Question

在Microsoft Visual Studio 2015的F＃教程中，这个代码虽然略有不同。

module Integers = 

    /// A list of the numbers from 0 to 99
    let sampleNumbers = [ 0 .. 99 ]

    /// A list of all tuples containing all the numbers from 0 to 99 andtheir squares
    let sampleTableOfSquares = [ for i in 0 .. 99 -> (i, i*i) ]

    // The next line prints a list that includes tuples, using %A for generic printing
    printfn "The table of squares from 0 to 99 is:\n%A" sampleTableOfSquares
    System.Console.ReadKey() |> ignore

此代码返回标题The table of squares from 0 to 99 is: 然后它发送1-99及其方块的数字。我不明白为什么需要\n%A，特别是为什么它必须是A。

以下是其他一些不同字母的类似例子：

使用%d

module BasicFunctions = 

    // Use 'let' to define a function that accepts an integer argument and returns an integer. 
    let func1 x = x*x + 3             

    // Parenthesis are optional for function arguments
    let func1a (x) = x*x + 3             

    /// Apply the function, naming the function return result using 'let'. 
    /// The variable type is inferred from the function return type.
    let result1 = func1 4573
    printfn "The result of squaring the integer 4573 and adding 3 is %d" result1

使用%s

module StringManipulation = 

    let string1 = "Hello"
    let string2  = "world"

    /// Use @ to create a verbatim string literal
    let string3 = @"c:\Program Files\"

    /// Using a triple-quote string literal
    let string4 = """He said "hello world" after you did"""

    let helloWorld = string1 + " " + string2 // concatenate the two strings with a space in between
    printfn "%s" helloWorld

    /// A string formed by taking the first 7 characters of one of the result strings
    let substring = helloWorld.[0..6]
    printfn "%s" substring

这让我有点困惑，因为他们必须有他们的信件或他们不会工作，所以可能有人。请解释%a，%d和%s以及其他任何其他\n的含义。

Answer 1

本页对此进行了解释：https://msdn.microsoft.com/en-us/library/ee370560.aspx

F＃使用类似于C的合理标准格式字符串。

总结：

jQuery.each([1,2,3], function () {
    if(conditionMet) {
        return false;
    }
});

唯一奇怪的是%s prints a string %d is an integer会尝试打印任何内容

%A只是换行符

Answer 2

符号％A，％s和％d是占位符。当函数printfn由其参数值调用时，它们将被替换。每个占位符都需要特定的参数类型：

％s - 字符串
％d - signed int
％A - 漂亮的打印元组，记录和联合类型

以下是一些可以在F＃REPL中执行的示例：

> printfn "a string: %s" "abc";;
a string: abc
val it : unit = ()

> printfn "a signed int: %d" -2;;
a signed int: -2
val it : unit = ()

> printfn "a list: %A" [1;2;3];;
a list: [1; 2; 3]
val it : unit = ()

> printfn "a list: %A" [(1, "a");(2, "b");(3, "c")];;
a list: [(1, "a"); (2, "b"); (3, "c")]
val it : unit = ()

> printfn "a signed int [%d] and a string [%s]" -2 "xyz";;
a signed int [-2] and a string [xyz]
val it : unit = ()

有关printfn及其占位符的更多信息，我建议使用此网站：

http://fsharpforfunandprofit.com/posts/printf/

字符串＆＃34; \ n＆＃34;与占位符没有直接关系。它插入一个新行。

F＃中％A的含义是什么？

2 个答案: