I use J for general signal processing/machine learning development. It allows for clear expression in terms of arrays. It's also decent infrastructure for talki

I use J for general signal processing/machine learning development. It allows for clear expression in terms of arrays. It's also decent infrastructure for talking to C libraries, and the database is quite powerful (it's fast and you can apply verbs directly to column groups). Downside for anything like this is lack of libraries. There's utility in knowing it in the same sense as knowing Lisp; makes you better at other languages. There's also social capital in that people who use and work on the APL family are a sort of "mafia" working on very interesting and lucrative problems (generally in quant finance).