I consciously avoided that because FORMAT and LOOP mastery is something that should wait until one knows Lisp well. Introduced too early, they can either scare someone (in the case of format) or tempt one to start writing Pascal (in the case of loop; which is why deliberately used it for its collected result, and not its side-effect, as more common.)
FWIW, my first Lisp programs where board-games and I learned quite a bit about recursion trying to format ASCII art in curses. If I knew FORMAT had control, I wouldn't have learned much lisp so quickly, since quirky little DSLs are fascinating.
