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).