It's just like Tcheko said: main loops are a thing of the past when oo programming waasn't very popular on Amiga. It's the same with hooks. So, in order to handle notifications from buttons and so on you subclass Application.mui, Window.mui or some Group.mui of your choice, define your own private methods there and setup notifications on your buttons to call these methods. This lets you keep a neat internal structure rather than having everything in a one huge switch statement.

To define your own private method and attribute ids you could start with TAG_USER.