I’m personally a fan of Clojure, in part due to how practical it is. Some of that practicality comes at the expense of simplicity, however.

I wonder if a Scheme dialect would be a better fit for you? They tend to be smaller and might let you focus on semantics more.

Full disclosure: I haven’t spent nearly as much time with any of the Scheme/Scheme-inspired dialects as I have with Clojure. I’m basing this off of their design philosophy and others’ observations.