Added stub (failwith) for type annotator

ParserMain.ml

@@ -106,6 +106,8 @@ let () =
 
 (* Temporary: force dune to build AST2.ml *)
 let () =
-  let open Typecheck2 in
-  let _ = temporary_force_dune in
+  if false then
+    let _ = Typecheck2.annotate in
+    ()
+  else
     ()

Typecheck2.ml

@@ -2,6 +2,8 @@
 
 module SMap = Map.Make(String)
 
+module I = AST2.O
+
 module O = struct
   type asttodo = [`TODO] (* occurrences of asttodo will point to some part of the original parser AST *)
 
@@ -102,4 +104,5 @@ module O = struct
     }
 end
 
-let temporary_force_dune = 123
+let annotate : I.ast -> O.ast =
+  failwith "type annotator is not implemented yet"

Typecheck2.mli

@@ -2,6 +2,8 @@
 
 module SMap : Map.S with type key = string
 
+module I = AST2.O
+
 module O : sig
   type asttodo = [`TODO] (* occurrences of asttodo will point to some part of the original parser AST *)
 
@@ -102,4 +104,4 @@ module O : sig
     }
 end
 
-val temporary_force_dune : int
+val annotate : I.ast -> O.ast