Bowling kata with kajgo 10 Jun 2013.

Bowling.hs

main = do
    print $ score (replicate 20 0) == 0
    print $ score (replicate 20 1) == 20
    print $ score ([4,6,1,0] ++ replicate 16 0) == 10 + 1 + 1
    print $ score ([10,6,1] ++ replicate 16 0) == 10 + 6 + 1 + 6 + 1
    print $ score (replicate 18 0 ++ [3,7,1]) == 11
    print $ score (replicate 18 0 ++ [10,5,2]) == 10 + 5 + 2
    print $ score (replicate 18 0 ++ [10,10,10]) == 30
    print $ score (replicate 12 10) == 300

score :: [Int] -> Int
score rolls = score' 10 rolls
    where
        score' :: Int -> [Int] -> Int
        score' framesLeft xs
            | framesLeft == 0 = 0
            | isStrike xs     = strikeScore (drop 1 xs) + score' (framesLeft - 1) (drop 1 xs)
            | isSpare  xs     = spareScore  (drop 2 xs) + score' (framesLeft - 1) (drop 2 xs)
            | otherwise       = sum (take 2 xs)         + score' (framesLeft - 1) (drop 2 xs)

isStrike :: [Int] -> Bool
isStrike rolls = head rolls == 10

isSpare :: [Int] -> Bool
isSpare rolls = head rolls + head (tail rolls) == 10

strikeScore :: [Int] -> Int
strikeScore nextRolls = 10 + head nextRolls + head (tail nextRolls)

spareScore :: [Int] -> Int
spareScore nextRolls = 10 + head nextRolls