Work on predicates.

member-record.scm

@@ -33,6 +33,7 @@
   member-destroyed?
   member-suspended?
   member-active?
+  member-student?
   member-nick
   member-record-tests!
   )
@@ -90,11 +91,24 @@
 	  (month<? (string->month destroyed)
 		   (*current-month*)))))
 
+ ;; Generic period-based predicate
+ (define ((member-period-predicate? key) mr)
+   (let ((periods (mr-ref mr key #f)))
+     (and periods
+	  (month-in-periods? periods))))
+
  ;; Returns true if the member is now suspended
- (define (member-suspended? mr)
-   (let ((suspend (mr-ref mr 'suspend #f)))
-     (and suspend
-	  (month-in-periods? suspend))))
+ (define member-suspended?
+   (member-period-predicate? 'suspend))
+
+ ;; True if the member is student
+ (define member-is-student?
+   (member-period-predicate? 'student))
+
+ ;; Only active members can be students.
+ (define (member-student? mr)
+   (and (member-active? mr)
+	(member-is-student? mr)))
 
  ;; Returns true if the member is active (not suspended or destroyed).
  (define (member-active? mr)