Welcome
Toplevel folders are for languages, inside each language dir they are divided by year to some extent. I didn't want to define separate projects for each year basically.
Haskell code is based on Sam Coy's template. Also shamefully, those solutions are his trying to get the feel for the template and parser library used.
Add a top-level nix-shell, so all the languages are available in each directory and I don't have to duplicate shell.nix && nix/*