Combining F# async functions

Question

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

Talljoe · Accepted Answer · 2011-04-17 16:41:52Z

6

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

edited Apr 17, 2011 at 16:41

answered Apr 17, 2011 at 11:45

Talljoe

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1 Comment

Kevin Cantu Over a year ago

Basically, since Async is a monad, you combine both of them in another Async. :)

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