diff --git a/flake.nix b/flake.nix
index 17cacf9..4538b63 100644
--- a/flake.nix
+++ b/flake.nix
@@ -7,10 +7,15 @@
       in {
         devShell = pkgs.mkShell {
           inputsFrom = with flakePkgs; [ main ];
-          packages = (with pkgs; [ ]) ++ (with pkgs.ocamlPackages; [ocaml-lsp ppxlib
-          alcotest
-          yojson
-          ezjsonm
+          packages = (with pkgs; [
+inotify-tools
+           ]) ++ (with pkgs.ocamlPackages; [
+            ocaml-lsp
+            ppxlib
+            ppx_deriving
+            alcotest
+            yojson
+            ezjsonm
           ]);
         };
       });
diff --git a/lib/dune b/lib/dune
index 40f1ec8..0c23ff0 100644
--- a/lib/dune
+++ b/lib/dune
@@ -1,6 +1,5 @@
 (library
- (name ppx_poplpaper)
- (public_name ppx_poplpaper)
- (kind ppx_rewriter)
+ (name ppx_poplpaper_lib)
+ (public_name ppx_poplpaper._lib)
  (libraries ppxlib)
  (preprocess (pps ppxlib.metaquot)))
diff --git a/lib/ppx_poplpaper.ml b/lib/ppx_poplpaper.ml
deleted file mode 100644
index 9867680..0000000
--- a/lib/ppx_poplpaper.ml
+++ /dev/null
@@ -1,19 +0,0 @@
-(* https://tarides.com/blog/2019-05-09-an-introduction-to-ocaml-ppx-ecosystem/ *)
-
-open Ppxlib
-
-let expand ~ctxt:_ (expr: expression) =
-  expr
-
-let ext = Extension.V3.declare
-  "monomorphic"
-  Extension.Context.expression
-  Ast_pattern.(single_expr_payload __)
-  expand
-
-let rule = Context_free.Rule.extension ext
-
-let () =
-  Driver.register_transformation
-    ~rules:[rule]
-    "monomorphic"
diff --git a/rewriter/dune b/rewriter/dune
new file mode 100644
index 0000000..8553806
--- /dev/null
+++ b/rewriter/dune
@@ -0,0 +1,6 @@
+(library
+ (name ppx_poplpaper)
+ (public_name ppx_poplpaper)
+ (kind ppx_deriver)
+ (libraries ppxlib ppx_deriving.api ppx_poplpaper_lib)
+ (preprocess (pps ppxlib.metaquot)))
\ No newline at end of file
diff --git a/rewriter/ppx_poplpaper.ml b/rewriter/ppx_poplpaper.ml
new file mode 100644
index 0000000..8b192f5
--- /dev/null
+++ b/rewriter/ppx_poplpaper.ml
@@ -0,0 +1,20 @@
+(* https://tarides.com/blog/2019-05-09-an-introduction-to-ocaml-ppx-ecosystem/ *)
+(* https://ocaml-ppx.github.io/ppxlib/ppxlib/writing-ppxs.html#extenders *)
+
+open Ppxlib
+
+let context = Extension.Context.expression
+
+let extender_name = "monomorphic"
+
+let extracter () = Ast_pattern.(single_expr_payload __)
+
+let expander ~ctxt (_: expression) =
+  let loc = Expansion_context.Extension.extension_point_loc ctxt in
+  [%expr 5]
+
+let my_extender = Extension.V3.declare extender_name context (extracter()) expander
+
+let extender_rule = Context_free.Rule.extension my_extender
+
+let _ = Driver.register_transformation ~rules:[extender_rule] "polycheck"
\ No newline at end of file
diff --git a/lib/ppx_poplpaper.mli b/rewriter/ppx_poplpaper.mli
similarity index 100%
rename from lib/ppx_poplpaper.mli
rename to rewriter/ppx_poplpaper.mli
diff --git a/test/bin/dune b/test/rewriter/bin/dune
similarity index 100%
rename from test/bin/dune
rename to test/rewriter/bin/dune
diff --git a/test/bin/pp.ml b/test/rewriter/bin/pp.ml
similarity index 100%
rename from test/bin/pp.ml
rename to test/rewriter/bin/pp.ml
diff --git a/test/dune b/test/rewriter/dune
similarity index 100%
rename from test/dune
rename to test/rewriter/dune
diff --git a/test/test.expected.ml b/test/rewriter/test.expected.ml
similarity index 100%
rename from test/test.expected.ml
rename to test/rewriter/test.expected.ml
diff --git a/test/rewriter/test.ml b/test/rewriter/test.ml
new file mode 100644
index 0000000..b818729
--- /dev/null
+++ b/test/rewriter/test.ml
@@ -0,0 +1,4 @@
+let prop0 (f : 'a -> 'b) (xs : 'a List.t) : bool =
+  List.length (List.map f xs) = 0
+
+let mono_prop0 = [%monomorphic prop0]
\ No newline at end of file
diff --git a/test/test.ml b/test/test.ml
deleted file mode 100644
index e9f0a6e..0000000
--- a/test/test.ml
+++ /dev/null
@@ -1,2 +0,0 @@
-let%monomorphic prop0 (f : 'a -> 'b) (xs : 'a List.t) : bool =
-  List.length (List.map f xs) = 0