Adding date->seconds

collects/mzlib/date.rkt

@@ -7,6 +7,7 @@
 
 (provide/contract
  [current-date (-> date?)]
+ [date->seconds (date? . -> . exact-integer?)]
  [date->string ((date?) (boolean?) . ->* . string?)]
  [date-display-format (parameter/c (symbols 'american 'chinese 'german 'indian 'irish 'julian 'iso-8601 'rfc2822))]
  [find-seconds ((integer-in 0 61)
@@ -251,6 +252,15 @@
     (lambda ()
       (force d))))
 
+(define (date->seconds date)
+  (find-seconds 
+   (date-second date) 
+   (date-minute date) 
+   (date-hour date) 
+   (date-day date) 
+   (date-month date) 
+   (date-year date)))
+
 (define (find-seconds sec min hour day month year)
   (define (signal-error msg)
     (error 'find-secs (string-append 

collects/scribblings/reference/time.scrbl

@@ -15,7 +15,6 @@ The value of @racket[(current-seconds)] increases as time passes
 seconds can be compared with a time returned by
 @racket[file-or-directory-modify-seconds].}
 
-
 @defproc[(seconds->date [secs-n exact-integer?]) date?]{
 
 Takes @racket[secs-n], a platform-specific time in seconds returned by
@@ -147,6 +146,10 @@ day only if @racket[time?]. See also @racket[date-display-format].}
 Parameter that determines the date string format. The initial format
 is @racket['american].}
 
+@defproc[(date->seconds [date date?]) exact-integer?]{
+Finds the representation of a date in platform-specific seconds.  If
+the platform cannot represent the specified date, an error is
+signaled, otherwise an integer is returned. }
 
 @defproc[(find-seconds [second (integer-in 0 61)]
                        [minute (integer-in 0 59)]

collects/tests/racket/date.rktl

@@ -20,11 +20,14 @@
 (test-find 0 0 0 1 4 2005)
 
 ; date->string
-(let ([d (seconds->date (find-seconds 1 2 3 4 5 2006))])
+(let* ([secs (find-seconds 1 2 3 4 5 2006)]
+       [d (seconds->date secs)])
   (define (test-string fmt time? result)
     (test (parameterize ([date-display-format fmt])
             (date->string d time?))
           fmt result))
+  (test secs date->seconds d)
+  
   (test-string 'american #f "Thursday, May 4th, 2006")
   (test-string 'american #t "Thursday, May 4th, 2006 3:02:01am")
   (test-string 'chinese #f "2006/5/4 星期四")