There are several reasonably well-known languages that bridge the functional and imperative worlds in one way or another. However, I’m looking for more than just that. In particular, I’d like to have good tools for both imperative/stateful and functional/data-transforming coding, but all within a safe, structured environment in terms of effects/external interactions/observable behaviour.

Now, I am by no means a Lisp expert, so it’s entirely possible that I’m completely unaware of something here. However, I’ve yet to encounter much of an effect system in any flavour of Lisp. Indeed, it’s hard to see how the sort of explicit visibility and control of effects that I’d find useful could be achieved in a language with primarily dynamic typing using any of the approaches I’ve encountered so far.