{ lib, ... }:
let
  inherit (builtins) attrNames isAttrs readDir listToAttrs;

  inherit (lib) filterAttrs hasSuffix mapAttrs' nameValuePair removeSuffix;

  # mapFilterAttrs ::
  #   (name -> value -> bool )
  #   (name -> value -> { name = any; value = any; })
  #   attrs
  mapFilterAttrs = seive: f: attrs: filterAttrs seive (mapAttrs' f attrs);

  # Generate an attribute set by mapping a function over a list of values.
  genAttrs' = values: f: listToAttrs (map f values);

in {
  inherit mapFilterAttrs genAttrs';

  recImport = { dir, _import ? base: import "${dir}/${base}.nix" }:
    mapFilterAttrs (_: v: v != null) (n: v:
      if n != "default.nix" && hasSuffix ".nix" n && v == "regular"

      then
        let name = removeSuffix ".nix" n; in nameValuePair (name) (_import name)

      else
        nameValuePair ("") (null)) (readDir dir);

  # Convert a list to file paths to attribute set
  # that has the filenames stripped of nix extension as keys
  # and imported content of the file as value.
  pathsToImportedAttrs = paths:
    genAttrs' paths (path: {
      name = removeSuffix ".nix" (baseNameOf path);
      value = import path;
    });

}