diff --git a/flake.nix b/flake.nix
index 7da1936..97256ba 100644
--- a/flake.nix
+++ b/flake.nix
@@ -31,39 +31,74 @@
       "aarch64-darwin"
     ];
 
-    forAllSystems = nixpkgs.lib.genAttrs supportedSystems;
+    # Uses lib.genAttrs to generate a attribute set, in this case using
+    # the systems as defined in `supportedSystems` as names.
+    # https://nixos.org/manual/nixpkgs/stable/#function-library-lib.attrsets.genAttrs
+    # This is a partial function as it misses the function param to lib.genAttrs
+    forEachSystem = nixpkgs.lib.genAttrs supportedSystems;
+
+    # Taken from https://github.com/Misterio77/nix-config
+    #
+    # Let's break that down, because it's a nice example.
+    #
+    # Let's assume, the function is called as in the formatter output below:
+    # pkgsForEachSystem(pkgs: pkgs.alejandra)
+    #
+    # pkgsForEachSystem is a function takes a function `f` as argument.
+    # So `(pkgs: pkgs.alejandra)` is the function passed as argument.
+    #
+    # In the function body lib.genAttrs takes the list of supportedSystems
+    # and maps the list to an attribute set using the function
+    # (system: f pkgsFor.${system})
+    #
+    # Let's assume the iteration passes `x86_64-linux` as system.
+    # The function body `(system: f pkgsFor.${system})` then becomes
+    # (x86_64-linux: (pkgs: pkgs.alejandra) pkgsFor.x86_64-linux)
+
+    # The function `(pkgs: pkgs.alejandra)` gets `pkgsFor.x86_64-linux` as
+    # argument for `pkgs` and finally evaluates to pkgs.x86_64-linux.alejandra.
+    pkgsForEachSystem = f: nixpkgs.lib.genAttrs supportedSystems (system: f pkgsFor.${system});
+
+    # Rewriting the function, taking inspiration from
+    # https://github.com/Misterio77/nix-config
+    # Using lib.genAttrs to import nixpkgs provides a nice way to quick
+    # access or pass pkgs for a certain targetSystem by simply access eg.
+    # pkgsFor.x86_64-linux or pkgsFor.${system} as pkgsFor is finally an
+    # attribute set, with system keys referencing to nixpkgs for that
+    # system.
+    pkgsFor = nixpkgs.lib.genAttrs supportedSystems (
+      system:
+        import nixpkgs {
+          inherit system;
+          overlays = [
+            localOverlays
+          ];
+          # activate unfree when I know that I need it.
+          config.allowUnfree = false;
+        }
+    );
+
+    unstablePkgsFor = nixpkgs.lib.genAttrs supportedSystems (
+      system:
+        import nixpkgs-unstable {
+          inherit system;
+          overlays = [];
+          # activate unfree when I know that I need it.
+          config.allowUnfree = false;
+        }
+    );
 
     # add local scripts as derivations using an overlay
     # could be also done by just passing additional args to the submodules
     # using the overlay approach, the repo local derivations are addressable
     # by pkgs.myderivation in the submodule
     localOverlays = import ./overlays;
-
-    pkgsForSystem = system:
-      import nixpkgs {
-        overlays = [
-          localOverlays
-        ];
-        inherit system;
-      };
-
-    unstablePkgsForSystem = system:
-      import nixpkgs-unstable {
-        # if you have additional overlays, you may add them here
-        overlays = [];
-        inherit system;
-      };
   in {
-    formatter = forAllSystems (
-      system: let
-        pkgs = nixpkgs.legacyPackages.${system};
-      in
-        pkgs.alejandra
-    );
+    formatter = pkgsForEachSystem (pkgs: pkgs.alejandra);
 
-    devShells = forAllSystems (
+    devShells = forEachSystem (
       system: let
-        pkgs = nixpkgs.legacyPackages.${system};
+        pkgs = pkgsFor.${system};
 
         # based on example
         # https://github.com/cachix/pre-commit-hooks.nix#nix-flakes-support
@@ -88,8 +123,8 @@
 
     darwinConfigurations = let
       system = "aarch64-darwin";
-      pkgs = pkgsForSystem system;
-      pkgsUnstable = unstablePkgsForSystem system;
+      pkgs = pkgsFor.${system};
+      pkgsUnstable = unstablePkgsFor.${system};
     in {
       defiant = import ./lib {
         inherit