Try Constraint Handling Rules Online

• Subject: Try Constraint Handling Rules Online
• From: Thom Fruehwirth <fruehwir@informatik.uni-muenchen.de>
• Date: Wed, 09 Feb 2000 10:17:14 +0100
• Organization: =?iso-8859-1?Q?Universit=E4t=20M=FCnchen?=
• Sender: fruehwir@informatik.uni-muenchen.de

Constraint Handling Rules (CHR) are available free and online now at:

http://www.pms.informatik.uni-muenchen.de/~webchr/

Click on the link above to run the latest release of CHR in Sicstus
Prolog on our server. Choose among dozens of constraint solvers written
in CHR. Ask any query. Or even write your own constraint solvers.

CHR are a rule-based high-level language to write constraint systems.
CHR make it easy to define constraint reasoning: simplification and
propagation as well as incremental solving (satisfaction) of
constraints. Also, CHR have been successfully used
      as general purpose concurrent constraint language with ask and
tell, 
      as fairly efficient production rule system, 
      as special kind of theorem prover, 
      as system combining forward and backward chaining, 
      as high-level language for manipulating attributed variables. 

CHR are essentially a committed-choice language consisting of guarded
rules with multiple head atoms. CHR define simplification of, and
propagation over, constraints. Simplification rewrites constraints to
simpler constraints while preserving logical equivalence (e.g. X>Y,Y>X
<=> false). Propagation adds new constraints which are logically
redundant but may cause further simplification (e.g. X>Y,Y>Z ==> X>Z).
Repeatedly applying the rules incrementally solves constraints (e.g.
A>B,B>C,C>A leads to false). With multiple heads and propagation rules,
CHR provide two features which are essential for non-trivial constraint
handling. 

Test-Drive CHR. Run CHR online. Do a demo. Try it out now!

Thom Fruehwirth

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