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Imperative Bowling Kata 20 Years On
Delegating Menial Tasks to Github Copilot Chat
using Scala in IntelliJ IDEA
@philip_schwarz
slides by https://fpilluminated.org/
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In this deck we carry out a code kata for the game of Ten Pin Bowling.
While we are going to use Test Driven Development (TDD), we are not going to write any code, and that
is because we are going to delegate manual/menial work to Github Copilot.
The tests that we are going to use, and the code that is going to get written, were captured 20 years ago
in a deck written by Robert Martin and used by him to demonstrate TDD-based code katas.
While the game is coded using the imperative programming paradigm, Robert Martin used Java,
whereas we are going to use Scala.
@philip_schwarz
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Be warned that what follows is just an experiment.
There is nothing prescriptive / exemplary / recommended about the experiment and about its parameters, e.g.
• The programming paradigm used (imperative programming - shudder)
• The contents of the copilot-instructions.md file used
• The Github Copilot mode used (Agent)
• The LLM model used (Claude Sonnet 4.6)
• The particular prompts used - e.g. their length, their approach to expressing details, etc.
Just because the above parameters had the intended consequences for the limited purpose of re-enacting a
classic sample code kata, it doesn’t mean that they are of any particular merit.
They were not the results of a planned strategy and/or tactics aimed at securing a desired outcome in terms of
e.g. optimality, effectiveness, efficiency, productivity.
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Bowling Game Code Kata
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https://x.com/unclebobmartin
http://cleancoder.com/products
http://butunclebob.com/ … (continued)
Robert C. Martin
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http://butunclebob.com/FrontPage
… (continuing)
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http://butunclebob.com/ArticleS.UncleBob.TheProgrammingDojo
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http://butunclebob.com/ArticleS.UncleBob.TheBowlingGameKata
http://butunclebob.com/files/downloads/Bowling%20Game%20Kata.ppt
… (continued)
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… (continuing)
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† slightly modified – e.g. with some highlighting and some annotations
Let’s look at Robert Martin’s preamble section: "A Quick Design Session” †.
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Bowling Game Kata
Object Mentor, Inc.
fitnesse.org
Copyright © 2005 by Object Mentor, Inc
All copies must retain this page unchanged.
www.junit.org
www.objectmentor.com
blog.objectmentor.com
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Scoring Bowling.
The game consists of 10 frames as shown above. In each frame the player has
two opportunities to knock down 10 pins. The score for the frame is the total
number of pins knocked down, plus bonuses for strikes and spares.
A spare is when the player knocks down all 10 pins in two tries. The bonus for
that frame is the number of pins knocked down by the next roll. So in frame 3
above, the score is 10 (the total number knocked down) plus a bonus of 5 (the
number of pins knocked down on the next roll.)
A strike is when the player knocks down all 10 pins on his first try. The bonus
for that frame is the value of the next two balls rolled.
In the tenth frame a player who rolls a spare or strike is allowed to roll the extra
balls to complete the frame. However no more than three balls can be rolled in
tenth frame.
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Scoring Bowling.
The game consists of 10 frames as shown above. In each frame the player has
two opportunities to knock down 10 pins. The score for the frame is the total
number of pins knocked down, plus bonuses for strikes and spares.
A spare is when the player knocks down all 10 pins in two tries. The bonus for
that frame is the number of pins knocked down by the next roll. So in frame 3
above, the score is 10 (the total number knocked down) plus a bonus of 5 (the
number of pins knocked down on the next roll.)
A strike is when the player knocks down all 10 pins on his first try. The bonus
for that frame is the value of the next two balls rolled.
In the tenth frame a player who rolls a spare or strike is allowed to roll the extra
balls to complete the frame. However no more than three balls can be rolled in
tenth frame.
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Scoring Bowling.
The game consists of 10 frames as shown above. In each frame the player has
two opportunities to knock down 10 pins. The score for the frame is the total
number of pins knocked down, plus bonuses for strikes and spares.
A spare is when the player knocks down all 10 pins in two tries. The bonus for
that frame is the number of pins knocked down by the next roll. So in frame 3
above, the score is 10 (the total number knocked down) plus a bonus of 5 (the
number of pins knocked down on the next roll.)
A strike is when the player knocks down all 10 pins on his first try. The bonus
for that frame is the value of the next two balls rolled.
In the tenth frame a player who rolls a spare or strike is allowed to roll the extra
balls to complete the frame. However no more than three balls can be rolled in
tenth frame.
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Scoring Bowling.
The game consists of 10 frames as shown above. In each frame the player has
two opportunities to knock down 10 pins. The score for the frame is the total
number of pins knocked down, plus bonuses for strikes and spares.
A spare is when the player knocks down all 10 pins in two tries. The bonus for
that frame is the number of pins knocked down by the next roll. So in frame 3
above, the score is 10 (the total number knocked down) plus a bonus of 5 (the
number of pins knocked down on the next roll.)
A strike is when the player knocks down all 10 pins on his first try. The bonus
for that frame is the value of the next two balls rolled.
In the tenth frame a player who rolls a spare or strike is allowed to roll the extra
balls to complete the frame. However no more than three balls can be rolled in
tenth frame.
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The Requirements.
• Write a class named “Game” that has two
methods
– 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.
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The Requirements.
• Write a class named “Game” that has two
methods
– 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.
Each pin
knocked
down adds
1 point to
the score
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The Requirements.
• Write a class named “Game” that has two
methods
– 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.
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A quick design session
Clearly we need the Game class.
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A quick design session
A game has 10 frames.
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A quick design session
A frame has 1 or two rolls.
In each frame the player has two opportunities to knock down 10 pins.
The score for the frame is the total number of pins knocked down, plus bonuses for strikes and spares.
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A quick design session
The tenth frame has two or three rolls.
It is different from all the other frames.
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A quick design session
The score function must
iterate through all the
frames, and calculate
all their scores.
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A quick design session
The score for a spare or a strike
depends on the frame’s successor
A spare is when the player knocks down all 10 pins in two tries.
The bonus for that frame is the number of pins knocked down by the next roll.
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A quick design session
The score for a spare or a strike
depends on the frame’s successor
A strike is when the player knocks down all 10 pins on his first try.
The bonus for that frame is the value of the next two balls rolled.
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The next slide contains links to YouTube videos that
• may help to reinforce one’s understanding of the game
• may appeal to people who prefer video over text
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https://www.youtube.com/shorts/Gn3MadD0rOM
https://youtu.be/a8lHGHJSmwQ
https://youtu.be/GwDcwpfN4Ro
https://youtu.be/yuSiy-D9ZdU
https://youtu.be/mPmqNRepLEA
https://youtu.be/XmSnZN5r0FU
https://youtu.be/zBS34YIGa3U
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Bowling Game Code Kata
2005 2025
imperative code
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The next two slides show how Copilot was used, on the
command line, to create the project used for the kata.
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Manually deleted these two files after executing the prompt:
- lightning-talk/src/main/scala/Main.scala
- lightning-talk/src/test/scala/ExampleSpec.scala
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Finally, a blow by blow account of the code kata session, in the form of
a sequence of screenshots capturing every TDD step that was taken.
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What was the cost of that code kata session, on
top of the monthly cost of Copilot’s Pro plan?
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The cost was $1.60, and was determined by the LLM model used and the number of premium requests made.
The session captured in the screenshots consisted of 39 premium requests using Claude Sonnet 4.6.
See next for examples of the cost of other similar sessions.
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$1.88
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$1.60
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That’s all.
I hope you found it useful.