Question

我尝试了以下代码来在F＃中实现do。

let listObjects bucketName = asyncSeq {
    use client = new AmazonS3Client(RegionEndpoint.USEast2)
    let request = new ListObjectsV2Request(BucketName = bucketName, MaxKeys = 10)

    while (
        let! response = client.ListObjectsV2Async(request) |> Async.AwaitTask
        for entry in response.S3Objects do
            yield entry.Key
        response.IsTruncated) do ()

但是，它不能编译？以下代码是唯一的选择吗？

let listObjects bucketName = asyncSeq {
    use client = new AmazonS3Client(RegionEndpoint.USEast2)
    let request = new ListObjectsV2Request(BucketName = bucketName, MaxKeys = 10)
    let! response = client.ListObjectsV2Async(request) |> Async.AwaitTask
    for entry in response.S3Objects do // do while
        yield entry.Key
    while response.IsTruncated do
        let! response = client.ListObjectsV2Async(request) |> Async.AwaitTask
        for entry in response.S3Objects do
            yield entry.Key

Answer 1

通常，您可以在F＃中使用尾递归来解决与C＃中的循环所要解决的同类问题。对于您打算的while循环行为，我还不太清楚，但是这是一个尾递归产生S3Objects直到response.IsTruncated为假的例子：

let listObjects bucketName = 
    asyncSeq {
        use client = new AmazonS3Client(RegionEndpoint.USEast2)
        let request = new ListObjectsV2Request(BucketName = bucketName, MaxKeys = 10)
        let! response = client.ListObjectsV2Async(request) |> Async.AwaitTask
        let rec getKeys () = 
            asyncSeq {
                for entry in response.S3Objects do
                    yield entry.Key
                if response.IsTruncated
                then yield! getKeys ()
            }   

        yield! getKeys()            
    }

在F＃中执行吗？

1 个答案: