Institute of Software Engineering and Programming Languages

CHR Research Group

Constraint Handling Rules (CHR) is a concurrent committed-choice constraint logic programming language consisting of guarded rules that transform multi-sets of atomic formulas (constraints) until exhaustion. It was designed by Thom Fruehwirth in 1991. CHR can embed many rule-based formalisms and systems, and it can describe algorithms in a compact declarative way without compromising efficiency. The clean semantics of CHR ensures that several desirable properties hold for CHR programs and also facilitates sophisticated program analysis. CHR libraries exist for Prolog, Haskell, Java, Javascript, Python and C. CHR is also available online for experimentation with many example programs. More than 250 academic and industrial projects worldwide use CHR, and about 2500 research papers reference it.

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2025

108.
Rechenberger, Sascha; Frühwirth, Thom
FreeCHR – An Algebraic Framework for Constraint Handling Rules Embeddings
Theory and Practice of Logic Programming, 25 (3) :340–373
May 2025
DOI:10.1017/S1471068425000043
107.
Rechenberger, Sascha; Frühwirth, Thom
FreeCHR – An Algebraic Framework for Constraint Handling Rules Embeddings
Theory and Practice of Logic Programming, 25 (3) :340–373
May 2025
DOI:10.1017/S1471068425000043
106.
Rechenberger, Sascha; Frühwirth, Thom
A refined operational semantics for FreeCHR
2025
File:https://arxiv.org/abs/2504.04962
105.
Rechenberger, Sascha; Frühwirth, Thom
A refined operational semantics for FreeCHR
2025
File:https://arxiv.org/abs/2504.04962
104.
Rechenberger, Sascha; Frühwirth, Thom
An instance of FreeCHR with refined operational semantics
2025
File:https://arxiv.org/abs/2505.22155
103.
Rechenberger, Sascha; Frühwirth, Thom
An instance of FreeCHR with refined operational semantics
2025
File:https://arxiv.org/abs/2505.22155
102.
Rechenberger, Sascha; Frühwirth, Thom
Optimized Execution of FreeCHR
2025
File:https://arxiv.org/abs/2506.14485
101.
Rechenberger, Sascha; Frühwirth, Thom
Optimized Execution of FreeCHR
2025
File:https://arxiv.org/abs/2506.14485

2023

100.
Rechenberger, Sascha; Frühwirth, Thom
FreeCHR: An Algebraic Framework for CHR Embeddings
7th International Joint Conference on Rules and Reasoning (RuleML+RR '23), Oslo, Norway
October 2023
DOI:10.1007/978-3-031-45072-3_14
ISBN:978-3-031-45072-3
99.
Rechenberger, Sascha; Frühwirth, Thom
FreeCHR: An Algebraic Framework for CHR-Embeddings
2023
DOI:10.48550/arXiv.2306.00642