The original code, exactly as it appears in the book is here. But in most cases you will want the production code which is a slimmed down version with most of the interesting functions/macros as well as bug-fixes and small additional features. If you are browsing the text online, you will see the original content, exactly as printed.
Thank you to everyone who has discovered errata. Please send any additional errata/comments to me.
You might also be interested in the clarifications page where I try to elaborate on Let Over Lambda's message.