Lisp：执行集合联合操作

Question

我是LISP.I的初学者，在ubuntu中使用clisp。我在lisp中有一段代码可以对两个lists.The逻辑进行并集运算correct.But 卡在一个错误是：

*** - APPEND: A proper list must not end with T

我的代码是：

(defun set-union (L1 L2)
(cond 
 ((null L2)   ;if l2 is null then union is l1 itself. 
  L1) 
 ((not (member (first L2) L1))  ;check if first member of l2 is in l1 or not
  (setq l1 (append (set-union L1 (rest L2)) (list (first L2))))) ;if not then append it with the union of l1 and rest of l2.
 (t
  (set-union L1 (rest L2)))
  )) ;if second condition is not true then carry out union on l1 and rest of the elements of l2
(setq l1 (list 'a 'c 'b 'g))
(setq l2 (list 'd 'g 't))
(set-union l1 l2)
(print l1)

我需要帮助！！谢谢。

Answer 1

(append (set-union L1 (rest L2)) (first L2))

在你的逻辑中的某个点尝试 append (A C B G . T) 和 E，但失败了，因为第一个不是正确的列表。

要么使用

(append (set-union L1 (rest L2)) (list (first L2)))

或者，更好

(cons (first L2) (set-union L1 (rest L2)))

Lisp：执行集合联合操作

Lisp: to perform set union operation

clisp

set-union