On Mar 11, 2014, at 12:32 PM, Ismael Figueroa <ifiguer...@gmail.com> wrote:
> Working with a custom handin-server, I have a date value which represents a
> deadline, but I also want to allow late submission up to 3 days later than
> that (well, an arbitrary number of days). Hence, I need to check whether the
> current date is at most 3 days later than the first one.
>
> In the configuration file I read a custom entry for the deadline, indicating
> year, month, day, hours, minutes and seconds. Then I guess I could do:
>
> (define d (seconds->date (find-seconds seconds minutes hours day month
> year)))
> (define d+1 (seconds->date (find-seconds seconds minutes hours (+ day 1)
> month year))
> (define d+2 (seconds->date (find-seconds seconds minutes hours (+ day 2)
> month year))
> (define d+3 (seconds->date (find-seconds seconds minutes hours (+ day 3)
> month year))
>
> And then do a comparison, like
>
> (let ([now (current-seconds)])
> (or (> now (date->seconds d)) (> now (date->seconds d+1) ...))
>
> But this looks too low level to me, and surprisingly the utilities provided
> by racket/date are somewhat sparse.
>
> Does anyone know about a higher-level library for manipulating dates, and
> performing arithmetic comparisons and operations?
Dates are harder than they look. In this case, for instance, I think it would
be a bad idea to add to the “day” without checking that the result is a legal
date. However, in this (and many other) instance(s), it seems like you can get
nearly everything you want simply by holding off on the “seconds->date” call.
#lang racket
(define DAY-SECONDS 86400)
;; ALL DATES IN SECONDS:
(define d (find-seconds seconds minutes hours day month year))
(define d+1 (+ d (* 1 DAY-SECONDS)))
(define d+2 (+ d (* 2 DAY-SECONDS)))
(define d+3 (+ d (* 3 DAY-SECONDS)))
;;And then do a comparison, like
(let ([now (current-seconds)])
(cond [(< now d) "on time!"]
[(< now d+1) "one day late!"]
[(< now d+2) "two days late!"]))
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