Textbook, Cambridge University Press, ISBN 9780521877763, 2009.
"The reference on Constraint Handling Rules, covering both theory and
"This is a great book illustrating both the simplicity and power of Constraint
Handling Rules, the purest form of rule based programming I know."
The standard reference authored by the designer of CHR
The companion book is "Constraint Handling Rules: Compilation, Execution, and Analysis" Thom Frühwirth, Frank Raiser (editors), March 2011.
"...one of the most powerful multiset rewriting languages."
"...a powerful, highly
optimized, lazy rule engine [...] consistently
outperforms Rete-based systems."
"... [Concurrent CHR in Haskell] exhibits significant speed up in most problems when executed on multi-core systems."
"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."
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,
CHR is also available as WebCHR for online experimentation
with more than 40 example programs. More than 200 academic and industrial
projects worldwide use CHR, and about 2000 research papers reference it.
- Slides of CHR Keynote Talk,
Thom Frühwirth at RuleML 2015.
This book, written by the creator of Constraint Handling Rules (CHR), describes the theory of CHR and how to use it in practice. 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. These include constraint solvers and implementations of classical algorithms. 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 CHR.
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
List of figures
List of illustrations
and Preface (preliminary version).
Book excerpt: First Steps in CHR.
Stock Broking - Mike Elston, Director of Systems Development, SecuritEase, Wellington, New Zealand.
Cognitive Brain for Service Robotics - Teresa Escrig, CEO, Cognitive Robots, Castellon, Spain and USA.
Injection Mold Design - Alan Baljeu, President, Cornerstone Intelligent Software Corp, Windsor, Canada.
Optical Network Routing - Jonathan Weston-Dawkes, Mitre Corp, Bedford, USA.
Automatic Test Data Generation - Ralf Gerlich, BSSE, Immenstaad, Germany.
WebCHR: Test-Drive CHR. Run full-fledged CHR online now! Play with 40+ example programs or write your own.
Some CHR implementations in Prolog
(SWI Prolog Reference Manual 7.1),
(Sicstus Prolog User's Manual),
ToyCHR (simple compiler and interpreter for any Prolog).
JCHR: CHR in
HaskellCHR: CHR in Haskell
The CHR IDE Eclipse plugin for SWI Prolog
The CHR Plug-in is an extension for Eclipse which allows users to develop CHR programs with a combined editor, executor and visual tracer. The editor provides syntax coloring, syntax checking, auto-completion etc. A wizard allows users to easily generate CHR files and projects. (Accompanying paper).
1. Download the Eclipse software
2. Install Java 7
3. Install SWI-Prolog
4. Download the Eclipse plugin for CHR
5. Open Eclipse and install the plug-in.
More software involving CHR
Online Tool that translates CHR extensions like priorities, negation and random execution and programs in other rule-based approaches and formalisms like term rewriting and functional programming to CHR according to Chapter 6 of the CHR book (see above).
Online Tool that inverts CHR rules for backwards execution. (Accompanying paper).
SMCHR: Satisfiability Modulo Constraint Handling Rules
From XML Schema to JSON Schema - Comparison and Translation with Constraint Handling Rules, (tool download).
An extensible Eclipse platform for analysing graph transformation systems in CHR (pdf) (Eclipse Plug-in tar-file)
More CHR Software Downloads...
Courses by the author based on the book were held for example at the University of Ulm in 2009 (and every year thereafter), at the University of Venice in 2009, at the The CHR Working Week 2009, First CHR Summer School 2010 , Second CHR Summer School 2011, 3rd CHR Summer School 2013.
CHR book Chapter 1
CHR book Chapter 2 (2015)
CHR book Chapter 3
CHR book Chapter 4
CHR book Chapter 5
CHR book Chapter 6 (extended version, 2015)
CHR book Chapter 7
A CHR course should be combined with a practical lab course. The book contains 55 exercises, here are some of the book and some new ones:
CHR Cheat Sheet, 2012.
CHR Exercises, 2014.
CHR Exercises, 2013.
CHR Exercises, 2012.
CHR Exercises, 2009: Exercise 1, Exercise 2, Exercise 3, Exercise 4, Exercise 5.
CHR CP Exercises, 2009: Exercise 2, Exercise 3, Exercise 4 (boole.pl), Exercise 5, Exercise 6 (dl-ex6.pl), Exercise 7 (fd-ex7.pl).
CHR CP Exercises, 2006: Exercise 5, Exercise 6, Exercise 7, Exercise 8, Exercise 9, Exercise 10, Exercise 11, Exercise 12, Exercise 13.
CHR Summary (pdf, 2 pages) "The story so far"
CHR Tutorial Slides (pdf, Thom Fruehwirth)
CHR Tutorial Slides (odp, Jon Sneyers)
CHR Tutorial Handouts (pdf, Jon Sneyers)
CHR Tutorial Slides (pdf, Tom Schrijvers)
CHR Keynote Talk Slides (pdf, Thom Frühwirth)
More CHR Tutorials...
Book excerpt: First Steps in CHR (pdf)
Welcome to Constraint Handling Rules (pdf)
Programming in Constraint Handling Rules (pdf)
CHR survey, Update to CHR survey
Hand-selected CHR bibliography with about 500 papers by 200 authors
2000 research papers mentioning Constraint Handling Rules
All you ever wanted to know about CHR (CHR website)
WebCHR: Test-Drive CHR. Run CHR online now!
Recent Research of Thom Fruehwirth on Constraint Handling Rules (CHR).
Thom Frühwirth, updated December 15, 2015