我是F#的新手,我正在编写一些小挑战来学习有关该语言的基本细节。由于不可变性,我认为我有一个问题。F#不变性,纯功能和副作用
场景: 我必须在控制台中读取高度线,每行包含一个整数。该整数代表山的大小。 阅读输入后,我需要写出最高山脉的行数。 如果给出的指数是最高的山,那么大小设置为零,否则我松动。 重复该场景,直到所有的山都将其大小设置为零。
下面的代码我写道:
open System
type Mountain = {Id:int; Height:int}
let readlineInt() = int(Console.In.ReadLine())
let readMountainData id = {Id = id; Height = readlineInt()}
let readAllMountainsData = [ for a in 0 .. 7 do yield readMountainData a ]
let rec mainLoop() =
let mountains = readAllMountainsData
let highestMountain = mountains |> List.maxBy (fun x -> x.Height)
printfn "%i" highestMountain.Id
mainLoop()
mainLoop()
该代码将无限循环,我相信这是因为
let readlineInt() = int(Console.In.ReadLine())
是不变的,所以该值设置一次,它的后永远不要再停下来阅读这一行。我试图把'可变'关键字
let mutable readAllMountainsData = [ for a in 0 .. 7 do yield readMountainData a ]
但它没有改变一件事。 你有什么想法吗?
编辑: 我知道这个代码进入无限循环,因为后面添加登录到主循环如下:
let rec mainLoop() =
let mountains = readAllMountainsData
Console.Error.WriteLine("Mountain Count:{0} ", mountains.Length)
mountains |> List.iter (fun x -> Console.Error.WriteLine("Mountain Id:{0} Height:{1}", x.Id, x.Height))
let highestMountain = mountains |> List.maxBy (fun x -> x.Height)
printfn "%i" highestMountain.Id
mainLoop()
然后,我有这样的输出:
Standard Error Stream:
Mountain Count:8
Mountain Id:0 Height:9
Mountain Id:1 Height:8
Mountain Id:2 Height:7
Mountain Id:3 Height:6
Mountain Id:4 Height:5
Mountain Id:5 Height:4
Mountain Id:6 Height:3
Mountain Id:7 Height:2
Mountain Count:8
Mountain Id:0 Height:9
Mountain Id:1 Height:8
Mountain Id:2 Height:7
Mountain Id:3 Height:6
Mountain Id:4 Height:5
Mountain Id:5 Height:4
Mountain Id:6 Height:3
Mountain Id:7 Height:2
Mountain Count:8
Mountain Id:0 Height:9
Mountain Id:1 Height:8
Mountain Id:2 Height:7
etc...
为什么我要重读该值?因为这些值是由外部来源提供的。所以工作流程如下:
Loop one:
I read 8 values for the height of the mountains in the console
I output the value of the highest mountain
Loop two:
I read 8 values for the height of the mountains in the console
I output the value of the highest mountain
Loop three:
I read 8 values for the height of the mountains in the console
I output the value of the highest mountain
etc
你为什么认为代码进入无限循环? –
我刚刚编辑帖子回答你的问题。这是因为如果我在错误流中打印数据,我可以看到它。 –