networks: Add list-interactions.

networks-tests.rkt

@@ -44,3 +44,9 @@
     (check-equal? ((hash-ref bn1 'a) s) #t)
     (check-equal? ((hash-ref bn2 'a) s) #t)
     (check-equal? ((hash-ref bn3 'a) s) #t)))
+
+(test-case "Inferring interaction graphs"
+  (let ([n #hash((a . (+ a b c))
+                 (b . (- b c)))])
+    (check-true (set=? (list-interactions n 'a) '(a b)))
+    (check-true (set=? (list-interactions n 'b) '(b)))))

networks.rkt

@@ -20,7 +20,8 @@
                [update-function-form->update-function (-> update-function-form? update-function/c)]
                [network-form->network (-> network-form? network?)]
                [make-network-from-forms (-> (listof (cons/c symbol? update-function-form?))
-                                            network?)])
+                                            network?)]
+               [list-interactions (-> network-form? variable? (listof variable?))])
  ;; Predicates
  (contract-out [variable? (-> any/c boolean?)]
                [state? (-> any/c boolean?)]
@@ -121,3 +122,10 @@
 ;;; interaction graphs, but since the inference of signed interaction
 ;;; graphs is based on analysing the dynamics of the networks, it may
 ;;; be quite resource-consuming.
+
+;;; Lists the variables of the network form appearing in the update
+;;; function form for x.
+(define (list-interactions nf x)
+  (set-intersect
+   (extract-symbols (hash-ref nf x))
+   (hash-keys nf)))