Constraint Handling Rules

The more you CHR, the better you are.

CHR for semantic analysis in voice-controlled systems

In a recent project, Fraunhofer Institute uses CHR for semantic analysis in voice-controlled systems. As part of the project Speech Assistance for Citizen Services (S4CS), the conversation logic is modelled in CHR. This approach is fast, flexible, and can be adapted for different dialogue scenarios. The system uses GoCHR, a new CHR interpreter written in the Go programming language.

CHR creates Art

The computer software VanDeGraphGenerator analyses, generates and visualizes line graphics. We used the VanDeGraphGenerator algorithm to classify and generate designs for mason’s marks. Now an extension of VanDeGraphGenerator VdGG+ turns this medieval craftsmanship into contemporary abstract digital art. More information on

New Edition of a CHR Book

Book coverThe book “Constraint Handling Rules – Compilation, Execution, and Analysis” has a new edition, because the old one is out of print. By popular request, the book format has been enlarged. See Google Books.

Call for Papers ICLP’18

As a PC-member I encourage submissions to

34th International Conference on Logic Programming (ICLP 2018)
Oxford, UK, July 14-17, 2018

ICLP is the premier conference on foundations and applications of logic programming, including but not restricted to answer-set programming, non-monotonic reasoning, unification and constraints based logic languages, constraint handling rules, argumentation logics, deductive databases, description logics, inductive and co-inductive logic programming.

Patents citing CHR

Call for Papers Spring 2017

As a PC-member I strongly welcome submissions dealing with Constraint Handling Rules at these fine conferences:

19th International Symposium on Principles and Practice of Declarative Programming (PPDP),
Namur, Belgium, 9 Oct. – 11 Oct. 2017.

International Joint Conference on Rules and Reasoning (RuleML+RR 2017),
London, UK from 12-15th July 2017.

21st International Conference on Logic for Programming, Artificial Intelligence and Reasoning,
Maun, Botswana, at Cresta Riley’s Hotel, 7-12th May 2017.

And another fine conference:

33rd International Conference on Logic Programming (ICLP 2017),
Melbourne, Australia, August 29 to September 1, 2017.

Persistent Constraint Store in newest SWI-Prolog

Yesterday Jan Wielemaker published version 7.3.28 of SWI-Prolog. It comes with a new flag toplevel_mode which might be especially useful to test and debug CHR programs. It was highlighted in the version announcements as follows:

After suggestion by Falco Nogatz, it is now possible to run the toplevel in recursive mode such that global variables remain bound. Nice for teaching CHR. Not clear what the other use cases are. Use ?- set_prolog_flag(toplevel_mode, recursive). to enable this.
Some insights on the discussion, implementation and usage of the new flag can be found in the related GitHub issue. It can be used to have a persistent constraint store over multiple queries in the toplevel. This way it is possible to, e.g., use the classical gcd/1 constraint solver incrementally for computing the greatest common divisor of numbers given on by one:
?- set_prolog_flag(toplevel_mode, recursive).
?- gcd(24).
?- gcd(42).
?- X = 3.
X = 3,
As seen in the last query, the contents of the constraint store are printed by default on every query. So, for more advanced usage, it might become handy to use the recursive toplevel mode with CHR’s flag chr_toplevel_show_store set to false and explicitly call the meta-predicate chr_show_store/1.

Call for Papers PADL’17

As a PC-member I encourage submissions to

19th International Symposium on Practical Aspects of Declarative Languages (PADL 2017) Paris, France, 16th and 17th January 2017

PADL 2017 welcomes new ideas and approaches pertaining to applications and implementation of declarative languages. PADL 2017 will be co-located with the Symposium on Principles of Programming Languages (POPL 2017), in Paris, France.