Sigs.REFPersistent references for OCaml
val ref : ?persistent:string -> 'a -> 'a tref ?persistent default creates a reference. If optional parameter ?persistent is absent, the reference will not be persistent (implemented using OCaml references). Otherwise, the value of persistent will be used as key for the value in the persistent reference table. If the reference already exists, the current value is kept. Be careful to change this name every time you change the type of the value.
val get : 'a t -> 'a Lwt.tGet the value of a reference
val set : 'a t -> 'a -> unit Lwt.tSet the value of a reference