Constraint Handlers

The CHR library comes with plenty of constraint handlers written in CHR. The most recent versions of these are maintained at:

     http://www.pst.informatik.uni-muenchen.de/~fruehwir/chr-solver.html
     

arc.pl

classical arc-consistency over finite domains

bool.pl

simple Boolean constraints

cft.pl

feature term constraints according to the CFT theory

domain.pl

finite domains over arbitrary ground terms and interval domains over integers and reals, but without arithmetic functions

gcd.pl

elegant two-liner for the greatest common divisor

interval.pl

straightforward interval domains over integers and reals, with arithmetic functions

kl-one.pl

terminological reasoning similar to KL-ONE or feature trees

leq.pl

standard introductory CHR example handler for less-than-or-equal

list.pl

equality constraints over concatenations of lists (or strings)

listdom.pl

a straightforward finite enumeration list domains over integers, similar to interval.pl

math-elim.pl

solves linear polynomial equations and inequations using variable elimination, several variations possible

math-fougau.pl

solves linear polynomial equations and inequations by combining variable elimination for equations with Fourier's algorithm for inequations, several variations possible

math-fourier.pl

a straightforward Fouriers algorithm to solve polynomial inequations over the real or rational numbers

math-gauss.pl

a straightforward, elegant implementation of variable elimination for equations in one rule

minmax.pl

simple less-than and less-than-or-equal ordering constraints together with minimum and maximum constraints

modelgenerator.pl

example of how to use CHR for model generation in theorem proving

monkey.pl

classical monkey and banana problem, illustrates how CHR can be used as a fairly efficient production rule system

osf.pl

constraints over order sorted feature terms according to the OSF theory

oztype.pl

rational trees with disequality and OZ type constraint with intersection

pathc.pl

the most simple example of a handler for path consistency - two rules

primes.pl

elegant implementations of the sieve of Eratosthenes reminiscent of the chemical abstract machine model, also illustrates use of CHR as a general purpose concurrent constraint language

scheduling.pl

simple classical constraint logic programming scheduling example on building a house

tarski.pl

most of Tarski's axiomatization of geometry as constraint system

term.pl

Prolog term manipulation built-in predicates functor/3, arg/3, =../2 as constraints

time-pc.pl

grand generic handler for path-consistency over arbitrary constraints, load via time.pl to get a powerful solver for temporal constraints based on Meiri's unifying framework. time-rnd.pl contains a generator for random test problems.

time-point.pl

quantitative temporal constraints over time points using path-consistency

tree.pl

equality and disequality over finite and infinite trees (terms)

type.pl

equalities and type constraints over finite and infinite trees (terms)

You can consult or compile a constraint handler from the CHR library using e.g.:

     ?- [library('chr/examples/gcd')].
     ?- compile(library('chr/examples/gcd')).
     

In addition, there are files with example queries for some handlers, their file name starts with examples- and the file extension indicates the handler, e.g. .bool:

     examples-adder.bool
     examples-benchmark.math
     examples-deussen.bool
     examples-diaz.bool
     examples-fourier.math
     examples-holzbaur.math
     examples-lim1.math
     examples-lim2.math
     examples-lim3.math
     examples-puzzle.bool
     examples-queens.bool
     examples-queens.domain
     examples-stuckey.math
     examples-thom.math