`NIL不是Lisp中所需的REAL类型
在我正在阅读的一本书中的示例代码中使用一个简单的贝叶斯概率推理网络进行实验时，似乎存在一个涉及更新节点概率的问题。更新节点`NIL不是Lisp中所需的REAL类型,lisp,common-lisp,Lisp,Common Lisp,在我正在阅读的一本书中的示例代码中使用一个简单的贝叶斯概率推理网络进行实验时，似乎存在一个涉及更新节点概率的问题。更新节点POPULARITY没有问题，但由于某种原因，一旦它尝试更新elevation，就会出现相关错误。我尝试在allegro中输入调试器，它将nil-nil定位为它试图更新的弧的previor prob和current prob的汽车。我不明白为什么，因为这不是第一个节点的问题。代码如下： ;;Network representation (defun odds (prob)
POPULARITYelevationnil-nilprevior probcurrent prob;;Network representation
(defun odds (prob)
(/ prob (- 1.0 prob)))
(defun prob (odds)
(/ odds (1+ odds)))
(defmacro define-node (name prior-prob current-prob arcs)
`(progn
(setf (get ',name 'prior-prob) ,prior-prob)
(setf (get ',name 'prior-odds) (odds ,prior-prob))
(setf (get ',name 'current-prob) ,current-prob)
(setf (get ',name 'current-odds) (odds ,current-prob))
(setf (get ',name 'arcs) ',arcs)))
(defun current-prob (n) (get n 'current-prob))
(defun prior-prob (n) (get n 'prior-prob))
(defun current-odds (n) (get n 'current-odds))
(defun prior-odds (n) (get n 'prior-odds))
(defun sufficiency (arc) (cadr arc))
(defun necessity (arc) (car (cddr arc)))
;Primary evidential variables
(define-node decor 0.5 0.9 ())
(define-node table-setting 0.5 0.8 ())
(define-node surface-cleanliness 0.8 0.8 ())
(define-node air 0.6 0.6 ())
(define-node sounds 0.5 0.5 ())
(define-node clientele 0.5 0.9 ())
(define-node menu 0.5 0.5 ())
(define-node prices 0.5 0.9 ())
(define-node services 0.3 0.9 ())
;Lumped evidential variables
(define-node popularity 0.5 0.6 (indep
(arc sounds 1.5 1.0)
(arc clientele 1.0 0.24)))
(define-node elegance 0.5 0.5 (indep
(arc decor 3.0 0.5)
(arc table-setting 1.0 0.74)
(arc sounds 1.5 0.74)
(arc clientele 1.0 0.5)
(arc menu 1.24 0.74)
(arc prices 1.24 0.74)
(arc service 1.0 0.5)))
(define-node artistry 0.5 0.9 (indep
(arc decor 1.0 0.5)
(arc table-setting 1.0 0.5)
(arc menu 1.5 0.74)
(arc service 1.0 0.5)))
(define-node cleanliness 0.7 0.7 (indep
(arc surface-cleanliness 1.5 0.2)
(arc air 1.5 0.5)))
(define-node taste 0.6 0.6 (indep
(arc popularity 1.5 0.7)
(arc elegance 1.5 0.8)))
(define-node texture 0.6 0.6 (indep
(arc popularity 1.5 0.7)
(arc elegance 1.5 0.8)))
(define-node appearance 0.5 0.5 (indep
(arc artistry 3.0 0.4)))
(define-node quantity 0.5 0.5 (indep
(arc popularity 1.5 0.5)))
(define-node correctness 0.5 0.5 (indep
(arc elegance 1.0 0.7)))
(define-node nutrition 0.6 0.6 (indep
(arc popularity 1.1 0.7)
(arc elegance 1.8 0.8)))
(define-node hygiene 0.8 0.8 (indep
(arc cleanliness 1.0 0.1)))
(define-node overall-food-quality 0.5 0.5
(indep
(and
(arc taste 3.0 0.3)
(arc texture 1.0 0.5))
(and
(arc appearence 1.0 0.3)
(arc correctness 1.3 0.8))
(arc quantity 1.2 0.8)
(arc nutrition 1.0 0.3)
(arc hygiene 1.5 0.2)))
;Update-prob computes P(H|E') for a single arc
(defun update-prob (h arc)
(cond
((> (current-prob (car arc))
(prior-prob (car arc)))
(report-progress 'supportive h arc)
(+ (prior-prob h)
(* (/ (- (prob (* (sufficiency arc)
(prior-odds h)))
(prior-prob h))
(- 1.0 (prior-prob (car arc))))
(- (current-prob (car arc))
(prior-prob (car arc))))))
(t (report-progress 'inhibitive h arc)
(+ (prob (* (necessity arc) (prior-odds h)))
(* (/ (- (prior-prob h)
(prob (* (necessity arc)
(prior-odds h))))
(prior-prob (car arc)))
(current-prob (car arc)))))))
;Report-porgres describes the progress of the updating
(defun report-progress (supp-inhib h arc)
(cond
((null reporting) nil)
(t
(format t "~%~a probability updating for node ~a" supp-inhib h)
(format t " along arc:~%~s with prior odds ~s." arc (prior-odds h))
(format t "~%Prior and current probabilities of E are ~s and ~s."
(prior-prob (car arc)) (current-prob (car arc))))))
(proclaim '(special *node*))
(defun effective-arc-lambda (arc)
(/ (odds (update-prob *node* arc))
(prior-odds *node*)))
(defun combine-indep-lambdas (arc-exp)
(apply #'*
(mapcar #'eval-arc-exp
(cdr arc-exp))))
(defun combine-conjunctive-lambdas (arc-exp)
(apply #'min
(mapcar #'eval-arc-exp
(cdr arc-exp))))
(defun combine-disjunctive-lambdas (arc-exp)
(apply #'max
(mapcar #'eval-arc-exp
(cdr arc-exp))))
(defun update-nodes (nodes)
(cond ((null nodes) nil)
(t (update-node (car nodes))
(update-nodes (cdr nodes)))))
;;Evaluates arc expression, finding odds updating factor
(defun eval-arc-exp (arc-exp)
(cond ((eq (car arc-exp) 'arc)
(effective-arc-lambda (cdr arc-exp)))
((eq (car arc-exp) 'indep)
(combine-indep-lambdas arc-exp))
((eq (car arc-exp) 'and)
(combine-conjunctive-lambdas arc-exp))
((eq (car arc-exp) 'or)
(combine-disjunctive-lambdas arc-exp))
(t (print '(illegal arc expression)) (print arc-exp))))
;;Update nde computes the new probability for a given node
(defun update-node (h)
(setq *node* h)
(setf (get h 'current-odds)
(* (prior-odds h)
(eval-arc-exp (get h 'arcs))))
(setf (get h 'current-prob) (prob (current-odds h)))
(format t "~%Current probability of a node ~a is ~s.~%" h (current-prob h)))
(defun test ()
(update-nodes '(popularity elegance artistry cleanliness
taste texture appearance quantity
correctness nutrition hygiene
overall-food-quality)))
(defmacro sp (name current-prob)
'(progn
(setf (get (car l) 'current-prob) (cadr l))
(setf (get (car l) 'current-odds) (odds (cadr l)))))
谢谢你能提供的任何帮助 出现问题的原因是图形节点名称中至少有两个不一致：
服务服务外观外观sp<>最后，如果你想继续在普通LISP中编程，就要强烈地考虑使用调试器，因为几乎可以立即找到适当的使用调试器的错误原因。 < P>你的问题的原因是图中节点的名称至少有两个不一致：
服务服务外观外观sp最后，如果您想继续使用普通LISP编程，那么强烈地考虑使用调试器，因为几乎可以立即使用适当的调试器找到错误的原因。
< P> <强>检查符号属性>/P>的存在性。 在缺少属性的情况下改进代码的一种方法是编写一个getgetCL-USER 54 > (get 'decor 'prior-prob-a)
NIL
nilgetget properties(defun safer-get (symbol property)
(multiple-value-bind (property0 value tail)
(get-properties (symbol-plist symbol)
(list property))
(declare (ignore property0))
(assert tail ()
"Property ~a not found for node ~a." property symbol)
value))
prior probdecorCL-USER 49 > (safer-get 'decor 'prior-prob)
0.5
CL-USER 47 > (safer-get 'decor 'prior-prob-a)
Error: Property PRIOR-PROB-A not found for node DECOR.
1 (continue) Retry assertion.
2 (abort) Return to level 0.
3 Return to top loop level 0.
装饰的属性prior-prob-a
不存在：
CL-USER 49 > (safer-get 'decor 'prior-prob)
0.5
CL-USER 47 > (safer-get 'decor 'prior-prob-a)
Error: Property PRIOR-PROB-A not found for node DECOR.
1 (continue) Retry assertion.
2 (abort) Return to level 0.
3 Return to top loop level 0.
这样，您就可以获得它是哪个属性和哪个符号的信息。因此，错误消息出现得更早（而不是稍后使用NIL
），并且包含更多信息。检查是否存在符号属性
在缺少属性的情况下改进代码的一种方法是编写一个get
替换，它提供了更多信息。不幸的是，如果属性不存在，get
没有给出指示：
CL-USER 54 > (get 'decor 'prior-prob-a)
NIL
该属性是否不存在，或者其值是nil
？我们不知道如何使用get
我们需要检查财产是否确实存在。这可以通过标准的通用Lisp函数get properties
实现
(defun safer-get (symbol property)
(multiple-value-bind (property0 value tail)
(get-properties (symbol-plist symbol)
(list property))
(declare (ignore property0))
(assert tail ()
"Property ~a not found for node ~a." property symbol)
value))
例如：
属性prior prob
存在于符号decor
：
CL-USER 49 > (safer-get 'decor 'prior-prob)
0.5
CL-USER 47 > (safer-get 'decor 'prior-prob-a)
Error: Property PRIOR-PROB-A not found for node DECOR.
1 (continue) Retry assertion.
2 (abort) Return to level 0.
3 Return to top loop level 0.
符号装饰的属性prior-prob-a
不存在：
CL-USER 49 > (safer-get 'decor 'prior-prob)
0.5
CL-USER 47 > (safer-get 'decor 'prior-prob-a)
Error: Property PRIOR-PROB-A not found for node DECOR.
1 (continue) Retry assertion.
2 (abort) Return to level 0.
3 Return to top loop level 0.
这样，您就可以获得它是哪个属性和哪个符号的信息。因此，错误消息出现得更早（而不是稍后使用NIL
），并且包含更多信息。它只是表明我是一个可怕的复制粘贴骑师，不是吗；）不过要记录在案，这本书是1992年出版的，没有随软盘一起提供。更不用说我喜欢手工输入代码，这样我就可以试验这些程序了。但是是的，我确实希望更频繁地使用调试器。谢谢大家!^_^这就表明我是一个可怕的复制粘贴骑师，不是吗；）不过要记录在案，这本书是1992年出版的，没有随软盘一起提供。更不用说我喜欢手工输入代码，这样我就可以试验这些程序了。但是是的，我确实希望更频繁地使用调试器。谢谢大家!^_^《人工智能要素》一书的完整来源：《人工智能要素》一书的完整来源：