Realm of Racket Realm of Racket learn to Program, one Game at a time! (list Forrest Bice Rose DeMaio Spencer Florence Feng-Yun Mimi Lin Scott Lindeman Nicole Nussbaum Eric Peterson Ryan Plessner David Van Horn Matthias Felleisen Conrad Barski, MD) San Francisco Realm of Racket. Copyright © 2013 by Matthias Felleisen, David Van Horn, Conrad Barski, MD, Forrest Bice, Rose DeMaio, Spencer Florence, Feng-Yun Mimi Lin, Scott Lindeman, Nicole Nussbaum, Eric Peterson, Ryan Plessner. All rights reserved. No part of this work may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, recording, or by any information storage or retrieval system, without the prior writ- ten permission of the copyright owner and the publisher. Printed in USA First printing 17 16 15 14 13 1 2 3 4 5 6 7 8 9 ISBN-10: 1-59327-491-2 ISBN-13: 978-1-59327-491-7 Publisher: William Pollock Production Editor: Alison Law Cover Illustration: Eric Peterson Illustrations: Feng-Yun Mimi Lin and Eric Peterson Interior Design and Composition: Rose DeMaio and Nicole Nussbaum Developmental Editors: Keith Fancher and William Pollock Copyeditor: Marilyn Smith Proofreader: Paula L. Fleming For information on distribution, translations, or bulk sales, please contact No Starch Press, Inc. directly: No Starch Press, Inc. 38 Ringold Street, San Francisco, CA 94103 phone: 415.863.9900; fax: 415.863.9950; [email protected]; www.nostarch.com Library of Congress Cataloging-in-Publication Data: Felleisen, Matthias. Realm of Racket : learn to program, one game at a time! / by Matthias Felleisen, Conrad Barski, Forrest Bice, Rose DeMaio, Spencer Florence, Feng-yun Mimi Lin, Scott Lindeman, Nicole Nussbaum, Eric Peterson, Ryan Plessner, and David Van Horn. pages cm Includes index. ISBN-13: 978-1-59327-491-7 ISBN-10: 1-59327-491-2 1. Racket (Computer program language) 2. LISP (Computer program language) 3. Computer programming. I. Title. QA76.73.R33F45 2013 005.1--dc23 2013002308 No Starch Press and the No Starch Press logo are registered trademarks of No Starch Press, Inc. Other product and com- pany names mentioned herein may be the trademarks of their respective owners. Rather than use a trademark symbol with every occurrence of a trademarked name, we are using the names only in an editorial fashion and to the benefit of the trademark owner, with no intention of infringement of the trademark. The information in this book is distributed on an “As Is” basis, without warranty. While every precaution has been taken in the preparation of this work, neither the author nor No Starch Press, Inc. shall have any liability to any person or entity with respect to any loss or damage caused or alleged to be caused directly or indirectly by the information contained in it. to the memory of John mccarthy September 4, 1927–october 24, 2011 and to my parents, Sarah and Steve my beloved Noni, and my insanely fantastic Mom and Dad my father, Brian my beloved family, especially my best friend and ger ger, Dennis my parents, Jeff and Amy M and D, Magoo and Sunny my parents, Joy and Dan Richard, Lynda, and Morgan Barbara and Pete Christopher and Rachel Lauren and Ava BRief contentS Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xv Preface: Hello World . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xvii Introduction: Open Paren . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 Chapter 1: Getting Started . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19 Chapter 2: A First Racket Program . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27 Chapter 3: Basics of Racket . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35 Chapter 4: Conditions and Decisions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51 Chapter 4½: define define 'define . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71 Chapter 5: big-bang . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79 Chapter 6: Recursion Is Easy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 95 Chapter 7: Land of Lambda . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 111 Chapter 8: Mutant Structs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 127 Chapter 9: The Values of Loops . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 153 Chapter 10: Dice of Doom . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 165 Chapter 11: Power to the Lazy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 193 Chapter 12: Artificial Intelligence . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 203 Chapter 13: The World Is Not Enough . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 213 Chapter 14: Hungry Henry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 231 Good-Bye: Close Paren . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 265