Koka: A fast functional programming language with algebraic effects (koka-lang.github.io)

This paper is an interesting read, and explains how Koka is fast: https://www.microsoft.com/en-us/research/uploads/prod/2023/0.... In short: they use a clever algorithm to transform functional code into imperative code that reuses memory where it can.

This post by the Koka-author is an update about what's currently being worked on: https://github.com/koka-lang/koka/discussions/339