teractive environment with excellent support for incremental program design, construction, testing, and debugging. We thank all the genera- tions of Lisp wizards, starting with John McCarthy, who have fashioned a fine tool of unprecedented power and elegance. Scheme, the dialect of Lisp that we use, is an aempt to bring to- gether the power and elegance of Lisp and Algol. From Lisp we take the metalinguistic power that derives from the simple syntax, the uniform representation of programs as data objects, and the garbage-collected heap-allocated data. From Algol we take lexical scoping and block struc- ture, which are gis from the pioneers of programming-language de- sign who were on the Algol commiee. We wish to cite John Reynolds and Peter Landin for their insights into the relationship of Church’s λ- calculus to the structure of programming languages. We also recognize our debt to the mathematicians who scouted out this territory decades before computers appeared on the scene. ese pioneers include Alonzo Church, Barkley Rosser, Stephen Kleene, and Haskell Curry. xxiv