CHRG, A grammar notation based on Constraint Handling Rules

Developed and maintained by Henning Christiansen
Computer Science Dept.
Roskilde University, Denmark

© Henning Christiansen 2002

The original CHRG system, which is available here, was written for SICStus Prolog 3. With the introduction of SICStus Prolog 4, low-level facilities of CHR, heavily used in the current implementation, have been removed, so the CHRG system don't work unless you have access to an old version of SICStus.
New versions of CHRG for SICStus 4 and SWI Prolog are under consideration, but currently (August 2010), nothing can be promised about the release date.

Web site with source code for CHRG that runs under SICStus Prolog, documentation, scientific papers on the subject, and sample files.
Freely available for any peaceful and noncommercial applications. For other purposes, write to the author.

Version 0.0, released july 2002.
Version 0.1, released nov 2002. Last modification 28 november 2002.
New feature added in 0.1: optional grammar symbols in head of rules.
Please report errors and suggestions for improvement

CHRG for "CHR Grammars" is a logical grammar system based on CHR analogously to the way Definite Clause Grammars are defined and implemented on top of Prolog. CHR is an extension to Prolog originally intended for writing constraint solvers in a declarative way, but it is also relevant for language processing as it provides a natural framework for bottom-up evaluation and easy ways to manipulate different kinds of hypotheses. -- CHRG provides the grammatical interface to CHR.

Features:

Ambiguity is not a problem for CHRG, all different parses are evaluated in parallel in the same constraint store - without backtracking.
Robustness in case of errors: The parser delivers those subphrases it has recognized as result.
A generalized lookahead mechanism so that arbitrary grammar symbols to the left and right of the string to be matched. Can be applied for disambiguation of simple and ambigous grammars, for coordination in natural language, and for tagger-like rule.
Abductive language interpretation and Assumption Grammmars supported.
Differents sorts of grammar rules that mirror CHR's propagation, simplification, and simpagation rules; full integration with Prolog and CHR.
Special grammatical operators for gaps and parallel matching.

Users Guide to CHR Grammars Source code for the CHRG system Examples of CHRGs Scientific papers on CHRG

Questions, problems, suggestions, add links to your applications of CHRG? Please, do not hessitate to contact the author.

Last modification 16 August 2010