lisp - deftype - 变量未绑定(bind)

Question

我正在尝试按照 C. Shapiro 的 Common Lisp: An interactive approach 学习 Common Lisp .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))))

当我将它喂给粘液时，它会给出错误 Undefined variable:ELEMENT。哪里出了问题，我该如何定义 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)