Acknowledgments Wdevelop      the many people who have helped us this book and this curriculum. Our subject is a clear intellectual descendant of “6.231,” a wonderful subject on programming linguistics and the λ-calculus taught at  in the late 1960s by Jack Wozencra and Arthur Evans, Jr. We owe a great debt to Robert Fano, who reorganized ’s intro- ductory curriculum in electrical engineering and computer science to emphasize the principles of engineering design. He led us in starting out on this enterprise and wrote the first set of subject notes from which this book evolved. Much of the style and aesthetics of programming that we try to teach were developed in conjunction with Guy Lewis Steele Jr., who collaborated with Gerald Jay Sussman in the initial development of the Scheme language. In addition, David Turner, Peter Henderson, Dan Fried- man, David Wise, and Will Clinger have taught us many of the tech- niques of the functional programming community that appear in this book. Joel Moses taught us about structuring large systems. His experi- ence with the Macsyma system for symbolic computation provided the insight that one should avoid complexities of control and concentrate xxv