LISP 6.3 动态变量

最新推荐文章于 2020-12-21 10:28:17 发布

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本文通过实例分析了词法绑定与赋予新值如何仅影响当前作用域，包括变量修改和作用域测试等内容。

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词法绑定与赋予新值仅会影响当前作用域

词法绑定案例

CL-USER> (defvar *x* 10)
*X*

CL-USER> (defun foo()
	   (format t "x:~a~%" *x*))
FOO

CL-USER> (foo)
x:10
NIL

CL-USER> (defun bar()
	   (foo)
	   (let ((*x* 20)) (foo))
	   (foo))
BAR
CL-USER> (bar)
x:10
x:20
x:10
NIL

赋予新值案例

;;;修改foo函数之后再次执行
CL-USER> (defun foo()
	   (format t "Before assignment~18tX:~d~%" *x*)
	   (setf *x* (+ 1 *x*))
	   (format t "After assignment~18tX:~d~%" *x*))
FOO

CL-USER> (foo)
Before assignment X:10
After assignment  X:11
NIL

CL-USER> (bar)
Before assignment X:11
After assignment  X:12
Before assignment X:20
After assignment  X:21
Before assignment X:12
After assignment  X:13
NIL

对作用域的案例测试

注：

(rotatef a b) 将两个变量值互换

(shiftf a b 10)值向左移动

1与2进行对比

CL-USER> (defun foo(a b)
	   (let ((a 2) (b 5)))
	   (rotatef a b)
	   (format t "~a~t~a" a b))
;Compiler warnings :
;   In FOO: Unused lexical variable B
;   In FOO: Unused lexical variable A
FOO
CL-USER> (foo 3 7 )
7 3
NIL

CL-USER> (defun foo(a b)
	   (let ((a 2) (b 5))
	   (rotatef a b)
	   (format t "~a~t~a" a b)))
;Compiler warnings :
;   In FOO: Unused lexical variable B
;   In FOO: Unused lexical variable A
FOO
CL-USER> (foo 3 7 )
5 2
NIL

CL-USER> (defun foo(a b)
	   (let ((a 2) (b 5))
	   (rotatef a b)
	  (format t "~a~t~a~%" a b)
	   (shiftf a b 10)
	   (format t "~a~t~a~%" a b)))

;Compiler warnings :
;   In FOO: Unused lexical variable B
;   In FOO: Unused lexical variable A
FOO
CL-USER> (foo 3 7 )
5 2
2 10
NIL