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CHR.js: A CHR Implementation in JavaScript

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Book cover Rules and Reasoning (RuleML+RR 2018)

Part of the book series: Lecture Notes in Computer Science ((LNPSE,volume 11092))

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Abstract

Constraint Handling Rules (CHR) is usually compiled to logic programming languages. While there are implementations for imperative programming languages such as C and Java, its most popular host language remains Prolog. In this paper, we present Chr.js, a CHR system implemented in JavaScript, that is suitable for both the server-side and interactive client-side web applications. Chr.js provides (i) an interpreter, which is based on the asynchronous execution model of JavaScript, and (ii) an ahead-of-time compiler, resulting in synchronous constraint solvers with better performances. Because of the great popularity of JavaScript, Chr.js is the first CHR system that runs on almost all and even mobile devices, without the need for an additional runtime environment. As an example application we present the Chr.js Playground, an offline-capable web-interface which allows the interactive exploration of CHRs in every modern browser.

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Notes

  1. 1.

    List of languages that compile to JS, https://github.com/jashkenas/coffeescript/wiki/list-of-languages-that-compile-to-js.

  2. 2.

    JSFiddle, https://jsfiddle.net/.

  3. 3.

    SWISH, https://swish.swi-prolog.org/.

  4. 4.

    The JavaScript language is standardised as ECMAScript [5]. The most recent version of the ECMAScript specification is the sixth version, often referred to as ES6 or ES2015 or by its codename Harmony. Although it defines TCO, it has not yet been implemented by the major browsers.

  5. 5.

    For example the equality check in JavaScript is performed using == or === (type-safe), instead of the often used unification = in Prolog.

  6. 6.

    PEG.js, https://pegjs.org/.

  7. 7.

    A more detailed discussion on using synchronous or asynchronous functions is given in [15, Sect. 3.4].

  8. 8.

    Travis Continuous Integration service, https://travis-ci.org/.

  9. 9.

    Copy available at https://svn.ulyssis.org/repos/sipa/cchr/.

  10. 10.

    Benchmarks available at https://github.com/fnogatz/CHR-Benchmarks.

  11. 11.

    Chr.js provides a command line utility to pre-compile CHR programs: chrjs –optimized program.in.

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Authors and Affiliations

  1. Department of Computer Science, University of Würzburg, Am Hubland, D-97074, Würzburg, Germany

    Falco Nogatz & Dietmar Seipel

  2. Institute of Software Engineering and Programming Languages, Ulm University, D-89069, Ulm, Germany

    Thom Frühwirth

Authors
  1. Falco Nogatz
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  2. Thom Frühwirth
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  3. Dietmar Seipel
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Correspondence to Falco Nogatz .

Editor information

Editors and Affiliations

  1. Computer Science, Freie Universität Berlin, Berlin, Germany

    Christoph Benzmüller

  2. University of Calabria, Rende, Italy

    Francesco Ricca

  3. Université du Luxembourg, Esch-sur-Alzette, Luxembourg

    Xavier Parent

  4. SINTEF/University of Oslo, Oslo, Norway

    Dumitru Roman

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Nogatz, F., Frühwirth, T., Seipel, D. (2018). CHR.js: A CHR Implementation in JavaScript. In: Benzmüller, C., Ricca, F., Parent, X., Roman, D. (eds) Rules and Reasoning. RuleML+RR 2018. Lecture Notes in Computer Science(), vol 11092. Springer, Cham. https://doi.org/10.1007/978-3-319-99906-7_9

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  • DOI: https://doi.org/10.1007/978-3-319-99906-7_9

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