templates/flake.nix

{
  description = "Templates of the Sieve of Eratosthenes implemented in various languages";

  outputs = { self, ... }:
    let
      # Get all project directories
      subdirs = dir:
        let sub = builtins.readDir dir;
        in builtins.filter
          (d: sub.${d} == "directory")
          (builtins.attrNames sub);

      vowelStart = str: builtins.elem (builtins.substring 0 1 str) [ "a" "e" "i" "o" "u" ];

      concatMapAttrs = func: attr:
        builtins.foldl' (x: y: x // y) {}
          (builtins.map func attr);

      templateDirs =
        builtins.concatMap (lang:
          builtins.map
            (pkg: { inherit lang pkg; })
            (subdirs ./${lang}))
          (subdirs ./.);
    in {
      templates = concatMapAttrs ({ lang, pkg }: {
        "${lang}-${pkg}" = {
          description = "Packaging a${if vowelStart lang
                                      then "n"
                                      else ""} ${lang} executable using ${pkg}";
          path = builtins.filterSource
            (path: type: builtins.baseNameOf path != "flake.lock")
            ./${lang}/${pkg};
        };
      }) templateDirs // concatMapAttrs (lang: {
        "${lang}" = self.templates."${lang}-nixpkgs" // {
          description = "Packaging a${if vowelStart lang
                                      then "n"
                                      else ""} ${lang} executable";
        };
      }) (subdirs ./.);
    };
}