diff --git a/src/cps/dune b/src/cps/dune
new file mode 100644
index 0000000..5da2306
--- /dev/null
+++ b/src/cps/dune
@@ -0,0 +1,4 @@
+
+(library
+  (name nanoev_cps)
+  (public_name nanoev.cps))
diff --git a/src/cps/nanoev_cps.ml b/src/cps/nanoev_cps.ml
new file mode 100644
index 0000000..4e7aa7e
--- /dev/null
+++ b/src/cps/nanoev_cps.ml
@@ -0,0 +1,74 @@
+type ('st, 'action, 'input, 'a, 'err) t = {
+  inputs: 'input Queue.t;
+  actions: 'action Queue.t;
+  mutable next: ('st, 'action, 'input, 'a, 'err) next;
+}
+
+and ('st, 'action, 'input, 'a, 'err) next =
+  | N_return of 'a
+  | N_fail of 'err
+  | N_run of ('st -> ('st, 'action, 'input, 'a, 'err) transition)
+  | N_await of ('st -> 'input -> ('st, 'action, 'input, 'a, 'err) transition)
+
+and ('st, 'action, 'input, 'a, 'err) transition =
+  | T_return of 'a
+  | T_fail of 'err
+  | T_perform of 'action * ('st, 'action, 'input, 'a, 'err) next
+  | T_await of ('st -> 'input -> ('st, 'action, 'input, 'a, 'err) transition)
+
+type ('a, 'err) res =
+  | Working
+  | Return of 'a
+  | Fail of 'err
+
+(**/*)
+
+let return x : _ transition = T_return x
+let fail err : _ transition = T_fail err
+let perform act f : _ transition = T_perform (act, N_run f)
+let perform_and_await act f : _ transition = T_perform (act, N_await f)
+let await f : _ transition = T_await f
+
+(**/*)
+
+let create run : _ t =
+  { actions = Queue.create (); inputs = Queue.create (); next = N_run run }
+
+let create_rec run : _ t =
+  let rec loop st = run st ~recurse:loop in
+  create loop
+
+let pop_action (self : _ t) : _ option = Queue.take_opt self.actions
+
+(** Add external input to the state machine *)
+let add_input self i : unit = Queue.push i self.inputs
+
+(** Perform some work *)
+let work self st : _ res =
+  let rec loop () =
+    match self.next with
+    | N_return x -> Return x
+    | N_fail err -> Fail err
+    | N_run f -> transition (f st)
+    | N_await f -> run_on_next_input f
+  and transition tr =
+    match tr with
+    | T_return x ->
+      self.next <- N_return x;
+      Return x
+    | T_fail err ->
+      self.next <- N_fail err;
+      Fail err
+    | T_perform (a, n) ->
+      Queue.push a self.actions;
+      self.next <- n;
+      loop ()
+    | T_await f -> run_on_next_input f
+  and run_on_next_input f =
+    match Queue.take self.inputs with
+    | exception Queue.Empty ->
+      self.next <- N_await f;
+      Working
+    | input -> transition (f st input)
+  in
+  loop ()