when to unless

csp/constraint.rkt

@@ -123,13 +123,13 @@
              (return-k)]))
         (when (and forward-check? (not (equal? singlevalue _unassigned)))
           (for ([variable (in-list variables)])
-            (when (not (variable . in? . assignments))
+            (unless (variable . in? . assignments)
               (set! domain (hash-ref domains variable))
-              (when (not (singlevalue . in? . (domain)))
+              (unless (singlevalue . in? . (domain))
                 (set! return-value #f)
                 (return-k))
               (for ([value (in-list (domain))])
-                (when (not (equal? value singlevalue))
+                (unless (equal? value singlevalue)
                   (send domain hide-value value))))))
         (set! return-value #t)
         (return-k))

csp/solver.rkt

@@ -49,8 +49,8 @@
           (set! pushdomains 
                 (if _forwardcheck
                     (for/list ([(var domain) (in-hash domains)] 
-                               #:unless (and (hash-has-key? possible-solution var) 
-                                           (equal? variable var)))
+                               #:unless (and (equal? variable var)
+                                             (hash-has-key? possible-solution var)))
                       domain)
                     null))   
           variable))
@@ -62,7 +62,7 @@
       (let/ec exit-k
         ;; mix the degree and minimum-remaining-values (MRV) heuristics
         (let main-loop ()
-          (when (not (get-next-unassigned-variable))
+          (unless (get-next-unassigned-variable)
             (yield (hash-copy possible-solution)) ; if there are no unassigned variables, solution is done. 
             (if (null? variable-queue) ; if queue isn't empty, return to previous variable, otherwise all done.
                 (exit-k)