When adding to a List, first remove existing elements in list.

lib/rdf_context/graph.rb

@@ -266,13 +266,25 @@ def add(*triples)
     end
 
     ##
-    # Adds a list of resources as an RDF list by creating bnodes and first/rest triples
+    # Adds a list of resources as an RDF list by creating bnodes and first/rest triples.
+    # Removes existing sequence nodes.
+    #
     # @param [URIRef, BNode] subject the subject of the triple
     # @param [URIRef] predicate the predicate of the triple
     # @param [Array] objects List of objects to serialize
     # @return [Graph] Returns the graph
     # @raise [Error] Checks parameter types and raises if they are incorrect.
     def add_seq(subject, predicate, objects)
+      self.triples(Triple.new(subject, predicate, nil)).each do |t, ctx|
+        bn = t.object
+        while bn != RDF_NS.nil
+          rest = properties(bn)[RDF_NS.rest.to_s].first
+          remove(Triple.new(bn, nil, nil))
+          bn = rest
+        end
+      end
+      remove(Triple.new(subject, predicate, nil))
+
       if objects.empty?
         add_triple(subject, predicate, RDF_NS.nil)
         return self

spec/graph_spec.rb

@@ -463,6 +463,18 @@
         l.should be_a(BNode)
         g.seq(l).should == [@ex.john, @ex.jane, @ex.rick]
       end
+
+      it "should remove existing sequence when adding entry to sequence" do
+        g = Graph.new(:store => ListStore.new)
+        g.add_seq(@ex.List, @ex.includes, [@ex.john, @ex.jane, @ex.rick])
+        g.add_seq(@ex.List, @ex.includes, [@ex.john, @ex.jane, @ex.rick, @ex.julie])
+        puts g.properties(@ex.List).inspect
+        l = g.properties(@ex.List)[@ex.includes.to_s].first
+        l.should be_a(BNode)
+        g.seq(l).should == [@ex.john, @ex.jane, @ex.rick, @ex.julie]
+
+        g.triples(Triple.new(nil, RDF_NS.first, @ex.john)).length.should == 1
+      end
     end
   end