let (|>) x f = f x      (* (for OCaml < 4.01) *)
let manual () = print_endline "Manual chosen..."
let automatic () = print_endline "Automatic chosen..."

let () =
  let dialog = GWindow.dialog
    ~title:"Partitioning"
    () in

  GMisc.label
    ~packing:(dialog#vbox#pack ~expand:true)
    ~text:"Automatic or manual?"
    () |> ignore;

  dialog#add_button "Cancel" `CANCEL;
  dialog#add_button "Manual" `MANUAL;
  dialog#add_button "Automatic" `AUTOMATIC;

  dialog#connect#response ~callback:(function
    | `AUTOMATIC -> automatic ()
    | `MANUAL -> manual ()
    | `CANCEL | `DELETE_EVENT -> GMain.Main.quit ()
  ) |> ignore;

  dialog#show ();
  GMain.Main.main ()