I think the emphasis on "in production" doesn't make sense for a lot of languages. Not everything has to be part of a highly engineered, user facing system to be useful.
For example, I would never use R "in production", however I have used R to make many important internal decisions, and generate recurring reports, etc. Very few people use Excel "in production" but there are plenty of very important companies using Excel.
Likewise I can imagine there are a few people out there using APL for something meaningful and important, even if that code is never truly "in production".
There are plenty of useful, wonderful programs written in the world that were never destined to be part of a production system. The code I've enjoyed writing the most and learned the most about the world from writing typically falls into this category.
My first employer used Excel "in production": A C# app would read numbers from a shared network drive, feed them into a timeseries database, and the real-time part of the system would be reloaded. Eventually a web-interface was put in place instead of the Excel sheet that provided for faster input validation.
I think the emphasis on “in production” is because it’s assumed that the only people really using APL are folks maintaining legacy codebases. I picture APL like COBOL: there’s no(?) reason someone would even toy around with it these days unless there was some intrinsic property of APL that makes it uniquely suited to some problem domain, and to such a degree that people can overlook its major shortcomings. _Is_ there something APL is actually useful for these days?
For example, I would never use R "in production", however I have used R to make many important internal decisions, and generate recurring reports, etc. Very few people use Excel "in production" but there are plenty of very important companies using Excel.
Likewise I can imagine there are a few people out there using APL for something meaningful and important, even if that code is never truly "in production".
There are plenty of useful, wonderful programs written in the world that were never destined to be part of a production system. The code I've enjoyed writing the most and learned the most about the world from writing typically falls into this category.