> ** What I'm actually working on is a web app library, where the > implementations of the functions in the library depend on a runtime > value (i.e., the web server request). So, e.g., current-user might be > a function in the library, and it *won't* require a request as an > argument -- it's "built-in" dynamically.  I also want clients of the > library to be able to override any of the default implementations of > the library functions.  This library, btw, is my attempt at striking a > balance in the library vs framework war. I have attempted to do similar things (if I read your email correctly) and my approach involves uses of parameters.  The parameters contain a set of default implementations, and users can override them as necessary.  Not sure if that'll match your needs, though. Regards, yc