I wrote my first trading system in Clojure because a few of the libraries we relied on were in java.
It was 2011 and I'd had about 3 years of lisp experience. I got a bit of side eye from people when I told them I was using a relatively new programming language but the fact that it was based on the JVM, which alot of HFT firms were using helped make the case.
We didn't use if for more than a few years before it was retired and rewritten, though that was due to new requirements that included C++ interop.
In the end tracking memory usage and allocations got too hard and if you've ever written something that is time sensitive you'll know just how slow memory allocation is, so you could argue I made a poor choice but for the rewrite was easy to reuse the java libraries when we moved to java.
The harder part was porting the algorithm implementation code.
The reason was that I chose a common lisp trick of first writing a DSL in Clojure that was then used to write the algos.
That was the one part that seemed worse in the rewrite as it became far more verbose and clunky.
But man was it fun, I learned more in a month than I often do in a year now.
Thanks Rich!! It's not often you get to experiment with cool tech and make lots of money doing it. I appreciate your work.