diff --git a/prototype/tango-prototype/src/tango_oid.erl b/prototype/tango-prototype/src/tango_oid.erl
index 726673b..0325cd9 100644
--- a/prototype/tango-prototype/src/tango_oid.erl
+++ b/prototype/tango-prototype/src/tango_oid.erl
@@ -23,7 +23,7 @@
 -behaviour(gen_server).
 
 %% API
--export([start_link/3, stop/1,
+-export([start_link/4, stop/1,
          put/3, get/2]).
 
 %% gen_server callbacks
@@ -41,17 +41,19 @@
 -type lpn() :: non_neg_integer().
 
 -record(state, {
-          page_size :: non_neg_integer(),
-          seq :: pid(),
-          proj :: term(),
-          last_read_lpn :: lpn(),
+          page_size :: non_neg_integer(),       % CORFU page size
+          seq :: pid(),                         % sequencer pid
+          proj :: term(),                       % projection
+          cb_mod :: atom(),                     % callback module
+          last_read_lpn :: lpn(),               %
           last_write_lpn :: lpn(),
-          back_ps :: [lpn()],
-          i_state :: orddict:orddict()
+          back_ps :: [lpn()],                   % back pointers (up to 4)
+          i_state :: orddict:orddict()          % internal state thingie
          }).
 
-start_link(PageSize, SequencerPid, Proj) ->
-    gen_server:start_link(?MODULE, [PageSize, SequencerPid, Proj], []).
+start_link(PageSize, SequencerPid, Proj, CallbackMod) ->
+    gen_server:start_link(?MODULE,
+                          [PageSize, SequencerPid, Proj, CallbackMod], []).
 
 stop(Pid) ->
     gen_server:call(Pid, {stop}, ?LONG_TIME).
@@ -64,32 +66,35 @@ get(Pid, Key) ->
 
 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
 
-init([PageSize, SequencerPid, Proj]) ->
+init([PageSize, SequencerPid, Proj, CallbackMod]) ->
     LastLPN = find_last_lpn(SequencerPid),
     {BackPs, Pages} = fetch_unread_pages(Proj, LastLPN, 0),
-    Dict = play_log_pages(Pages, orddict:new()),
+    I_State = play_log_pages(Pages, CallbackMod:fresh(), CallbackMod),
     {ok, #state{page_size=PageSize,
                 seq=SequencerPid,
                 proj=Proj,
+                cb_mod=CallbackMod,
                 last_read_lpn=LastLPN,
                 last_write_lpn=LastLPN,
                 back_ps=BackPs,
-                i_state=Dict}}.
+                i_state=I_State}}.
 
-handle_call({put, Key, Val}, _From,
-            #state{proj=Proj0, page_size=PageSize, back_ps=BackPs} = State) ->
-    Page = term_to_binary({put, Key, Val}),
-    FullPage = tango:pack_v1([{?OID_STREAM_NUMBER, BackPs}], Page, PageSize),
-    {{ok, LPN}, Proj1} = corfurl_client:append_page(Proj0, FullPage),
-    NewBackPs = tango:add_back_pointer(BackPs, LPN),
-    {reply, garrr, State#state{proj=Proj1,
-                               last_write_lpn=LPN,
-                               back_ps=NewBackPs}};
-handle_call({get, Key}, _From, State) ->
+handle_call({put, _Key, _Val}=Op, _From,
+            #state{proj=Proj0, cb_mod=CallbackMod,
+                   page_size=PageSize, back_ps=BackPs, i_state=I_State}=State) ->
+    {Res, I_State2, Proj1, LPN, NewBackPs} =
+        CallbackMod:do_dirty_op(Op, I_State, ?OID_STREAM_NUMBER,
+                                Proj0, PageSize, BackPs),
+    {reply, Res, State#state{i_state=I_State2,
+                             proj=Proj1,
+                             last_write_lpn=LPN,
+                             back_ps=NewBackPs}};
+handle_call({get, _Key}=Op, _From, #state{cb_mod=CallbackMod} = State) ->
     {Pages, State2} = fetch_unread_pages(State),
     %% ?D(Pages),
-    #state{i_state=Dict} = State3 = play_log_pages(Pages, State2),
-    {reply, orddict:find(Key, Dict), State3};
+    #state{i_state=I_State} = State3 = play_log_pages(Pages, State2),
+    Reply = CallbackMod:do_pure_op(Op, I_State),
+    {reply, Reply, State3};
 handle_call({stop}, _From, State) ->
     {stop, normal, ok, State};
 handle_call(_Request, _From, State) ->
@@ -137,14 +142,9 @@ fetch_unread_pages(Proj, LastLPN, StopAtLPN) ->
                          [], LPNs),
     {BackPs, Pages}.
 
-play_log_pages(Pages, #state{i_state=Dict} = State) ->
-    Dict2 = play_log_pages(Pages, Dict),
-    State#state{i_state=Dict2};
-play_log_pages(Pages, Dict) ->
-    %% ?D({play_log_pages, Pages}),
-    lists:foldl(fun({put, K, V}=_Op, D) ->
-                        %% ?D(_Op),
-                        orddict:store(K, V, D)
-                end,
-                Dict,
-                [binary_to_term(Page) || Page <- Pages]).
+play_log_pages(Pages, #state{cb_mod=CallbackMod, i_state=I_State} = State) ->
+    I_State2 = play_log_pages(Pages, I_State, CallbackMod),
+    State#state{i_state=I_State2}.
+
+play_log_pages(Pages, I_State, CallbackMod) ->
+    CallbackMod:play_log_mutate_i_state(Pages, I_State).
diff --git a/prototype/tango-prototype/test/tango_oid_test.erl b/prototype/tango-prototype/test/tango_oid_test.erl
index 39d37dc..b19270d 100644
--- a/prototype/tango-prototype/test/tango_oid_test.erl
+++ b/prototype/tango-prototype/test/tango_oid_test.erl
@@ -36,7 +36,7 @@ tango_oid_smoke_test() ->
                              fun tango_oid_smoke_test_int/3).
 
 tango_oid_smoke_test_int(PageSize, Seq, Proj) ->
-    {ok, OID_Map} = tango_oid:start_link(PageSize, Seq, Proj),
+    {ok, OID_Map} = tango_oid:start_link(PageSize, Seq, Proj, tango_dt_map),
 
     ok = tango_oid:stop(OID_Map),
     ok.
@@ -46,15 +46,15 @@ tango_oid_one_test() ->
                              fun tango_oid_one_test_int/3).
 
 tango_oid_one_test_int(PageSize, Seq, Proj) ->
-    {ok, OID_Map} = tango_oid:start_link(PageSize, Seq, Proj),
+    {ok, OID_Map} = tango_oid:start_link(PageSize, Seq, Proj, tango_dt_map),
 
     try
         K1 = foo,
         V1 = bar1,
         V2 = bar2,
-        garrr = tango_oid:put(OID_Map, K1, V1),
+        ok = tango_oid:put(OID_Map, K1, V1),
         {ok, V1} = tango_oid:get(OID_Map, K1),
-        garrr = tango_oid:put(OID_Map, K1, V2),
+        ok = tango_oid:put(OID_Map, K1, V2),
         {ok, V2} = tango_oid:get(OID_Map, K1),
         error = tango_oid:get(OID_Map, "does not exist"),