anchor.diff:      (declare ((or null fixnum) length start))
       (if (or (null length)
               (> (+ start length) end))
  -        'eof
  +        (values 'eof nil)
           (let* ((end (+ start length))
                  (next (1+ end))
                  (payload-type (aref bytes end)))
  
positive.code:      with length of-type fixnum = 0
       when (eq b #.(char-code #\:)) return (values length (1+ i))
       do (setf length
                (+ (* length 10)
                   (- b (char-code #\0))))
       finally (return nil)))
  
  (defun parse-tnetstring (bytes &optional (start 0) (end (length bytes)))
    (declare ((simple-array (unsigned-byte 8)) bytes)
  
negative.code:                    ;; list
                     (#.(char-code #\])
                        (or
                         (parsing (bytes start end)
                           (loop
                              for val = (next-tnetstring)
                              until (eq val 'eof)
                              collect val))
                         *empty-list*))
                     ;; boolean
  