F# idiomatic conversion of async while loop accumulation - f#

Question

What is the idiomatic F# way of handling an asynchronous while loop accumulation?
I'm working with the new (still in preview) Azure Cosmos DB SDK. Querying the database returns a CosmosResultSetIterator<T> which has a HasMoreResults property and a FetchNextSetAsync() method. My straight-up translation of the C# code looks like this:
let private fetchItemsFromResultSet (resultSetIterator: CosmosResultSetIterator<'a>) =
let results = ResizeArray<'a>()
async {
while resultSetIterator.HasMoreResults do
let! response = resultSetIterator.FetchNextSetAsync() |> Async.AwaitTask
results.AddRange(response |> Seq.toArray)
return Seq.toList results
}

Answer 1

I would take a look at the AsyncSeq package. You can use it to create asynchronously computed sequences and then iterate them asynchronously or in parallel. This allows for the async-binding to be inside the sequence and the yield to occur asynchronously, so you don't have to build up an accumulator explicitly.
You can use it to do something like:
open FSharp.Control
let private fetchItemsFromResultSet (resultSetIterator: CosmosResultSetIterator<'a>) =
asyncSeq {
while resultSetIterator.HasMoreResults do
let! response = resultSetIterator.FetchNextSetAsync() |> Async.AwaitTask
yield! response |> AsyncSeq.ofSeq
}

Answer 2

IMHO tail-recursion is preferable to while loops as it's one way to avoid mutation.
For example:
let fetchItemsFromResultSet (resultSetIterator: CosmosResultSetIterator<'a>) =
let rec loop results =
async {
if resultSetIterator.HasMoreResults then
let! vs = resultSetIterator.FetchNextSetAsync () |> Async.AwaitTask
let vs = vs |> Seq.toList
return! loop (vs::results)
else
// List.rev needed because batches are in reverse
return results |> List.rev |> List.concat
}
loop []

Answer 3

Very recently, FSharp.Control.TaskSeq was added to support tasks natively with seqs. The answer here by #Just another metaprogrammer can be rewritten as
#r "nuget: FSharp.Control.TaskSeq"
open FSharp.Control
let private fetchItemsFromResultSet (resultSetIterator: CosmosResultSetIterator<'a>) = taskSeq {
while resultSetIterator.HasMoreResults do
let! response = resultSetIterator.FetchNextSetAsync()
yield! response |> TaskSeq.ofSeq
}