Language of Choice of the Year: Haskell! It's just really fun, powerful and flexible now that I know what I'm doing
Run nix develop in the folder to get into the dev shell. If you want to be able to download inputs from https://adventofcode.com, you also have to have your session token stored in the TOKEN environment variable.
If you use direnv, optionally create a .env file containing your token, and finally run direnv allow — you should be all set.
The .env file should look like:
TOKEN=<your token here>Install Cabal and Just, and optionally set your session token (see Nix instructions).