APL has a long an interesting history. It was successfully used for decades in Wall Street firms.

It's also worth looking at

* The A+ programming language, an APL derivative created at Morgan Stanley by Arthur Whitney. https://en.wikipedia.org/wiki/A%2B_(programming_language).

Roger Hui also worked there for a number of year.s

* The J language from Roger Hui - https://en.wikipedia.org/wiki/Roger_Hui#J_language

* Arthur Whitney and Kx Systems - https://en.wikipedia.org/wiki/Arthur_Whitney_(computer_scien...

Kona, a K implementation that's open source. https://github.com/kevinlawler/kona

Useful for reading K-tradition C programming style, too.

I've been puzzled about Kona for a while, since I don't really see a purpose for it. K/Q is specifically intended as a very high-efficiency language, and Kona doesn't say anything about benchmarks.

The original reason may have been that k3 was not open source and the free version was limited. But in general people write these things for all sorts of reasons. Just as there are dozens of Scheme interpreters.

And one chicago firm with APL in its name since its founding: https://www.manta.com/c/mm2mvtr/security-apl