deftype - 变量未绑定

Question

我正在尝试学习 Common Lisp，跟随 C. Shapiro 的 Common Lisp: An interactive approach。我尝试定义第 18 章中的 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))))

当我把它喂给粘液时，它给出了错误 Undefined variable:ELEMENT。有什么问题，如何定义 bstreep 函数？

Answer 1

您是否尝试过在所有 typep 用法中以这种方式使用引号形式？:

(typep tree 'element)

deftype - 变量未绑定

deftype - variable unbound

lisp

common-lisp