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What Readers Are Saying About
Seven Languages in Seven Weeks
Knowing multiple paradigms greatly influences our design abilities, so
I’m always on the lookout for good books that’ll help me learn them.
This book nicely brings prominent paradigms together. Bruce has
experience learning and using multiple languages. Now you can gain
from his experience through this book. I highly recommend it.
Dr. Venkat Subramaniam
Award-winning author and founder, Agile Developer, Inc.
As a programmer, the importance of being exposed to new program-
ming languages, paradigms, and techniques cannot be overstated.
This book does a marvelous job of introducing seven important and
diverse languages in a concise—but nontrivial—manner, revealing
their strengths and reasons for being. This book is akin to a dim-sum
buffet for any programmer who is interested in exploring new horizons
or evaluating emerging languages before committing to studying one
in particular.
Antonio Cangiano
Software engineer and technical evangelist, IBM
Fasten your seat belts, because you are in for a fast-paced journey.
This book is packed with programming-language-learning action.
Bruce puts it all on the line, and the result is an engaging, reward-
ing book that passionate programmers will thoroughly enjoy. If you
love learning new languages, if you want to challenge your mind, if
you want to take your programming skills to the next level—this book
is for you. You will not be disappointed.
Frederic Daoud
Author, Stripes ...and Java Web Development Is Fun Again and
Getting Started with Apache Click
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Do you want seven kick starts into learning your “language of the
year”? Do you want your thinking challenged about programming in
general? Look no further than this book. I personally was taken back
in time to my undergraduate computer science days, coasting through
my programming languages survey course. The difference is that
Bruce won’t let you coast through this course! This isn’t a leisurely
read—you’ll have to work this book. I believe you’ll find it both mind-
blowing and intensely practical at the same time.
Matt Stine
Group leader, Research Application Development at St. Jude
Children’s Research Hospital
I spent most of my time as a computer sciences student saying I didn’t
want to be a software developer and then became one anyway. Seven
Languages in Seven Weeks expanded my way of thinking about prob-
lems and reminded me what I love about programming.
Travis Kaspar
Software engineer, Northrop Grumman
I have been programming for 25 years in a variety of hardware and
software languages. After reading Seven Languages in Seven Weeks, I
am starting to understand how to evaluate languages for their objec-
tive strengths and weaknesses. More importantly, I feel as if I could
pick one of them to actually get some work done.
Chris Kappler
Senior scientist, Raytheon BBN Technologies
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Seven Languages in Seven Weeks
A Pragmatic Guide to Learning
Programming Languages
Bruce A. Tate
The Pragmatic Bookshelf
Raleigh, North Carolina Dallas, Texas
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Many of the designations used by manufacturers and sellers to distinguish their prod-
ucts are claimed as trademarks. Where those designations appear in this book, and The
Pragmatic Programmers, LLC was aware of a trademark claim, the designations have
been printed in initial capital letters or in all capitals. The Pragmatic Starter Kit, The
Pragmatic Programmer, Pragmatic Programming, Pragmatic Bookshelf and the linking g
device are trademarks of The Pragmatic Programmers, LLC.
Every precaution was taken in the preparation of this book. However, the publisher
assumes no responsibility for errors or omissions, or for damages that may result from
the use of information (including program listings) contained herein.
Our Pragmatic courses, workshops, and other products can help you and your team
create better software and have more fun. For more information, as well as the latest
Pragmatic titles, please visit us at http://www.pragprog.com.
The team that produced this book includes:
Editor: Jackie Carter
Indexing: Potomac Indexing, LLC
Copy edit: Kim Wimpsett
Layout: Steve Peter
Production: Janet Furlow
Customer support: Ellie Callahan
International: Juliet Benda
Copyright © 2010 Pragmatic Programmers, LLC.
All rights reserved.
No part of this publication may be reproduced, stored in a retrieval system, or transmit-
ted, in any form, or by any means, electronic, mechanical, photocopying, recording, or
otherwise, without the prior consent of the publisher.
Printed in the United States of America.
ISBN-10: 1-934356-59-X
ISBN-13: 978-1-934356-59-3
Printed on acid-free paper.
P1.0 printing, October 2010
Version: 2010-10-28
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Contents
Dedication 9
Acknowledgments 11
Foreword 14
1 Introduction 17
1.1 Method to the Madness . . . . . . . . . . . . . . . . . . 17
1.2 The Languages . . . . . . . . . . . . . . . . . . . . . . . 19
1.3 Buy This Book . . . . . . . . . . . . . . . . . . . . . . . . 21
1.4 Don’t Buy This Book . . . . . . . . . . . . . . . . . . . . 22
1.5 A Final Charge . . . . . . . . . . . . . . . . . . . . . . . . 24
2 Ruby 25
2.1 Quick History . . . . . . . . . . . . . . . . . . . . . . . . 26
2.2 Day 1: Finding a Nanny . . . . . . . . . . . . . . . . . . 28
2.3 Day 2: Floating Down from the Sky . . . . . . . . . . . 35
2.4 Day 3: Serious Change . . . . . . . . . . . . . . . . . . . 48
2.5 Wrapping Up Ruby . . . . . . . . . . . . . . . . . . . . . 56
3 Io 60
3.1 Introducing Io . . . . . . . . . . . . . . . . . . . . . . . . 60
3.2 Day 1: Skipping School, Hanging Out . . . . . . . . . . 61
3.3 Day 2: The Sausage King . . . . . . . . . . . . . . . . . 74
3.4 Day 3: The Parade and Other Strange Places . . . . . . 83
3.5 Wrapping Up Io . . . . . . . . . . . . . . . . . . . . . . . 92
4 Prolog 95
4.1 About Prolog . . . . . . . . . . . . . . . . . . . . . . . . . 96
4.2 Day 1: An Excellent Driver . . . . . . . . . . . . . . . . . 97
4.3 Day 2: Fifteen Minutes to Wapner . . . . . . . . . . . . 109
4.4 Day 3: Blowing Up Vegas . . . . . . . . . . . . . . . . . . 120
4.5 Wrapping Up Prolog . . . . . . . . . . . . . . . . . . . . . 132
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CONTENTS 8
5 Scala 135
5.1 About Scala . . . . . . . . . . . . . . . . . . . . . . . . . 135
5.2 Day 1: The Castle on the Hill . . . . . . . . . . . . . . . 139
5.3 Day 2: Clipping Bushes and Other New Tricks . . . . . 153
5.4 Day 3: Cutting Through the Fluff . . . . . . . . . . . . . 167
5.5 Wrapping Up Scala . . . . . . . . . . . . . . . . . . . . . 176
6 Erlang 181
6.1 Introducing Erlang . . . . . . . . . . . . . . . . . . . . . 181
6.2 Day 1: Appearing Human . . . . . . . . . . . . . . . . . 185
6.3 Day 2: Changing Forms . . . . . . . . . . . . . . . . . . 195
6.4 Day 3: The Red Pill . . . . . . . . . . . . . . . . . . . . . 207
6.5 Wrapping Up Erlang . . . . . . . . . . . . . . . . . . . . 219
7 Clojure 223
7.1 Introducing Clojure . . . . . . . . . . . . . . . . . . . . . 224
7.2 Day 1: Training Luke . . . . . . . . . . . . . . . . . . . . 225
7.3 Day 2: Yoda and the Force . . . . . . . . . . . . . . . . . 243
7.4 Day 3: An Eye for Evil . . . . . . . . . . . . . . . . . . . 256
7.5 Wrapping Up Clojure . . . . . . . . . . . . . . . . . . . . 264
8 Haskell 268
8.1 Introducing Haskell . . . . . . . . . . . . . . . . . . . . . 268
8.2 Day 1: Logical . . . . . . . . . . . . . . . . . . . . . . . . 269
8.3 Day 2: Spock’s Great Strength . . . . . . . . . . . . . . 285
8.4 Day 3: The Mind Meld . . . . . . . . . . . . . . . . . . . 294
8.5 Wrapping Up Haskell . . . . . . . . . . . . . . . . . . . . 309
9 Wrap-Up 313
9.1 Programming Models . . . . . . . . . . . . . . . . . . . . 313
9.2 Concurrency . . . . . . . . . . . . . . . . . . . . . . . . . 317
9.3 Programming Constructs . . . . . . . . . . . . . . . . . 319
9.4 Finding Your Voice . . . . . . . . . . . . . . . . . . . . . 321
A Bibliography 322
Index 323
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Dedication
The five months from December 2009 through April 2010 were among
the most difficult of my life. My brother, not yet 47 years old, had emer-
gency bypass surgery. No one had any clue that anything was wrong
at all. (He came through the surgery without further incident and is
doing well.) In late March, my sister was diagnosed with breast cancer.
The biggest shock of all came in early March. My mother was diagnosed
with terminal cancer. A few short weeks later, she was gone.
As you would expect, I am left to struggle with the grief of a jarring
and unexpected loss because of a brutally efficient disease. I would
not be human otherwise. But strangely, this experience has not been
an entirely negative one. You see, my mother was at peace with the
remarkable life she lived, her relationships with her family were strong
and fulfilling, and she was exactly where she wanted to be with her
faith.
Lynda Lyle Tate put her creative energy into painting with watercolors.
She shared her art primarily through her Madison Avenue Art Gallery
and her classes. Before I left home, I had the opportunity to take a few
lessons from her. For someone from a technical profession, the experi-
ence was always a little disorienting. I would visualize the masterpiece
on my blank canvas. As the actual image took shape, it drifted further
and further from my original vision. When I despaired that things were
beyond my ability to fix, Mom looked over my shoulder and told me
what she saw. After a few flicks of her talented wrist added darks to
accentuate depth and highlights to add clarity and detail, I would real-
ize that I had not been too far astray at all. It just took a gifted touch to
bring back my creation from the brink of disaster. Then, I would throw
my excited arms up in victory and tell everyone in the class about this
thing I had created, not yet realizing that each member of the class was
going through their own private burst of joy.
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DEDICATION 10
After a little while, I learned that Mom was working on another canvas
as well. Through her church and through her profession, she’d find
broken people. Encountering a lost spouse here or a troubled marriage
there, my mother would bring them into class where she would use the
paint and paper to slightly open a door that had been slammed shut.
As we spent our last week together, person after person would come
through her room devastated at the thought of losing their teacher, but
Mom would tell the perfect joke or offer the right word of kindness,
comforting those who came to comfort her. I got to meet the human
canvases who had been put right by the master and gone on to do great
things. It was a humbling experience.
When I told my mother that I would dedicate this book to her, she
said that she would like that, but she had nothing to do with com-
puters. That is true enough. The very thought of Windows would leave
her helpless. But Mom, you have had everything to do with me. Your
well-timed words of encouragement inspired me, your love of creativity
shaped me, and your enthusiasm and love of life guide me even now.
As I think about these experiences, I can’t help but feel a little better
and a little stronger because I, too, am a canvas shaped by the master.
This book is dedicated with love to Lynda Lyle Tate, 1936–2010.
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