Ah, the Bret-Victor-dream. There are IDEs which provide this. For example, Eclipse can do hot code replace for Java. The Unreal Editor can also hot reload dlls.

Ah, the Bret-Victor-dream. There are IDEs which provide this. For example, Eclipse can do hot code replace for Java. The Unreal Editor can also hot reload dlls. Many web frameworks come with auto-update functionality.