[kerkeslager]

Racket and Common Lisp probably both fit the bill for what you're saying. Racket is more "batteries included", while Common Lisp has a wider variety of third-party libraries. Both have mature JSON implementations.

That said, I think you're underestimating the value of learning Lisp with no intention of using it to solve real-world problems. There are some big benefits:

1. It shows you a different way to structure programs, which I think is simpler and more powerful than OO.

2. It's a lingua franca of academia, which allows you to read a lot of papers you wouldn't otherwise be able to read.

3. For better or for worse, Lisp is a secret handshake that will get you into a lot of clubs. I've gotten more than one full stack Python/Django/JS job offer after interviews where all we talked about was the Lisp implementation on my GitHub. And while you definitely don't need Lisp experience to write full stack Python/Django/JS, there are jobs which require FP experience for good reason, even if you aren't writing in a very FP-focused language, especially if you're solving hard problems.