when to unless, etc

csp/constraint.rkt

@@ -31,7 +31,7 @@
         (set-field! _list domain
                     (for/fold ([domain-values (domain)]) 
                       ([value (in-list (domain))] 
-                       #:when (not (broken? variables domains (make-hash (list (cons variable value))))))
+                       #:unless (broken? variables domains (make-hash (list (cons variable value)))))
                       (remove value domain-values)))        
         (set! constraints (remove (list this variables) constraints))
         (hash-update! vconstraints variable (λ(val) (remove (list this variables) val)))))

csp/solver.rkt

@@ -29,10 +29,11 @@
     (field [_forwardcheck forwardcheck]) 
     
     (define/override (get-solution-iter domains constraints vconstraints)
-      (define work-list (sort (for/list ([variable (in-hash-keys domains)])
+      (define sorted-variables 
-                                (list (* -1 (length (hash-ref vconstraints variable)))
+        (map last (sort (for/list ([(variable domain) (in-hash domains)])
-                                      (length ((hash-ref domains variable)))
+                          (list (- (length (hash-ref vconstraints variable))) ; first two elements used for sorting 
-                                      variable)) list-comparator))
+                                (length (domain))
+                                variable)) list-comparator)))
       ;; state-retention variables
       (define possible-solution (make-hash))
       (define variable-queue null)
@@ -41,14 +42,14 @@
       (define pushdomains null)
       
       (define (get-next-unassigned-variable)
-        (for/first ([last-item (in-list (map last work-list))]
+        (for/first ([sorted-variable (in-list sorted-variables)]
-                    #:when (not (hash-has-key? possible-solution last-item)))
+                    #:unless (hash-has-key? possible-solution sorted-variable))
-          (set! variable last-item)
+          (set! variable sorted-variable)
           (set! values ((hash-ref domains variable)))
           (set! pushdomains 
                 (if _forwardcheck
                     (for/list ([(var domain) (in-hash domains)] 
-                               #:when (nor (hash-has-key? possible-solution var) 
+                               #:unless (and (hash-has-key? possible-solution var) 
                                            (equal? variable var)))
                       domain)
                     null))