/*
* Encog(tm) Core v3.3 - Java Version
* http://www.heatonresearch.com/encog/
* https://github.com/encog/encog-java-core
* Copyright 2008-2014 Heaton Research, Inc.
*
* Licensed 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.
*
* For more information on Heaton Research copyrights, licenses
* and trademarks visit:
* http://www.heatonresearch.com/copyright
*/
package org.encog.ml.prg.train.rewrite;
import org.encog.ml.ea.genome.Genome;
import org.encog.ml.ea.rules.RewriteRule;
import org.encog.ml.prg.EncogProgram;
import org.encog.ml.prg.ProgramNode;
import org.encog.ml.prg.expvalue.ExpressionValue;
import org.encog.ml.prg.extension.StandardExtensions;
/**
* Basic rewrite rules for boolean expressions.
*/
public class RewriteBoolean implements RewriteRule {
/**
* True, if the value has been rewritten.
*/
private boolean rewritten;
/**
* Returns true, if the specified constant value is a true const. Returns
* false in any other case.
*
* @param node The node to check.
* @return True if the value is a true const.
*/
private boolean isTrue(ProgramNode node) {
if (node.getTemplate() == StandardExtensions.EXTENSION_CONST_SUPPORT) {
ExpressionValue v = node.evaluate();
if (v.isBoolean()) {
if (v.toBooleanValue()) {
return true;
}
}
}
return false;
}
/**
* Returns true, if the specified constant value is a false const. Returns
* false in any other case.
*
* @param node The node to check.
* @return True if the value is a false const.
*/
private boolean isFalse(ProgramNode node) {
if (node.getTemplate() == StandardExtensions.EXTENSION_CONST_SUPPORT) {
ExpressionValue v = node.evaluate();
if (v.isBoolean()) {
if (!v.toBooleanValue()) {
return true;
}
}
}
return false;
}
/**
* {@inheritDoc}
*/
@Override
public boolean rewrite(final Genome g) {
this.rewritten = false;
final EncogProgram program = (EncogProgram) g;
final ProgramNode node = program.getRootNode();
final ProgramNode rewrittenRoot = internalRewrite(node);
if (rewrittenRoot != null) {
program.setRootNode(rewrittenRoot);
}
return this.rewritten;
}
/**
* Attempt to rewrite the specified node.
* @param parent The node to attempt to rewrite.
* @return The rewritten node, or the original node, if no change was made.
*/
private ProgramNode internalRewrite(final ProgramNode parent) {
ProgramNode rewrittenParent = parent;
rewrittenParent = tryAnd(rewrittenParent);
// try children
for (int i = 0; i < rewrittenParent.getChildNodes().size(); i++) {
final ProgramNode childNode = (ProgramNode) rewrittenParent
.getChildNodes().get(i);
final ProgramNode rewriteChild = internalRewrite(childNode);
if (childNode != rewriteChild) {
rewrittenParent.getChildNodes().remove(i);
rewrittenParent.getChildNodes().add(i, rewriteChild);
this.rewritten = true;
}
}
return rewrittenParent;
}
/**
* Try to rewrite true and true, false and false.
* @param parent The node to attempt to rewrite.
* @return The rewritten node, or the original node if not rewritten.
*/
private ProgramNode tryAnd(final ProgramNode parent) {
if (parent.getTemplate() == StandardExtensions.EXTENSION_AND) {
final ProgramNode child1 = parent.getChildNode(0);
final ProgramNode child2 = parent.getChildNode(1);
if (isTrue(child1)
&& child2.getTemplate() != StandardExtensions.EXTENSION_CONST_SUPPORT) {
this.rewritten = true;
return child2;
}
if (isTrue(child2)
&& child1.getTemplate() != StandardExtensions.EXTENSION_CONST_SUPPORT) {
this.rewritten = true;
return child1;
}
}
return parent;
}
}