lisp - clisp: 变量 x 没有值

Question

我在我的 Common Lisp 代码中收到错误 variable MAP has no value(我在 Ubuntu 终端中使用 clisp shell)。我的代码如下所示(*map* 只是一个关联列表，因此您可以跳过它):

(setf *map* '((shore (stars cast reflections on the rippling sea.  
                            it fills you with a strong but unplaceable emotion.) 
                     (east forest))
              (forest (a roof of treetops blots out the sun.  something rustles 
                         behind you.) 
                      (west shore) 
                      (north cliff))
              (cliff (you nearly stumble into a long and fatal fall into the 
                          sea far below you.  you feel a strange urge to throw 
                          yourself off the ledge.  it would probably wisest to 
                          leave this place.) 
                     (south forest))))

(defun walk-direction (direction room map)
  (second (assoc direction (cddr (assoc room map)))))

(defmacro defspel (&rest rest) `(defmacro ,@rest))

(defspel walk-to (direction room map)
  `(walk-direction ',direction ',room map))

(walk-to east shore *map*)

(我正在学习 liserpati 教程，对于那些想知道我可能会犯的任何奇怪行为的人)

如果把walk-to改成

(defspel walk-to (direction room)
  `(walk-direction ',direction ',room *map*))

然后一切顺利。然而，这打破了函数式编程的美丽约定，我希望尽可能保持原样——更不用说我仍然不知道为什么我的代码不起作用。

Answer 1

walk-to 的定义在 map 之前缺少一个逗号。看一下输出:

(macroexpand-1 '(walk-to east shore *map*))