The SWI-Prolog CHR compiler exploits
term_expansion/2
rules to translate the constraint handling rules to plain Prolog. These
rules are loaded from the library
library(chr). They are
activated if the compiled file has the
.chr extension or
after finding a declaration in the following format:
:- chr_constraint ...
It is advised to define CHR rules in a module file, where the module
declaration is immediately followed by including the library(chr)
library as exemplified below:
:- module(zebra, [ zebra/0 ]).
:- use_module(library(chr)).
:- chr_constraint ...
Using this style, CHR rules can be defined in ordinary Prolog .pl
files and the operator definitions required by CHR do not leak into
modules where they might cause conflicts.
