rs: Add union-products.

rs-tests.rkt

@@ -13,4 +13,5 @@
     (check-true (enabled? r1 s1))
     (check-false (enabled? r1 s2))
     (check-equal? (list-enabled rs s1) '(a b))
-    (check-equal? (list-enabled rs s2) '(b))))
+    (check-equal? (list-enabled rs s2) '(b))
+    (check-equal? (union-products rs '(a b)) (set 'y 'z))))

rs.rkt

@@ -10,7 +10,7 @@
  ;; Type names
  Species ReactionSystem
  ;; Functions
- enabled? list-enabled)
+ enabled? list-enabled union-products)
 
 ;;; =================
 ;;; Basic definitions
@@ -42,3 +42,16 @@
   (for/list ([(name reaction) (in-hash rs)]
              #:when (enabled? reaction s))
     name))
+
+;;; Returns the union of the product sets of the given reactions in a
+;;; reaction system.
+;;;
+;;; This function can be seen as producing the result of the
+;;; application of the given reactions to a set.  Clearly, it does not
+;;; check whether the reactions are actually enabled.
+(: union-products (-> ReactionSystem (Listof Symbol) (Setof Species)))
+(define (union-products rs as)
+  (apply set-union
+         ((inst set Species))           ; set-union requires at least one argument
+         (for/list : (Listof (Setof Species))
+             ([a as]) (reaction-products (hash-ref rs a)))))