Bowling Kata

Bowling.hs

module Bowling  where

import Test.QuickCheck
import Data.List

data Frame = 
    Roll Int Int 
  | Spare Int Int 
  | SpareExtra Int
  | Strike
  | StrikeExtra Int Int
  deriving (Show)
type Game = [Frame]


score :: Game -> Int
score [] = 0
score (Roll x y : rest) = x+y + (score rest)
score (Spare x y : rest) = x+y + (bonusForSpare rest) + (score rest)
score [SpareExtra _] = 0
score (Strike : rest) = 10 + (bonusForStrike rest) + (score rest)
score [StrikeExtra _ _] = 0

bonusForSpare [] = 0
bonusForSpare (Roll x _ : _) = x
bonusForSpare (Spare x _ : _) = x
bonusForSpare (SpareExtra x : _) = x
bonusForSpare (Strike : _) = 10
bonusForSpare _ = error "Inconceivable"

bonusForStrike [] = 0
bonusForStrike (Roll x y : _) = x + y
bonusForStrike (Spare x y : _) = x + y
bonusForStrike (Strike : []) = 10
bonusForStrike (Strike : Roll x _ : _) = 10 + x
bonusForStrike (Strike : Spare x _  : _) = 10 + x
bonusForStrike (Strike : Strike : _) = 10 + 10
bonusForStrike (Strike : StrikeExtra x _ : []) = 10 + x
bonusForStrike (StrikeExtra x y : []) = x + y

Some tests, they are all True

let gutter = Roll 0 0 
let ones = Roll 1 1

0 == score []
0 == score [gutter]
0 == score (replicate 10 gutter)
20 == score (replicate 10 ones)
5 == score [(Roll 5 0)]
6 == score [(Roll 5 1)] 
10+5 + 5+5 == score [(Spare 9 1), (Roll 5 5)]
24 == score [Strike, (Roll 3 4)]
20 + 10 == score [Strike, Strike]
30 + 20 + 10 == score [Strike, Strike, Strike]
284 == score ((replicate 10 Strike) ++ [StrikeExtra 5 4])
300 == score ((replicate 10 Strike) ++ [StrikeExtra 10 10])