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Article contents:== Outdated egg! This is an egg for CHICKEN 4, the unsupported old release. You're almost certainly looking for [[/eggref/5/csp|the CHICKEN 5 version of this egg]], if it exists. If it does not exist, there may be equivalent functionality provided by another egg; have a look at the [[https://wiki.call-cc.org/chicken-projects/egg-index-5.html|egg index]]. Otherwise, please consider porting this egg to the current version of CHICKEN. [[tags: egg data]] [[toc:]] This page is maintained in the package's [[https://github.com/abarbu/csp|github repository]]. == CSP This is a Chicken Scheme egg which solves constraint satisfaction problems. A CSP is composed of a number of ''domain-variable''s that have a domain, a set of bindings they can assume, along with a number of constraints. This egg supports 5 kinds of constraints: ''efd'' (early failure detection), ''fc'' (forward checking), ''vp'' (value propagation), ''gfc'' (generalized forward checking) and ''ac'' (arc consistency). ==== High-level <procedure>(csp-solution domain-variables select)</procedure> Given a list of domain variables and a function to select which one to try to bind next, one can simply pass in ''first'', this produces a solution to the CSP. <procedure>(create-domain-variable domain)</procedure> Create a domain variable whose domain is ''domain''. <parameter>*csp-strategy*</parameter> <procedure>(assert-constraint! constraint domain-variables)</procedure> Assert a constraint, a function that returns a boolean, between a number of domain variables. The kind of constraint is determined by inspecting ''*csp-strategy*''. Valid types are: ''efd'' (early failure detection), ''fc'' (forward checking), ''vp'' (value propagation), ''gfc'' (generalized forward checking) and ''ac'' (arc consistency). The default is ''ac''. For constraints of low arity, a small number of domain variables, it will use an optimized version of the constraint propagation code. <procedure>(bound? domain-variable)</procedure> <procedure>(binding domain-variable)</procedure> Determine if the domain variable is bound and what its binding is. ==== Constraints <procedure>(assert-unary-constraint-efd! constraint x)</procedure> <procedure>(assert-binary-constraint-efd! constraint x y)</procedure> <procedure>(assert-ternary-constraint-efd! constraint x y z)</procedure> <procedure>(assert-unary-constraint-fc! constraint x)</procedure> <procedure>(assert-binary-constraint-fc! constraint x y)</procedure> <procedure>(assert-ternary-constraint-fc! constraint x y z)</procedure> <procedure>(assert-unary-constraint-vp! constraint x)</procedure> <procedure>(assert-binary-constraint-vp! constraint x y)</procedure> <procedure>(assert-ternary-constraint-vp! constraint x y z)</procedure> <procedure>(assert-unary-constraint-gfc! constraint x)</procedure> <procedure>(assert-binary-constraint-gfc! constraint x y)</procedure> <procedure>(assert-ternary-constraint-gfc! constraint x y z)</procedure> <procedure>(assert-unary-constraint-ac! constraint x)</procedure> <procedure>(assert-binary-constraint-ac! constraint x y)</procedure> <procedure>(assert-ternary-constraint-ac! constraint x y z)</procedure> Assert each of the 5 kinds of constraints between domain-variables ''x'', ''y'' and ''z''. You can always use ''assert-constraint!'' instead and it will default to these functions if your constraint is of low arity. <procedure>(assert-constraint-efd! constraint ds)</procedure> <procedure>(assert-constraint-fc! constraint ds)</procedure> <procedure>(assert-constraint-vp! constraint ds)</procedure> <procedure>(assert-constraint-gfc! constraint ds)</procedure> <procedure>(assert-constraint-ac! constraint ds)</procedure> Assert each of the 5 kinds of constraints between the list of domain-variables ds. You can always use ''assert-constraint!'' instead as it will pick an optimized version for each of the above if the arity of the constraint is low. ==== Low-level <procedure>(attach-before-demon! demon x)</procedure> <procedure>(attach-after-demon! demon x)</procedure> <procedure>(restrict-domain! x domain)</procedure> Only of interest to implementers. === Examples This solves [[http://projecteuler.net/problem=43|Project Euler problem 43]]. (use traversal nondeterminism csp) (let* ((ds (map-n (lambda _ (create-domain-variable (map-n identity 10))) 10)) (d3 (lambda (ns) (+ (* (first ns) 100) (* (second ns) 10) (third ns)))) (div (lambda (n) (lambda ns (= (modulo (d3 ns) n) 0)))) (nthd (lambda (a b) (sublist ds (- a 1) b)))) (assert-constraint! (div 17) (nthd 8 10)) (assert-constraint! (div 13) (nthd 7 9)) (assert-constraint! (div 11) (nthd 6 8)) (assert-constraint! (div 7) (nthd 5 7)) (assert-constraint! (div 5) (nthd 4 6)) (assert-constraint! (div 3) (nthd 3 5)) (assert-constraint! (div 2) (nthd 2 4)) (map-all-pairs (lambda l (assert-constraint! (lambda (a b) (not (= a b))) l)) ds) (foldl + 0 (map (lambda (l) (foldl (lambda (a b) (+ (* a 10) b)) 0 l)) (all-values (csp-solution ds last))))) === License Copyright 1993-1995 University of Toronto. All rights reserved. Copyright 1996 Technion. All rights reserved. Copyright 1996 and 1997 University of Vermont. All rights reserved. Copyright 1997-2001 NEC Research Institute, Inc. All rights reserved. Copyright 2002-2013 Purdue University. All rights reserved. Contact Andrei Barbu, andrei@0xab.com. Originally written by Jeff Siskind. This program is free software: you can redistribute it and/or modify it under the terms of the GNU Lesser General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public License for more details. You should have received a copy of the GNU Lesser General Public License along with this program. If not, see http://www.gnu.org/licenses. Description of your changes:

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