Print for cyclic structures

gistfile1.txt

(defun print-env-stack (env-stack)
  (let ((*print-circle* t))
    (if (atom env-stack)
        nil
      (progn (format t "~&~a: " (caar env-stack))
             (mapcar (lambda (b) (format t "~&   ~w = ~w" (car b) (cdr b)))
                     (cdar env-stack))
             (print-env-stack (cdr env-stack))))))