BennyG

I think my solution is close to the optimum!?

But I had to modify the subscibtion from deltas to absolute points.

   var query = mouseDown.Join(mouseMove, l => mouseUp, r => Observable.Empty<Point>(),(l,r)=> Subtract(r,l));

           query.Subscribe(pos=>
            {
                Canvas.SetLeft(image, pos.X);
                Canvas.SetTop(image, pos.Y);
            });

Am I allowed to post the solution of the challange?

Benny

Nice, but have a look on F# Object Expressions. I already use F# in my Unit-Tests for mocking interfaces.

With Object Expression you could write something like :

let obj1 = { new System.Object() with member x.ToString() = "F#" }

or

let personComparer = {
new
 IComparable<Person> with
 

but you cannot write this, because DateTime is sealed.

let now = {
new
 System.DateTime() with
member
 x.Now() = new
 DateTime(2000,1,1) }

Benny

    member this.Compare(a,b) =

           if a.First
 > b.First then
 1
           elif
 a.First = b.First then
 0

           else
 0 }