#lang racket

(require racket/date)

(define (p . args)
  (for-each displayln args))

(define (main)
  ; We'll start by getting the current time.
  (define now (current-date))
  (p now)

  ; You can build a date struct by providing the
  ; year, month, day, etc. Times are always associated
  ; with a time zone.
  (define then (date* 2009 11 17 20 34 58 651387237 0 "UTC"))
  (p then)

  ; You can extract the various components of the date
  ; value as expected.
  (p (date-year then))
  (p (date-month then))
  (p (date-day then))
  (p (date-hour then))
  (p (date-minute then))
  (p (date-second then))
  (p (date-nanosecond then))
  (p (date-time-zone-name then))

  ; The day of the week is also available.
  (p (date-week-day then))

  ; These functions compare two dates, testing if the
  ; first occurs before, after, or at the same time
  ; as the second, respectively.
  (p (date<? then now))
  (p (date>? then now))
  (p (date=? then now))

  ; The time-difference function returns a time-duration struct
  ; representing the interval between two times.
  (define diff (time-difference (date->time-utc now) 
                                (date->time-utc then)))
  (p diff)

  ; We can compute the length of the duration in
  ; various units.
  (p (/ (time-duration-nanoseconds diff) 3600000000000))  ; hours
  (p (/ (time-duration-nanoseconds diff) 60000000000))    ; minutes
  (p (/ (time-duration-nanoseconds diff) 1000000000))     ; seconds
  (p (time-duration-nanoseconds diff))

  ; You can use date-add to advance a date by a given
  ; duration, or with a negative duration to move backwards.
  (p (date->string (date-add then diff)))
  (p (date->string (date-add then (time-duration- diff)))))

(main)