diff --git a/src/core/Internal.ml b/src/core/Internal.ml
index cee6eae4..7e704403 100644
--- a/src/core/Internal.ml
+++ b/src/core/Internal.ml
@@ -831,7 +831,9 @@ module Make(Plugin : PLUGIN)
     mutable clause_incr : float;
     (* increment for clauses' activity *)
 
-    mutable on_conflict : (atom array -> unit);
+    mutable on_conflict : (atom array -> unit) option;
+    mutable on_decision : (atom -> unit) option;
+    mutable on_new_atom: (atom -> unit) option;
   }
   type solver = t
 
@@ -868,12 +870,20 @@ module Make(Plugin : PLUGIN)
     var_incr = 1.;
     clause_incr = 1.;
     store_proof;
-    on_conflict = _nop_on_conflict;
+    on_conflict = None;
+    on_decision= None;
+    on_new_atom = None;
   }
 
-  let create ?(store_proof=true) ?(size=`Big) (th:theory) : t =
+  let create
+      ?on_conflict ?on_decision ?on_new_atom
+      ?(store_proof=true) ?(size=`Big) (th:theory) : t =
     let st = create_st ~size () in
-    create_ ~st ~store_proof th
+    let st = create_ ~st ~store_proof th in
+    st.on_new_atom <- on_new_atom;
+    st.on_decision <- on_decision;
+    st.on_conflict <- on_conflict;
+    st
 
   let[@inline] st t = t.st
   let[@inline] nb_clauses st = Vec.size st.clauses_hyps
@@ -947,13 +957,14 @@ module Make(Plugin : PLUGIN)
   let make_term st t =
     let l = Lit.make st.st t in
     if l.l_level < 0 then (
-      insert_elt_order st (E_lit l)
+      insert_elt_order st (E_lit l);
     )
 
   let make_atom st (p:formula) : atom =
     let a = mk_atom st p in
     if a.var.v_level < 0 then (
       insert_elt_order st (E_var a.var);
+      (match st.on_new_atom with Some f -> f a | None -> ());
     ) else (
       assert (a.is_true || a.neg.is_true);
     );
@@ -1923,14 +1934,16 @@ module Make(Plugin : PLUGIN)
       | Solver_intf.Unknown ->
         new_decision_level st;
         let current_level = decision_level st in
-        enqueue_bool st atom ~level:current_level Decision
+        enqueue_bool st atom ~level:current_level Decision;
+        (match st.on_decision with Some f -> f atom | None -> ());
       | Solver_intf.Valued (b, l) ->
         let a = if b then atom else atom.neg in
         enqueue_semantic st a l
     ) else (
       new_decision_level st;
       let current_level = decision_level st in
-      enqueue_bool st atom ~level:current_level Decision
+      enqueue_bool st atom ~level:current_level Decision;
+      (match st.on_decision with Some f -> f atom | None -> ());
     )
 
   and pick_branch_lit st =
@@ -1986,7 +1999,7 @@ module Make(Plugin : PLUGIN)
         ) else (
           add_clause_ st confl
         );
-        st.on_conflict confl.atoms;
+        (match st.on_conflict with Some f -> f confl.atoms | None -> ());
 
       | None -> (* No Conflict *)
         assert (st.elt_head = Vec.size st.trail);
@@ -2063,7 +2076,7 @@ module Make(Plugin : PLUGIN)
                 check_is_conflict_ c;
                 Array.iter (fun a -> insert_elt_order st (Elt.of_var a.var)) c.atoms;
                 Log.debugf info (fun k -> k "(@[sat.theory-conflict-clause@ %a@])" Clause.debug c);
-                st.on_conflict c.atoms;
+                (match st.on_conflict with Some f -> f c.atoms | None -> ());
                 Vec.push st.clauses_to_add c;
                 flush_clauses st;
             end;
@@ -2187,20 +2200,14 @@ module Make(Plugin : PLUGIN)
     | E_unsat (US_false c) ->
       st.unsat_at_0 <- Some c
 
-  let solve ?on_conflict ?(assumptions=[]) (st:t) : res =
+  let solve ?(assumptions=[]) (st:t) : res =
     cancel_until st 0;
     Vec.clear st.assumptions;
     List.iter (Vec.push st.assumptions) assumptions;
-    begin match on_conflict with
-      | None -> ()
-      | Some f -> st.on_conflict <- f;
-    end;
     try
       solve_ st;
-      st.on_conflict <- _nop_on_conflict;
       Sat (mk_sat st)
     with E_unsat us ->
-      st.on_conflict <- _nop_on_conflict;
       Unsat (mk_unsat st us)
 
   let true_at_level0 st a =
diff --git a/src/core/Solver_intf.ml b/src/core/Solver_intf.ml
index a772e7c9..ab375a4d 100644
--- a/src/core/Solver_intf.ml
+++ b/src/core/Solver_intf.ml
@@ -444,6 +444,9 @@ module type S = sig
   (** Main solver type, containing all state for solving. *)
 
   val create :
+    ?on_conflict:(atom array -> unit) ->
+    ?on_decision:(atom -> unit) ->
+    ?on_new_atom:(atom -> unit) ->
     ?store_proof:bool ->
     ?size:[`Tiny|`Small|`Big] ->
     theory ->
@@ -482,7 +485,6 @@ module type S = sig
   (** Lower level addition of clauses *)
 
   val solve :
-    ?on_conflict:(atom array -> unit) ->
     ?assumptions:atom list ->
     t -> res
   (** Try and solves the current set of clauses.