type mark = int
-let mark = ref 1
+let mark = ref 0
(* interface functions ******************************************************)
let new_mark () =
incr mark; !mark
-let to_string i = string_of_int i
+let null_mark = 0
+
+let string_of_mark i = string_of_int i
+
+let clear_marks () =
+ mark := 0