There doesn't seem to be much information about the content of this book. But the quote by Dan Friedman is intriguing:

“Hanson and Sussman's Software Design for Flexibility has introduced additive programming, a game changer. An additive style allows for making changes to existing designs without the programmer's efforts looking like the work of a contortionist. With elegance, clarity, and care, they point out long-overlooked problems in software design and offer their Scheme-friendly, clever solutions. Enjoy!”

Dan FriedmanProfessor of Computer Science, University of Indiana; author of The Little Prover