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<H2><A NAME="sec:7.1"><SPAN class="sec-nr">7.1</SPAN> <SPAN class="sec-title">Introduction</SPAN></A></H2>
<A NAME="sec:chrintro"></A> Constraint Handling Rules (CHR) is a
committed-choice rule-based language embedded in Prolog. It is designed
for writing constraint solvers and is particularly useful for providing
application-specific constraints. It has been used in many kinds of
applications, like scheduling, model checking, abduction, type checking
among many others.
<P>CHR has previously been implemented in other Prolog systems (SICStus,
Eclipse, Yap), Haskell and Java. This CHR system is based on the
compilation scheme and runtime environment of CHR in SICStus.
<P>In this documentation we restrict ourselves to giving a short
overview of CHR in general and mainly focus on elements specific to this
implementation. For a more thorough review of CHR we refer the reader to
<CITE><A class="cite" href="Bibliography.html#Freuhwirth:98">Frühwirth,
1998</A></CITE>. More background on CHR can be found at
<CITE><A class="cite" href="Bibliography.html#chrSite">Frühwirth,</A></CITE>.
<P>In <A class="sec" href="SyntaxAndSemantics.html">section 7.2</A> we
present the syntax of CHR in Prolog and explain informally its
operational semantics. Next, <A class="sec" href="practical.html">section
7.3</A> deals with practical issues of writing and compiling Prolog
programs containing CHR. <A class="sec" href="debugging.html">Section
7.4</A> explains the currently primitive CHR debugging facilities. <A class="sec" href="debugging.html">Section
7.4.3</A> provides a few useful predicates to inspect the constraint
store and <A class="sec" href="examples.html">section 7.5</A>
illustrates CHR with two example programs. In <A class="sec" href="sicstus-chr.html">section
7.6</A> some compatibility issues with older versions of this system and
SICStus' CHR system. Finally, <A class="sec" href="guidelines.html">section
7.7</A> concludes with a few practical guidelines for using CHR.
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