The lack of an AD primitive is something I've discussed with the creator of BQN, coming from a JAX world I really miss it and feel that it's such an obvious feature, especially in a language which has a way to turn a tacit function into its AST[1], which has been used for symbolic differentiation[2]. Going from symbolic to reverse-mode AD is not much of a leap and users can define their own primitives with ReBQN[3].

I see what you mean by obfuscation, but I think that it's one of those things that feels really hard and stupid until you start being able to do it really quickly. When you learn a foreign language, you first read letters, then words, then sentences because you become accustomed to larger pieces of the language that you can predict what's coming next without reading it. A similar sort of thing happens with APL/BQN, you read letters (primitives), then you begin to recognise words (small, commonly used groups of primitives), then you see larger patterns which look like magical incantations to an inexperienced user.

These "words" are (typically) tacit phrases, many of them only existing due to specific primitives like swap. Once I used BQN to golf, I started wishing Julia had a swap for operators i.e.

  -(3, 5) = -2
  swap(-)(3, 5) = 2

I won't defend these languages to the death, but they are fun to puzzle your brain with in codegolf. Maybe Dex[4] will go somewhere too.

[1]: https://mlochbaum.github.io/BQN/spec/system.html#operation-p...

[2]: https://saltysylvi.github.io/blog/bqn-macros.html

[3]: https://mlochbaum.github.io/BQN/doc/rebqn.html

[4]: https://github.com/google-research/dex-lang