(examples-for date
 ("creates a single date"            (to-string (date 1965 6 8))                                 "1965-06-08" )
 ("navigates to next day"            (let d (date 2004  3 11) (to-string d.tomorrow))            "2004-03-12" )
 ("navigates to previous day"        (let d (date 2006  6 22) (to-string d.yesterday))           "2006-06-21" )
 ("navigates to previous year"       (let d (date 1971 12 18) (to-string d.last-year))           "1970-12-18" )
 ("navigates to next year"           (let d (date 1974  1 11) (to-string d.next-year))           "1975-01-11" )
 ("navigates to previous month"      (let d (date 1971 12 18) (to-string d.last-month))          "1971-11-18" )
 ("navigates to next month"          (let d (date 1974  1 11) (to-string d.next-month))          "1974-02-11" )
 ("jumps a year to previous month"   (let d (date 1974  1 11) (to-string d.last-month))          "1973-12-11" )
 ("navigates to previous week"       (let d (date 2008  2 16) (to-string d.last-week))           "2008-02-09" )
 ("navigates to next week"           (let d (date 1972 11 13) (to-string d.next-week))           "1972-11-20" )
 ("navigates to year start"          (let d (date 1972 11 13) (to-string d.beginning-of-year))   "1972-01-01" )
 ("navigates to year end"            (let d (date 1972 11 13) (to-string d.end-of-year))         "1972-12-31" )
 ("navigates to month start"         (let d (date 1971 11 18) (to-string d.beginning-of-month))  "1971-11-01" )
 ("navigates to month end"           (let d (date 1971 11 18) (to-string d.end-of-month))        "1971-11-30" )
 ("navigates to week start"          (let d (date 2015 11  6) (to-string d.beginning-of-week))   "2015-11-02" )
 ("navigates to week start from sun" (let d (date 2015 11  1) (to-string d.beginning-of-week))   "2015-10-26" )
 ("navigates to week end from sun"   (let d (date 2015 11  1) (to-string d.end-of-week))         "2015-11-01" )
 ("navigates to week end"            (let d (date 2015 11  6) (to-string d.end-of-week))         "2015-11-08" )

 ("can act as hash key"
  (with (h {} d (date 2015 11 8))
    (hash-set h d "on this day")
    (to-string (hash-get h (date 2015 11 8))))
  "on this day")

 ("returns its year"      (let d (date 1999 12 31) d.year)     1999)
 ("returns its month"     (let d (date 1999 12 31) d.month)    12  )
 ("returns its day"       (let d (date 1999 12 31) d.day)      31  )
 ("returns its week-day"  (let d (date 1999 12 31) d.week-day) 5   )
 ("recognises not monday" (let d (date 2015 11  1) d.monday?   ) nil )
 ("recognises monday"     (let d (date 2015 11  2) d.monday?   ) t   )
 ("recognises tuesday"    (let d (date 2015 11  3) d.tuesday?  ) t   )
 ("recognises wednesday"  (let d (date 2015 11  4) d.wednesday?) t   )
 ("recognises thursday"   (let d (date 2015 11  5) d.thursday? ) t   )
 ("recognises friday"     (let d (date 2015 11  6) d.friday?   ) t   )
 ("recognises not friday" (let d (date 2015 11  7) d.friday?   ) nil )
 ("recognises saturday"   (let d (date 2015 11  7) d.saturday? ) t   )
 ("recognises sunday"     (let d (date 2015 11  8) d.sunday?   ) t   )
 ("adds days"             (let d (date 2015 11  8) (to-string (+ d  1))) "2015-11-09")
 ("adds more days"        (let d (date 2015 11  8) (to-string (+ d 10))) "2015-11-18")
 ("subtracts a day"       (let d (date 2015 11 18) (to-string (- d  1))) "2015-11-17")
 ("subtracts more days"   (let d (date 2015 11 18) (to-string (- d  5))) "2015-11-13"))