(define (parse-timestamp input)
  (parse
    (bind
      (followed-by
        (sequence
          (map
            (lambda (suffix p)
              (maybe
                (sequence* ((number (as-string (one-or-more (in char-set:digit))))
                            (_ (char-seq (symbol->string suffix))))
                           (result (* (string->number number) (expt 60 p))))
                0))
            '(h m s)
            (reverse (iota 3))))
        end-of-input)
      (o result (cut fold + 0 <>)))
    input))