[Common Lisp] Wassar のコード片

(defun map-fringe (function tree)
  (with-ca/dr tree
    (cond ((endp tree)
           nil)
          ((atom car)
           (cons (funcall function car)
                 #1=(map-fringe function cdr)))
          (t
           (cons (map-fringe function car)
                 #1#)))))

(defun maybe-anaphora-symbol (sym)
  (and (symbolp sym)
       (< 1 (length (symbol-name sym)))
       (char= (char (symbol-name sym) 0) #\@)
       (intern (subseq (symbol-name sym) 1))))

(defmacro with-status (status &body body)
  (let* (syms
         (form (map-fringe (lambda (x)
                             (aif (maybe-anaphora-symbol x)
                                  (progn (pushnew it syms)
                                         it)
                                  x))
                           body)))
    `(json:json-bind ,syms ,status
       ,@form)))

(mapc {with-status _
      (format t "~&~a(~a): ~a" @user_login_id @user.screen_name @text)}
      (json:decode-json-from-string
       (http-request "http://api.wassr.jp/statuses/friends_timeline.json"
                     :basic-authorization *basic-authorization*)))