This difference in array models is also part of the reason why Dyalog's ⍸ does a "deep where". In APL it's not considered "deep" at all, because the argument is a numeric array; it would be called "high rank". There's still a problem with this version though, because the high-rank version of ⍸ needs each index[1] to be a list, but the normal version (when the argument is 1-dimensional) uses one number for an index. The results of ⍸ for different rank arguments are actually inconsistent. In BQN, I decided Where should just be restricted to the 1-dimensional case. I wrote a little more about the kinds of array indices at [2]. It's worth noting that K has this problem a lot less than APL, because most of the time you will only index into a single dimension. But with constructs like deep where these problems appear in K as well, and you'll end up with the same inconsistency if you try to combine the two versions.
[0] https://mlochbaum.github.io/BQN/doc/search.html#higher-ranks (in the code examples, "high"≍"rank" couples rows to give the 2x4 shape seen below, and similarly 3‿2⥊4 creates a 3x2 array)
There's not much of a custom DSL problem, because APL/K emphasize using the primitives that are built in, and user-defined functions will have names not symbols. Some codebases will be a challenge to read because these languages tend to attract programmers who write things their own way, and for K in particular many users—the inventor Arthur Whitney most of all—don't like to write long explanations of how their code works. The OP, while well explained, is pretty advanced material. Knowing a lot about array programming makes the high-level picture clear but I would say many of the code examples would take some effort for even a good array programmer to understand.
If anything, K is the opposite of a language where everyone disappears into DSLs- you can write expressive code without wrapping it in custom abstractions. An anti-lisp, if you will. It's not uncommon for K programmers playing with a puzzle to independently arrive at character-for-character identical solutions.
Don't know DSL ability, though aware someone wrote expanders from symbols to words, - imagine DSL doable but forth, lisp macros spring to mind first in the DSL space
Yep. For this reason deep where ideally wouldn't live on '&'. It should be able to absorb any structure for subsequent use with deep indexing etc, regardless of rank. Perhaps another reason to make 'explode' an adverb...?
I wouldn't call it "common", but it's pretty well known.
kdb+/q devs certainly have good job security, heh.
The beauty of ngn k is I can compile it on NetBSD and with musl on Linux.
