Clean up flake and add modifiers file

flake.nix

@@ -14,15 +14,8 @@
     nixpkgs.url = "github:nixos/nixpkgs/nixpkgs-unstable";
   };
 
-  outputs =
-    inputs@
-    { self
-    , flake-parts
-    , horizon-advance
-    , nixpkgs
-    , ...
-    }:
-    flake-parts.lib.mkFlake { inherit inputs; } {
+  outputs = inputs:
+    inputs.flake-parts.lib.mkFlake { inherit inputs; } {
       systems = [
         "aarch64-darwin"
         "aarch64-linux"
@@ -32,22 +25,18 @@
       imports = [
         inputs.horizon-hoogle.flakeModule
       ];
-      perSystem = { config, system, ... }:
-        let
-          pkgs = nixpkgs.legacyPackages.${system};
-
-        in
+      perSystem = { pkgs, config, system, ... }:
         with pkgs.lib;
         let
           haskellLib = pkgs.haskell.lib;
-
+          modifiers = import ./modifiers.nix { inherit pkgs; };
           overrides = composeManyExtensions [
-            (import ./overlay.nix { inherit pkgs;   f = _: prev: name: v: if hasAttr name prev then warn "${name} exists in parent set" v else v;})
+            (import ./overlay.nix { inherit pkgs; f = modifiers; })
             (import ./configuration/common.nix { inherit pkgs haskellLib; })
             (import (./configuration + "/${system}.nix") { inherit pkgs haskellLib; })
           ];
 
-          legacyPackages = horizon-advance.legacyPackages.${system}.extend overrides;
+          legacyPackages = inputs.horizon-advance.legacyPackages.${system}.extend overrides;
 
           packages = filterAttrs (_: isDerivation) legacyPackages;
 

modifiers.nix

+{ pkgs, ... }:
+
+with pkgs.lib;
+
+_: prev: name: v: if hasAttr name prev then warn "${name} exists in parent set" v else v