> But do you think you could provide a
> more "real world" example of an application
> of the "Holy Trinity" ideas?
A commonly cited real-world example that illustrates the first key idea (recursive data type) is a binary tree:
I'd have used lists, since in Haskell we make use of infinite lists quite a bit; a simple example being zipping some list against [0..] (a list comprising an infinitely ascending sequence of numbers) to pair each item with its index.