Question

In F# I know how to wait asynchronously for one event using Async.AwaitEvent:

let test = async {
  let! move = Async.AwaitEvent(form.MouseMove)
  ...handle move... }

Suppose I want to wait for either the MouseMove or the KeyDown event. I’d like to have something like this:

let! moveOrKeyDown = Async.AwaitEvent(form.MouseMove, form.KeyDown)

This function doesn’t exist but is there another way to do this?

Answer 1

let ignoreEvent e = Event.map ignore e

let merged = Event.merge (ignoreEvent f.KeyDown) (ignoreEvent f.MouseMove)
Async.AwaitEvent merged

EDIT: another version that preserves original types

let merged = Event.merge (f.KeyDown |> Event.map Choice1Of2) (f.MouseMove |> Event.map Choice2Of2)
Async.AwaitEvent merged

EDIT 2: according to comments of Tomas Petricek

let e1 = f.KeyDown |> Observable.map Choice1Of2
let e2 = f.MouseMove |> Observable.map Choice2Of2
let! evt = Observable.merge e1 e2 |> Async.AwaitObservable

AwaitObservable primitive can be taken from here (‘Reactive demos in Silverlight’ by Tomas Petricek).