The more constraints one imposes, the more one frees oneself.
CHR has taken off. After five dedicated workshops, two special journal issues, and hundreds of related research articles, it was time to write this book about CHR.
About this book
This book is about programming with rules. It presents a rule-based constraint programming language called CHR (short for Constraint Handling Rules). While conceptually simple, CHR embeds the essential aspects of many rule-based and logic-based formalisms and can implement algorithms in a declarative yet highly effective way. The combination of information propagation and multiset transformation of relations in a concurrent, constraint-based language makes CHR a powerful declarative tool for knowledge representation and reasoning. Over the last decade CHR has not only cut its niche as a special-purpose language for writing constraint solvers, but has matured into a general-purpose language for computational logic and beyond.
This intermediate-level book with a gentle introduction and more advanced chapters gives an overview of CHR for readers of various levels of experience. The book is addressed to researchers, lecturers, graduate students, and professional programmers interested in languages for innovative applications. The book supports both self-study and teaching. It is accompanied by a website at chr.informatik.uni-ulm.de.
In short, this book concentrates on the basics of CHR while keeping in mind dozens of research papers. In 2009, there will be a companion book on recent advances in CHR and a survey article in a journal. A book on implementation of CHR and a collection of classical CHR papers is also planned.