outputs: merge pipe expression

add comments too

outputs.nix

@@ -19,26 +19,24 @@ self = {
     versionInfoFixup = import ./pkgs/overlays/version-info-fixup.nix { inherit inputs; };
   };
   nixosConfigurations = let
-    # list nix file paths in ./hosts to attributes in nixosConfigurations
-    filePaths = lib.pipe ./hosts [
-      builtins.readDir
-      ( lib.filterAttrs (name: type:
-        ( # regular .nix files
-          (type == "regular" && lib.hasSuffix ".nix" name)
-          || # directories that contain a default.nix file
-          (type == "directory" && builtins.pathExists "${./.}/hosts/${name}/default.nix")
-        )
-        # filter out files that start with .
-        && !lib.hasPrefix "." name
-      ))
-    ];
     nixosSystem = import "${inputs.nixpkgs}/nixos/lib/eval-config.nix";
   in
-    # mapped list of nix file paths to attrSet with initialized NixOS configurations,
+    # mapped atrrsed of nix file paths to attrSet with initialized NixOS configurations,
     # whose names are derived from file names
-    lib.pipe filePaths [
+    lib.pipe ./hosts [
+      builtins.readDir
+      # filter out files that are not .nix files, directories with default.nix or starting with . (dot, hidden files)
+      ( lib.filterAttrs (name: type:
+        (
+          (type == "regular" && lib.hasSuffix ".nix" name)
+          || (type == "directory" && builtins.pathExists "${./.}/hosts/${name}/default.nix")
+        )
+        && !lib.hasPrefix "." name
+      ))
       (builtins.mapAttrs (name: type: {
+        # remove .nix extension
         name = if type == "directory" then name else builtins.substring 0 (builtins.stringLength name - 4) name;
+        # initialize NixOS configuration
         value = nixosSystem {
           inherit lib;
           modules = [