How to Design Programs, Second Edition

© 2004–2013 Matthias Felleisen, Robert Bruce Findler, Matthew Flatt, Shriram Krishnamurthi; comments to: matthias at

Matthias Felleisen, Robert Bruce Findler, Matthew Flatt, Shriram Krishnamurthi

Do you notice the italics? Italicized words refer to technical terms. Here they refer to books on programming currently in bookstores.

Bad programming is easy. Idiots can learn it in 21 days, even if they are Dummies.

Good programming requires thought, but everyone can do it and everyone can experience the satisfaction that comes with it. The price is worth paying for the sheer joy of the discovery process, the elegance of the result, and the commercial benefits of a systematic program design process.

The goal of our book is to introduce readers of all ages and backgrounds to the craft of designing programs systematically. We assume few prerequisites: arithmetic, a tiny bit of middle school algebra, and the willingness to think through issues. We promise that the travails will pay off not just for future programmers but for anyone who has to follow a process or create one for others.

We are grateful to Ada Brunstein, our editor at MIT Press, who gave us permission to develop this second edition of "How to Design Programs" on-line.

Friday, August 30th, 2013

Note: this document is the current release of HtDP/2e. It is updated in conjunction with PLT software releases, roughly in sync with semester spans. It is thus well-suited for courses. In contrast, the current draft changes on a frequent basis; it should be consulted when people discover problems and/or errors in this document. If such flaws exist in both documents, please report them to the first author.

Acknowledgments: We thank Ennas Abdussalam, Saad Bashir, Steven Belknap, Stephen Bloch, Rodolfo Carvalho, Nelson Chiu, Richard Cleis, John Clements, Christopher Felleisen, Sebastian Felleisen, Ryan Golbeck, Josh Grams, Jack Gitelson, Scott Greene, Kyle Gillette, Nadeem Abdul Hamid, Wayne Iba, , Jordan Johnson, Blake Johnson, Gregor Kiczales, Eugene Kohlbecker, Jackson Lawler, Jay McCarthy, Mike McHugh, Wade McReynolds, Ann E. Moskol, Scott Newson, Paul Ojanen, Prof. Robert Ordóñez, Klaus Ostermann, Nick Pleatsikas, Luis Sanjuán, Lisa Scheuing, Willi Schiegel, Vinit Shah, Nick Shelley, Stephen Siegel, Joe Snikeris, Vincent St-Amour, Marc Smith, Dave Smylie, Kevin Sullivan, Yuwang Yin, David Van Horn, Mitchell Wand, Michael Wijaya, Ewan Whittaker-Walker, and Roelof Wobben for comments on previous drafts of this second edition.

Differences: This second edition of “How to Design Programs” continues to present an introduction to systematic program design and problem solving. Here are some important differences:

  1. The recipes are applied in two different, typical settings: interactive graphical programs and so-called “batch” programs. The former mode of interaction is typical for games, the latter for data processing in business centers. Both kinds of programs are still created with our design recipes.

  2. While testing has always been a part of the “How to Design Programs” philosophy, the software started supporting it properly only in 2002, just after we had released the first edition. This new edition heavily relies on this testing support now.

  3. This edition of the book drops the design of imperative programs. The old chapters remain available on-line. The material will flow into the next volume of the book, “How to Design Components.”

  4. The book and its programs employ new libraries, also known as teachpacks. The preferred style is to link in these libraries via so-called require specifications, but it is still possible to add teachpacks via a menu in DrRacket.

  5. Finally, we decided to use a slightly different terminology: