I usually would not post a link to a book that does not even provide a sample chapter, but Edi Weitz' code is of outstanding clarity and quality[1] - if his writing is only half as good as his code, the book is a must read.
There is no sample chapter, ok, but all of the book's code (quite a lot) can be downloaded and worked through in Slime (see top of each file), even without buying the book!
[1] don't take my word for it, check out http://weitz.de/cl-ppcre/ to see for yourself