How do you use Observable.create in the FSharp.Control.Reactive library?

Question

I'm trying to figure out how to use the Observable.create function in the FSharp.Control.Reactive library but seem to be missing something.

The function signature is defined as:

((IObserver<'a> -> unit -> unit) -> IObservable<'a>)

I've tried a few different ways of creating the observable such as:

  Observable.create (fun obs -> fun _ -> obs.OnNext("xxx") )
  |> Observable.subscribe (fun x -> printfn "%A" x)

and

  Observable.create (fun obs -> obs.OnNext("xxx"); fun _ -> () )
  |> Observable.subscribe (fun x -> printfn "%A" x)

Which compiles but doesn't ever execute the OnNext so the printfn statement in the subscribe isn't called.

I can call the Observable.Create method directly from the System.Reactive.Linq namespace as follows:

  Observable.Create(fun (obs : IObserver<string>) -> obs.OnNext("www"); Action( fun _ -> () ) )
  |> Observable.subscribe (fun x -> printfn "%A" x)

And this will print "www" to the interactive. Likewise, I can use the Observable.createWithDisposable as follows:

Observable.createWithDisposable(fun obs -> obs.OnNext("yyy") ; Disposable.Empty )
|> Observable.subscribe (fun x -> printfn "%A" x)

And sending this to interactive prints "yyy"

So it is just the FSharp.Control.Reactive.Observable.create that I am having trouble with.

I've had a look but can't find any examples on how this should be called so any help would be appreciated.

Thanks

That signature looks quite bizarre to me, but try `fun obs () -> obs.OnNext("xxx")`. — ildjarn, Apr 03 '15 at 16:44
Thanks. I tried this and it compiled but I didn't get the OnNext called. I've been looking at the implementation of Observable.create and it's defined like this: /// Creates an observable sequence from a specified Subscribe method implementation. let create subscribe = let subscribe observer = Action (subscribe observer) Observable.Create(Func,Action> subscribe) Which I don't think is correct. I might raise an issue on GitHub with the author. — Andy B, Apr 03 '15 at 18:20

score 1 · Answer 1 · answered Apr 03 '15 at 20:24

I raised an issue with the developer. They've removed the Observable.create functions now so you create the observable using the System.Reactive.Linq.Observable.Create() methods now.

That makes this question invalid now.

https://github.com/fsprojects/FSharp.Control.Reactive/commit/c8f6d245e75d55b2bd6077c53b311119422c97a1

score 0 · Answer 2 · answered Sep 30 '17 at 01:11

I once asked that using c#.

Using F# Control.Reactive would be:

        Observable.create(
            fun observer ->                        
                Action (fun () -> 
                    foo.OnBar(
                       fun (args : Args) -> 
                         observer.OnNext(args)            
                         observer.OnCompleted())))

How do you use Observable.create in the FSharp.Control.Reactive library?

2 Answers2