我正在阅读函数式语言，我想知道如何用纯函数式语言实现'尝试'。所以我决定尝试用F＃
来做但我无法获得一半的基础知识。我无法弄清楚如何使用随机数，如何使用返回/继续（起初我以为我做了一个多语句如果错了但似乎我做得对）我无法弄清楚如何打印一个数字在F＃所以我用C＃方式做到了。
更难的问题是tryparse中的out参数，我仍然不确定如何在不使用可变变量的情况下实现tries。也许你们中的一些人可以告诉我如何正确实现这个
我上周要做的C＃代码
using System;
namespace CS_Test
{
class Program
{
static void Main(string[] args)
{
var tries = 0;
var answer = new Random().Next(1, 100);
Console.WriteLine("Guess the number between 1 and 100");
while (true)
{
var v = Console.ReadLine();
if (v == "q")
{
Console.WriteLine("you have quit");
return;
}
int n;
var b = Int32.TryParse(v, out n);
if (b == false)
{
Console.WriteLine("This is not a number");
continue;
}
tries++;
if (n == answer)
{
Console.WriteLine("Correct! You win!");
break;
}
else if (n < answer)
Console.WriteLine("Guess higher");
else if (n > answer)
Console.WriteLine("Guess lower");
}
Console.WriteLine("You guess {0} times", tries);
Console.WriteLine("Press enter to exist");
Console.ReadLine();
}
}
}
非常破碎和错误的F＃代码
open System;
let main() =
let tries = 0;
let answer = (new Random()).Next 1, 100
printfn "Guess the number between 1 and 100"
let dummyWhileTrue() =
let v = Console.ReadLine()
if v = "q" then
printfn ("you have quit")
//return
printfn "blah"
//let b = Int32.TryParse(v, out n)
let b = true;
let n = 3
if b = false then
printfn ("This is not a number")
//continue;
//tries++
(*
if n = answer then
printfn ("Correct! You win!")
//break;
elif n < answer then
printfn ("Guess higher")
elif n>answer then
printfn ("Guess lower")
*)
dummyWhileTrue()
(Console.WriteLine("You guess {0} times", tries))
printfn ("Press enter to exist")
Console.ReadLine()
main()
答案 0 :(得分：6)
欢迎来到F＃！
这是一个工作计划;解释如下。
open System
let main() =
let answer = (new Random()).Next(1, 100)
printfn "Guess the number between 1 and 100"
let rec dummyWhileTrue(tries) =
let v = Console.ReadLine()
if v = "q" then
printfn "you have quit"
0
else
printfn "blah"
let mutable n = 0
let b = Int32.TryParse(v, &n)
if b = false then
printfn "This is not a number"
dummyWhileTrue(tries)
elif n = answer then
printfn "Correct! You win!"
tries
elif n < answer then
printfn "Guess higher"
dummyWhileTrue(tries+1)
else // n>answer
printfn "Guess lower"
dummyWhileTrue(tries+1)
let tries = dummyWhileTrue(1)
printfn "You guess %d times" tries
printfn "Press enter to exit"
Console.ReadLine() |> ignore
main()
很多事情......
如果您正在调用具有多个参数的方法（例如Random.Next），请在args（.Next(1,100)）周围使用parens。
您似乎正在处理递归函数（dummyWhileTrue）而不是while循环;一个while循环也可以，但我保持你的方式。请注意，F＃中没有break或continue，因此您必须使用if内容更加结构化。
我将您的Console.WriteLine更改为printfn，以展示如何使用参数调用它。
我展示了调用最像C＃的TryParse的方式。首先声明你的变量（使其变为可变，因为TryParse将写入该位置），然后使用&n作为参数（在此上下文中，&n就像ref n或C＃中的out n。或者，在F＃中你可以这样做：
let b, n = Int32.TryParse(v)
其中F＃允许你省略trailing-out-parameters，而是在元组结尾返回它们的值;这只是一种语法上的便利。
Console.ReadLine返回一个字符串，在程序结束时你不关心它，所以将它传递给ignore函数以丢弃该值（并删除关于该值的警告未使用的字符串值。）
答案 1 :(得分：6)
这是我的看法，只是为了好玩：
open System
let main() =
let answer = (new Random()).Next(1, 100)
printfn "Guess the number between 1 and 100"
let rec TryLoop(tries) =
let doneWith(t) = t
let notDoneWith(s, t) = printfn s; TryLoop(t)
match Console.ReadLine() with
| "q" -> doneWith 0
| s ->
match Int32.TryParse(s) with
| true, v when v = answer -> doneWith(tries)
| true, v when v < answer -> notDoneWith("Guess higher", tries + 1)
| true, v when v > answer -> notDoneWith("Guess lower", tries + 1)
| _ -> notDoneWith("This is not a number", tries)
match TryLoop(1) with
| 0 -> printfn "You quit, loser!"
| tries -> printfn "Correct! You win!\nYou guessed %d times" tries
printfn "Hit enter to exit"
Console.ReadLine() |> ignore
main()
注意事项：
TryParse
dummyWhileTrue重命名为TryLoop，似乎更具描述性doneWith和notDoneWith，（仅出于美学原因）答案 2 :(得分：5)
我在@ Huusom的解决方案中解除了Evaluate的主模式匹配，但选择了递归循环和累加器而不是@Hussom（非常酷）区分联合和Seq.unfold的应用，以获得非常紧凑的解决方案。 / p>
open System
let guessLoop answer =
let rec loop tries =
let guess = Console.ReadLine()
match Int32.TryParse(guess) with
| true, v when v < answer -> printfn "Guess higher." ; loop (tries+1)
| true, v when v > answer -> printfn "Guess lower." ; loop (tries+1)
| true, v -> printfn "You won." ; tries+1
| false, _ when guess = "q" -> printfn "You quit." ; tries
| false, _ -> printfn "Not a number." ; loop tries
loop 0
let main() =
printfn "Guess a number between 1 and 100."
printfn "You guessed %i times" (guessLoop ((Random()).Next(1, 100)))
答案 3 :(得分：3)
还有以下方面的乐趣：
open System
type Result =
| Match
| Higher
| Lower
| Quit
| NaN
let Evaluate answer guess =
match Int32.TryParse(guess) with
| true, v when v < answer -> Higher
| true, v when v > answer -> Lower
| true, v -> Match
| false, _ when guess = "q" -> Quit
| false, _ -> NaN
let Ask answer =
match Evaluate answer (Console.ReadLine()) with
| Match ->
printfn "You won."
None
| Higher ->
printfn "Guess higher."
Some (Higher, answer)
| Lower ->
printfn "Guess lower."
Some (Lower, answer)
| Quit ->
printfn "You quit."
None
| NaN ->
printfn "This is not a number."
Some (NaN, answer)
let main () =
printfn "Guess a number between 1 and 100."
let guesses = Seq.unfold Ask ((Random()).Next(1, 100))
printfn "You guessed %i times" (Seq.length guesses)
let _ = main()
我使用state的枚举和输入的Seq.unfold来查找结果。