The Goose Game Kata

This repository contains a Scala implementation of the Goose Game Kata. It implements all the requirements, mandatory and optional, see src/test/scala/chaordic/goose/GameSpec.scala for test coverage of all cases (there are other tests as well, but game logic is contained in this test).

This code is released under a MIT License.

Installation & running instructions

• A recent version of SBT and the Java Development Kit is required (this implementation has been tested with SBT 1.3.3 and OpenJDK 11.0.2).
• Run sbt
• To run the application from sbt, simply type run at the prompt after starting sbt.
• To run as a standalone executable jar:
  • Build with assembly through the sbt interactive prompt, then
  • Exit sbt
  • Run java -jar target/scala-2.12/game-of-goose.jar
• To run the test-suite, run test from the sbt prompt.

Comments on the implementation

This implementation uses a purely functional style using Cats IO-monad. This gives us a couple of benefits:

• Side-effecting code is clearly separated from pure code by return type-signature.
• IO allows us to use stack-safe recursion (more).
• Which in turn allows us to implement the entire application immutably with an event-loop, with no mutable state whatsoever.
  • Immutability has clear benefits in reducing the potential number of bugs.

Furthermore, we use Scalas Parser Combinators to safely parse user input in a less error-prone way than hand-munging Strings at no extra code-weight.

Finally, we use JLine3 to give a more pleasant experience when entering game commands.

The application has comprehensive test-coverage (100% branch coverage), which can be inspected with the coverage plugin: run coverageOn, followed by clean, test and coverageReport in sbt to generate the report.

There are many ways this could be implemented, this is one flavour of it!