《通链参考手册》


Variable +, ++, +++

●值类型:

an object.

●初始值:

implementation-dependent.

●详情:

The variables +, ++, and +++ are maintained by the Lisp read-eval-print loop to save forms that were recently evaluated.

The value of + is the last form that was evaluated, the value of ++ is the previous value of +, and the value of +++ is the previous value of ++.

●例子:

(+ 0 1) =>  1
(- 4 2) =>  2
(/ 9 3) =>  3
(list + ++ +++) =>  ((/ 9 3) (- 4 2) (+ 0 1))
(setq a 1 b 2 c 3 d (list a b c)) =>  (1 2 3)
(setq a 4 b 5 c 6 d (list a b c)) =>  (4 5 6)
(list a b c) =>  (4 5 6)
(eval +++) =>  (1 2 3)
#.`(,@++ d) =>  (1 2 3 (1 2 3))

●受制于:

Lisp read-eval-print loop.

●更多信息:

- (variable), * (variable), / (variable), Section 25.1.1 (Top level loop)

●说明: 无。


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