RewriteBoolean.java

/*
 * Encog(tm) Core v3.4 - Java Version
 * http://www.heatonresearch.com/encog/
 * https://github.com/encog/encog-java-core
 
 * Copyright 2008-2016 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;
	}
}