Question

在C＃中，我会这样写：

这将提示用户重复输入等式，直到他们输入可以解析的等式。我怎么在F＃中做到这一点？

Answer 1

你可以写一个递归函数：

let rec readInput () =
    Console.Write("Enter an equation: ")
    let input = Console.ReadLine()
    match Infix.TryParse(input) with
    | Some(e) -> e
    | None -> readInput()

Answer 2

可能会有点过头，但我曾写过以下内容：

let inputParseLoop msg parser =
    let isNull x = Core.obj.ReferenceEquals (x, null)
    Seq.initInfinite (fun _ ->
        printf "%s " msg
        try Some (stdin.ReadLine ()) with _ -> None)
    |> Seq.takeWhile Option.isSome
    |> Seq.map Option.get
    |> Seq.takeWhile (fun s -> not (isNull s))
    |> Seq.map parser
    |> Seq.skipWhile Option.isNone
    |> Seq.head
    |> Option.get

对于您的用例，请将其命名为：

inputParseLoop "Enter an equation: " Infix.TryParse

如何在F＃中编写输入循环？

2 个答案: