Compatability with AsyncSeq?

So FSharp.Control.AsyncSeq extends async so that you can do this:

async {
  let xs = asyncSeq {
    yield 1
    yield 2 
    yield 3
  }

  for x in xs do
    printfn "%A" x
}

But this is not implemented for asyncResult:

async {
  let xs = asyncSeq {
    yield 1
    yield 2 
    yield 3
  }

  for x in xs do // Only seq allowed here
    printfn "%A" x
}

I would be great if this worked, although I’m not sure how it could be implemented. Perhaps this is just a limitation of F#?

[njlr]

I was able to design an async version like this:

[<AutoOpen>]
module AsyncSeqExtensions =

  // Add asynchronous for loop to the 'asyncResult' computation builder
  type FsToolkit.ErrorHandling.AsyncResultCE.AsyncResultBuilder
    with
      member x.For (seq : AsyncSeq<Result<'T, 'TError>>, action : 'T -> Async<Result<unit, 'TError>>) : Async<Result<unit, 'TError>> =
        seq
        |> AsyncSeq.foldAsync
          (fun acc x ->
            async {
              match acc, x with
              | Ok (), Ok x ->
                return! action x
              | Ok (), Error e ->
                return Error e
              | acc, _ ->
                return acc
            })
          (Ok ())

I’m still unsure of the best semantics though…

• Should the for stop at the first Result.Error?
• Should only AsyncSeq<Result<_, _>> be supported?

[njlr]

Basics here: https://github.com/demystifyfp/FsToolkit.ErrorHandling/pull/138