Weak Subscribe to an IObservable Source

namespace Reactive

[<System.Runtime.CompilerServices.Extension>]

module Extensions =

    open System

    open System.Runtime.CompilerServices

    type IObserver<'a> =

        abstract member OnNext : 'a -> unit

    type IObservable<'a> =

        abstract member Subscribe : IObserver<'a> -> IDisposable

    [<Extension>]

    let Subscribe<'a> (o:IObservable<'a>, f) =

        o.Subscribe({ new IObserver<'a> with

                          member this.OnNext x = f x })

    [<Extension>]

    let SubscribeWeakly<'a> (o:IObservable<'a>, a:Action<'a>) =

        let (m, r) = (a.Method, new WeakReference(a.Target))

        let rec disposable = Subscribe(o, fun x -> if (r.IsAlive) then

                                                      ignore (m.Invoke (r.Target, [|x|]))

                                                   else

                                                      disposable.Dispose ())

        disposable