Hi. Paul Graham's great book on macros: On Lisp could download for FREE. I'm wondering why not his intro book: ANSI Common Lisp download for FREE? Because On Lisp is for certain people who have enough Lisp experience. And ANSI Common Lisp is that experience they need.
This is usually up to the publisher, in cases where the author has signed a traditional publishing deal.<p>It looks like Prentice Hall has taken <i>On Lisp</i> out of print. After publishers do that, they often let the author post a version online, since they are no longer selling it anyway. <i>ANSI Common Lisp</i>, on the other hand, is still in print.