[dzaima]

Once you've learned the syntax of the language, long expressions like that are about as readable as however-many-dozen lines of JS/Python with 1-to-3-character variable names; i.e. some parts may be obvious if they're a common pattern or simple enough, but the big picture may take a while to dig out.

Probably the biggest readability concern of overly-golfed expressions really is just being dynamically typed, a problem shared with all dynamically-typed languages. But array languages have the problem worse, as nearly all operations are polymorphic over array vs number inputs, whereas in e.g. JS you can use 'a+b' as a hint that 'a' and 'b' are numbers, & similar.

If you want readable/maintainable code, adding comments and splitting things into many smaller lines is just as acceptable as in other languages.

[upghost]

I am kind of curious if you have to mentally keep track of the rank/shape/dimensions in your head or if there is some implicit/explicit convention for conveying that to the reader. Does tracking rank/shape become second nature after awhile?

I'm also wondering about things like (APL-style) inner products -- they are undeniably powerful, but it's hard for me to conceptual use cases above rank 3.

[lokedhs]

That depends on the specific code. Some code is written to be agnostic to the rank, while others make certain assumptions.

In my code I'd sometimes write assertions in the beginning of a function to not only ensure it's called with the right shape but also as documentation.

Also, in practice really high rank arrays aren't used much. Even 4 is pretty rare.

[dzaima]

If there's information on input format, it is simple enough to trace through the following shapes, but it does force reading the code rather linearly. Operations which implicitly restrict the allowed shapes are unfortunately intentionally rather few.

I basically never use the generalized inner product; it's rather unique to the original APL - J has a variant that doesn't have the built-in reduction, and k and BQN and many if not most other array languages don't have any builtin for it at all. And in general I don't typically use rank higher than like one plus the natural dimensionality of the operation/data in question.

[realo]

I programmed in APL a long time ago... even got 'not bad' at it.

The best analogy i can give of my thought process is that first i unfolded the problem into one or more many-dimension object(s) ... then took a different "stance" of looking at the object, then refolded them into the final solution.

So yes... I had it all in my head at some point.