如何使用LINQ查询在Select with F#中包含索引

Question

我在C#中有这个代码示例,它从数组输出索引和值:

static void Sample_Select_Lambda_Indexed()
{
    string[] arr = { "my", "three", "words" };

    var res = arr.Select((a, i) => new
    {
        Index = i,
        Val = a
    });

    foreach(var element in res)
        Console.WriteLine(String.Format("{0}: {1}", element.Index, element.Val));
}

输出是:

0: my
1: three
2: words

我想在F#中进行类似的查询,并且像这样开始:

let arr = [|"my"; "three"; "words"|]

let res = query {
    for a in arr do
    // ???
}

我该如何完成这个LINQ查询？

Answer 1

你可以使用Seq.mapi:

let res = arr |> Seq.mapi (fun i a -> ...)

或直接使用Seq.iteri:

arr |> Seq.iteri (fun i v -> printfn "%i: %s" i v)

要不就:

arr |> Seq.iteri (printfn "%i: %s")