I'm looking for some inspiration. (I think) I'd love to use one "for real"/"in anger" for something but are they too niche to use as CV/Resume enhancement?
It was alright. I don't think I was able to invest enough in APL to make it really stick but have the impression that if I did it could be very useful.
Fwiw, Aaron Hsu is really the guy to follow for all things APL. He's also super nice and helpful and a model for anyone who wishes to represent a technology.
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).
I've been surprised at how much I liked writing it. J can be derided for being a "puzzle language"[1], which isn't entirely unfair, but I've found the paradigm of array programming carries over into more widely used languages and libraries ("Iverson ghost"[2]).
I wouldn't bother learning to put it on a resume, I would try it out for fun.
[0]: https://idle.nprescott.com/2020/ray-tracing-in-j.html
[1]: https://prog21.dadgum.com/219.html
[2]: https://analyzethedatanotthedrivel.org/2018/03/31/numpy-anot...
What's good about Matlab? Maybe the best comparison I've seen in a normal language would be LINQ in C#. If you've been writing (or reading) code that makes heavy use of LINQ, imagine re-implementing all that stuff using explicit loops with dummy indices and all the rest of that line noise. Yuck. Hard to write and worst of all hard to read.
Matlab takes that further than LINQ does ... in certain directions. Basically stuff with arrays.
I don't know whether the APL-likes take the same idea even further than Matlab, or just use short keywords.
Downside: when your problem doesn't break down into array patterns that Matlab is good at, then Matlab stops being fun. At all. For stuff like that, where you really do need to supervise every line of C-ish code personally, something like Ruby or C# is way more fun. (Except if you're doing say EE or optical physics. Then Matlab's libraries are still a huge time saver.)
Sometimes, when the logic of a program is clear, J could be like a calculator for quickly getting a result. Actually, with J you're pretty soon at a point where you're refining the specification, not actually solving the problem (because solving is easy). There is a saying that an hour-long task APLer solves in 5 minutes and then spends the remaining 55 minutes refining the solution - and the problem - so they'd be clearer.
At some point J feels easier than other tools and it does feel like a "tool for thought" - a shorter way between what you think and what the program does. There can be even shorter ways, I don't know.