element-of-set-p：Symbol 的变量值是 void：false

Question

我从 sicp

中 minic 一个 intersction-set 操作

#+name: case-2.3.3-element-of-set-p
#+BEGIN_SRC elisp :session sicp :results value
(defun element-of-set-p(x set)
  (cond ((null set) false)
        ((equal x (car set)) t)
        (t (element-of-setp x (cdr set)))))
(element-of-set-p 1 (list 1 2 3))
#+END_SRC

#+RESULTS: case-2.3.3-element-of-set-p
: t

和交集

#+BEGIN_SRC elisp :session sicp :results value
(defun intersection-set (set1 set2)
  (cond ((or (null set1) (null set2))
         '())
        ((element-of-set-p (car set1) set2)
         (cons (car set1)
               (intersection-set (cdr set1)
                                 set2)))
        (t (intresection-set (cdr set1)
                                set2))))
(trace-function #'intersection-set)
(intersection-set  (list 1 2) (list 2 3 4))
#+END_SRC

报错：

 element-of-set-p: Symbol’s value as variable is void: false

有什么问题吗？

Answer 1

您的代码中有几个拼写错误：

不是element-of-setp，是element-of-set-p
不是intresection-set，是intersection-set
不是false，是nil

这应该有效：

(defun element-of-set-p (x set)
  (cond ((null set) nil)
        ((equal x (car set)) t)
        (t (element-of-set-p x (cdr set)))))

(defun intersection-set (set1 set2)
  (cond ((or (null set1) (null set2))
         '())
        ((element-of-set-p (car set1) set2)
         (cons (car set1)
               (intersection-set (cdr set1) set2)))
        (t (intersection-set (cdr set1) set2))))

element-of-set-p：Symbol 的变量值是 void：false

element-of-set-p: Symbol’s value as variable is void: false

debugging

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sicp