Clojure Koans

The Clojure Koans are a fun way to get started with Clojure - no experience assumed or required. Follow the instructions below to start making tests pass!

Getting Started

I recommend starting from a cloned or forked repo. This way you’ll be able to track your progress in Git. You might want to create your own branch - that way if you pull back the latest koans from master, it’ll be a bit easier to manage the inevitable conflicts if we make changes to exercises you’ve already completed.

You have a few options for installation:

Install the dependencies for the koans (such as Clojure) on your machine
Use Vagrant and the configuration in this repository
Use Docker

Instructions for each option are below!

Installation on Your Machine

The only things you’ll need to run the Clojure Koans are:

JDK (I suggest version 8, but anything 6 or above should work fine)
Leiningen, a build tool for Clojure

Once you’ve cloned this repo and installed the dependencies, you can run:

lein repl

to make sure all the dependencies get downloaded properly (and then (exit) when you want to quit). See below for details on the REPL.

Installation with Vagrant

Make sure you have Vagrant and VirtualBox installed. In the root directory of the project, execute:

vagrant up
vagrant ssh
cd /vagrant
lein koan run

Installation with Docker

Once you’ve got Docker installed, you’re basically all set. You can run these commands to get started:

To run koans:

docker run --rm -it -v $(pwd):/app -w /app clojure lein koan run

To start up a REPL:

docker run --rm -it -v $(pwd):/app -w /app clojure lein repl

Running the Koans

Run the koans via:

lein koan run

If want to run directly from a REPL, once you are inside the lein repl prompt you can run the koans with

(exec "run")

Either way, it’s an auto-runner, so as you save your files with the correct answers, it will advance you to the next koan or file (conveniently, all files are prefixed with the sequence that you should follow).

You’ll see something like this:

Now meditate on /home/colin/Projects/clojure-koans/src/koans/01_equalities.clj:3
---------------------
Assertion failed!
We shall contemplate truth by testing reality, via equality.
(= __ true)

The output is telling you that you have a failing test in the file named 01_equalities.clj, on line 3. So you need to open that file up and make it pass! You’ll always be filling in the blanks to make tests pass. Sometimes there could be several correct answers (or even an infinite number): any of them will work in these cases. Some tests will pass even if you replace the blanks with whitespace (or nothing) instead of the expected answer. Make sure you give one correct expression to replace each blank.

The koans differ from normal TDD in that the tests are already written for you, so you’ll have to pay close attention to the failure messages, because up until the very end, making a test pass means that the next failure message comes up.

While it might be easy (especially at first) to fill in the blanks making things pass, you should work thoughtfully, making sure you understand why the answer is what it is. Enjoy your path to Clojure enlightenment!

Trying more things out

It’s very useful to try things out in a REPL (Read-Evaluate-Print Loop) whenever you get stuck or curious. Run:

lein repl

and you’ll be able to type expressions in, and see what output they produce.

Here are some interesting commands you might try, once you’re in a running REPL:

(find-doc "vec")
(find-doc #"vec$")
(doc vec)

And if those still don’t make sense:

(doc doc)
(doc find-doc)

will show you what those commands mean.

You can exit the REPL with CTRL-d, (exit), or (quit).

Contributing

Patches are encouraged! Make sure the answer sheet still passes (lein koan test), and send a pull request.

The file ideaboard.txt has lots of good ideas for new koans to start, or things to add to existing koans. So write some fun exercises, add your answers to resources/koans.clj, and we’ll get them in there!

Please follow the guidelines in http://tbaggery.com/2008/04/19/a-note-about-git-commit-messages.html for commit messages, and put your code in a feature branch (not master) before making the pull request. This makes patches easier to review.

Feel free to contact me (Colin Jones / trptcolin) on Github or elsewhere if you have any questions or want more direction before you start pitching in.

Contributors

https://github.com/functional-koans/clojure-koans/contributors

Credits

These exercises were started by Aaron Bedra of Relevance, Inc. in early 2010, as a learning tool for newcomers to functional programming. Aaron’s macro-fu makes these koans clear and fun to use and improve upon, and without Relevance’s initiative, this project would not exist.

Using the koans metaphor as a tool for learning a programming language started with the Ruby Koans by EdgeCase.

License

The use and distribution terms for this software are covered by the Eclipse Public License 1.0 (http://opensource.org/licenses/eclipse-1.0.php) which can be found in the file epl-v10.html at the root of this distribution. By using this software in any fashion, you are agreeing to be bound by the terms of this license.