Debugging scheme中的小型仿人文本搜索程序

我试图在scheme中制作一个类似于人类的文本搜索程序

但是这个程序有时不能正常工作

而且我有好几个小时都抓不到虫子

谁能告诉我我的密码有什么问题吗

搜索文本不是一个好主意吗

当我搜索字符串“exp”时 在只包含字符串“explorer”的文本文件中 出错 它告诉我们找到了0

(define (search str)
  (set! count 0)
  (define len (length str))
  ;null character calculating 
  (define data-len (- (length data) 1))
  ;when string length is less than or equal to data-length
  (when (and (not (= 0 len)) (>= data-len len))
    (define first-char (first str))
    (define last-char (last str))
    ;is it correct?
    (define (exact? str len index)
      (if (equal? str (drop (take data (+ index len)) index))
          #t
          #f))
    ;check first and last character of string if correct, check whether this string is correct completely, if so, skip to next index
    (define (loop [index 0])
      (when (> data-len index)
        (if (and (equal? first-char (list-ref data index)) 
                 (equal? last-char (list-ref data (+ index len -1))))
            (when (exact? str len index)
              (set! count (+ count 1))
              (loop (+ index len)))
            (loop (+ index 1)))))
    (loop))
  (send msg set-label (format "Found : ~a" count)))

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我知道已经四年了，但我很怀念我的计划课，所以我做了一件事。（我会发表评论而不是回答，但我的名声还不够好……而且我可能会少一些。）

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编辑：我的意思是这个问题已经四年了，而不是计划课。这可能有点令人毛骨悚然，但话说回来，谁知道三年后我会有什么感觉？

在什么意义上它不起作用？它应该做什么。当我试图在只包含“explorer”的文本文件中查找“exp”时，列表引用：索引8对于列表来说太大了：（#\e#\x#\p#\l#\o#\r#\e#\r）是否使用scheme作为项目的重要部分？有这么多的搜索引擎已经建成。另外，您知道unix的reg exp工具吗？Yur“exp”的示例问题可以在unix中通过

grep“exp”文件实现。祝你好运。在Racket：（regexp search#px“exp”str）你最好把你的代码贴上去——里面有很多难看的地方。
(define (find-pattern pat str); Returns a list of locations of PATturn in STRing.
  (define (pattern-found? pat-list str-list); Is the pattern (pat-list) at the beginning of this string (str-list)? Also, they're lists, now.
    (cond ((null? pat-list) #t); The base case for the recursion.
          ((null? str-list) #f); Obvious
          ((eq? (car pat-list) (car str-list)); First letter matches
           (pattern-found? (cdr pat-list) (cdr str-list))); Recurse
          (else #f)))
  (define (look-for-pattern pat-list str-list counter results-list)
    (cond ((null? str-list) results-list); Base case
          ((pattern-found? pat-list str-list)
           (look-for-pattern pat-list
                             (cdr str-list)
                             (+ counter 1)
                             (cons counter results-list)))
          (else (look-for-pattern pat-list
                                  (cdr str-list)
                                  (+ counter 1)
                                  results-list))))
  (look-for-pattern (string->list pat)
                    (string->list str)
                    0
                    '()))