@Override
public QueryIterator execOneList(Binding binding, Node listNode, Node predicate, Node length, ExecutionContext execCxt)
{
Graph graph = execCxt.getActiveGraph() ;
if ( Var.isVar(listNode) )
throw new ARQInternalErrorException("listLength: Subject is a variable") ;
// Case : arg 1 (the list) is bound and arg 2 not bound => generate possibilities
// Case : arg 1 is bound and arg 2 is bound => test for membership.
if ( Var.isVar(length) )
return length(binding, graph, listNode, Var.alloc(length) , execCxt) ;