Factor out i18n settings

machine/backyard/default.nix

@@ -17,21 +17,6 @@
   # Enable networking
   networking.networkmanager.enable = true;
 
-  # Select internationalisation properties.
-  i18n.defaultLocale = "en_US.UTF-8";
-
-  i18n.extraLocaleSettings = {
-    LC_ADDRESS = "en_US.UTF-8";
-    LC_IDENTIFICATION = "en_US.UTF-8";
-    LC_MEASUREMENT = "en_US.UTF-8";
-    LC_MONETARY = "en_US.UTF-8";
-    LC_NAME = "en_US.UTF-8";
-    LC_NUMERIC = "en_US.UTF-8";
-    LC_PAPER = "en_US.UTF-8";
-    LC_TELEPHONE = "en_US.UTF-8";
-    LC_TIME = "en_US.UTF-8";
-  };
-
   # Define a user account. Don't forget to set a password with ‘passwd’.
   users.users.tvb = {
     isNormalUser = true;

modules/beatific.nix

@@ -1,36 +1,67 @@
 { config, lib, pkgs, ... }:
 
 let
-  inherit (lib) mkIf mkMerge mkOption types;
+  inherit (lib) mkDefault mkIf mkMerge mkOption types;
   cfg = config.beatific;
 in {
   options = {
     beatific = {
+      # The host name is reused for beatific-specific configuration.
+      # The bulk of common config is handled in beatific.defaults below, but
+      # having one option without a default ensures that the module cannot be
+      # imported accidentally.
       hostName = mkOption {
         type = types.str;
         description = "Hostname";
       };
 
+      # Groups of related defaults can be disabled by flipping off the switches here:
+      #   beatific.defaults.${category} = false;
+      # They default to true because the point is to do these things by default.
       defaults = {
         time = mkOption {
           type = types.bool;
           description = "Default time zone and NTP";
           default = true;
         };
+
+        i18n = mkOption {
+          type = types.bool;
+          description = "Default locale settings";
+          default = true;
+        };
       };
     };
   };
 
   config = mkMerge [
     {
+      # Options to always set
       networking.hostName = cfg.hostName;
-
       nix.extraOptions = "experimental-features = nix-command flakes";
     }
+
     (mkIf cfg.defaults.time {
-      time.timeZone = "UTC";
+      # mkDefault time zone to make it easy to configure it to non-UTC
+      time.timeZone = mkDefault "UTC";
       services.ntp.enable = true;
       services.ntp.servers = [ "time.nist.gov" ];
     })
+
+    (mkIf cfg.defaults.i18n {
+      # en_US.UTF-8
+      i18n.defaultLocale = "en_US.UTF-8";
+      i18n.extraLocaleSettings = {
+        LC_ADDRESS = "en_US.UTF-8";
+        LC_IDENTIFICATION = "en_US.UTF-8";
+        LC_MEASUREMENT = "en_US.UTF-8";
+        LC_MONETARY = "en_US.UTF-8";
+        LC_NAME = "en_US.UTF-8";
+        LC_NUMERIC = "en_US.UTF-8";
+        LC_PAPER = "en_US.UTF-8";
+        LC_TELEPHONE = "en_US.UTF-8";
+        LC_TIME = "en_US.UTF-8";
+      };
+    })
   ];
 }