(* A source which can poll for changes and call an action on the new value
 * when one is found. *)

con changePoller :: Type -> Type
(* The type of pollers over the given type. *) 

val create : t ::: Type -> eq t -> t -> transaction (changePoller t)
(* From an initial value get a poller. *)

val addChangeListener : t ::: Type -> eq t -> (t -> transaction unit) -> int -> changePoller t -> transaction unit
(* Add an action to run on changed values with a polling period given by the int. *)

val ctl : t ::: Type -> changePoller t -> source t
(* Get a source to control or set the current value. *)

val value : t ::: Type -> changePoller t -> signal t
(* A signal holding the current value. *)