/*******************************************************************************
 * Copyright (c) 2000, 2004 IBM Corporation and others.
 * All rights reserved. This program and the accompanying materials 
 * are made available under the terms of the Common Public License v1.0
 * which accompanies this distribution, and is available at
 * http://www.eclipse.org/legal/cpl-v10.html
 * 
 * Contributors:
 *     IBM Corporation - initial API and implementation
 *******************************************************************************/

package org.eclipse.jface.text.rules;

/**
 * Defines the interface for a rule used in the scanning of text for the purpose of
 * document partitioning or text styling. A predicate rule can only return one single 
 * token after having successfully detected content. This token is called success token.
 * Also, it also returns a token indicating that this rule has not been successful. 
 *
 * @see ICharacterScanner
 * @since 2.0
 */
public interface IPredicateRule extends IRule {
	
	/**
	 * Returns the success token of this predicate rule.
	 *
	 * @return the success token of this rule
	 */
	IToken getSuccessToken();
	
	/**
	 * Evaluates the rule by examining the characters available from 
	 * the provided character scanner. The token returned by this rule 
	 * returns <code>true</code> when calling <code>isUndefined</code>,
	 * if the text the rule investigated does not match the rule's requirements. Otherwise,
	 * this method returns this rule's success token. If this rules relies on a text pattern
	 * comprising a opening and a closing character sequence this method can also be called
	 * when the scanner is positioned already between the opening and the closing sequence.
	 * In this case, <code>resume</code> must be set to <code>true</code>.
	 * 
	 * @param scanner the character scanner to be used by this rule
	 * @param resume indicates that the rule starts working between the opening and the closing character sequence
	 * @return the token computed by the rule
	 */
	IToken evaluate(ICharacterScanner scanner, boolean resume);
}
