I just started to use WPF. I made a drag and drop UI for my file processing scripts (F#). How can I update the textBlock to give progress feedback? The UI in the current version only updates after processing all files. Do I need to define a DependencyProperty type and set a Binding? What would be a minimal version of that in F# ?

Here is my current app converted to a F# script:

```
#r "WindowsBase.dll"
#r "PresentationCore.dll"
#r "PresentationFramework.dll"

open System
open System.Windows
open System.Windows.Controls

[< STAThread >] 
do 
    let textBlock = TextBlock()        
    textBlock.Text <- "Drag and drop a folder here"

    let getFiles path =         
        for file in IO.Directory.EnumerateFiles path do
            textBlock.Text <- textBlock.Text + "\r\n" + file // how to make this update show in the UI immediatly?                                
            // do some slow file processing here..
            Threading.Thread.Sleep 300 // just a placeholder to simulate the delay of file processing

    let w = Window()        
    w.Content <- textBlock    
    w.Title <- "UI test"
    w.AllowDrop <- true        
    w.Drop.Add(fun e ->
        if e.Data.GetDataPresent DataFormats.FileDrop then
            e.Data.GetData DataFormats.FileDrop 
            :?> string []
            |> Seq.iter getFiles)

    let app = Application()  
    app.Run(w)
    |> ignore

```