parsing todoist style times in emacs lisp

times.el

(rx-define do-rx
  (and word-start
       (or
        ;; today/tomorrow
        (and (group-n 1 "tom") (optional "orrow"))
        (or (and (group-n 1 "tod") (optional "ay")))
        ;; next <thing>
        (and "next "
             (group-n 2 (or "week" "month" "year")))
        ;; in x <duration>
        (and "in " do-duration-rx)
        ;; every <duration>
        (and "every " do-duration-rx)
        ;; for <duration>
        (and "for " do-duration-rx)
        )
       word-end))

(rx-define do-duration-rx
  (and (group-n 3 (or "a" (one-or-more digit)))
       " "
       (group-n 4 (or "day" "week" "month" "year"))
       (optional "s")))

(rx-define do-priority-rx
  (and word-start
       (group (or "p0" "p1" "p2" "p3"))
       word-end))

(defun do-parse-rx (str)
  "Parse the result of `do-time-rx' from LIST and STR into an integer of days."
  (cond
   ;; today/tomorrow
   ((string= (match-string 1 str) "tod") `(:today))
   ((string= (match-string 1 str) "tom") `(:tomorrow))
   ;; next <thing>
   ((string= (match-string 2 str) "week") `(:next-week))
   ((string= (match-string 2 str) "month") `(:next-month))
   ((string= (match-string 2 str) "year") `(:next-year))
   ;; in x <things>.
   ((string= (match-string 3 str) "a")
    `(:n-things
      . (:count 1 :thing ,(match-string 4 str))))
   ((match-string 3 str)
    `(:n-things
      . (:count ,(string-to-number (match-string 3 str)) :thing ,(match-string 4 str))))
   ))

(defun do-parse (string)
  "Parse STRING and extract any interesting keywords."
  (let ((start 0)
        (matches (list)))
    (while (string-match (rx do-rx) string start)
      (setq matches (cons (do-parse-rx string) matches))
      (setq start (match-end 0))
      (message "match: %s" (substring string (match-beginning 0) (match-end 0))))
    matches))