diff --git a/lib/dot_of_tast.ml b/lib/dot_of_tast.ml
index a123df6..3a7a7ae 100644
--- a/lib/dot_of_tast.ml
+++ b/lib/dot_of_tast.ml
@@ -68,7 +68,7 @@ let str_of_primary_value (exp : Typedtree.expression) =
   | Texp_ifthenelse (_, _, None) -> Fmt.str "if/then"
   | _ -> "????"
 
-let dot_of_impl (s : Typedtree.structure) : unit =
+let graph_of_impl (s : Typedtree.structure) : G.t =
   let g = G.create () in
   let iterator =
     {
@@ -104,9 +104,10 @@ let dot_of_impl (s : Typedtree.structure) : unit =
   in
   iterator.structure iterator s;
   Log.info (fun m ->
-      m "dot_of_impl fprint_graph:@ %a" Dot.fprint_graph g)
+      m "g_of_impl fprint_graph:@ %a" Dot.fprint_graph g);
+  g
 
-let merlin_parse str : unit =
+let merlin_parse str : G.t =
   let config, _command_args =
     Mconfig.parse_arguments ~wd:(Sys.getcwd ())
       ~warning:(fun _ -> ())
@@ -127,5 +128,12 @@ let merlin_parse str : unit =
             (Untypeast.untype_structure t));
       Log.info (fun m ->
           m "Printtyped:@ %a" Ocaml_typing.Printtyped.implementation t);
-      dot_of_impl t
-  | `Interface _ -> ()
+      graph_of_impl t
+  | `Interface _ -> G.create ()
+
+let dot_of_tast ?(fname = "x.dot") str : unit =
+  let oc = open_out fname in
+  F.pf
+    (Format.formatter_of_out_channel oc)
+    "%a" Dot.fprint_graph (merlin_parse str);
+  close_out oc
diff --git a/lib/dot_of_tast.mli b/lib/dot_of_tast.mli
index 70d2ec1..3dad9f1 100644
--- a/lib/dot_of_tast.mli
+++ b/lib/dot_of_tast.mli
@@ -1 +1 @@
-val merlin_parse : string -> unit
+val dot_of_tast : ?fname:string -> string -> unit