Simple F# ViewModel for Silverlight MVVM

Mainpage.xaml

//View xaml
<UserControl
	xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
	xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
	xmlns:i="http://schemas.microsoft.com/expression/2010/interactivity" xmlns:ei="http://schemas.microsoft.com/expression/2010/interactions"
	xmlns:d="http://schemas.microsoft.com/expression/blend/2008" xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006" mc:Ignorable="d"
	x:Class="HelloApp.MainPage"
	Width="640" Height="480">

	<Grid x:Name="LayoutRoot" Background="White" d:DataContext="{d:DesignData /SampleData/MainViewModelSampleData.xaml}">
		<StackPanel HorizontalAlignment="Left" VerticalAlignment="Top" Width="400">
			<TextBlock TextWrapping="Wrap" Text="Input your name:"/>
			<StackPanel Orientation="Horizontal">
				<TextBox x:Name="MyNameTextbox" TextWrapping="Wrap" Text="{Binding MyName, Mode=TwoWay}" HorizontalAlignment="Left" VerticalAlignment="Top" Width="200">
					<i:Interaction.Triggers>
						<i:EventTrigger EventName="TextChanged">
							<ei:ChangePropertyAction TargetName="HelloLabel" PropertyName="Visibility"/>
						</i:EventTrigger>
					</i:Interaction.Triggers>
				</TextBox>
				<Button Content="Hi!" HorizontalAlignment="Right" VerticalAlignment="Top"/>
			</StackPanel>
			<TextBlock x:Name="HelloLabel" TextWrapping="Wrap" Text="{Binding HiLabel}">
				<i:Interaction.Triggers>
					<i:EventTrigger>
						<ei:ChangePropertyAction PropertyName="Visibility">
							<ei:ChangePropertyAction.Value>
								<Visibility>Collapsed</Visibility>
							</ei:ChangePropertyAction.Value>
						</ei:ChangePropertyAction>
					</i:EventTrigger>
				</i:Interaction.Triggers>
			</TextBlock>
		</StackPanel>
	</Grid>
</UserControl>

MainPage.xaml.cs

//View codebehind

using System.Windows.Controls;
namespace HelloApp
{
	public partial class MainPage : UserControl
	{
		public MainPage()
		{
			  // Required to initialize variables
			  InitializeComponent();
            this.DataContext = new HelloAppViewModel.MainViewModel();
		}
	}
}

MainViewModel.fs

#light
//ViewModel
//Expression Blend support: wrap to namespace, not module
namespace HelloAppViewModel

open System
open System.ComponentModel

type MainViewModel() =

    let mutable myname = ""
    
    let event = new Event<_,_>()
    interface INotifyPropertyChanged with
        [<CLIEvent>]
        member x.PropertyChanged = event.Publish
    
    member x.TriggerPropertyChanged(name)=
        event.Trigger(x, new PropertyChangedEventArgs(name))
    
    member x.MyName 
        with get() = myname
        and set t = 
                myname <- t
                x.TriggerPropertyChanged "MyName"
                x.TriggerPropertyChanged "HiLabel"

    member x.HiLabel = "Hello " + x.MyName + "!"