module Cell = struct
  type t
  external global : unit -> t = "caml_global_cell"
  external create : int -> t = "caml_cell_create"
  external set : t -> int -> unit = "caml_cell_set"
  external get : t -> int = "caml_cell_get"

  external throw : unit -> string = "caml_cell_throw"
  external call : string -> string = "caml_cell_call"
end

let test_cell c =
  Printf.printf "c=%d\n" (Cell.get c); flush stdout;
  Printf.printf "set 42... "; flush stdout;
  Cell.set c 42;
  Printf.printf "c=%d\n" (Cell.get c); flush stdout;
  begin try
    Printf.printf "set -1... "; flush stdout;
    Cell.set c (-1);
  with e -> print_endline (Printexc.to_string e); flush stdout
  end

let _ =
  print_endline "start"; flush stdout;
  test_cell (Cell.create 271828);
  Gc.full_major (); print_newline ();
  test_cell (Cell.global ()); print_newline ()

let _ =
  Callback.register "caml-throw" Cell.throw;
  print_endline ("callback: "^Cell.call "caml-throw"); flush stdout