Running Function from a string

Hi

If I have the name of the function I want to run in a string called function_name and the params I want to pass to the function in another string called function_params, how would I could this to go in a button with the following code:

mc.button1.addEventListener(MouseEvent.MOUSE_DOWN, button1_handler);
function button1_handler(Event:MouseEvent):void {
// Dont know what to put here
}