35.7 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')).
If you want to learn more about the handlers,
look at their documented source code.
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