I have recently read "The Little Learner" and was quite amazed how much I knew already just because I know APL/J. With the right libraries, these vector languages would be perfect for neural network / deep learning tasks.

Not criticizing you, here, just asking a sincere question.

It was obvious to me on first encounter that APL would never become widespread. Its character set was too abstruse for most programmers and at the time required a special monitor. Plus it seemed hard to maintain if you weren’t either a mathematician or a full-time APL developer.

Your thoughts?

Not OP, but I'll say you're right, but for the wrong reasons. Having embarked on learning APL by doing a project in it, the character set becomes second nature in a few days time. No special monitor needed, at least on my Mac, just a new font and it all worked flawlessly.

What caused me to hang up my glyphs were the inconsistencies and head scratching behavior of the language in so many corner cases. Working with very nice mentors I found that one could get around them, but because of the legacy of the language they have to be kept around to support existing code bases.

I loved the notion of having a language that gave a first class experience with matrices, though, and after looking around the space, I finally came to Julia and have been very happy.

Thanks for your perspective, which is easy to understand. I hasten to say that when I talk about special monitors, I first encountered APL in the early 80s.