type t = Time_Zone.t = UTC | Local | UTC_Plus of int
val current : unit -> t
val change : t -> unit
val gap : t -> t -> int
val from_gmt : unit -> int
val to_gmt : unit -> int
val is_dst : unit -> bool
val hour_of_dst : unit -> int
val on : ('a -> 'b) -> t -> 'a -> 'b