Preface

Learn Prolog Now! has a long and twisted history. In 1995, all three authors were based at the Department of Computational Linguistics, at the University of the Saarland, in Saarbrücken, Germany. Johan, who was teaching the introduction to Prolog that year, was working with Patrick on a Prolog-based introduction to natural language semantics. ¹ He decided to prepare a short set of lecture notes on Prolog which could also be used as an Appendix to the computational semantics book.

Nice idea, but that’s not the way things worked out. First, between 1996 and 2000, Patrick and Johan rethought the structure of the Prolog courses, and along the way the notes became book-sized. Then, from 2001 till 2004, Kristina took over the teaching, added new material and (most importantly of all) turned Learn Prolog Now! into a web-book.

It quickly became apparent that we had a hit on our hands: the website got up to 4,000 visitors a month, and we received many emails. Actually, this put us in a bit of a quandary. We wanted to publish Learn Prolog Now! as a (low-budget) book — but at the same time we did not want a publisher telling us that we had to get rid of the free online version.

Luckily, Vincent Hendricks came to the rescue (thanks Vincent!). He told us about College Publications, Dov Gabbay’s new publication house, which was specifically designed to enable authors to retain copyright. It was a marriage made in heaven. Thanks to College Publications we could make Learn Prolog Now! available in book form at a reasonable price, and keep the web-book in place.

And that’s the book you’re now reading. It has been thoroughly tested, first on nearly a decade’s worth of students at Saarbrücken, and at the 16th European Summer School in Logic, Language and Information which took place in Nancy, France, in August 2004, where Kristina taught a hands-on introduction to Prolog. Though, as we hope you will swiftly discover, you don’t need to be doing a course to follow this book. We’ve tried to make Learn Prolog Now! self-contained and easy to follow, so that it can be used without a teacher. And as the feedback we have received confirms, this is one of the most popular ways of using it.

So — over to you. We had a lot of fun writing this. We hope you have a lot of fun reading it, and that it really will help you to learn Prolog now!

Acknowledgments

Over the years that Learn Prolog Now! existed as course notes and web-book, we received many emails, ranging from helpful comments to requests for answers to problems (a handful of which verged on demands that we do their homework assignments!). We can’t thank everyone by name, but we did receive a lot of useful feedback this way and are very grateful. And if we did any homework assignments, we ain’t telling…

We are extremely grateful to Gertjan van Noord and Robbert Prins, who used early versions of Learn Prolog Now! in their teaching at the University of Groningen. They gave us detailed feedback on its weak points, and we’ve tried to take their advice into account; we hope we’ve succeeded. We’d also like to say Grazie! to Malvina Nissim, who supplied us with an upgrade of Exercise  2.4 , helped format the final hardcopy version, and generally gave us her enthusiastic support over many years.

Some special thanks are in order. First, we’d like to thank Dov Gabbay for founding College Publications; may it do for academic publishing what the GNU Public License did for software! Second, heartfelt thanks to Jane Spurr; we’ve never had a more helpful, competent, or enthusiastic editor, and nobody reacts faster than Jane. Thirdly, we like to thank Jan Wielemaker (the Linus Torvalds of the Prolog world) for making SWI Prolog freely available over the internet. SWI Prolog is a an ISO-compliant Free Software Prolog environment, licensed under the Lesser GNU Public License. We don’t know what we’d have done without it. We’re also very grateful to him for the speedy and informative feedback he gave us on a number of technical issues, and for encouraging us to go for ISO-standard Prolog. Finally, a big thank you to Ian Mackie and an anonymous referee for all the time and energy they put into the penultimate version of the book.