Lisp 为什么我会得到这个lambda表达式错误，我能做些什么呢？

我对lisp很陌生；我想知道这里是否有人能帮我

我有以下代码片段：

(defun write-lookup (binding-list pattern fact)
(cond
        ; No bindings have been stored
        ; Return the binding list with a new one!
        ((not binding-list) (cons (cons pattern fact) nil))

        ; A list of bindings is being stored
        (cond

            ; The current binding matches
            ((equal (caar binding-list) pattern)
                ; Return the binding-list if value matches, nil else
                (if (compare pattern fact) binding-list nil))

            ; Recursively search the rest of the list for the binding
            ((cdr binding-list) (write-lookup (cdr binding-list) pattern fact))

            ; The list doesn't have the binding.
            ; Return the binding-list with the added pattern
            ( T (cons (cons pattern fact) binding-list)))))

当我尝试运行它时，我得到以下结果：

*** - SYSTEM::%EXPAND-FORM: (EQUAL (CAAR BINDING-LIST) PATTERN) should be a
  lambda expression

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有人能指出我的错误吗？谢谢

您嵌套使用cond看起来可疑。您可以使用以下条件尝试以下表单：

(defun write-lookup (binding-list pattern fact) ; No bindings have been stored ; Return the binding list with a new one! (if (not binding-list) (cons (cons pattern fact) nil) (cond ; The current binding matches ((equal (caar binding-list) pattern) ; Return the binding-list if value matches, nil else (if (compare pattern fact) binding-list nil)) ; Recursively search the rest of the list for the binding ((cdr binding-list) (write-lookup (cdr binding-list) pattern fact)) ; The list doesn't have the binding. ; Return the binding-list with the added pattern (T (cons (cons pattern fact) binding-list))))) （定义写查找（绑定列表模式事实） ；未存储任何绑定 ；使用新的绑定列表返回绑定列表！ （如有）（非约束性清单） （反对（反对模式事实）无） （续） ；当前绑定匹配 （（相等（caar绑定列表）模式） ；如果值匹配，则返回绑定列表，否则返回nil （if（比较模式事实）绑定列表nil）） ；递归搜索列表的其余部分以查找绑定 （（cdr绑定列表）（写查找（cdr绑定列表）模式事实）） ；列表没有绑定。 ；返回带有添加模式的绑定列表 （T（cons（cons模式事实）约束列表()()))）

---

很抱歉，格式有轻微更改；emacs喜欢将注释放在右边。

您嵌套使用cond看起来很可疑。您可以使用以下条件尝试以下表单：

(defun write-lookup (binding-list pattern fact) ; No bindings have been stored ; Return the binding list with a new one! (if (not binding-list) (cons (cons pattern fact) nil) (cond ; The current binding matches ((equal (caar binding-list) pattern) ; Return the binding-list if value matches, nil else (if (compare pattern fact) binding-list nil)) ; Recursively search the rest of the list for the binding ((cdr binding-list) (write-lookup (cdr binding-list) pattern fact)) ; The list doesn't have the binding. ; Return the binding-list with the added pattern (T (cons (cons pattern fact) binding-list))))) （定义写查找（绑定列表模式事实） ；未存储任何绑定 ；使用新的绑定列表返回绑定列表！ （如有）（非约束性清单） （反对（反对模式事实）无） （续） ；当前绑定匹配 （（相等（caar绑定列表）模式） ；如果值匹配，则返回绑定列表，否则返回nil （if（比较模式事实）绑定列表nil）） ；递归搜索列表的其余部分以查找绑定 （（cdr绑定列表）（写查找（cdr绑定列表）模式事实）） ；列表没有绑定。 ；返回带有添加模式的绑定列表 （T（cons（cons模式事实）约束列表()()))）

---

很抱歉，格式有轻微更改；emacs喜欢将注释放在右边。

首先，您需要正确缩进代码：

(defun write-lookup (binding-list pattern fact)
  (cond
        ; No bindings have been stored
        ; Return the binding list with a new one!
   ((not binding-list) (cons (cons pattern fact) nil))

        ; A list of bindings is being stored
   (cond

            ; The current binding matches
    ((equal (caar binding-list) pattern)
                ; Return the binding-list if value matches, nil else
     (if (compare pattern fact) binding-list nil))

            ; Recursively search the rest of the list for the binding
    ((cdr binding-list) (write-lookup (cdr binding-list) pattern fact))

            ; The list doesn't have the binding.
            ; Return the binding-list with the added pattern
    (T (cons (cons pattern fact) binding-list)))))

典型的Lisp编辑器会在击键时为您执行此操作

现在您可以很容易地发现第一个COND缺少一个T子句。让我补充一点：

(defun write-lookup (binding-list pattern fact)
  (cond
        ; No bindings have been stored
        ; Return the binding list with a new one!
   ((not binding-list) (cons (cons pattern fact) nil))

        ; A list of bindings is being stored
   (t (cond

            ; The current binding matches
       ((equal (caar binding-list) pattern)
                ; Return the binding-list if value matches, nil else
        (if (compare pattern fact) binding-list nil))

            ; Recursively search the rest of the list for the binding
       ((cdr binding-list) (write-lookup (cdr binding-list) pattern fact))

            ; The list doesn't have the binding.
            ; Return the binding-list with the added pattern
       (T (cons (cons pattern fact) binding-list))))))

我还要将注释移出代码：

(defun write-lookup (binding-list pattern fact)
  (cond ((not binding-list)                          ; No bindings have been stored
         (cons (cons pattern fact) nil))             ; Return the binding list with a new one!
        (t                                           ; A list of bindings is being stored
         (cond ((equal (caar binding-list) pattern)  ; The current binding matches
                (if (compare pattern fact)           ; Return the binding-list if value matches, nil else
                    binding-list
                  nil))   
               ((cdr binding-list)                   ; Recursively search the rest list for the binding
                (write-lookup (cdr binding-list) pattern fact))
               (T                                    ; The list doesn't have the binding.
                (cons (cons pattern fact)            ; Return the binding-list adding the pattern
                      binding-list)))))) 

---

首先，您需要正确缩进代码：

(defun write-lookup (binding-list pattern fact)
  (cond
        ; No bindings have been stored
        ; Return the binding list with a new one!
   ((not binding-list) (cons (cons pattern fact) nil))

        ; A list of bindings is being stored
   (cond

            ; The current binding matches
    ((equal (caar binding-list) pattern)
                ; Return the binding-list if value matches, nil else
     (if (compare pattern fact) binding-list nil))

            ; Recursively search the rest of the list for the binding
    ((cdr binding-list) (write-lookup (cdr binding-list) pattern fact))

            ; The list doesn't have the binding.
            ; Return the binding-list with the added pattern
    (T (cons (cons pattern fact) binding-list)))))

典型的Lisp编辑器会在击键时为您执行此操作

现在您可以很容易地发现第一个COND缺少一个T子句。让我补充一点：

(defun write-lookup (binding-list pattern fact)
  (cond
        ; No bindings have been stored
        ; Return the binding list with a new one!
   ((not binding-list) (cons (cons pattern fact) nil))

        ; A list of bindings is being stored
   (t (cond

            ; The current binding matches
       ((equal (caar binding-list) pattern)
                ; Return the binding-list if value matches, nil else
        (if (compare pattern fact) binding-list nil))

            ; Recursively search the rest of the list for the binding
       ((cdr binding-list) (write-lookup (cdr binding-list) pattern fact))

            ; The list doesn't have the binding.
            ; Return the binding-list with the added pattern
       (T (cons (cons pattern fact) binding-list))))))

我还要将注释移出代码：

(defun write-lookup (binding-list pattern fact)
  (cond ((not binding-list)                          ; No bindings have been stored
         (cons (cons pattern fact) nil))             ; Return the binding list with a new one!
        (t                                           ; A list of bindings is being stored
         (cond ((equal (caar binding-list) pattern)  ; The current binding matches
                (if (compare pattern fact)           ; Return the binding-list if value matches, nil else
                    binding-list
                  nil))   
               ((cdr binding-list)                   ; Recursively search the rest list for the binding
                (write-lookup (cdr binding-list) pattern fact))
               (T                                    ; The list doesn't have the binding.
                (cons (cons pattern fact)            ; Return the binding-list adding the pattern
                      binding-list)))))) 

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我认为这种级别的评论的惯例是

，Emacs很乐意将其缩进到与代码相同的位置。我认为这一级别注释的约定是
，Emacs很乐意将其缩进到与代码相同的位置。谢谢！失踪的T是罪魁祸首。嵌套的COND有什么作用吗？看起来，将嵌套COND中的子句带到主COND的子句级别将产生相同的结果。@Vatine，这是一个很好的观察结果。我不想重写代码，但那是一回事。另外（cons foo nil）=（list foo），…谢谢！失踪的T是罪魁祸首。嵌套的COND有什么作用吗？看起来，将嵌套COND中的子句带到主COND的子句级别将产生相同的结果。@Vatine，这是一个很好的观察结果。我不想重写代码，但那是一回事。另外（cons foo nil）=（list foo）。。。