Drracket:创建一个函数，它将返回一个使用冒泡排序的比较器的排序列表

Question

这就是我要对字符串进行排序的内容：

;create a function that checks if a list of strings is sorted
(define (stringCmpr l)
         (if (<= (length l) 1)
            true
            (and (string<=? (car l) (cadr l))(stringCmpr (cdr l))
                 )
            )
  )
;Create a funciton that checks if a list of numbers is sorted
(define (numCmpr l)
         (if (<= (length l) 1)
            true
            (and (<= (car l) (cadr l)) (numCmpr (cdr l))
                 )
            )
  )
;create function that checks whether a list containes numbers of 
strings checks if the list is sorted
(define (is-sorted? l)
         (if (number? (car l))
            (numCmpr l)
            (stringCmpr l)
            )
  )
    (define (bubble-pass lst)
      (cond
        ((empty? lst) lst)
        ((= (length lst) 1) lst)
        ((and (= (length lst) 2) (string>? (first lst) (second lst))) 
(list 
    (second lst) (first lst)))
        ((and (= (length lst) 2) (string<? (first lst) (second lst))) 
lst)
        ((string>? (first lst) (second lst))
         (append
          (list (second lst))
          (bubble-pass (append (list (first lst)) (rest (rest lst))))
          )
         )
        (else
         (append (list (first lst) (second lst)) (bubble-pass (rest 
(rest lst))))
         )
        )
      )

(define (string-bubble-sort lst)
  (if (is-sorted? lst)
      lst
      (string-bubble-sort (bubble-pass last))
      )
  )

这适用于按从A到Z的顺序对字符串进行排序

这就是我到目前为止的通用排序(func表示比较器：<，> =，string

;create a function that checks if a list of strings is sorted
(define (gen-stringCmpr l func)
         (if (<= (length l) 1)
            true
            (and (func (car l) (cadr l))(gen-stringCmpr (cdr l) func)
                 )
             )
  )
;Create a funciton that checks if a list of numbers is sorted
(define (gen-numCmpr l func)
         (if (<= (length l) 1)
            true
            (and (func (car l) (cadr l)) (gen-numCmpr (cdr l) func)
                 )
            )
  )
;create funciton that checks whether a list contains numbers or 
strings checks if the list is sorted
(define (general-sorted? l func)
         (if (number? (car l))
            (gen-numCmpr l func)
            (gen-stringCmpr l func)
            )
  )
; Purpose: Create a function that bubble sorts a list given a 
; comparison function

;Signature:
; list function-> list

;Examples:
(check-expect (general-bubble-sort (list "B" "A" "C") string<?) (list 
"A" "B" "C"))
(check-expect (general-bubble-sort (list "B" "A" "C") string>?) (list 
"C" "B" "A"))
(check-expect (general-bubble-sort (list 6 4 5) <) (list 4 5 6))
(check-expect (general-bubble-sort (list 2 3 1) >) (list 3 2 1))

Stub:
(define (general-bubble-sort lst func) '( "spinach")

 Template:

Code:

(define (general-bubble-pass lst func)
  (cond
    ((empty? lst) last)
    ((= (length lst) 1) last)
    ((and (= (length lst) 2) (equal? (func (first lst) (second lst)) 
false)) (list (second lst) (first lst)))
    ((and (= (length lst) 2) (func (first lst) (second lst))) last)
    ((equal? (func (first lst) (second lst)) false)
     (append
      (list (second last))
      (general-bubble-pass (append (list (first lst)) (rest (rest 
lst))) func)
      )
     )
    (else
     (append (list (first lst) (second lst)) (general-bubble-pass 
(rest (rest lst)) func))
     )
    )
  )

(define (general-bubble-sort lst func)
  (if (general-sorted? lst func)
      lst
      (general-bubble-sort (general-bubble-pass lst func) func)
      )
  )

Answer 1

由于过于宽松的签名，您在这里没有正确使用您的抽象。从技术上讲，您希望最终的冒泡排序是这样工作的：

; general-bubble-sort: (X) [List-of X] [X X -> Boolean] -> [List-of X]

通过限制我们接收的内容的类型，并告诉用户他们应该如何使用它，我们消除了需要在general-sorted?中执行的检查。我们只知道我们必须将正确的函数传递给它，否则就是用户的错，因为没有传递正确的函数。您还可以在两个函数之间抽象更多的代码。如下所示：

(define (general-sorted? l func)
  (or (<= (length l) 1) (and (func (car l) (cadr l)) (general-sorted? (cdr l)))))

你的第二个函数有很多功能，让我们结合一些情况，也不要使用(equal? x boolean)。这是一种糟糕的做法。相反，我们应该在适当的时候使用布尔表达式来获取true。我们还应该在这里使用累加器，因为它清楚地说明了我们在向下递归时跟踪的是哪一块数据：

(define (general-bubble-pass lst func)
  (local [(define (general-bubble-pass-acc lst bubble)
            (cond
              [(empty? lst) (list bubble)]
              [(not (func (first lst) bubble)) (cons bubble (general-bubble-pass-acc (rest lst) (first lst)))]
              [else (cons (first lst) (general-bubble-pass-acc (rest lst) bubble))]))]
    (if (<= (length lst) 1) lst (general-bubble-pass-acc (rest lst) (first lst)))))

最后的冒泡排序函数不会改变。