结合 F# 异步函数 [英] Combining F# async functions

问题描述

我在这里有点沮丧.我知道我已经掌握了所有的部分，但我不知道如何组合它们...

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

推荐答案

您可以使用 async 表达式将两者结合起来:

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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