Constraint Handling Rules

Thom Frühwirth
Textbook, Cambridge University Press, ISBN 9780521877763, 2009.
"The reference on Constraint Handling Rules, covering both theory and practice."
Professor Pascal Van Hentenryck, Brown University, Rhode Island, USA
"This is a great book illustrating both the simplicity and power of Constraint Handling Rules, the purest form of rule based programming I know."
Professor Peter J. Stuckey, University of Melbourne, and National ICT Australia
The standard reference authored by the designer of CHR - Provides a CHR tutorial for easy introduction - An essential source for researchers, lecturers, graduate students and professional programmers
Order at Cambridge University Press, amazon.de, amazon.co.uk, amazon.com.
Errata (not yet).

What are Constraint Handling Rules?

"CHR was designed as a language for defining constraint solvers, but at the same time it is one of the most powerful multiset rewriting languages."
Professor Kazunori Ueda, Waseda University, Japan, and Norio Kato in 'Programming Logical Links'

"...a powerful, highly optimized, lazy rule engine, building on [...] novel analyses and optimizations recently produced by the CHR community. [...] Our empirical study again shows that for many problems and practical applications, a lazy approach [taken by CHR] consistently outperforms Rete-based [rule-based] systems."
Peter Van Weert, K.U. Leuven, in 'Efficient Lazy Evaluation of Rule-Based Programs'

"... [Concurrent CHR in Haskell] exhibits significant speed up in most problems when executed on multi-core systems."
Members of the National University of Singapore at the Concurrent Constraint Handling Rules Home Page

"Since CHR seems to subsume most of the other formalisms that have been related to it, it has the potential to become a lingua franca, a hub which collects and dispenses research efforts from and to the various related fields."
Jon Sneyers, K.U. Leuven, in 'Optimizing Compilation and Complexity of CHR'

Constraint Handling Rules (CHR) is both a versatile theoretical formalism based on logic and an efficient practical high-level programming language based on rules and constraints.

Procedural knowledge is often expressed by if-then rules, events and actions are related by reaction rules, change is expressed by update rules. Algorithms are often specified using inference rules, rewrite rules, transition rules, sequents, proof rules, or logical axioms. All these kinds of rules can be directly written in CHR. The clean logical semantics of CHR facilitates non-trivial program analysis and transformation. About a dozen implementations of CHR exist in Prolog, Haskell, Java and C. Some of them allow to apply millions of rules per second. CHR is also available as WebCHR for online experimentation with more than 40 example programs. More than 100 academic and industrial projects worldwide use CHR, and more than 1000 research papers reference it.

Some CHR Industrial Users

Stock Broking - Contact: Mike Elston, Director of Systems Development, SecuritEase, Wellington, New Zealand.

Injection Mold Design - Contact: Alan Baljeu, President, Cornerstone Intelligent Software Corp, Windsor, Canada.

Optical Network Routing - Contact: Jonathan Weston-Dawkes, Mitre Corp, Bedford, USA.

Automatic Test Data Generation - Contact: Ralf Gerlich, BSSE, Immenstaad, Germany.

Book Contents

This book, written by the creator of Constraint Handling Rules (CHR), describes the theory of CHR and how to use it in practice. It is supported by a website containing teaching materials, online demos, and free downloads of the language. After a basic tutorial, the author describes in detail the CHR language and discusses guaranteed properties of CHR programs. The author then compares CHR with other formalisms and languages and illustrates how it can capture their essential features. Finally, larger programs are introduced and analyzed in detail. The book is ideal for graduate students and lecturers, and for more experienced programmers and researchers, who can use it for self-study. Exercises with selected solutions, and bibliographic remarks are included at the ends of chapters. The book is the definitive reference on the subject.

Preface
Part I. CHR Tutorial:
1. Getting started
2. My first CHR programs
Part II. The CHR Language:
3. Syntax and semantics
4. Properties of CHR
5. Program analysis
6. Rule-based and graph-based formalisms in CHR
Part III. CHR Programs and Applications:
7. My first CHR programs, revisited for analysis
8. Finite domain constraint solvers
9. Infinite domain constraint solvers
10. Union-find algorithm
Bibliography
List of figures
List of illustrations
Index.