start new dynamic apply function

modules/dynamicism/dynamicism.nix

@@ -23,6 +23,8 @@ let
 
   subOpts = lib.mapAttrs (_: metaAttr: metaAttr.configuration.options) options.dynamicism.for.valueMeta.attrs;
 
+  seqTrue = v: lib.seq v true;
+
   finalSettingsFor = { ... }@submod: recUpdateFoldl (optPath:
     lib.setAttrByPath optPath (lib.getAttrFromPath optPath config)
   ) submod.source-options;
@@ -55,7 +57,9 @@ in
       type = t.attrsOf (t.submoduleWith {
         modules = [ ./submodule.nix ];
         shorthandOnlyDefinesConfig = false;
-        specialArgs = { inherit pkgs; };
+        specialArgs = {
+          host = { inherit pkgs options config; };
+        };
       });
       default = { };
     };
@@ -69,6 +73,12 @@ in
       '';
     };
 
+    applyDynamicConfiguration = mkOption {
+      #type = t.functionTo t.pathInStore;
+      type = t.functionTo t.raw;
+      readOnly = true;
+    };
+
     doChange = mkOption {
       type = t.functionTo t.pathInStore;
       readOnly = true;
@@ -95,6 +105,45 @@ in
     '';
   };
   config.dynamicism = {
+
+    applyDynamicConfiguration = {
+      baseConfiguration ? builtins.getEnv "NIXOS_CONFIG",
+      newConfiguration ? baseConfiguration + "/dynamic.nix",
+    }: let
+      locFor = appendage: lib.concatLists [
+        opts.applyDynamicConfiguration.loc
+        [ "(function argument)" ]
+        (lib.toList appendage)
+      ];
+
+      _file = "«inline module in ${showOption opts.applyDynamicConfiguration.loc}»";
+
+      nixosBefore = evalNixos {
+        configuration = { ... }: {
+          inherit _file;
+          imports = [ baseConfiguration ];
+        };
+      };
+
+      nixosAfter = evalNixos {
+        configuration = { ... }: {
+          inherit _file;
+          imports = [ baseConfiguration newConfiguration ];
+        };
+      };
+
+      submodulesChanged = lib.filter (submodName:
+        nixosBefore.config.dynamicism.for.${submodName}.finalSettings
+        !=
+        nixosAfter.config.dynamicism.for.${submodName}.finalSettings
+      ) (lib.attrNames config.dynamicism.for);
+    in
+      assert seqTrue (typeCheck (locFor "baseConfiguration") t.deferredModule baseConfiguration);
+      assert seqTrue (typeCheck (locFor "newConfiguration") t.deferredModule newConfiguration);
+    {
+      inherit submodulesChanged;
+    };
+
     doChange = {
       option,
       value,