Add days-after helper

Currently, shuttlebot doesn't take the number of days before the booking into
consideration, apart from not changing bookings on today's date.

To help with fixing this, add days-after Given a base date and number of days,
it will produce a consecutive list of days. Then, when searching for available
bookings, we can use this list to ask "is the date I'm booking for in the list
of days-after?"

1 files changed, 3 insertions, 0 deletions

diff --git a/util.scm b/util.scm
index a550427..fad9451 100644
--- a/util.scm
+++ b/util.scm
@@ -10,6 +10,9 @@
      (append-map
       (lambda (x) (map (lambda (y) (cons x y)) ys)) xs)) '(()) lists))
 
+(define (days-after base-date min-lookahead-days)
+  (unfold (cut = <> min-lookahead-days) (cut date+ base-date <>) 1+ 0))
+
 (define* (api-request #:key method path (query #f) (request #f) (transformer identity) (token #f))
   (let*-values
       (((record-name)