signature HASHTABLE = sig
  type 'a t

  exception Full and Exists

  val createLog: int -> 'a t
  val insert: 'a t -> string -> 'a -> unit
  val lookup: 'a t -> string -> 'a option
  val lookup2: 'a t -> string ->
        ('a -> 'a option * 'b) -> (unit -> 'b) -> 'b
end