refactor(core/term): tracer is now a class

this way we can inherit it in tracers that can trace many things,
including terms.

src/core/t_tracer.ml

@@ -15,12 +15,9 @@ type Tr.entry_view +=
   (* FIXME: remove when we decode *)
   [@@ocaml.warning "-38"]
 
-(* tracer *)
-type t = { sink: Tr.Sink.t; emitted: Tr.Entry_id.t T.Weak_map.t }
+type state = { sink: Tr.Sink.t; emitted: Tr.Entry_id.t T.Weak_map.t }
 
-let create ~sink () : t = { sink; emitted = T.Weak_map.create 16 }
-
-let emit (self : t) (t : T.t) : term_ref =
+let emit_term_ (self : state) (t : Term.t) =
   let module V = Ser_value in
   let rec loop t =
     match T.Weak_map.find_opt self.emitted t with
@@ -58,4 +55,13 @@ let emit (self : t) (t : T.t) : term_ref =
   in
   loop t
 
+(* tracer *)
+class t ~sink =
+  object
+    val state = { sink; emitted = T.Weak_map.create 16 }
+    method emit_term (t : Term.t) : term_ref = emit_term_ state t
+  end
+
+let create ~sink () : t = new t ~sink
+let emit (self : #t) (t : T.t) : term_ref = self#emit_term t
 let emit' self t : unit = ignore (emit self t : term_ref)

src/core/t_tracer.mli

@@ -22,15 +22,15 @@ type Tr.entry_view +=
   (* FIXME: remove *)
   [@@ocaml.warning "-38"]
 
-type t
+class t :
+  sink:Tr.Sink.t
+  -> object
+       method emit_term : Term.t -> term_ref
+     end
 
 val create : sink:Tr.Sink.t -> unit -> t
 (** [create ~sink ()] makes a tracer that will write terms
     into the given sink. *)
 
-val emit : t -> Term.t -> term_ref
-val emit' : t -> Term.t -> unit
-
-(* TODO
-   val reader : Term.store -> Tr.Entry_read.reader
-*)
+val emit : #t -> Term.t -> term_ref
+val emit' : #t -> Term.t -> unit