小编Mic*_*lle的帖子

我已经有了生成元素列表的所有排列的代码。然而，我意识到，如果我想操作生成的列表，我需要遍历这个列表。该列表可能会很大，因此维护成本很高。我想知道是否有一种方法可以通过每次调用生成排列，以便我可以检查列表是否与我需要的匹配，如果不匹配，我将生成下一个排列。（每次该函数都会一次返回一个列表。）

我的代码：

(defun allPermutations (list) 
  (cond
     ((null list)  nil) 
     ((null (cdr list))  (list list)) 
     (t  (loop for element in list 
               append (mapcar (lambda (l) (cons element l))
                              (allPermutations (remove element list))))))) 

这是我生成笛卡尔积的代码:

(defun cartesian-product (LIST)
  (LOOP FOR X IN LIST
    NCONC
        (LOOP FOR Y IN LIST
         COLLECT (LIST X Y))))

我尝试输出其中一个笛卡儿产品:

(defun cartesian-product-generator (CALLBACK LIST)
  (LOOP FOR X IN LIST
    NCONC
        (LOOP FOR Y IN LIST
        DO(FUNCALL CALLBACK (LIST X Y)))))

但是当我尝试使用以下测试时出现错误:

(cartesian-product-generator '(A B C))

Error: Too few arguments in call to #<Compiled-function cartesian-product-generator #x30200097E60F>:
       1 argument provided, at least 2 required.  While executing: cartesian-product-generator, in process listener(1).

我是LISP的新手,想知道为什么会出现错误以及如何修复此错误.最终,我希望每次调用函数输出每个笛卡尔积.

例如,如果列表包含((1 1) (1 2) (2 1) (2 2)).我想生成(1 …

我的超类定义如下:

(defclass missionary-state (state)
  ((missionary-left :initarg :missionary-left :initform nil :accessor missionary-left
    :documentation "the number of missionaries on the left side of the river")
   (missionary-right :initarg :missionary-right :initform nil :accessor missionary-right
    :documentation "the number of missionaries on the right side of the river")
   (cannibal-left :initarg :cannibal-left :initform nil :accessor cannibal-left
    :documentation "the number of cannibals on the left side of the river")
   (cannibal-right :initarg :cannibal-right :initform nil :accessor cannibal-right
     :documentation "the number of cannibals on the right side of the river") …