+class logger =
+ object
+ val mutable level = 0 (* indentation level *)
+ method log (msg: msg) =
+ match msg with
+ | `Start_type_checking _ ->
+ level <- level + 1;
+ log ~level msg
+ | `Type_checking_completed _ ->
+ log ~level msg;
+ level <- level - 1;
+ | _ -> log ~level msg
+ end
+
+let log msg = log ~level:1 msg
+