You can code your app in whatever scripting language you want, but it can't download and execute code arbitrarily. For example, the unity game engine for iPhon

You can code your app in whatever scripting language you want, but it can't download and execute code arbitrarily. For example, the unity game engine for iPhone uses mono & C#/javascript for all it's game programming/scripting. But when you use the app, the app doesn't act as a player but as a standalone application.