E.OptionOption events
on_some e is e when Some _ occurs:
on_some e]t = Some v if [e]t = Some (Some v)on_some e]t = None otherwise.value e default is default when e occurs with None:
value e ~default]t = None if [e]t = Nonevalue e ~default]t = Some v if [e]t = Some (Some v)value e ~default]t = [default]t if [e]t = Some Nonebind e f is map (fun v -> Option.bind v f) e.