open System
open System.Drawing
open System.Windows.Forms

let form = new Form(Text = "Hello World", BackColor = Color.Blue, TopMost = true)
form.Show()

let helloButtonClick = EventHandler(fun _ _ -> MessageBox.Show("Hello World") |> ignore)

let button = new Button(Text = "Hello World")
button.Click.AddHandler(helloButtonClick)

form.Controls.Add(button)

form.Text <- "Goodby World"
form.BackColor <- Color.Pink


button.Text <- "Goodby World"
let goodbyButtonClick = EventHandler(fun _ _ -> MessageBox.Show("Goodby World") |> ignore)

button.Click.RemoveHandler(helloButtonClick)
button.Click.AddHandler(goodbyButtonClick)

button.Width <- 100;;
button.Top <- 100;;
button.Left <- 90;;