package react

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

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.