open Cupto;;

type 'a exn = 'a prompt;;
let new_exn = new_prompt;;

let raise p v = cupto p (fun _ -> v);;

let handle p h a =
  let q = new_prompt() in
  set q (fun () ->
           h (set p (fun () ->
                       let v = a() in cupto q (fun _ -> v))))
;;