 # mbraak's solution

## to Bowling in the OCaml Track

Published at Oct 31 2018 · 0 comments
Instructions
Test suite
Solution

#### Note:

This exercise has changed since this solution was written.

Score a bowling game.

Bowling is a game where players roll a heavy ball to knock down pins arranged in a triangle. Write code to keep track of the score of a game of bowling.

## Scoring Bowling

The game consists of 10 frames. A frame is composed of one or two ball throws with 10 pins standing at frame initialization. There are three cases for the tabulation of a frame.

• An open frame is where a score of less than 10 is recorded for the frame. In this case the score for the frame is the number of pins knocked down.

• A spare is where all ten pins are knocked down by the second throw. The total value of a spare is 10 plus the number of pins knocked down in their next throw.

• A strike is where all ten pins are knocked down by the first throw. The total value of a strike is 10 plus the number of pins knocked down in the next two throws. If a strike is immediately followed by a second strike, then the value of the first strike cannot be determined until the ball is thrown one more time.

Here is a three frame example:

Frame 1 Frame 2 Frame 3
X (strike) 5/ (spare) 9 0 (open frame)

Frame 1 is (10 + 5 + 5) = 20

Frame 2 is (5 + 5 + 9) = 19

Frame 3 is (9 + 0) = 9

This means the current running total is 48.

The tenth frame in the game is a special case. If someone throws a strike or a spare then they get a fill ball. Fill balls exist to calculate the total of the 10th frame. Scoring a strike or spare on the fill ball does not give the player more fill balls. The total value of the 10th frame is the total number of pins knocked down.

For a tenth frame of X1/ (strike and a spare), the total value is 20.

For a tenth frame of XXX (three strikes), the total value is 30.

## Requirements

Write code to keep track of the score of a game of bowling. It should support two operations:

• `roll(pins : int)` is called each time the player rolls a ball. The argument is the number of pins knocked down.
• `score() : int` is called only at the very end of the game. It returns the total score for that game.

## Getting Started

For installation and learning resources, refer to the exercism help page.

## Installation

To work on the exercises, you will need `Opam` and `Core`. Consult opam website for instructions on how to install `opam` for your OS. Once `opam` is installed open a terminal window and run the following command to install core:

``````opam install core
``````

To run the tests you will need `OUnit`. Install it using `opam`:

``````opam install ounit
``````

## Running Tests

A Makefile is provided with a default target to compile your solution and run the tests. At the command line, type:

``````make
``````

## Interactive Shell

`utop` is a command line program which allows you to run Ocaml code interactively. The easiest way to install it is via opam:

``````opam install utop
``````

Consult utop for more detail.

## Feedback, Issues, Pull Requests

The exercism/ocaml repository on GitHub is the home for all of the Ocaml exercises.

If you have feedback about an exercise, or want to help implementing a new one, head over there and create an issue. We'll do our best to help you!

## Source

The Bowling Game Kata at but UncleBob http://butunclebob.com/ArticleS.UncleBob.TheBowlingGameKata

## Submitting Incomplete Solutions

It's possible to submit an incomplete solution so you can see how others have completed the exercise.

### test.ml

``````(* Test/exercise version: "1.0.1" *)

open Base
open OUnit2
open Bowling

type game = Bowling.t

let to_ok = function
| Ok x -> x
| Error e -> failwith @@ "should be OK but got Error " ^ e

let set_previous_frames (frames : int list): game =
List.fold frames ~init:new_game ~f:(fun g f -> roll f g |> to_ok)

let score_printer = function
| Ok n -> Int.to_string n
| Error e -> e
let assert_score exp game = assert_equal ~printer:score_printer exp (score game)

let roll_printer = function
| Ok _ -> "Ok <some game>"
| Error e -> e
let assert_roll exp frame game = assert_equal ~printer:roll_printer exp (roll frame game)

let tests = [
"should be able to score a game with all zeros" >:: (fun _ ->
let g = set_previous_frames [0; 0; 0; 0; 0; 0; 0; 0; 0; 0; 0; 0; 0; 0; 0; 0; 0; 0; 0; 0] in
assert_score (Ok 0) g
);
"should be able to score a game with no strikes or spares" >:: (fun _ ->
let g = set_previous_frames [3; 6; 3; 6; 3; 6; 3; 6; 3; 6; 3; 6; 3; 6; 3; 6; 3; 6; 3; 6] in
assert_score (Ok 90) g
);
"a spare followed by zeros is worth ten points" >:: (fun _ ->
let g = set_previous_frames [6; 4; 0; 0; 0; 0; 0; 0; 0; 0; 0; 0; 0; 0; 0; 0; 0; 0; 0; 0] in
assert_score (Ok 10) g
);
"points scored in the roll after a spare are counted twice" >:: (fun _ ->
let g = set_previous_frames [6; 4; 3; 0; 0; 0; 0; 0; 0; 0; 0; 0; 0; 0; 0; 0; 0; 0; 0; 0] in
assert_score (Ok 16) g
);
"consecutive spares each get a one roll bonus" >:: (fun _ ->
let g = set_previous_frames [5; 5; 3; 7; 4; 0; 0; 0; 0; 0; 0; 0; 0; 0; 0; 0; 0; 0; 0; 0] in
assert_score (Ok 31) g
);
"a spare in the last frame gets a one roll bonus that is counted once" >:: (fun _ ->
let g = set_previous_frames [0; 0; 0; 0; 0; 0; 0; 0; 0; 0; 0; 0; 0; 0; 0; 0; 0; 0; 7; 3; 7] in
assert_score (Ok 17) g
);
"a strike earns ten points in a frame with a single roll" >:: (fun _ ->
let g = set_previous_frames [10; 0; 0; 0; 0; 0; 0; 0; 0; 0; 0; 0; 0; 0; 0; 0; 0; 0; 0] in
assert_score (Ok 10) g
);
"points scored in the two rolls after a strike are counted twice as a bonus" >:: (fun _ ->
let g = set_previous_frames [10; 5; 3; 0; 0; 0; 0; 0; 0; 0; 0; 0; 0; 0; 0; 0; 0; 0; 0] in
assert_score (Ok 26) g
);
"consecutive strikes each get the two roll bonus" >:: (fun _ ->
let g = set_previous_frames [10; 10; 10; 5; 3; 0; 0; 0; 0; 0; 0; 0; 0; 0; 0; 0; 0] in
assert_score (Ok 81) g
);
"a strike in the last frame gets a two roll bonus that is counted once" >:: (fun _ ->
let g = set_previous_frames [0; 0; 0; 0; 0; 0; 0; 0; 0; 0; 0; 0; 0; 0; 0; 0; 0; 0; 10; 7; 1] in
assert_score (Ok 18) g
);
"rolling a spare with the two roll bonus does not get a bonus roll" >:: (fun _ ->
let g = set_previous_frames [0; 0; 0; 0; 0; 0; 0; 0; 0; 0; 0; 0; 0; 0; 0; 0; 0; 0; 10; 7; 3] in
assert_score (Ok 20) g
);
"strikes with the two roll bonus do not get bonus rolls" >:: (fun _ ->
let g = set_previous_frames [0; 0; 0; 0; 0; 0; 0; 0; 0; 0; 0; 0; 0; 0; 0; 0; 0; 0; 10; 10; 10] in
assert_score (Ok 30) g
);
"a strike with the one roll bonus after a spare in the last frame does not get a bonus" >:: (fun _ ->
let g = set_previous_frames [0; 0; 0; 0; 0; 0; 0; 0; 0; 0; 0; 0; 0; 0; 0; 0; 0; 0; 7; 3; 10] in
assert_score (Ok 20) g
);
"all strikes is a perfect game" >:: (fun _ ->
let g = set_previous_frames [10; 10; 10; 10; 10; 10; 10; 10; 10; 10; 10; 10] in
assert_score (Ok 300) g
);
"rolls cannot score negative points" >:: (fun _ ->
let g = set_previous_frames [] in
assert_roll (Error "Negative roll is invalid") (-1) g
);
"a roll cannot score more than 10 points" >:: (fun _ ->
let g = set_previous_frames [] in
assert_roll (Error "Pin count exceeds pins on the lane") 11 g
);
"two rolls in a frame cannot score more than 10 points" >:: (fun _ ->
let g = set_previous_frames  in
assert_roll (Error "Pin count exceeds pins on the lane") 6 g
);
"bonus roll after a strike in the last frame cannot score more than 10 points" >:: (fun _ ->
let g = set_previous_frames [0; 0; 0; 0; 0; 0; 0; 0; 0; 0; 0; 0; 0; 0; 0; 0; 0; 0; 10] in
assert_roll (Error "Pin count exceeds pins on the lane") 11 g
);
"two bonus rolls after a strike in the last frame cannot score more than 10 points" >:: (fun _ ->
let g = set_previous_frames [0; 0; 0; 0; 0; 0; 0; 0; 0; 0; 0; 0; 0; 0; 0; 0; 0; 0; 10; 5] in
assert_roll (Error "Pin count exceeds pins on the lane") 6 g
);
"two bonus rolls after a strike in the last frame can score more than 10 points if one is a strike" >:: (fun _ ->
let g = set_previous_frames [0; 0; 0; 0; 0; 0; 0; 0; 0; 0; 0; 0; 0; 0; 0; 0; 0; 0; 10; 10; 6] in
assert_score (Ok 26) g
);
"the second bonus rolls after a strike in the last frame cannot be a strike if the first one is not a strike" >:: (fun _ ->
let g = set_previous_frames [0; 0; 0; 0; 0; 0; 0; 0; 0; 0; 0; 0; 0; 0; 0; 0; 0; 0; 10; 6] in
assert_roll (Error "Pin count exceeds pins on the lane") 10 g
);
"second bonus roll after a strike in the last frame cannot score more than 10 points" >:: (fun _ ->
let g = set_previous_frames [0; 0; 0; 0; 0; 0; 0; 0; 0; 0; 0; 0; 0; 0; 0; 0; 0; 0; 10; 10] in
assert_roll (Error "Pin count exceeds pins on the lane") 11 g
);
"an unstarted game cannot be scored" >:: (fun _ ->
let g = set_previous_frames [] in
assert_score (Error "Score cannot be taken until the end of the game") g
);
"an incomplete game cannot be scored" >:: (fun _ ->
let g = set_previous_frames [0; 0] in
assert_score (Error "Score cannot be taken until the end of the game") g
);
"cannot roll if game already has ten frames" >:: (fun _ ->
let g = set_previous_frames [0; 0; 0; 0; 0; 0; 0; 0; 0; 0; 0; 0; 0; 0; 0; 0; 0; 0; 0; 0] in
assert_roll (Error "Cannot roll after game is over") 0 g
);
"bonus rolls for a strike in the last frame must be rolled before score can be calculated" >:: (fun _ ->
let g = set_previous_frames [0; 0; 0; 0; 0; 0; 0; 0; 0; 0; 0; 0; 0; 0; 0; 0; 0; 0; 10] in
assert_score (Error "Score cannot be taken until the end of the game") g
);
"both bonus rolls for a strike in the last frame must be rolled before score can be calculated" >:: (fun _ ->
let g = set_previous_frames [0; 0; 0; 0; 0; 0; 0; 0; 0; 0; 0; 0; 0; 0; 0; 0; 0; 0; 10; 10] in
assert_score (Error "Score cannot be taken until the end of the game") g
);
"bonus roll for a spare in the last frame must be rolled before score can be calculated" >:: (fun _ ->
let g = set_previous_frames [0; 0; 0; 0; 0; 0; 0; 0; 0; 0; 0; 0; 0; 0; 0; 0; 0; 0; 7; 3] in
assert_score (Error "Score cannot be taken until the end of the game") g
);
]

let () =
run_test_tt_main ("bowling tests" >::: tests)``````
``````open Base

type t = {
game_score: int;
frame_index: int;
throw_index: int;
frame_score: int;
double_counts: int list;
bonus_rolls: int;
}

let new_game = {
game_score=0;
frame_index=1;
throw_index=0;
frame_score=0;
double_counts=[];
bonus_rolls=0;
}

let double_count_factor (game: t): int =
(List.length game.double_counts) + 1

let throw_score (pins: int) (game: t): int =
pins * (double_count_factor game)

let decrease_double_counts (double_counts: int list): int list =
double_counts
|> List.map ~f: (fun c -> c - 1)
|> List.filter ~f: (fun c -> c <> 0)

let add_new_double_count (game: t) (double_counts: int list): int list =
if game.frame_score = 10 && game.throw_index = 0 && game.frame_index < 10 then
List.cons 2 double_counts
else if game.frame_score = 10 && game.throw_index = 1 && game.frame_index < 10 then
List.cons 1 double_counts
else
double_counts

let update_double_counts (game: t): t =
let double_counts = game.double_counts
|> decrease_double_counts
in
{ game with double_counts=double_counts }

let update_bonus_rolls (game: t) t =
let bonus_rolls =
if game.frame_index = 10 then
if game.frame_score <> 10 then
0
else if game.throw_index = 0 then
2
else
1
else if game.frame_index = 11 then
game.bonus_rolls - 1
else
game.bonus_rolls
in
{ game with bonus_rolls=bonus_rolls }

let set_bonus_rolls (game: t): t =
let bonus_rolls =
if game.frame_score <> 10 then
0
else if game.throw_index = 0 then
2
else
1
in
{ game with bonus_rolls=bonus_rolls }

let next_frame (game: t): t =
let { frame_index; throw_index; frame_score } = game in
let frame_index, throw_index =
match throw_index, frame_score with
| 0, 10 -> frame_index + 1, throw_index
| 0, _ -> frame_index, 1
| _ -> frame_index + 1, 0
in
{
game with
frame_index=frame_index;
throw_index=throw_index
}

let next_bonus_roll (game: t): t =
let bonus_rolls = game.bonus_rolls - 1 in
let throw_index = if game.frame_score = 10 then 0 else game.throw_index + 1 in
{
game with
bonus_rolls=bonus_rolls;
throw_index=throw_index
}

let update_frame_score (pins: int) (game: t): t =
let frame_score = if game.throw_index = 0 then 0 else game.frame_score in
{
game with
frame_score=frame_score + pins
}

let update_game_score (pins: int) (game: t): t =
let game_score = game.game_score + throw_score pins game in
{
game with
game_score=game_score
}

let roll pins game =
let new_game = game
|> update_frame_score pins
|> update_game_score pins
|> update_double_counts
|> (fun (game: t): t ->
if (game.frame_index = 10) then
game |> set_bonus_rolls |> next_frame
else if (game.frame_index = 11) then
game |> next_bonus_roll
else
game |> next_frame
)
in

if pins < 0 then
Error "Negative roll is invalid"
else if pins > 10 then
Error "Pin count exceeds pins on the lane"
else if new_game.frame_score > 10 then
Error "Pin count exceeds pins on the lane"
else if game.frame_index >= 11 && game.bonus_rolls = 0 then
Error "Cannot roll after game is over"
else
Ok new_game

let score game =
if game.frame_index = 11 && game.bonus_rolls = 0 then
Ok game.game_score
else
Error "Score cannot be taken until the end of the game"``````