Module S.Option

val none : 'a option signal

none is S.const None.

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

some s is S.map ~eq (fun v -> Some v) None, where eq uses s's equality function to test the Some v's equalities.

val value : ?eq:('a -> 'a -> bool) -> default:[ `Init of 'a signal | `Always of 'a signal ] -> 'a option signal -> 'a signal

value default s is s with only its Some v values. Whenever s is None, if default is `Always dv then the current value of dv is used instead. If default is `Init dv the current value of dv is only used if there's no value at creation time, otherwise the last Some v value of s is used.

  • [value ~default s]t = v if [s]t = Some v
  • [value ~default:(`Always d) s]t = [d]t if [s]t = None
  • [value ~default:(`Init d) s]0 = [d]0 if [s]0 = None
  • [value ~default:(`Init d) s]t = [value ~default:(`Init d) s]t' if [s]t = None and t' is the greatest t' < t with [s]t' <> None or 0 if there is no such t'.