nixos-config/overlays/util.nix

self: super: {
    util = rec {
        dirEntries = path: builtins.attrNames (builtins.readDir path);
        mapHosts = f: builtins.map f (dirEntries ../hosts);
        mapHostAttrs = key_f: val_f: builtins.listToAttrs (mapHosts (host: {name = key_f host; value = val_f host;}));
        mapObjKeys = obj: f: builtins.map f (builtins.attrNames obj);
        mapKeys = obj: f: builtins.map f obj;
        nixFilesIn = path: builtins.map
            (e: import (path + /${e}))
            (builtins.filter (x: (builtins.match ".*\\.nix$" x) != null) (dirEntries path));
        without = exclusions: list: builtins.filter (x: !builtins.elem x exclusions) list;
    };
}