JSON encoding in Lisp!

json-encode.cl

(defun alist? (lst)
  (cond ((null lst) t)
        ((listp lst) (and (consp (car lst))
                          (alist? (cdr lst))))
        (t nil)))

(defun json-encode-obj (v)
  (format nil "~{~a~^,~}"
          (mapcar (lambda (pair)
                    (format nil "\"~(~a~)\":~a"
                            (car pair)
                            (json-encode (cdr pair))))
                  v)))

(defun json-encode-lst (v)
  (format nil "~{~a~^,~}"
          (mapcar #'json-encode v)))

(defun json-encode (v)
  (cond ((eq t v)    (format nil "true"))
        ((null v)    (format nil "false"))
        ((alist? v)  (format nil "{~a}" (json-encode-obj v)))
        ((listp v)   (format nil "[~a]" (json-encode-lst v)))
        ((stringp v) (format nil "~s" v))
        (t           (format nil "~a" v))))

(let ((var `((a . 1)
             (b . (1 "2" ,t , nil ((foo . "bar\"")) 3)))))
  (format t "~a~%" (json-encode var)))