Beyond what others have mentioned, I think another big differentiating factor between APL and the rest of those languages is that APL isn't focused on allowing the user to expand the language meaningfully, but rather on being a well-rounded language by itself (which is how it can be reasonably useful without objects with named fields, mutation, explicit loops (or only gotos in APLs infancy!), no first-class functions, no macros, and only one level of higher-order function (though of course most APL implementations have some of those anyway)).

As such there's really no pretty "core" that pulls its weight to implement in 1000LoC and is useful for much.

Here's a simple minimal APL parser in JS that I wrote once to display one way of parsing APL: https://gist.github.com/dzaima/5130955a1c2065aa1a94a4707b309...

Couple that with an implementation of whatever primitives you want, and a simple AST walker, and you've got a simple small APL interpreter. But those primitive implementations already take a good chunk of code, and adding variables/functions/nested functions/scoping/array formatting/etc adds more and more bits of independent code.

Perhaps if you accept defining bits in the language in itself via a bootstrap step, BQN is a good candicate for existing small implementations - a BQN vm + minimal primitive set is ~500LoC of JS[0] (second half of the file is what you could call the native components of a stdlib), 2KLoC for first public commit of a C impl[1], both of those having the rest of the primitives being self-hosted[2], and the compiler (source text → bytecode) being self-hosted too[3]. (the C impl also used r0.bqn for even less required native primitives, but modern CBQN uses very little of even r1.bqn, having most important things native and heavily optimized)

[0]: https://github.com/mlochbaum/BQN/blob/master/docs/bqn.js though earlier revisions might be more readable

[1]: https://github.com/dzaima/CBQN/tree/bad822447f703a584fe7338d...

[2]: https://github.com/mlochbaum/BQN/blob/master/src/r1.bqn (note that while this has syntax that looks like assigning to primitives, that's not actual BQN syntax and is transpiled away)

[3]: https://github.com/mlochbaum/BQN/blob/master/src/c.bqn