/*
* Licensed to the Apache Software Foundation (ASF) under one
* or more contributor license agreements. See the NOTICE file
* distributed with this work for additional information
* regarding copyright ownership. The ASF licenses this file
* to you under the Apache License, Version 2.0 (the
* "License"); you may not use this file except in compliance
* with the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package org.apache.jena.reasoner.rulesys.builtins;
import org.apache.jena.graph.* ;
import org.apache.jena.reasoner.rulesys.* ;
import org.apache.jena.vocabulary.RDF ;
/**
* listEntry(?list, ?index, ?val) will bind ?val to the ?index'th entry
* in the RDF list ?list. If there is no such entry the variable will be unbound
* and the call will fail. Only useable in rule bodies.
*/
public class ListEntry extends BaseBuiltin {
/**
* Return a name for this builtin, normally this will be the name of the
* functor that will be used to invoke it.
*/
@Override
public String getName() {
return "listEntry";
}
/**
* Return the expected number of arguments for this functor or 0 if the number is flexible.
*/
@Override
public int getArgLength() {
return 3;
}
/**
* This method is invoked when the builtin is called in a rule body.
* @param args the array of argument values for the builtin, this is an array
* of Nodes, some of which may be Node_RuleVariables.
* @param length the length of the argument list, may be less than the length of the args array
* for some rule engines
* @param context an execution context giving access to other relevant data
* @return return true if the buildin predicate is deemed to have succeeded in
* the current environment
*/
@Override
public boolean bodyCall(Node[] args, int length, RuleContext context) {
checkArgs(length, context);
BindingEnvironment env = context.getEnv();
Node list = getArg(0, args, context);
Node index = getArg(1, args, context);
if ( ! Util.isNumeric(index) ) return false;
Node elt = getEntry(list, Util.getIntValue(index), context);
if (elt == null) {
return false;
} else {
env.bind(args[2], elt);
return true;
}
}
/**
* Return the i'th element of the list, starting from 0
* @param list the start of the list
* @param i the element to return
* @param context the context through which the data values can be found
* @return the entry or null if the there isn't such an entry
*/
protected static Node getEntry(Node list, int i, RuleContext context ) {
int count = 0;
Node node = list;
while (node != null && !node.equals(RDF.Nodes.nil)) {
if (count == i) {
return Util.getPropValue(node, RDF.Nodes.first, context);
} else {
node = Util.getPropValue(node, RDF.Nodes.rest, context);
count++;
}
}
return null;
}
}