How to Contribute

Yay, we are happy that you want to contribute to the language. Here is how you get started:

Building Effekt

While this document might age and outdate, the most current and up-to-date instructions can be found in the Github Workflows file. This might be a bit tricky to read but contains all necessary information.

If you notice that something does not work as expected, please consider opening an issue. Also feel free to update this page on Github and opening a pull request.

Software Requirements

You need to have the following software installed to build and use Effekt:

Why three package management tools? The main build tool we use is Effekt, but we use Maven to extract dependencies and aggregate license files of the library dependencies. Finally, we use npm simply as a way to deploy the language as an npm-package.


Additionally, since Effekt uses Scala.js to compile to JavaScript, you also need a Scala.js compatible fork of

Once you have sbt installed, you can obtain and build the fork as follows:

git clone
cd kiama
git checkout scala-js
sbt publishLocal

Compiling the Effekt Compiler

Great, you made it so far! We can finally compile the Effekt project. For this enter the sbt terminal:

sbt:root> project effektJVM
sbt:effekt> test

As mentioned before, the Effekt compiler can be run as a java program, but also as a Scala program. Hence, we need a slightly complicate Cross-build setup with two projects effektJVM and effektJS.

Locally Installing your Compiler Build

The easiest way to install your version of Effekt is by running

sbt:root> project effektJVM
sbt:effekt> install

Please note that this also requires mvn to generate license files.

Generating the Effekt Binary

The Effekt binary is actually just a simple wrapper that invokes java -jar effekt.jar. To generate the jar-file and assembly everything simply run:

sbt deploy

Afterwards, you can find the effekt.jar in the bin/ folder.

Working on the “Standard Library”

The Effekt standard library is still in its infancy. If you want to work on it, we recommend the following workflow: Check out the effekt repository and start the repl in the project directory. This will enable using the library in folder lib instead of the bundled one.

You can now go ahead and create a test file in examples that uses your new / improved library module, like

module examples/mynewmoduletester

import io/mynewmodule

def main() = mynewfunction()

This makes sure that you are always interacting with the most up-to-date version of the standard library you are currently working on.