BowlingScore.fs

let score game =
    let rec aux sum frame =
        function
        | 10 :: 10 :: [ x ] when frame = 10 && x <= 10               -> Some(sum + 20 + x)
        | 10 :: x :: [ y ]  when frame = 10 && x + y <= 10           -> Some(sum + 10 + x + y)
        | x :: y :: [ z ]   when frame = 10 && x + y = 10 && z <= 10 -> Some(sum + 10 + z)
        | x :: [ y ]        when frame = 10 && x + y < 10            -> Some(sum + x + y)

        | 10 :: x :: y :: rest                           -> aux (sum + 10 + x + y) (frame + 1) (x :: y :: rest)
        | x :: y :: z :: rest when x + y = 10 && z <= 10 -> aux (sum + 10 + z) (frame + 1) (z :: rest)
        | x :: y :: rest when x + y < 10                 -> aux (sum + x + y) (frame + 1) rest
        | _                                              -> None
    aux 0 1 (List.rev game)