list - LISP - 如何从嵌套列表中获取平均长度？一步一步的解释

Question

我知道这个答案已得到解答，但我是 LISP 的新手，我不明白!

LISP - How to get the average length for nested lists?

(defun nested-lists-average-length (ls &aux (i 0) (n 0))
  (dolist (a ls (float (/ _______))) ;maybe (/ i n) ;;get average lenght of list
    (if (_______ a) ;??
      (progn (_______ i) ;??
             (incf n (_______ a) ))))) ;?

我写了这个函数:

(defun average-sublist-length (list &aux (sum 0) (n 0))
  (dolist (x list (when (plusp n) (/ sum n))) 
    (when (plusp x)
      (incf sum (min x 100)) 
      (incf n)))) 

(average-sublist-length '(1 2 3 4 (5 6 7) 8 9)) 

如果我想让它执行，我会得到错误:

PLUSP: (5 6) is not a real number Now I've got problems with calling it.

感谢您的帮助!

Answer 1

添加调试信息:

  ....
  (dolist (a ls ....)
    (print `(:debug :i ,i :n ,n :a ,a))
    (if ....) 
  ....

the question you link to 中的示例打印以下内容:

(nested-lists-average-length '(1 (2 3 4) 5 (6 7) 8 (9)))

(:DEBUG :I 0 :N 0 :A 1) 
(:DEBUG :I 0 :N 0 :A (2 3 4)) 
(:DEBUG :I 1 :N 3 :A 5) 
(:DEBUG :I 1 :N 3 :A (6 7)) 
(:DEBUG :I 2 :N 5 :A 8) 
(:DEBUG :I 2 :N 5 :A (9))