module Force_once: Force_oncetype 'a t
val create : (unit -> 'a) -> 'a tcreate f creates a new force_onceval force : 'a t -> 'aforce t runs the thunk if it hadn't already been forced, else it raises an
exception.val ignore : unit -> unit tignore () = create (fun () -> ())val sexp_of_t : ('a -> Sexplib.Sexp.t) -> 'a t -> Sexplib.Sexp.t