So far this looks like the most attractive idea to me.

The code stays very clean, with all the error-handling kept out of the main routine and the loose coupling is certainly a bonus. It also looks like it would work beautifully with Carp for extra verbosity in the errors.

My || usage is just a habit now; I might think about changing it. I do prefer to use the extra brackets though, even if they aren't always needed.

Thanks for the suggestion. If that Serbian contractor hadn't pinched my camel book, I might have figured it out myself :)