The book still works even if you assume every specific line of lisp in it is hopelessly outdated (I wouldn't know, I'm not a lisp programmer). Suppose you were

The book still works even if you assume every specific line of lisp in it is hopelessly outdated (I wouldn't know, I'm not a lisp programmer). Suppose you were looking at lisps and got around to the part where you realize homiconicity makes it possible (and/or sensible) to have language facilities like syntax macros. What would such a facility look like in practice? What would it be used for and how? What could go wrong defining it or using it? That's the sort of thing that's covered in On Lisp and it makes it an interesting read for any sort of programmer, rather than just a lisp one. The book is short, without being incomprehensibly dense, you get easily get a feel for it from just browsing the PDF for a bit. And the concepts being presented are a lot easier to digest than, say, 'what if your language was really good at category theory'.