AddToPage.xaml.cs

// Add the following methods to the calculator's 
// Page.xaml.cs Page class

// Execute the script code in the Functions buffer, 
// and add buttons to the UI to call the function 
// if it doesn't exist.
public void Functions_TextChanged(object sender, TextChangedEventArgs e) {
  FunctionDefinitions.Children.Clear();
  try {
    object result = _engine.Execute(Functions.Text.ToString());
    foreach(var method in _engine.ListOfMethods()) {
      if (!method.StartsWith("__")) {
        var b = new Button();
        b.Tag = method;
        b.Content = method + "(x)";
        b.Click += new RoutedEventHandler(RunCustomFunction);
        FunctionDefinitions.Children.Add(b);
      }
    }
  } catch (Exception) {
    // Ignore
  }
}

// Call a user-defined function
public void RunCustomFunction(object sender, RoutedEventArgs e) {
  try {
    object result = _engine.CallMethod((string)((Button)sender).Tag, (object)Decimal.Parse(Calculator.CurrentNumber.ToString()));
    Calculator.CurrentNumber = new NumberProject.Number(result.ToString());
    Calculator.OnValueChanged();
  } catch (Exception) {
    HtmlPage.Window.Alert("The user-defined function returned None");
  }
}

AlsoAddToPage.xaml.cs

// To hook up the above methods, add a PythonEngine 
// field to the Page class
private PythonEngine _engine;

// And in the Page constructor, initialize the 
// engine and hook the Functions.KeyUp event 
_engine = new PythonEngine();
Functions.TextChanged += new TextChangedEventHandler(Functions_TextChanged);