[ccapndave]

I suppose if anything it is the customer subscribes. But actually, in practice, it doesn't really feel quite like this because in FP you just have a bunch of functions and there isn't the concept of things 'owning' other things like you have in more OO based language. What actually happens is that you add a (sort of) listener to the subscription that fires a message in a particular update function, which manipulates some part of the model.