{
  pkgs,
  prev,
  lib,
  ...
}:
let
  dirs = path: lib.attrNames (lib.filterAttrs (_: t: t == "directory") (builtins.readDir path));

  packagesFromTree =
    base: callPackage:
    lib.foldl' (
      acc: shorthand:
      let
        shorthandDir = base + "/${shorthand}";
        names = dirs shorthandDir;

        addOne =
          name:
          let
            pkgDir = shorthandDir + "/${name}";
          in
          if builtins.pathExists (pkgDir + "/default.nix") then
            { ${name} = callPackage pkgDir { }; }
          else
            { };
      in
      acc // lib.foldl' (a: n: a // addOne n) { } names
    ) { } (dirs base);

  byNamePkgs =
    if builtins.pathExists ./by-name then packagesFromTree ./by-name pkgs.callPackage else { };

  byCategoryPkgs = import ./by-category {
    inherit
      pkgs
      prev
      lib
      packagesFromTree
      ;
  };
in
byNamePkgs // byCategoryPkgs