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Ξ Effekt

Compared to other languages with effect handlers (and support for polymorphic effects) the Effekt language aims to be significantly more lightweight in its concepts.

Disclaimer: Use at your own risk

Effekt is a research-level language. We are actively working on it and the language (and everything else) is very likely to change.

Also, Effekt comes with no warranty and there are (probably) many bugs -- If this does not discourage you, feel free to play with it and give us your feedback :)


You need to have Java (>= 11) and Node (>= 10) and npm installed.

The recommended way of installing Effekt is by running:

npm install -g

Alternatively, you can download the effekt.tgz file from another release and then run

npm install -g effekt.tgz

This will make the effekt command globally available. You can start the Effekt REPL by entering:

> effekt

You can find more information about the Effekt language and how to use it on the website (