(defn validated
"Return a function which constructs and instant by calling constructor
after first validating that those arguments are in range and otherwise
plausible. The resulting function will throw an exception if called
with invalid arguments."
[new-instance]
(fn [years months days hours minutes seconds nanoseconds
offset-sign offset-hours offset-minutes]
(verify (<= 1 months 12))
(verify (<= 1 days (days-in-month months (leap-year? years))))
(verify (<= 0 hours 23))
(verify (<= 0 minutes 59))
(verify (<= 0 seconds (if (= minutes 59) 60 59)))
(verify (<= 0 nanoseconds 999999999))
(verify (<= -1 offset-sign 1))
(verify (<= 0 offset-hours 23))
(verify (<= 0 offset-minutes 59))
(new-instance years months days hours minutes seconds nanoseconds
offset-sign offset-hours offset-minutes)))