Lisp - 逻辑运算符

Common LISP 提供三个逻辑运算符：and、or 和 not，它们作用于布尔值。假设A的值为 nil，B的值为 5，则：

运算符	描述	示例
and	它可以接受任意数量的参数。参数从左到右计算。如果所有参数都计算为非 nil，则返回最后一个参数的值。否则返回 nil。	(and A B) 将返回 NIL。
or	它可以接受任意数量的参数。参数从左到右计算，直到一个参数计算为非 nil，在这种情况下返回该参数的值；否则返回nil。	(or A B) 将返回 5。
not	它接受一个参数，如果参数计算为nil，则返回t。	(not A) 将返回 T。

示例 - and 运算符

创建一个名为 main.lisp 的新源代码文件，并在其中输入以下代码。这里我们使用and运算符来检查各种情况。

main.lisp

; set a as 10
(setq a 10)
; set b as 20
(setq b 20)

; perform and operation on a and b
(format t "~% A and B is ~a" (and a b))

; terminate printing
(terpri)
; set a as nil
(setq a nil)
; set b as 5
(setq b 5)

; perform and operation on a and b
(format t "~% A and B is ~a" (and a b))

; terminate printing
(terpri)
; set a as nil
(setq a nil)
; set b as 0
(setq b 0)

; perform and operation on a and b
(format t "~% A and B is ~a" (and a b))

; terminate printing
(terpri)

; set values to variables
(setq a 10)
(setq b 0)
(setq c 30)
(setq d 40)

; print and operation on all four variables
(format t "~% Result of and operation on 10, 0, 30, 40 is ~a" (and a b c d))

; terminate printing
(terpri)
; set values to variables
(setq a 10)
(setq b 20)
(setq c nil)
(setq d 40)

; print and operation on all four variables
(format t "~% Result of and operation on 10, 20, nil, 40 is ~a" (and a b c d))

输出

单击“执行”按钮或键入 Ctrl+E 时，LISP 会立即执行它，并返回结果：

A and B is 20
A and B is NIL

 A and B is NIL
Result of and operation on 10, 0, 30, 40 is 40
Result of and operation on 10, 20, nil, 40 is NIL

示例 - or 运算符

更新名为 main.lisp 的源代码文件，并在其中输入以下代码。这里我们使用or运算符来检查各种情况。

main.lisp

; set a as 10
(setq a 10)
; set b as 20
(setq b 20)

; print or operation on a and b
(format t "~% A or B is ~a" (or a b))
; terminate printing
(terpri)
; set a as nil
(setq a nil)
; set b as 5
(setq b 5)
; perform or operation on a and b
(format t "~% A or B is ~a" (or a b))

; terminate printing
(terpri)
; set a as nil
(setq a nil)
; set b as 0
(setq b 0)
; perform or operation on a and b
(format t "~% A or B is ~a" (or a b))

; terminate printing
(terpri)
; set values of variables
(setq a 10)
(setq b 0)
(setq c 30)
(setq d 40)

; perform or operation on variables
(format t "~% Result of and operation on 10, 0, 30, 40 is ~a" (or a b c d))

; terminate printing
(terpri)
; set values of variables
(setq a 10)
(setq b 20)
(setq c nil)
(setq d 40)
; perform or operation on variables
(format t "~% Result of and operation on 10, 20, nil, 40 is ~a" (or a b c d))

输出

单击“执行”按钮或键入 Ctrl+E 时，LISP 会立即执行它，并返回结果：

A or B is 10

 A or B is 5

 A or B is 0

 Result of and operation on 10, 0, 30, 40 is 10

 Result of and operation on 10, 20, nil, 40 is 10

示例 - not 运算符

更新名为 main.lisp 的源代码文件，并在其中输入以下代码。这里我们使用not运算符来检查各种情况。

main.lisp

; set a as 10
(setq a 10)
; perform not operation on a
(format t "~% not A is ~a" (not a))
; terminate printing
(terpri)
; set q as nil
(setq a nil)
; perform not operation on a
(format t "~% not A is ~a" (not a))
; terminate printing
(terpri)
; set q as 0
(setq a 0)
; perform not operation on a
(format t "~% not A is ~a" (not a))

输出

单击“执行”按钮或键入 Ctrl+E 时，LISP 会立即执行它，并返回结果：

not A is NIL

 not A is T

 not A is NIL

请注意，逻辑运算作用于布尔值，其次，数值零和 NIL 不相同。

lisp_operators.htm

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