Type Driven Bowling Kata

TypeDrivenBowlingKata.fs

type Frame = StandardFrame of int * int
           | SpareFrame of int * int
           | StrikeFrame
type Game = Frame list

let score game =
    let nextRoll frames =
        match frames with
        | [] -> 0
        | StandardFrame(a,_)::_ -> a
        | SpareFrame(a,_)::_ -> a
        | StrikeFrame::_ -> 10
    let secondRoll frames =
        match frames with
        | [] -> 0
        | StandardFrame(_,b)::t -> b
        | SpareFrame(_,b)::t -> b
        | StrikeFrame::t ->  nextRoll t
    let scoreFrame frame frames =
        match frame with
        | StandardFrame(a,b) -> a+b
        | SpareFrame(a,b) -> a+b + nextRoll frames
        | StrikeFrame -> 10 + (nextRoll frames) + (secondRoll frames)
    let rec foldScore i score game =
        match i,game with
        | 0,_ -> score
        | _,[] -> score
        | _,StandardFrame(a,b) :: t ->  foldScore (i-1) ((scoreFrame (StandardFrame(a,b)) t)+score) t
        | _,SpareFrame(a,b) :: t -> foldScore (i-1) ((scoreFrame (SpareFrame(a,b)) t)+score) t
        | _,StrikeFrame :: t -> foldScore (i-1) ((scoreFrame StrikeFrame t)+score) t
    foldScore 10 0 game
  
score [StandardFrame(4,5); StandardFrame(0,0)]
score [SpareFrame(5,5); StandardFrame(2,3)]
[1..12] |> List.map (fun _ -> StrikeFrame) |> score