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#lang debug racket
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(require racket/generator graph)
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(provide (all-defined-out))
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(define-syntax when-debug
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(let ()
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(define debug #t)
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(if debug
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(make-rename-transformer #'begin)
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(λ (stx) (syntax-case stx ()
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[(_ . rest) #'(void)])))))
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(define-syntax-rule (in-cartesian x)
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(in-generator (let ([argss x])
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(let loop ([argss argss][acc empty])
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(if (null? argss)
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(yield (reverse acc))
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(for ([arg (car argss)])
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(loop (cdr argss) (cons arg acc))))))))
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(struct csp (vars constraints) #:mutable #:transparent)
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(define constraints csp-constraints)
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(define vars csp-vars)
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(define-syntax-rule (in-constraints csp) (in-list (csp-constraints csp)))
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(define-syntax-rule (in-vars csp) (in-list (vars csp)))
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(define-syntax-rule (in-var-names csp) (in-list (map var-name (vars csp))))
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(struct constraint (names proc) #:transparent
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#:property prop:procedure
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(λ (const prob)
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(unless (csp? prob)
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(raise-argument-error 'constraint "csp" prob))
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;; apply proc in many-to-many style
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(for/and ([args (in-cartesian (map (λ (name) (find-domain prob name)) (constraint-names const)))])
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(apply (constraint-proc const) args))))
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(define name? symbol?)
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(define/contract (make-constraint [names null] [proc values])
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(() ((listof name?) procedure?) . ->* . constraint?)
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(constraint names proc))
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(define/contract (csp->graphviz prob)
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(csp? . -> . string?)
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(define g (csp->graph prob))
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(graphviz g #:colors (coloring/brelaz g)))
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(define/contract (csp->graph prob)
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(csp? . -> . graph?)
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(for*/fold ([gr (unweighted-graph/undirected (map var-name (vars prob)))])
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([constraint (in-constraints prob)]
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[edge (in-combinations (constraint-names constraint) 2)])
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(apply add-edge! gr edge)
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gr))
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(struct var (name domain) #:transparent)
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(define domain var-domain)
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(struct checked-variable var (history) #:transparent)
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(define history checked-variable-history)
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(define cvar checked-variable)
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(define cvar? checked-variable?)
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(struct assigned-var var () #:transparent)
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(define avar assigned-var)
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(define avar? assigned-var?)
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(define/contract (make-csp [vars null] [consts null])
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(() ((listof var?) (listof constraint?)) . ->* . csp?)
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(csp vars consts))
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(define/contract (add-vars! prob names-or-procedure [vals-or-procedure empty])
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((csp? (or/c (listof name?) procedure?)) ((or/c (listof any/c) procedure?)) . ->* . void?)
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(for/fold ([vrs (vars prob)]
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#:result (set-csp-vars! prob vrs))
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([name (in-list (match names-or-procedure
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[(? procedure? proc) (proc)]
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[names names]))])
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(when (memq name (map var-name vrs))
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(raise-argument-error 'add-vars! "var that doesn't already exist" name))
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(append vrs (list (var name
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(if (procedure? vals-or-procedure)
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(vals-or-procedure)
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vals-or-procedure))))))
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(define/contract (add-var! prob name [vals-or-procedure empty])
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((csp? name?) ((or/c (listof any/c) procedure?)) . ->* . void?)
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(add-vars! prob (list name) vals-or-procedure))
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(define/contract (add-constraints! prob proc namess [proc-name #false])
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((csp? procedure? (listof (listof name?))) ((or/c #false name?)) . ->* . void?)
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(set-csp-constraints! prob (append (constraints prob)
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(for/list ([names (in-list namess)])
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(for ([name (in-list names)])
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(check-name-in-csp! 'add-constraints! prob name))
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(make-constraint names (if proc-name
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(procedure-rename proc proc-name)
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proc))))))
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(define/contract (add-pairwise-constraint! prob proc names [proc-name #false])
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((csp? procedure? (listof name?)) (name?) . ->* . void?)
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(add-constraints! prob proc (combinations names 2) proc-name))
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(define/contract (add-constraint! prob proc names [proc-name #false])
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((csp? procedure? (listof name?)) (name?) . ->* . void?)
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(add-constraints! prob proc (list names) proc-name))
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(define/contract (alldiff= x y)
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(any/c any/c . -> . boolean?)
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(not (= x y)))
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(struct backtrack (names) #:transparent)
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(define (backtrack! [names null]) (raise (backtrack names)))
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(define current-select-variable (make-parameter #f))
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(define current-order-values (make-parameter #f))
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(define current-inference (make-parameter #f))
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(define current-solver (make-parameter #f))
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(define current-random (make-parameter #t))
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(define current-decompose (make-parameter #t))
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(define current-thread-count (make-parameter 4))
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(define current-node-consistency (make-parameter #f))
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(define current-arity-reduction (make-parameter #t))
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(define/contract (check-name-in-csp! caller prob name)
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(symbol? csp? name? . -> . void?)
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(define names (map var-name (vars prob)))
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(unless (memq name names)
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(raise-argument-error caller (format "one of these existing csp var names: ~v" names) name)))
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(define/contract (find-var prob name)
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(csp? name? . -> . var?)
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(check-name-in-csp! 'find-var prob name)
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(for/first ([vr (in-vars prob)]
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#:when (eq? name (var-name vr)))
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vr))
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(define/contract (find-domain prob name)
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(csp? name? . -> . (listof any/c))
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(check-name-in-csp! 'find-domain prob name)
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(domain (find-var prob name)))
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(define order-domain-values values)
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(define/contract (assigned-name? prob name)
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(csp? name? . -> . any/c)
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(for/or ([vr (in-vars prob)]
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#:when (assigned-var? vr))
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(eq? name (var-name vr))))
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(define/contract (reduce-function-arity proc pattern)
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(procedure? (listof any/c) . -> . procedure?)
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(unless (match (procedure-arity proc)
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[(arity-at-least val) (<= val (length pattern))]
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[(? number? val) (= val (length pattern))])
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(raise-argument-error 'reduce-function-arity (format "list of length ~a, same as procedure arity" (procedure-arity proc)) pattern))
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(define reduced-arity-name (string->symbol (format "reduced-arity-~a" (object-name proc))))
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(define-values (boxed-id-names vals) (partition box? pattern))
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(define new-arity (length boxed-id-names))
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(procedure-rename
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(λ xs
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(unless (= (length xs) new-arity)
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(apply raise-arity-error reduced-arity-name new-arity xs))
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(apply proc (for/fold ([acc empty]
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[xs xs]
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[vals vals]
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#:result (reverse acc))
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([pat-item (in-list pattern)])
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(if (box? pat-item)
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(values (cons (car xs) acc) (cdr xs) vals)
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(values (cons (car vals) acc) xs (cdr vals))))))
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reduced-arity-name))
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(define/contract (reduce-constraint-arity prob [minimum-arity 3])
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((csp?) ((or/c #false natural?)) . ->* . csp?)
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(define assigned? (curry assigned-name? prob))
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(define (partially-assigned? constraint)
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(ormap assigned? (constraint-names constraint)))
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(make-csp (vars prob)
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(for/list ([const (in-constraints prob)])
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(cond
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;; no point reducing 2-arity functions because they will be consumed by forward checking
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[(and (or (not minimum-arity) (<= minimum-arity (constraint-arity const)))
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(partially-assigned? const))
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(match-define (constraint cnames proc) const)
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;; pattern is mix of values and boxed symbols (indicating variables to persist)
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;; use boxes here as cheap way to distinguish id symbols from value symbols
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(define arity-reduction-pattern (for/list ([cname (in-list cnames)])
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(if (assigned? cname)
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(first (find-domain prob cname))
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(box cname))))
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(constraint (filter-not assigned? cnames)
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(reduce-function-arity proc arity-reduction-pattern))]
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[else const]))))
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(define nassns 0)
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(define nfchecks 0)
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(define nchecks 0)
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(define (reset-nassns!) (set! nassns 0))
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(define (reset-nfchecks!) (set! nfchecks 0))
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(define (reset-nchecks!) (set! nchecks 0))
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(define/contract (assign-val prob name val)
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(csp? name? any/c . -> . csp?)
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(when-debug (set! nassns (add1 nassns)))
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(make-csp
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(for/list ([vr (in-vars prob)])
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(if (eq? name (var-name vr))
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(assigned-var name (list val))
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vr))
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(constraints prob)))
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(define/contract (unassigned-vars prob)
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(csp? . -> . (listof (and/c var? (not/c assigned-var?))))
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(filter-not assigned-var? (vars prob)))
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(define/contract (first-unassigned-variable csp)
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(csp? . -> . (or/c #false (and/c var? (not/c assigned-var?))))
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(match (unassigned-vars csp)
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[(? empty?) #false]
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[xs (first xs)]))
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(define/contract (minimum-remaining-values prob)
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(csp? . -> . (or/c #false (and/c var? (not/c assigned-var?))))
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(match (unassigned-vars prob)
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[(? empty?) #false]
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[xs (argmin (λ (var) (length (domain var))) xs)]))
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(define mrv minimum-remaining-values)
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(define/contract (var-degree prob var)
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(csp? var? . -> . natural?)
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(for/sum ([const (in-constraints prob)]
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#:when (memq (var-name var) (constraint-names const)))
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1))
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(define/contract (domain-length var)
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(var? . -> . natural?)
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(length (domain var)))
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(define/contract (mrv-degree-hybrid prob)
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(csp? . -> . (or/c #f var?))
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(match (unassigned-vars prob)
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[(? empty?) #false]
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[uvars
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;; minimum remaining values (MRV) rule
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(define mrv-arg (argmin domain-length uvars))
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(match (filter (λ (var) (= (domain-length mrv-arg) (domain-length var))) uvars)
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[(list winning-uvar) winning-uvar]
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[(list mrv-uvars ...)
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;; use degree as tiebreaker for mrv
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(define degrees (map (λ (var) (var-degree prob var)) mrv-uvars))
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(define max-degree (apply max degrees))
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;; use random tiebreaker for degree
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(random-pick (for/list ([uv (in-list mrv-uvars)]
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[degree (in-list degrees)]
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#:when (= max-degree degree))
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uv))])]))
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(define first-domain-value values)
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(define (no-inference prob name) prob)
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(define/contract (relating-only constraints names)
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((listof constraint?) (listof name?) . -> . (listof constraint?))
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(for*/list ([const (in-list constraints)]
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[cnames (in-value (constraint-names const))]
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#:when (and (= (length names) (length cnames))
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(for/and ([name (in-list names)])
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(memq name cnames))))
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const))
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(define (one-arity? const) (= 1 (constraint-arity const)))
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(define (two-arity? const) (= 2 (constraint-arity const)))
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(define (constraint-relates? const name)
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(memq name (constraint-names const)))
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(struct arc (name const) #:transparent)
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(define/contract (two-arity-constraints->arcs constraints)
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((listof (and/c constraint? two-arity?)) . -> . (listof arc?))
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(for*/list ([const (in-list constraints)]
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[name (in-list (constraint-names const))])
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(arc name const)))
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(require sugar/debug)
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(define/contract (reduce-domain prob ark)
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(csp? arc? . -> . csp?)
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(match-define (arc name (constraint names constraint-proc)) ark)
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(match-define (list other-name) (remove name names))
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(define proc (if (eq? name (first names)) ; name is on left
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constraint-proc ; so val stays on left
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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 (find-domain prob other-name))])
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(proc val other-val)))
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(make-csp
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(for/list ([vr (in-vars prob)])
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(cond
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[(assigned-var? vr) vr]
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[(eq? name (var-name vr))
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(var name (match (filter satisfies-arc? (domain vr))
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[(? empty?) (backtrack!)]
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[vals vals]))]
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[else vr]))
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(constraints prob)))
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(define/contract (terminating-at? arcs name)
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((listof arc?) name? . -> . (listof arc?))
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(for/list ([arc (in-list arcs)]
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#:when (and
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(memq name (constraint-names (arc-const arc)))
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(not (eq? name (arc-name arc)))))
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arc))
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(define/contract (ac-3 prob . _)
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((csp?) (any/c) . ->* . csp?)
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;; csp is arc-consistent if every pair of variables (x y)
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;; has values in their domain that satisfy every binary constraint
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(define starting-arcs (two-arity-constraints->arcs (filter two-arity? (constraints prob))))
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(for/fold ([prob prob]
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[arcs starting-arcs]
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#:result (prune-singleton-constraints prob))
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([i (in-naturals)]
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#:break (empty? arcs))
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(length starting-arcs)
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(match-define (cons (arc name proc) other-arcs) arcs)
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(length other-arcs)
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(define reduced-csp (reduce-domain prob (arc name proc)))
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(values reduced-csp (if (= (length (find-domain prob name)) (length (find-domain 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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(remove-duplicates (append (starting-arcs . terminating-at? . name) other-arcs))))))
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(define/contract (forward-check-var prob ref-name vr)
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(csp? name? var? . -> . var?)
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(cond
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;; don't check against assigned vars, or the reference var
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;; (which is probably assigned but maybe not)
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[(assigned-var? vr) vr]
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[(eq? (var-name vr) ref-name) vr]
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[else
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(match-define (var name vals) vr)
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(match ((constraints prob) . relating-only . (list ref-name name))
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[(? empty?) vr]
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[constraints
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(define new-vals
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(for/list ([val (in-list vals)]
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#:when (for/and ([const (in-list constraints)])
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(let ([proc (constraint-proc const)]
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[ref-val (first (find-domain prob ref-name))])
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(if (eq? name (first (constraint-names const)))
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(proc val ref-val)
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(proc ref-val val)))))
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val))
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(checked-variable name new-vals (cons ref-name (match vr
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[(checked-variable _ _ history) history]
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[else null])))])]))
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(define/contract (prune-singleton-constraints prob [ref-name #false])
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((csp?) ((or/c #false name?)) . ->* . csp?)
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(define singleton-var-names (for/list ([vr (in-vars prob)]
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#:when (singleton-var? vr))
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(var-name vr)))
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(make-csp
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(vars prob)
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(for/list ([const (in-constraints prob)]
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#:unless (and (two-arity? const)
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(or (not ref-name) (constraint-relates? const ref-name))
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(for/and ([cname (in-list (constraint-names const))])
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(memq cname singleton-var-names))))
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const)))
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(define/contract (forward-check prob ref-name)
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(csp? name? . -> . csp?)
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(define checked-vars (map (λ (vr) (forward-check-var prob ref-name vr)) (vars prob)))
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(when-debug (set! nfchecks (+ (length checked-vars) nchecks)))
|
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|
;; conflict-set will be empty if there are no empty domains (as we would hope)
|
|
|
(define conflict-set (for*/list ([cvr (in-list checked-vars)]
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|
|
#:when (empty? (domain cvr))
|
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|
[name (in-list (history cvr))])
|
|
|
name))
|
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|
;; for conflict-directed backjumping it's essential to forward-check ALL vars
|
|
|
;; (even after an empty domain is generated) and combine their conflicts
|
|
|
;; so we can discover the *most recent past var* that could be the culprit.
|
|
|
;; If we just bail out at the first conflict, we may backjump too far based on its history
|
|
|
;; (and thereby miss parts of the search tree)
|
|
|
(when (pair? conflict-set)
|
|
|
(backtrack! conflict-set))
|
|
|
;; Discard constraints that have produced singleton domains
|
|
|
;; (they have no further use)
|
|
|
(prune-singleton-constraints (make-csp checked-vars (constraints prob)) ref-name))
|
|
|
|
|
|
(define/contract (constraint-checkable? const names)
|
|
|
(constraint? (listof name?) . -> . any/c)
|
|
|
;; constraint is checkable if all constraint names
|
|
|
;; are in target list of names.
|
|
|
(for/and ([cname (in-list (constraint-names const))])
|
|
|
(memq cname names)))
|
|
|
|
|
|
(define/contract (constraint-arity const)
|
|
|
(constraint? . -> . natural?)
|
|
|
(length (constraint-names const)))
|
|
|
|
|
|
(define/contract (singleton-var? var)
|
|
|
(var? . -> . boolean?)
|
|
|
(= 1 (domain-length var)))
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|
|
|
|
|
(define/contract (check-constraints prob [mandatory-names #f] #:conflicts [conflict-count? #f])
|
|
|
((csp?) ((listof name?) #:conflicts boolean?) . ->* . (or/c csp? natural?))
|
|
|
;; this time, we're not limited to assigned variables
|
|
|
;; (that is, vars that have been deliberately assigned in the backtrack process thus far)
|
|
|
;; we also want to use "singleton" vars (that is, vars that have been reduced to a single domain value by forward checking)
|
|
|
(define singleton-varnames (for/list ([vr (in-vars prob)]
|
|
|
#:when (singleton-var? vr))
|
|
|
(var-name vr)))
|
|
|
(define-values (checkable-consts other-consts)
|
|
|
(partition (λ (const) (and (constraint-checkable? const singleton-varnames)
|
|
|
(or (not mandatory-names)
|
|
|
(for/and ([name (in-list mandatory-names)])
|
|
|
(constraint-relates? const name)))))
|
|
|
(constraints prob)))
|
|
|
(cond
|
|
|
[conflict-count?
|
|
|
(define conflict-count
|
|
|
(for/sum ([constraint (in-list checkable-consts)]
|
|
|
#:unless (constraint prob))
|
|
|
1))
|
|
|
(when-debug (set! nchecks (+ conflict-count nchecks)))
|
|
|
conflict-count]
|
|
|
[else
|
|
|
(for ([(constraint idx) (in-indexed checkable-consts)]
|
|
|
#:unless (constraint prob))
|
|
|
(when-debug (set! nchecks (+ (add1 idx) nchecks)))
|
|
|
(backtrack!))
|
|
|
;; discard checked constraints, since they have no further reason to live
|
|
|
(make-csp (vars prob) other-consts)]))
|
|
|
|
|
|
(define/contract (make-nodes-consistent prob)
|
|
|
(csp? . -> . csp?)
|
|
|
(define-values (unary-constraints other-constraints)
|
|
|
(partition one-arity? (constraints prob)))
|
|
|
(if (empty? unary-constraints)
|
|
|
prob
|
|
|
(make-csp
|
|
|
(for/list ([vr (in-vars prob)])
|
|
|
(match-define (var name vals) vr)
|
|
|
(var name (for/fold ([vals vals])
|
|
|
([const (in-list unary-constraints)]
|
|
|
#:when (constraint-relates? const name))
|
|
|
(filter (constraint-proc const) vals))))
|
|
|
other-constraints)))
|
|
|
|
|
|
(define/contract (backtracking-solver
|
|
|
prob
|
|
|
#:select-variable [select-unassigned-variable
|
|
|
(or (current-select-variable) first-unassigned-variable)]
|
|
|
#:order-values [order-domain-values (or (current-order-values) first-domain-value)]
|
|
|
#:inference [inference (or (current-inference) no-inference)])
|
|
|
((csp?) (#:select-variable procedure? #:order-values procedure? #:inference procedure?) . ->* . generator?)
|
|
|
(generator ()
|
|
|
(define reduce-arity-proc (if (current-arity-reduction) reduce-constraint-arity values))
|
|
|
(let loop ([prob ((if (current-node-consistency) make-nodes-consistent values) prob)])
|
|
|
(match (select-unassigned-variable prob)
|
|
|
[#false (yield prob)]
|
|
|
[(var name domain)
|
|
|
(define (wants-backtrack? exn)
|
|
|
(and (backtrack? exn) (or (let ([btns (backtrack-names exn)])
|
|
|
(or (empty? btns) (memq name btns))))))
|
|
|
(for/fold ([conflicts null]
|
|
|
#:result (void))
|
|
|
([val (in-list (order-domain-values domain))])
|
|
|
(with-handlers ([wants-backtrack?
|
|
|
(λ (bt) (append conflicts (remq name (backtrack-names bt))))])
|
|
|
(let* ([prob (assign-val prob name val)]
|
|
|
;; reduce constraints before inference,
|
|
|
;; to create more forward-checkable (binary) constraints
|
|
|
[prob (reduce-arity-proc prob)]
|
|
|
[prob (inference prob name)]
|
|
|
[prob (check-constraints prob)])
|
|
|
(loop prob)))
|
|
|
conflicts)]))))
|
|
|
|
|
|
(define (random-pick xs)
|
|
|
(list-ref xs (random (length xs))))
|
|
|
|
|
|
(define (assign-random-vals prob)
|
|
|
(for/fold ([new-csp prob])
|
|
|
([name (in-var-names prob)])
|
|
|
(assign-val new-csp name (random-pick (find-domain prob name)))))
|
|
|
|
|
|
(define (make-min-conflcts-thread prob-start thread-count max-steps [main-thread (current-thread)])
|
|
|
(thread
|
|
|
(λ ()
|
|
|
(let loop ()
|
|
|
;; Generate a complete assignment for all variables (probably with conflicts)
|
|
|
(for/fold ([prob (assign-random-vals prob-start)])
|
|
|
([nth-step (in-range max-steps)])
|
|
|
;; Now repeatedly choose a random conflicted variable and change it
|
|
|
(match (conflicted-variable-names prob)
|
|
|
[(? empty?) (thread-send main-thread prob) (loop)]
|
|
|
[names
|
|
|
(define name (random-pick names))
|
|
|
(define val (min-conflicts-value prob name (find-domain prob-start name)))
|
|
|
(assign-val prob name val)]))))))
|
|
|
|
|
|
(define/contract (min-conflicts-solver prob [max-steps 100])
|
|
|
((csp?) (integer?) . ->* . generator?)
|
|
|
(generator ()
|
|
|
(for ([thread-count (or (current-thread-count) 1)]) ; todo: what is ideal thread count?
|
|
|
(make-min-conflcts-thread prob thread-count max-steps))
|
|
|
(for ([i (in-naturals)])
|
|
|
(yield (thread-receive)))))
|
|
|
|
|
|
(define/contract (optimal-stop-min proc xs)
|
|
|
(procedure? (listof any/c) . -> . any/c)
|
|
|
(define-values (sample candidates) (split-at xs (inexact->exact (floor (* .458 (length xs))))))
|
|
|
(define threshold (argmin proc sample))
|
|
|
(or (for/first ([candidate (in-list candidates)]
|
|
|
#:when (<= (proc candidate) threshold))
|
|
|
candidate)
|
|
|
(last candidates)))
|
|
|
|
|
|
(define/contract (conflicted-variable-names prob)
|
|
|
(csp? . -> . (listof name?))
|
|
|
;; Return a list of variables in current assignment that are conflicted
|
|
|
(for/list ([name (in-var-names prob)]
|
|
|
#:when (positive? (nconflicts prob name)))
|
|
|
name))
|
|
|
|
|
|
(define/contract (min-conflicts-value prob name vals)
|
|
|
(csp? name? (listof any/c) . -> . any/c)
|
|
|
;; Return the value that will give var the least number of conflicts
|
|
|
(define vals-by-conflict (sort vals < #:key (λ (val) (nconflicts prob name val))
|
|
|
#:cache-keys? #true))
|
|
|
(for/first ([val (in-list vals-by-conflict)]
|
|
|
#:unless (equal? val (first (find-domain prob name)))) ;; but change the value
|
|
|
val))
|
|
|
|
|
|
(define no-value-sig (gensym))
|
|
|
|
|
|
(define/contract (nconflicts prob name [val no-value-sig])
|
|
|
((csp? name?) (any/c) . ->* . natural?)
|
|
|
;; How many conflicts var: val assignment has with other variables.
|
|
|
(check-constraints (if (eq? val no-value-sig)
|
|
|
prob
|
|
|
(assign-val prob name val)) (list name) #:conflicts #true))
|
|
|
|
|
|
(define/contract (csp->assocs prob)
|
|
|
(csp? . -> . (listof (cons/c name? any/c)))
|
|
|
(for/list ([vr (in-vars prob)])
|
|
|
(match vr
|
|
|
[(var name (list val)) (cons name val)])))
|
|
|
|
|
|
(define/contract (combine-csps probs)
|
|
|
((listof csp?) . -> . csp?)
|
|
|
(make-csp
|
|
|
(apply append (map vars probs))
|
|
|
(apply append (map csp-constraints probs))))
|
|
|
|
|
|
|
|
|
(define/contract (extract-subcsp prob names)
|
|
|
(csp? (listof name?) . -> . csp?)
|
|
|
(make-csp
|
|
|
(for/list ([vr (in-vars prob)]
|
|
|
#:when (memq (var-name vr) names))
|
|
|
vr)
|
|
|
(for/list ([const (in-constraints prob)]
|
|
|
#:when (for/and ([cname (in-list (constraint-names const))])
|
|
|
(memq cname names)))
|
|
|
const)))
|
|
|
|
|
|
(define/contract (solve* prob
|
|
|
#:finish-proc [finish-proc csp->assocs]
|
|
|
#:solver [solver (or (current-solver) backtracking-solver)]
|
|
|
#:limit [max-solutions +inf.0])
|
|
|
((csp?) (#:finish-proc procedure? #:solver procedure? #:limit natural?)
|
|
|
. ->* . (listof any/c))
|
|
|
(when-debug (reset-nassns!) (reset-nfchecks!) (reset-nchecks!))
|
|
|
|
|
|
(define subcsps ; decompose into independent csps. `cc` determines "connected components"
|
|
|
(if (current-decompose)
|
|
|
(for/list ([nodeset (in-list (cc (csp->graph prob)))])
|
|
|
(extract-subcsp prob nodeset))
|
|
|
(list prob)))
|
|
|
|
|
|
(define solgens (map solver subcsps))
|
|
|
(define solstreams (for/list ([solgen (in-list solgens)])
|
|
|
(for/stream ([sol (in-producer solgen (void))])
|
|
|
sol)))
|
|
|
|
|
|
(for/list ([solution-pieces (in-cartesian solstreams)]
|
|
|
[idx (in-range max-solutions)])
|
|
|
(finish-proc (combine-csps solution-pieces))))
|
|
|
|
|
|
(define/contract (solve prob
|
|
|
#:finish-proc [finish-proc csp->assocs]
|
|
|
#:solver [solver (or (current-solver) backtracking-solver)]
|
|
|
#:limit [max-solutions 1])
|
|
|
((csp?) (#:finish-proc procedure? #:solver procedure? #:limit natural?)
|
|
|
. ->* . (or/c #false any/c))
|
|
|
(match (solve* prob #:finish-proc finish-proc #:solver solver #:limit max-solutions)
|
|
|
[(list solution) solution]
|
|
|
[(list solutions ...) solutions]
|
|
|
[else #false]))
|
|
|
|
|
|
(define (<> a b) (not (= a b)))
|
|
|
(define (neq? a b) (not (eq? a b)))
|
|
|
|