将对追加到球拍/方案中的列表 [英] Append pair to list in racket/scheme

问题描述

如下所示，我具有 load-mobile-plan 函数，该函数迭代文本并将第n行和n + 1行(n =奇数)构造为一对，然后将其附加到列表.

As shown below, I have the load-mobile-plan function which iterate the text and construct the nth and n+1 lines(n = odd) into a pair, it then append it to a list.

(define temp-pair '())
(define mobile-plan '())

(define load-mobile-plan
  (lambda (file)
    (let [(line (read-line file))]
      (unless (eof-object? line)
        (set! temp-pair (cons line (read-line file)))
        (set! mobile-plan (cons temp-pair mobile-plan))
        (load-mobile-plan file)))))

(call-with-input-file "xxx.txt" load-mobile-plan)

我的问题:
-这在函数式编程中是否合适?我听说函数式编程中的函数不应有副作用，而应仅取决于其自身的输入变量.
-如果是这样，如何修改我的代码以实现相同的目标?

My questions:
-Is this an appropriate method in functional programming? As i heard that function in functional programming should not have side-effects and depends on its own input variables only.
-If so, how to modify my codes to achieve same goal?

推荐答案

在对函数式编程进行调查"几天后，确定，我设法编写了以下代码，与我所讨论的代码具有相同的功能:

OK after few days of "investigation" into functional programming, i manage to code the following, which do the same job as my codes in question:

(define load-mobile-plan
  (lambda (file)
    (let [(mobile-plan '())]
      (read-file file mobile-plan))))

(define read-file
  (lambda (file mobile-plan)
    (let [(line (read-line file))]
      (if [eof-object? line]mobile-plan
          (let* [(temp-pair (cons (string-normalize-spaces line)
                                  (string-normalize-spaces (read-line file))))
                 (mobile-plan (cons temp-pair mobile-plan))]
            (read-file file mobile-plan))))))

(call-with-input-file "xxx.txt" load-mobile-plan)

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