全局特殊变量在各处都很特殊

因此这些变量将使用动态绑定。

(defparameter count 0)
;; All uses of count will refer to this one 

(defun handle-number (number)
  (incf count)
  (format t "~&~d~%" number))
  
(dotimes (count 4)
  ;; count is shadowed, but still special
  (handle-number count))
  
(format t "~&Calls: ~d~%" count)
==>
0
2
Calls: 0

为特殊变量提供不同的名称以避免此问题：

(defparameter *count* 0)

(defun handle-number (number)
  (incf *count*)
  (format t "~&~d~%" number))
  
(dotimes (count 4)
  (handle-number count))
  
(format t "~&Calls: ~d~%" *count*)
==>
0
1
2
3
Calls: 4

注 1：在某个范围内不可能使全局变量非特殊。没有声明来制作变量词法。

注 2：可以使用 special 声明在本地上下文中声明一个特殊变量。如果该变量没有全局特殊声明，则声明仅在本地并且可以被遮蔽。

(defun bar ()
  (declare (special a))
  a)                       ; value of A is looked up from the dynamic binding

(defun foo ()
  (let ((a 42))            ; <- this variable A is special and
                           ;    dynamically bound
    (declare (special a))
    (list (bar)
          (let ((a 0))     ; <- this variable A is lexical
            (bar)))))

> (foo)
(42 42)