Preface to the Second Edition

Is it possible that software is not like anything else that
it is meant to be discarded: that the whole point is to
always see it as a soap bubble?
Alan J. Perlis



The material in this book has been the basis of MIT's entry-level com-
puter science subject since 1980. We had been teaching this material
for four years when the first edition was published, and twelve more
years have elapsed until the appearance of this second edition. We are
pleased that our work has been widely adopted and incorporated into
other texts. We have seen our students take the ideas and programs in
this book and build them in as the core of new computer systems and
languages. In literal realization of an ancient Talmudic pun, our students
have become our builders. We are lucky to have such capable students
and such accomplished builders.
In preparing this edition, we have incorporated hundreds of clarifica-
tions suggested by our own teaching experience and the comments of
colleagues at MIT and elsewhere. We have redesigned most of the ma-
jor programming systems in the book, including the generic-arithmetic
system, the interpreters, the register-machine simulator, and the com-
piler; and we have rewritten all the program examples to ensure that any
Scheme implementation conforming to the IEEE Scheme standard (IEEE
1990) will be able to run the code.
This edition emphasizes several new themes. The most important of
these is the central role played by different approaches to dealing with
time in computational models: objects with state, concurrent program-
ming, functional pogramming, lazy evaluation, and nondeterministic stic
programming. We have included new sections on concurrency and non-
determimism, and we have tried to integrate this theme throughout the
book.
The first edition of the book closely followed the syllabus of our MIT
one-semester subject. With all the new material in the second edition, it
will not be possible to cover everything in a single semester, so the in-
structor will have to pick and choose. In our own teaching, we sometimes
skip the section on logic pogramming (section 4.4), we have students
use the register-machine simulator but we do not cover its implementa-
tion (section 5.2), and we give only a cursory overview of the compiler
(section 5.5). Even so, this is still an intense course. Some instructors
may wish to cover only the first three or four chapters, leaving the other
material for subsequent courses.
The World-Wide-Web site www-mitpress .mit . edu/sicp provides
support for users of this book. This includes programs from the book,
sample programming assignments, supplementary materials, and down-
loadable implementations of the Scheme dialect of Lisp.

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