Class virtual Wutil.handler

class virtual ['a] handler : object .. end
Defines on_xxx in term of connect.

method virtual connect : ('a -> unit) -> unit
method on_check : 'a -> (bool -> unit) -> unit
on_check v emits boolean signal (s=v) on signal s.
method on_value : 'a -> (unit -> unit) -> unit
on_value v emits a unit signal on signal s=v.
method on_event : (unit -> unit) -> unit
on_event emits a unit signal on any signal s.