flatMap<S>(f: (T) => Future<S>): Future<S> {
        let p = new CompletablePromise<S>();
        let fut = p.future;
        this.next = (v) => {
            if (v.isSuccess()) {
                let result: Try<Future<S>> = Try.doWork(() => f(v.get()));
                if (result.isSuccess()) {
                    let nextFut = result.get();
                    nextFut.onComplete((v) => {
                        p.complete(v)
                    })
                } else {
                    p.complete(result as Try<any> as Try<S>)
                }
            } else {
                p.complete(v as Try<any> as Try<S>);
            }
        };

        return fut;
    }