Question

我必须编写一个函数，给定一个文件名，指针和一个替换，它交换给定文本文档中的两个字符串。该函数必须使用System.IO.File.OpenText，WriteLine和ReadLine语法。我现在被困在这里，其中函数似乎覆盖给定的文本文档而不是替换针。

 open System


let fileReplace (filename : string) (needle : string) (replace : string) : unit = 
    try // uses try-with to catch fail-cases
        let lines = seq {
                        use file = IO.File.OpenText filename // uses OpenText
                        while not file.EndOfStream // runs through the file 
                            do yield file.ReadLine().Replace(needle, replace)
                        file.Close()
                        }
        use writer = IO.File.CreateText filename // creates the file 
        for line in lines
            do writer.Write line
    with
        _ -> failwith "Something went wrong opening this file" // uses failwith exception

let filename = @"C:\Users\....\abc.txt"
let needle = "string" // given string already appearing in the text
let replace = "string" // Whatever string that needs to be replaced
fileReplace filename needle replace

Answer 1

您的代码的问题在于您在阅读lines时使用了延迟序列。当您使用seq { .. }时，在需要之前不会对实体进行评估。在您的示例中，这是在for循环中迭代行时 - 但在代码到达之前，您调用CreateText并覆盖该文件！

您可以使用列表来解决此问题，该列表会立即进行评估。您还需要将Write替换为WriteLine，但其余的都可以使用！

let fileReplace (filename : string) (needle : string) (replace : string) : unit = 
    try // uses try-with to catch fail-cases
        let lines = 
            [ use file = IO.File.OpenText filename // uses OpenText
              while not file.EndOfStream do // runs through the file 
                yield file.ReadLine().Replace(needle, replace)
            ]
        use writer = IO.File.CreateText filename // creates the file 
        for line in lines do
            writer.WriteLine line
    with
        _ -> failwith "Something went wrong opening this file" // uses failwith exception

我还删除了Close来电，因为use会为您解决此问题。

编辑：我放回了所需的do个关键字 - 我对您的格式感到困惑。大多数人会像在我的更新版本中那样在上一行的末尾写下它们。

编写一个使用OpenText，ReadLine和WriteLine替换字符串的函数

1 个答案: