method private differences_with selection () =
      match selection with
        [] -> ()
      | file :: _ ->
          let filename = (self#cvs_info_of_t file).Ocvs_types.cvs_file in
          let f () =
            match self#select_revision filename with
              None -> ()
            | Some rev ->
                let (diffs, _) = cvs#cvs_diff_file
                    ~rev: rev filename
                in
                Ocamlcvs.Diffs.display_diffs
                  ~title: (filename^" : "^
                           (Ocvs_revision.string_of_revision_number rev.Ocvs_types.rev_number)^
                           " -> "^Ocvs_messages.working_rev)
                  ~file: filename
                  diffs
          in
          handle_error f () ()