Move hosts to a dedicated folder

lib/attrs.nix

@@ -0,0 +1,26 @@
+{ lib, ... }:
+
+with builtins;
+with lib;
+rec {
+  # attrsToList
+  attrsToList = attrs:
+    mapAttrsToList (name: value: { inherit name value; }) attrs;
+
+  # mapFilterAttrs ::
+  #   (name -> value -> bool)
+  #   (name -> value -> { name = any; value = any; })
+  #   attrs
+  mapFilterAttrs = pred: f: attrs: filterAttrs pred (mapAttrs' f attrs);
+
+  # Generate an attribute set by mapping a function over a list of values.
+  genAttrs' = values: f: listToAttrs (map f values);
+
+  # anyAttrs :: (name -> value -> bool) attrs
+  anyAttrs = pred: attrs:
+    any (attr: pred attr.name attr.value) (attrsToList attrs);
+
+  # countAttrs :: (name -> value -> bool) attrs
+  countAttrs = pred: attrs:
+    count (attr: pred attr.name attr.value) (attrsToList attrs);
+}