Content deleted Content added
adding a reference |
No edit summary |
||
Line 14:
A CHR program, sometimes called a ''constraint handler'', is a set of rules that maintain a ''constraint store'', a [[multi-set]] of logical formulas. Execution of rules may add or remove formulas from the store, thus changing the state of the program. The order in which rules "fire" on a given constraint store is [[non-deterministic programming|non-deterministic]].<ref name="timegoesby">{{Cite journal | doi = 10.1017/S1471068409990123| title = As time goes by: Constraint Handling Rules – A Survey of CHR Research between 1998 and 2007| journal = Theory and Practice of Logic Programming| volume = 10| pages = 1| year = 2009| last1 = Sneyers | first1 = Jon| last2 = Van Weert | first2 = Peter| last3 = Schrijvers | first3 = Tom| last4 = De Koninck | first4 = Leslie| url = http://dtai.cs.kuleuven.be/projects/CHR/papers/draft_chr_survey.pdf}}</ref>
Although CHR is [[Turing complete]],<ref name="complexity">{{cite journal |first1=Jon |last1=Sneyers |first2=Tom |last2=Schrijvers |first3=Bart |last3=Demoen |title=The computational power and complexity of constraint handling rules |journal=ACM Trans. Program. Lang. Syst. |volume=31 |issue=2 |year=2009 |url=https://lirias.kuleuven.be/bitstream/123456789/218524/1/p1-sneyers.pdf}}</ref> it is not commonly used as a programming language in its own right. Rather, it is used to extend a ''host language'' with constraints. Prolog is by far the most popular host language and CHR is included in several Prolog implementations, including [[SICStus Prolog|SICStus]] and [[SWI-Prolog]], although CHR implementations also exist for [[Haskell (programming language)|Haskell]], [[Java (programming language)|Java]], [[C (programming language)|C]],<ref name="imperative">{{cite encyclopedia |title=CHR for imperative host languages |author1=Peter Van Weert |author2=Pieter Wuille |author3=Tom Schrijvers |author4=Bart Demoen |encyclopedia=Constraint Handling Rules — Current Research Topics |publisher=Springer |url=https://lirias.kuleuven.be/handle/123456789/197033}}</ref> [[SQL]],<ref>https://github.com/awto/chr2sql</ref> and JavaScript.<ref>[https://fnogatz.github.io/paper-now-chrjs/ CHR.js - A CHR Transpiler for JavaScript]</ref> In contrast to Prolog, CHR rules are multi-headed and are executed in a committed-choice manner using a [[forward chaining]] algorithm.
==Language overview==
| |||