Implements a value that is either in a file, or in memory, but not both. Is used by live and the friend to store sequence numbers and counters. If the value is moved to memory, changed, and then the process crashes, the file will correctly reflect that the value has been lost.
module type Arg = Core.Std.Sexpable
module type S = sig .. end
type persistent_singleton
val load : string ->
default:persistent_singleton -> persistent_singleton Import.Deferred.t
val save : string -> value:persistent_singleton -> unit Import.Deferred.t
module Make : 
functor (Z : Arg) -> S with type persistent_singleton = Z.t