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@ -19,8 +19,8 @@
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[else
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(match-define (cons name other-names) names)
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(for/and ([val (in-list ($csp-vals csp name))])
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;; todo: reconsider efficiency of currying every value
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(($constraint other-names (curry proc val)) csp))])))
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;; todo: reconsider efficiency of currying every value
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(($constraint other-names (curry proc val)) csp))])))
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(define/contract (check-name-in-csp! caller csp name)
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(symbol? $csp? $var-name? . -> . void?)
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@ -28,8 +28,7 @@
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(unless (memq name names)
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(raise-argument-error caller (format "csp variable name: ~v" names) name)))
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(define/contract (nary-constraint? constraint n)
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($constraint? exact-nonnegative-integer? . -> . boolean?)
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(define (nary-constraint? constraint n)
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(= n (length ($constraint-names constraint))))
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(define/contract (unary-constraint? constraint)
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@ -40,31 +39,33 @@
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($constraint? . -> . boolean?)
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(nary-constraint? constraint 2))
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(define/contract (add-var! csp name [vals empty])
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(($csp? $var-name?) ((listof any/c)) . ->* . void?)
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(add-vars! csp (list name) vals))
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(define/contract (add-vars! csp names [vals empty])
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(($csp? (listof $var-name?)) ((listof any/c)) . ->* . void?)
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(for ([name (in-list names)]
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#:when (memq name (map $var-name ($csp-vars csp))))
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(raise-argument-error 'add-var! "var that doesn't exist" name))
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(for ([name (in-list names)])
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(set-$csp-vars! csp (cons ($var name vals) ($csp-vars csp)))))
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(define (unique-varnames? xs)
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(and (andmap $var-name? xs) (not (check-duplicates xs eq?))))
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(define/contract (add-vars! csp names [vals-or-procedure empty])
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(($csp? (listof $var-name?)) ((or/c (listof any/c) procedure?)) . ->* . void?)
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(for/fold ([vars ($csp-vars csp)]
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#:result (set-$csp-vars! csp vars))
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([name (in-list names)])
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(when (memq name (map $var-name vars))
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(raise-argument-error 'add-vars! "var that doesn't exist" name))
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(append vars
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(let ([vals (if (procedure? vals-or-procedure)
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(vals-or-procedure)
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vals-or-procedure)])
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(list ($var name vals))))))
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(define/contract (add-var! csp name [vals-or-procedure empty])
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(($csp? $var-name?) ((or/c (listof any/c) procedure?)) . ->* . void?)
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(add-vars! csp (list name) vals-or-procedure))
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(define/contract (add-constraint! csp proc var-names)
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($csp? procedure? (listof $var-name?) . -> . void?)
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(for ([name (in-list var-names)])
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(check-name-in-csp! 'add-constraint! csp name))
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(set-$csp-constraints! csp (cons ($constraint var-names proc) ($csp-constraints csp))))
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(check-name-in-csp! 'add-constraint! csp name))
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(set-$csp-constraints! csp (append ($csp-constraints csp) (list ($constraint var-names proc)))))
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(define/contract (no-solutions? csp)
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($csp? . -> . boolean?)
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(for/or ([var (in-list ($csp-vars csp))])
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(empty? ($var-vals var))))
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(empty? ($var-vals var))))
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(struct $csp-inconsistent () #:transparent)
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@ -72,12 +73,12 @@
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($csp? unary-constraint? . -> . $csp?)
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(match-define ($constraint (list constraint-name) proc) constraint)
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(define new-csp ($csp (for/list ([var (in-list ($csp-vars csp))])
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(match-define ($var name vals) var)
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(if (eq? name constraint-name)
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($var name (if (promise? proc)
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(force proc)
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(filter proc vals)))
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var))
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(match-define ($var name vals) var)
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(if (eq? name constraint-name)
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($var name (if (promise? proc)
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(force proc)
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(filter proc vals)))
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var))
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;; once the constraint is applied, it can go away
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(remove constraint ($csp-constraints csp))))
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(when (no-solutions? new-csp) (raise ($csp-inconsistent)))
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@ -95,11 +96,11 @@
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(check-name-in-csp! '$csp-vals csp name)
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(for/first ([var (in-list ($csp-vars csp))]
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#:when (eq? name ($var-name var)))
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($var-vals var)))
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($var-vals var)))
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(struct $arc (name constraint) #:transparent)
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(define/contract (revise csp arc)
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(define/contract (reduce-domains-by-arc csp arc)
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($csp? $arc? . -> . $csp?)
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(match-define ($arc name ($constraint names constraint-proc)) arc)
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(match-define (list other-name) (remove name names))
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@ -108,7 +109,7 @@
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(λ (val other-val) (constraint-proc other-val val)))) ; otherwise reverse arg order
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(define (satisfies-arc? val)
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(for/or ([other-val (in-list ($csp-vals csp other-name))])
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(proc val other-val)))
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(proc val other-val)))
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(apply-unary-constraint csp ($constraint (list name)
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(procedure-rename
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satisfies-arc?
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@ -118,30 +119,26 @@
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((listof binary-constraint?) . -> . (listof $arc?))
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(for*/list ([constraint (in-list constraints)]
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[name (in-list ($constraint-names constraint))])
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($arc name constraint)))
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($arc name constraint)))
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(define/contract (terminating-at arcs name)
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((listof $arc?) $var-name? . -> . (listof $arc?))
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(for/list ([arc (in-list arcs)]
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#:when (eq? name (second ($constraint-names ($arc-constraint arc)))))
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arc))
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(define/contract (constraint-names-assigned? csp constraint)
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($csp? $constraint? . -> . boolean?)
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(define assigned-var-names
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(for/list ([var (in-list (assigned-vars csp))])
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($var-name var)))
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(match-define ($constraint names _) constraint)
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(for/and ([name (in-list names)])
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(memq name assigned-var-names)))
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(define/contract (remove-obsolete-constraints csp)
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arc))
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(define/contract (constraint-assigned? csp constraint)
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($csp? $constraint? . -> . any/c)
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(for/and ([name (in-list ($constraint-names constraint))])
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(memq name (map $var-name (assigned-vars csp)))))
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(define/contract (remove-assigned-constraints csp)
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($csp? . -> . $csp?)
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($csp
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($csp-vars csp)
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(for/list ([constraint (in-list ($csp-constraints csp))]
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#:unless (constraint-names-assigned? csp constraint))
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constraint)))
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#:unless (constraint-assigned? csp constraint))
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constraint)))
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(define/contract (ac-3 csp)
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($csp? . -> . $csp?)
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@ -149,13 +146,13 @@
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(define all-arcs (binary-constraints->arcs (filter binary-constraint? ($csp-constraints csp))))
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(for/fold ([csp csp]
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[arcs all-arcs]
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#:result (remove-obsolete-constraints csp))
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#:result (remove-assigned-constraints csp))
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([i (in-naturals)]
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#:break (empty? arcs))
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(match-define (cons arc other-arcs) arcs)
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(match-define ($arc name _) arc)
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(define revised-csp (revise csp arc))
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(values revised-csp (if (= (length ($csp-vals csp name)) (length ($csp-vals revised-csp name)))
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(define reduced-csp (reduce-domains-by-arc csp arc))
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(values reduced-csp (if (= (length ($csp-vals csp name)) (length ($csp-vals reduced-csp name)))
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;; revision did not reduce the domain, so keep going
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other-arcs
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;; revision reduced the domain, so supplement the list of arcs
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@ -189,10 +186,10 @@
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(define/contract (select-unassigned-var csp)
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($csp? . -> . $var?)
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;; minimum remaining values (MRV) rule
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(define uvars (unassigned-vars csp))
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(when (empty? uvars)
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(raise-argument-error 'select-unassigned-var "nonempty list of vars" uvars))
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(raise-argument-error 'select-unassigned-var "csp with unassigned vars" csp))
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;; minimum remaining values (MRV) rule
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(argmin (λ (var) (length ($var-vals var))) uvars))
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(define/contract (order-domain-values vals)
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@ -203,57 +200,46 @@
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;; todo: inferences between assignments
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(define infer values)
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(define/contract (constraint-has-name? constraint name)
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($constraint? $var-name? . -> . boolean?)
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(and (memq name ($constraint-names constraint)) #true))
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(define/contract (assign-val csp name val)
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($csp? $var-name? any/c . -> . $csp?)
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(validate-assignment (apply-unary-constraint csp ($constraint (list name) (delay (list val)))) name))
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(define/contract (validate-assignment csp name)
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($csp? $var-name? . -> . $csp?)
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(define assigned-names (map $var-name (assigned-vars csp)))
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(for/fold ([csp csp])
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(define csp-with-assignment (apply-unary-constraint csp ($constraint (list name) (delay (list val)))))
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(for/fold ([csp csp-with-assignment])
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([constraint (in-list ($csp-constraints csp))]
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#:when (match-let ([($constraint cnames _) constraint])
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(and (memq name cnames)
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(for/and ([cname (in-list cnames)])
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(memq cname assigned-names)))))
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#:when (and (constraint-has-name? constraint name)
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(constraint-assigned? csp constraint)))
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(unless (constraint csp) (raise ($csp-inconsistent)))
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(remove-obsolete-constraints csp)))
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(remove-assigned-constraints csp)))
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(define solver-stop-val (gensym 'solver-stop))
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(define/contract (backtracking-solution-generator csp)
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(define/contract (backtracking-solver csp)
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($csp? . -> . generator?)
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(generator ()
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(begin0
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solver-stop-val
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(let backtrack ([csp csp])
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(cond
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[(assignment-complete? csp) (yield csp)]
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[else ;; we have at least 1 unassigned var
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(match-define ($var name vals) (select-unassigned-var csp))
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(for ([val (in-list (order-domain-values vals))])
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(with-handlers ([$csp-inconsistent? (const #f)])
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(backtrack (infer (assign-val csp name val)))))])))))
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(define (backtracking-solver csp)
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(backtracking-solution-generator (make-arcs-consistent (make-nodes-consistent csp))))
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(define/contract (solve csp [finish-proc values])
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(($csp?) (procedure?) . ->* . any/c)
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(or
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(for/first ([solution (in-producer (backtracking-solver csp) solver-stop-val)])
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(finish-proc solution))
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(raise ($csp-inconsistent))))
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(define/contract (solve* csp [finish-proc values])
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(($csp?) (procedure?) . ->* . (listof any/c))
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(define solutions (for/list ([solution (in-producer (backtracking-solver csp) solver-stop-val)])
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(finish-proc solution)))
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(when (empty? solutions) (raise ($csp-inconsistent)))
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(let backtrack ([csp (make-arcs-consistent (make-nodes-consistent csp))])
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(cond
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[(assignment-complete? csp) (yield csp)]
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[else ;; we have at least 1 unassigned var
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(match-define ($var name vals) (select-unassigned-var csp))
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(for ([val (in-list (order-domain-values vals))])
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(with-handlers ([$csp-inconsistent? (const #f)])
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(backtrack (infer (assign-val csp name val)))))]))))
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(define/contract (solve* csp [finish-proc values][solution-limit +inf.0])
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(($csp?) (procedure? integer?) . ->* . (listof any/c))
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(define solutions
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(for/list ([solution (in-producer (backtracking-solver csp) (void))]
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[idx (in-range solution-limit)])
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(finish-proc solution)))
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(unless (pair? solutions) (raise ($csp-inconsistent)))
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solutions)
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(define/contract (solve csp [finish-proc values])
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(($csp?) (procedure?) . ->* . any/c)
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(first (solve* csp finish-proc 1)))
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(define ($csp-ref csp name)
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(car ($csp-vals csp name)))
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(define ($csp-ref csp name) (car ($csp-vals csp name)))
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(define/contract (alldiff . xs)
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(() #:rest (listof any/c) . ->* . boolean?)
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