@dlakelan MiniKanren and MicroKanren were a big deal in logic programming about ten years ago. They're not so much functional programming languages as *concepts* for a very, very simple prolog like language, so simple you could plausibly implement it yourself as a DSL inside another language of your choice. Which means you can use it for the logic part only, and the parts that are hard in Prolog can be done in the host language. It looked cool but I never got the hang of it.