s [] = "Vm"
s xs = xs ++ "V" ++ (invert xs) ++ "m" ++ xs

z [] = "mV"
z xs = xs ++ "m" ++ (invert xs) ++ "V" ++ xs

u [] = "VV"
u xs = (invert xs) ++ "V" ++ xs ++ "V" ++ (invert xs)


solve xs = foldr applyFunc "" xs
    where
        applyFunc :: Char -> String -> String
        applyFunc c xs = charToFunc c xs

        charToFunc :: Char -> (String -> String)
        charToFunc 'J' = j
        charToFunc 'L' = l
        charToFunc 'S' = s
        charToFunc 'Z' = z
        charToFunc 'U' = u

main = do
    line <- getLine
    let [input, expect] = words line
    let output = solve input
    putStrLn $ if expect == output then "OK" else "NG"
    main