Utils.assert(buf!=null);
    public void visitNode(FlatNode node)     {	if (node.contents instanceof SIRFilter) {	    SIRFilter filter = (SIRFilter)node.contents;	    buf.append(Namer.getName(node.contents) + "[ label = \"" +		       Namer.getName(node.contents) + 		       " peek: " + filter.getPeekInt() + 		       " pop: " + filter.getPopInt() + 		       " push: " + filter.getPushInt() +		       "\"];");	}		for (int i = 0; i < node.ways; i++) {	    buf.append(Namer.getName(node.contents) + " -> " 		       + Namer.getName(node.edges[i].contents));	    buf.append("[label=\"" + node.weights[i] + "\"];\n");	    	}    }