Events with option occurences.

val some : 'a event -> 'a option event

some e is map (fun v -> Some v) e.

val value : ?default:'a signal -> 'a option event -> 'a event

value default e either silences None occurences if default is unspecified or replaces them by the value of default at the occurence time.

  • [value ~default e]t = v if [e]t = Some (Some v).
  • [value ?default:None e]t = None if [e]t = None.
  • [value ?default:(Some s) e]t = v if [e]t = None and [s]t = v.