Question

我正试图在C. Shapiro的Common Lisp: An interactive approach之后学习Common Lisp。我尝试从第18章定义bstree类型。我的代码如下

(defun elementp (e)
  (or (characterp e) (numberp e) (packagep e)))
(deftype element ()
  '(satisfies elementp))
(defun bstreep (tree)
  (or (typep tree element)
      (and (listp tree)
           (= (length tree) 3)
           (typep (first tree) element))))

当我将它送入粘液时，会出现错误Undefined variable:ELEMENT。有什么问题，如何定义bstreep函数？

Answer 1

您是否尝试在所有typep次使用中以这种方式使用引用的表单？：

(typep tree 'element)

deftype - 变量未绑定

1 个答案: