anchor.diff:  # TODO: add assert statements
   
   let
  +  pkgs = import ./../../default.nix (if include-overlays then { } else { overlays = []; });
  +
  +  inherit (pkgs) lib;
  +
     /* Remove duplicate elements from the list based on some extracted value. O(n^2) complexity.
      */
     nubOn = f: list:
  
positive.code: 
    packagesWithUpdateScript = path:
      let
        attrSet = pkgs.lib.attrByPath (pkgs.lib.splitString "." path) null pkgs;
      in
        if attrSet == null then
          builtins.throw "Attribute path `${path}` does not exists."
  
negative.code:   packagesWithUpdateScriptAndMaintainer = maintainer':
      let
        maintainer =
          if ! builtins.hasAttr maintainer' lib.maintainers then
            builtins.throw "Maintainer with name `${maintainer'} does not exist in `maintainers/maintainer-list.nix`."
          else
            builtins.getAttr maintainer' lib.maintainers;
      in
        packagesWith (name: pkg: builtins.hasAttr "updateScript" pkg &&
                                   (if builtins.hasAttr "maintainers" pkg.meta
  