[chongli]

I think the main reason to use any of these array languages (for work) is job security. Since it's so hard to find expert programmers if you can get your employer to sign off on an array language for all the mission-critical stuff then you can lock in your job for life! How can they possibly replace you if they can't find anyone else who understands the code?

Otherwise, I don't see anything you can do in an array language that you couldn't do in any other language, albeit less verbosely. But I believe in this case a certain amount of verbosity is a feature if you want people to be able to read and understand the code. Array languages and their symbol salad programs are like the modern day equivalent of medieval alchemists writing all their lab notes in a bespoke substitution cipher. Not unbreakable (like modern cryptography) but a significant enough barrier to dissuade all but the most determined investigators.

As an aside, I think the main reason these languages took off among quants is that investing as an industry tends toward the exultation of extremely talented geniuses. Perhaps unintelligible "secret sauce" code has an added benefit of making industrial espionage more challenging (and of course if a rival firm steals all your code they can arbitrage all of your trades into oblivion).

[rscho]

I'm sorry but you really sound like you judge APLs from an outsider pov. For sure, it's not job security that's keeping APLs afloat, because APLs are very easy to learn. A pro programmer would never use K or any APL. But pro mathematicians or scientists needing some array programming for their job will.

[nathan_compton]

I have been a programmer, scientist, etc, at various times in my life and I have programmed in J. I don't think there is any compelling reason to use J over Matlab, R, or Python and very many reasons not to. Vector languages are mind expanding, for sure, but they have done a very poor job keeping up with the user experience and network effects of newer languages.

A few years ago I wrote a pipeline in J and then re-implemented it R. The J code was exactingly crafted and the R code was naive, but the R code was still faster, easier to read and maintain and, frankly, easier to write. J gives a certain perverse frisson, but beyond that I don't really see the use case.

[rscho]

I disagree. For the stuff I'm doing, I've been rewriting the same 1-screen program in different ways many times. J made that easy, R would make that much more tedious since I'd have >250 lines instead of 30. Of course if I'm doing something for which R has libs, I'll do it in R. Additionally, I'll very probably end up rewriting my final program in another language for speed and libs, because by then I'll know precisely what I want to write. IMO, the strength of array languages lies in easy experimentation.

[nathan_compton]

I think there is an element of truth to this, but the context where this ends up being an advantage is personal and idiosyncratic.