type uri = string;;

let eq uri1 uri2 =
 uri1 == uri2
;;

let string_of_uri uri = uri;;

let name_of_uri uri =
 let l = Str.split (Str.regexp "/") uri in
  let name_suf = List.nth l (List.length l - 1) in
   List.hd (Str.split (Str.regexp "\.") name_suf)
;;

let depth_of_uri uri =
 List.length (Str.split (Str.regexp "/") uri) - 2
;;

module OrderedStrings =
 struct
  type t = string
  let compare (s1 : t) (s2 : t) = compare s1 s2
 end
;;

module SetOfStrings = Map.Make(OrderedStrings);;

(* Invariant: the map is the identity function,      *)
(*  i.e. (SetOfStrings.find str !set_of_uri) == str  *)
let set_of_uri = ref SetOfStrings.empty;;

let uri_of_string str =
 try
  SetOfStrings.find str !set_of_uri
 with
  Not_found ->
   set_of_uri := SetOfStrings.add str str !set_of_uri ;
   str
;;