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Exercism exercises in Kotlin.

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Exercism Kotlin Track

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Source for Exercism Exercises in Kotlin.

Contributing Guide

For general information about how to contribute to Exercism, please refer to the contributing guide.

Table of Contents


This guide covers contributing to the Kotlin track. If you are new, this guide is for you.

If, at any point, you're having any trouble, pop in the Gitter exercism/dev room for help.

Contributing With Minimal Setup

First things first: by contributing to Exercism, you are making this learning tool that much better and improving our industry as a whole... thank you!!!

To submit a fix for an existing exercise or port an exercise to Kotlin with the least amount of setup:

  1. Ensure you have the basic Java tooling installed: JDK 1.8+, an editor and Gradle 2.x.

(see Installing Kotlin) - Setup a branch on a fork of exercism/kotlin on your computer.

Next steps: * "fork" a repository on GitHub; - install

; - "clone" a copy of your fork; - configure an "upstream remote" (in this case,
); - create a branch to house your work - Write the codes. Do your work on that branch you just created.

The Getting Familiar With the Codebase section, below, is an orientation. - Commit, push and create a pull request.

Something like:

   $ git add .
   $ git commit -m "(An intention-revealing commit message)"
   $ git push

It is advised you write meaningful commit messages. Chris Beams wrote about "How to Write a Git Commit Message".

  • Verify that your work passes all tests. When you create a pull request (PR), GitHub triggers a build on Travis CI. Your PR will not be merged unless those tests pass.

Getting Familiar With the Codebase

There are two objectives to the design of this build:

  1. when a problem is built from within the
    repo (i.e. when you, the contributor, are developing the exercise), the tests run against the reference solution;
  2. when a problem is built outside the
    repo (when a participant is solving the exercise), the tests run against the "main" code.

This repo is a multi-project gradle build.


This is the top-level module, contained in the

directory. It is a container for the problem sub-modules.
  • its
    points the "main" sourceset to the reference solution.
  • its
    names each of the subprojects, one for each problem in the set.

The Problem Submodules


subdirectory contains all of the problem submodules. Each problem/submodule is a subdirectory of the same name as its slug.
  • its
    names dependencies required to work that problem.

Each problem/submodule has three source sets:

  • src/test/kotlin/
    — a test suite defining the edges of the problem
  • .meta/src/reference/kotlin/
    — a reference solution that passes all the tests
  • src/main/kotlin/
    — starter source files, if required/desired (this directory usually only has a
    file in it)

To run the tests for a specific exercise, run the

Gradle task from the exercises directory. For example:
cd exercises bob:test

Steps for modifying an exercise: 1. Change the test(s). 2. Watch the changes fail. 3. Update the reference solution to make the test(s) pass.

Advanced: Complete Local Setup

If you are going to make significant contribution(s) to the track, you might find it handy to have a complete local install of exercism on your computer. This way, you can run the full suite of tests without having to create/update a PR.

The easiest way to achieve this is simply use the

script. However, you may want to perform other tests, depending on what you are doing. You can do so by duplicating the setup performed by the

gradle clean
exercism fetch

If you

exercism fetch
after doing a build, the CLI will fail with the following error message:
$ exercism fetch kotlin bob
2015/09/06 15:03:21 an internal server error was received.
Please file a bug report with the contents of 'exercism debug' at:

and if you review the logs of your x-api, you'll find: - - [06/Sep/2015:15:20:56 -0700] "GET /v2/exercises/kotlin/bob HTTP/1.1" 500 514949 0.2138
2015-09-06 15:21:01 - JSON::GeneratorError - source sequence is illegal/malformed utf-8:

This is because some files generated by the build can't be served from the x-api. This is by design: the CLI does not serve binaries. To fix this, simply make sure you do a clean in your

repo before you fetch:
cd ~/workspace/exercism/kotlin/exercises
gradle clean
cd ~/workspace/exercism/exercises
exercism fetch kotlin bob

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