This folder contains a Logtalk port of ToyCHR, a reference implementation of Constraint Handling Rules (CHR) available from:

The port is work in progress and includes significant modifications to the original code:

  • Instead of compiling .chr files, it uses the term-expansion mechanism, by defining toychrdb as a hook object, to support writing rules inside objects and categories. As a consequence, the original chr_compile/1 is not available.

  • The port is portable and should run on all supported backends.

The port also includes examples ported from the SWI-Prolog CHR package examples and documentation. These examples are ported using the same license of the original code (BSD-2-Clause).

For sample queries, please see the SCRIPT.txt file.

API documentation

Open the ../../docs/library_index.html#toychr link in a web browser.


To load all entities in this port, load the loader.lgt file:

| ?- logtalk_load(toychr(loader)).


To test this port predicates, load the tester.lgt file:

| ?- logtalk_load(toychr(tester)).