/* Copyright 2009-2016 David Hadka
 *
 * This file is part of the MOEA Framework.
 *
 * The MOEA Framework is free software: you can redistribute it and/or modify
 * it under the terms of the GNU Lesser General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or (at your
 * option) any later version.
 *
 * The MOEA Framework is distributed in the hope that it will be useful, but
 * WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
 * or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU Lesser General Public
 * License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public License
 * along with the MOEA Framework.  If not, see <http://www.gnu.org/licenses/>.
 */
package org.moeaframework.util.tree;

/**
 * The node for repeatedly executing an expression while a condition, a
 * boolean expression, remains {@code true}.  The inputs and outputs to this
 * node are shown below:
 * 
 * <table border="1" cellpadding="3" cellspacing="0">
 *   <tr class="TableHeadingColor">
 *     <th width="25%" align="left">Name</th>
 *     <th width="25%" align="left">Type</th>
 *     <th width="50%" align="left">Description</th>
 *   </tr>
 *   <tr>
 *     <td>Argument 1</td>
 *     <td>Boolean</td>
 *     <td>The condition that determines how long the loop is executed</td>
 *   </tr>
 *   <tr>
 *     <td>Argument 2</td>
 *     <td>User-Defined</td>
 *     <td>The expression to execute when the condition is {@code true}</td>
 *   </tr>
 *   <tr>
 *     <td>Return Value</td>
 *     <td>User-Defined</td>
 *     <td>The return value of the last executed expression; or {@code null}
 *         if the loop was never executed</td>
 *   </tr>
 * </table>
 */
public class While extends Node {

	/**
	 * Constructs a new node for repeatedly executing an expression while a
	 * condition remains {@code true}.
	 */
	public While() {
		super(Object.class, Boolean.class, Object.class);
	}

	@Override
	public While copyNode() {
		return new While();
	}

	@Override
	public Object evaluate(Environment environment) {
		Object value = null;
		
		while ((Boolean)getArgument(0).evaluate(environment)) {
			value = getArgument(1).evaluate(environment);
		}
		
		return value;
	}

}