在Scheme/Racket中实现A*搜索算法

(define (a-star-search start-node goal-node)
  (define open-list (list (list start-node 0 (heuristic-function start-node))))
  (define closed-list '())
  
  (define (heuristic-function node)
    ; 启发函数的实现，根据问题特点设计
    
  (define (expand-node node g-cost)
    ; 扩展节点的实现，生成子节点并计算代价
    
  (define (update-open-list node g-cost h-cost)
    ; 更新开放列表的实现，根据代价选择插入或更新节点
    
  (define (find-node-in-list node list)
    ; 在列表中查找节点的实现
    
  (define (construct-path node)
    ; 构建最优解路径的实现
    
  (define (search-loop)
    (cond
      ((null? open-list) #f) ; 未找到最优解
      ((equal? (caar open-list) goal-node) (construct-path (caar open-list))) ; 找到最优解
      (else
       (let* ((current-node (caar open-list))
              (g-cost (cadr (car open-list)))
              (h-cost (caddr (car open-list))))
         (set! open-list (cdr open-list))
         (set! closed-list (cons current-node closed-list))
         (expand-node current-node g-cost)
         (search-loop)))))
  
  (search-loop))