结合F＃异步功能 [英] Combining F# async functions

问题描述

我有点沮丧这里。我知道我得到了所有的位，但我不知道如何把它们混合起来......

 让saveImageToDisk路径含量=
    异步{
        使用S =新的FileStream（路径，FileMode.OpenOrCreate）
        做！ s.AsyncWrite（内容）
        printfn写完％A路径
        } //返回异步＆LT;部＆gt;让getImages imageUrls =
    imageUrls
        |＆GT; Seq.map（URL乐趣 - ＆GT; topath URL，URL的getImage）
        //下一行不开心，因为内容异步＆LT;字节[]＆GT;而不是字节[]
        |＆GT; Seq.map（FUN（路径，内容） -  GT; saveImageToDisk路径内容）
        |＆GT; Async.Parallel
        |＆GT; Async.RunSynchronously
 

解决方案

您可以使用异步前pression将二者结合起来：

 让getImages imageUrls =
    imageUrls
        |＆GT; Seq.map（URL乐趣 - ＆GT;异步{
              让！内容=的getImage网址
              返回！ saveImageToDisk（topath URL）内容}）
        |＆GT; Async.Parallel
        |＆GT; Async.RunSynchronously
 

I'm a bit frustrated here. I know I've got all the bits, but I can't work out how to combine them...

let saveImageToDisk path content =
    async {
        use s = new FileStream(path, FileMode.OpenOrCreate)
        do! s.AsyncWrite(content)
        printfn "Done writing %A" path
        } // returns Async<unit>

let getImages imageUrls =
    imageUrls
        |> Seq.map (fun url -> topath url, getImage url)
        //Next line not happy because content is Async<byte[]> instead of byte[]
        |> Seq.map (fun (path, content) -> saveImageToDisk path content)
        |> Async.Parallel
        |> Async.RunSynchronously

解决方案

You can combine the two using the async expression:

let getImages imageUrls =
    imageUrls
        |> Seq.map (fun url -> async {
              let! content = getImage url
              return! saveImageToDisk (topath url) content })
        |> Async.Parallel
        |> Async.RunSynchronously

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