Porting some C# code to F# with Action<T> - f#

Question

I have the following C# code:
_Client.Streams.InfoStream.Subscribe(async info =>
{
Console.WriteLine($"reconnection, message: {info.Info}, version: {info.Version:D}"));
await _Client.Send(new PingRequest());
...
}
and the following definitions are of interest:
public IObservable<InfoResponse> InfoStream => InfoSubject.AsObservable();
public static IDisposable Subscribe<T>(this IObservable<T> source, Action<T> onNext)
when I want to call the _Client.Streams.InfoStream.Subscribe method from F#, I do not know what the syntax should be:
Client.Streams.InfoStream
.Subscribe(
fun x -> ( printfn "%s" x.Info )
)
doesn't work. It tells me I'm returning an IDisposable type instead of a unit type. And this doesn't touch the async part yet.
what should the syntax be?
Edit:
Following the answer, here is the solution I came up with to run async code inside the callback:
Client.Streams.InfoStream
.Subscribe(
fun _ ->
(
async {
[
Client.Send(new PingRequest()) |> Async.AwaitTask;
Client.Send(new BookSubscribeRequest()) |> Async.AwaitTask;
Client.Send(new TradesSubscribeRequest()) |> Async.AwaitTask;
Client.Send(new AuthenticationRequest(id, key)) |> Async.AwaitTask
]
|> Async.Parallel
|> Async.Ignore
|> Async.Start
|> ignore
} |> ignore
)
) |> ignore

Answer 1

The Subscribe operation of an IObservable returns an IDisposable value that you can later use to cancel the subscription. In C#, you can just ignore return values, so C# implicitly treats this as an operation that returns void. In F#, you need to explicitly ignore results if you are not using them.
In your case, you probably need to write:
Client.Streams.InfoStream
.Subscribe(fun x -> printfn "%s" x.Info)
|> ignore
EDIT: In your edited example, I think you just want to start all the individual tasks. For this, you don't need any F# async. Assuming the Send method creates a "hot task" (i.e. a task that has already started), the following should work just fine:
Client.Streams.InfoStream.Subscribe(fun _ ->
Client.Send(new PingRequest()) |> ignore
Client.Send(new BookSubscribeRequest()) |> ignore
Client.Send(new TradesSubscribeRequest()) |> ignore
Client.Send(new AuthenticationRequest(id, key)) |> ignore
)