I'm going to try Lean4. It's interesting for us at work, for gamedev, and I'm personally interested in it too.

It's not only a programming language, but also a theorem prover, and the boundaries between those two aspects are rather blurry. For instance, if does not take a Boolean as argument, but a Decideable logical proposition. if also does not only choose which branch to evaluate, but also offers a proof that the proposition is True or False in the respective branches, that one can later use to argue with the compiler if a certain function call is allowed or not (for instance, one can make a type that only contains natural numbers that are prime - and making an instance of that type requires a proof that the passed in number is indeed prime - and such a proof can be materialized using if).

I'm still learning the language though, and am not certain if I can finish reading the book Functional Progrmaming in Lean till AoC starts... If I can't manage, I'm just going to start AoC in Lean anyhow, and see how far I get.

Factor, for sure. But I'll be surprised if I get though the whole first week without falling behind.

I’m going for zig and gerbil this year! Love AOC for learning new langs a day at a time :)

I often pick languages or modules to learn for the easier puzzles, or even languages that should be hard too challenge myself. 2 years ago I used bash and CLI apps for the first five levels. And I've forced myself to get better at numpy and pandas too before I knew then as well.

TLDR: user it as an opportunity to learn.

Probably rust, so I can push myself to do some real practice with it.

Wait when is it.