I was trawling through Ron Garret’s site (see yesterday’s post) and came upon two excellent short papers. The first, The Idiot’s Guide to Special Variables discusses the difference between lexical and special (or dynamic) variables. The second, The Idiot’s Guide to Common Lisp Packages, discusses CL packages, what they are, how they operate, and the many non-obvious pitfalls you can find yourself in when using them.
These are both excellent little tutorials and despite the Idiot in the titles they are not at all trivial. If you’re a CL user, you might find them helpful.