formatter is much cleaner

flake.nix

@@ -181,24 +181,11 @@
           chmod +x $out/bin/tests
         '';
       };
-      devShell.x86_64-linux = nixpkgs.mkShell {
-        packages = [
-          # nix formatter
-          nixpkgs-dyn.nixpkgs-fmt
-          # python formatter
-          nixpkgs-dyn.black
-          # cpp formatter
-          nixpkgs-dyn.clang-tools
-        ];
-        shellHook = ''
-          fmt () {
-            set -ex
-            nixpkgs-fmt .
-            black ./tests
-            clang-format -i --verbose src/*.cpp
-            set +ex
-          }
+      packages.x86_64-linux.formatter = nixpkgs.writeShellScriptBin "formatter" ''
+        set -x
+        ${nixpkgs-dyn.clang-tools}/bin/clang-format -i --verbose ./src/*.cpp
+        ${nixpkgs-dyn.nixpkgs-fmt}/bin/nixpkgs-fmt .
+        ${nixpkgs-dyn.black}/bin/black ./tests
       '';
     };
-    };
 }

readme.md

@@ -47,9 +47,7 @@ Test books can be found [here](https://www.adobe.com/solutions/ebook/digital-edi
 ### Formatting
 
 ```
-nix develop
-fmt
-exit
+nix run .#formatter
 ```
 
 ## The Name