type 'a t = 'a Global.t
exception Global_not_initialized of string
val empty : string -> 'a t
val name : 'a t -> string
val set : 'a t -> 'a -> unit
val get : 'a t -> 'a
val undef : 'a t -> unit
val isdef : 'a t -> bool
val opt : 'a t -> 'a option