Lisp - 邏輯運算子

Common LISP 提供三個邏輯運算子：and、or 和 not，它們作用於布林值。假設A的值為 nil，B的值為 5，則：

運算子	描述	示例
and	它可以接受任意數量的引數。引數從左到右計算。如果所有引數都計算為非 nil，則返回最後一個引數的值。否則返回 nil。	(and A B) 將返回 NIL。
or	它可以接受任意數量的引數。引數從左到右計算，直到一個引數計算為非 nil，在這種情況下返回該引數的值；否則返回nil。	(or A B) 將返回 5。
not	它接受一個引數，如果引數計算為nil，則返回t。	(not A) 將返回 T。

示例 - and 運算子

建立一個名為 main.lisp 的新原始碼檔案，並在其中輸入以下程式碼。這裡我們使用and運算子來檢查各種情況。

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))

輸出

單擊“執行”按鈕或鍵入 Ctrl+E 時，LISP 會立即執行它，並返回結果：

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 運算子

更新名為 main.lisp 的原始碼檔案，並在其中輸入以下程式碼。這裡我們使用or運算子來檢查各種情況。

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))

輸出

單擊“執行”按鈕或鍵入 Ctrl+E 時，LISP 會立即執行它，並返回結果：

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 運算子

更新名為 main.lisp 的原始碼檔案，並在其中輸入以下程式碼。這裡我們使用not運算子來檢查各種情況。

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))

輸出

單擊“執行”按鈕或鍵入 Ctrl+E 時，LISP 會立即執行它，並返回結果：

not A is NIL

 not A is T

 not A is NIL

請注意，邏輯運算作用於布林值，其次，數值零和 NIL 不相同。

lisp_operators.htm

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