bowling score calculater on Haskell

bowling.hs

import System.Environment (getArgs)
import Data.Char (digitToInt)

spare = (==) '/'
strike = (==) 'X'

updateBonus r (b1, b2)
    | spare r = (b2 + 1, 0)
    | strike r = (b2 + 1, 1)
    | otherwise = (b2, 0)

scoreForThrow :: (Char, Int) -> Int
scoreForThrow (result, before)
    | result == '-' = 0
    | spare result  = 10 - before
    | strike result = 10
    | otherwise = digitToInt result

scoreForThrowWithBonus :: (Char, Int, (Int, Int)) -> Int
scoreForThrowWithBonus (result, before, (b, _)) = sum [score, score * b]
    where score = scoreForThrow (result, before)

scoringTotal :: (Char, Int, Int, (Int, Int)) -> (Int, Int, (Int, Int))
scoringTotal (result, total, before, bonus) = (total + this, current, updateBonus result bonus)
    where current = scoreForThrow (result, before)
          this = scoreForThrowWithBonus (result, before, bonus)

scoring :: String -> Int
scoring result = score
    where (score, _, _) = foldl (\(t, b, bonus) r -> scoringTotal (r, t, b, bonus)) (0, 0, (0, 0)) result

resultFor10Frame (t1:ts)
    | length (t1:ts) < 4 = (t1:ts)
    | t1 == 'X' = resultFor10Frame ts
    | otherwise = resultFor10Frame $ drop 2 (t1:ts)

bonusFor10Frame = foldl (\(t, (b1, b2)) r -> (t + scoreForThrow (r, 0) * b1, updateBonus r (b1, b2))) (0, (0, 0))

ajust results = -bonus where (bonus, _) = bonusFor10Frame $ resultFor10Frame results

bowlingScore results = sum $ map ($ results) [scoring, ajust]

{-
main = do
    (results:_) <- getArgs
    print $ bowlingScore results
-}

printTest (testCase, result) = do
    putStrLn $ "test case: " ++ testCase
    putStrLn $ if (bowlingScore testCase) == result then "CLEAR" else "FAIL"

testCases = [
        ("9-9-9-9-9-9-9-9-9-9-",  90),
        ("X54----------------",  28),
        ("1/5-----------------",  20),
        ("1/5-2/-/8-----------",  56),
        ("------XX----------",    30),
        ("------XXX--------",     60),
        ("XXXXXXXXXXXX",          300),
        ("--------------------",  0),
        ("-------------------/5", 15),
        ("------------------X54", 19),
        ("5/5/5/5/5/5/5/5/5/5/5", 150)
    ]

test = mapM_ printTest testCases

main = test