001    /*
002     * Licensed to the Apache Software Foundation (ASF) under one or more
003     * contributor license agreements.  See the NOTICE file distributed with
004     * this work for additional information regarding copyright ownership.
005     * The ASF licenses this file to You under the Apache License, Version 2.0
006     * (the "License"); you may not use this file except in compliance with
007     * the License.  You may obtain a copy of the License at
008     *
009     *     http://www.apache.org/licenses/LICENSE-2.0
010     *
011     * Unless required by applicable law or agreed to in writing, software
012     * distributed under the License is distributed on an "AS IS" BASIS,
013     * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
014     * See the License for the specific language governing permissions and
015     * limitations under the License.
016     */
017    package org.apache.commons.scxml;
018    
019    import org.w3c.dom.Node;
020    
021    /**
022     * Interface for a component that may be used by the SCXML engines to
023     * evaluate the expressions within the SCXML document.
024     *
025     */
026    public interface Evaluator {
027    
028        /**
029         * Evaluate an expression.
030         *
031         * @param ctx variable context
032         * @param expr expression
033         * @return a result of the evaluation
034         * @throws SCXMLExpressionException A malformed exception
035         */
036        Object eval(Context ctx, String expr)
037        throws SCXMLExpressionException;
038    
039        /**
040         * Evaluate a condition.
041         * Manifests as "cond" attributes of <transition>,
042         * <if> and <elseif> elements.
043         *
044         * @param ctx variable context
045         * @param expr expression
046         * @return true/false
047         * @throws SCXMLExpressionException A malformed exception
048         */
049        Boolean evalCond(Context ctx, String expr)
050        throws SCXMLExpressionException;
051    
052        /**
053         * Evaluate a location that returns a Node within an XML data tree.
054         * Manifests as "location" attributes of <assign> element.
055         *
056         * @param ctx variable context
057         * @param expr expression
058         * @return The location node.
059         * @throws SCXMLExpressionException A malformed exception
060         */
061        Node evalLocation(Context ctx, String expr)
062        throws SCXMLExpressionException;
063    
064        /**
065         * Create a new child context.
066         *
067         * @param parent parent context
068         * @return new child context
069         */
070        Context newContext(Context parent);
071    
072    }
073