[求助]请高手指点一下

bh5280

用求交点程序得到下面这个点表，赋值给变量a

((7374.49 697.953 0.0) (15009.6 697.953 0.0) (7374.49 697.953 0.0) (15009.6
697.953 0.0))

为什么 (eq (nth 0 a) (nth 2 a)) 执行的结果为nil呢？

请高手指导一下，万分感谢！

bh5280

ZZXXQQ

结果不相等，EQ函数当然返回nil。

rongyifei

下面是有关eq的定义 :

Determines whether two expressions are identical

(eq expr1 expr2) 

The eq function determines whether expr1 and expr2 are bound to the same object (by setq, for example).

Examples

Given the following assignments:

(setq f1 '(a b c)) 

(setq f2 '(a b c)) 

(setq f3 f2)

Compare f1 and f3:

Command: (eq f1 f3)

nil

eq returns nil because f1 and f3, while containing the same value, do not refer to the same list.

Compare f3 and f2:

Command: (eq f3 f2)

T

eq returns T because f3 and f2 refer to the same list.

rongyifei

为什么不用equal!

bh5280

谢谢楼上，equal好用！