content: /*
   * Licensed to the Apache Software Foundation (ASF) under one or more
   * contributor license agreements.  See the NOTICE file distributed with
   * this work for additional information regarding copyright ownership.
   * The ASF licenses this file to you 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.
   */
  package org.apache.calcite.plan.volcano;
  
  import org.apache.calcite.rel.RelNode;
  
  /**
   * A rule driver applies rules with designed algorithms.
   */
  interface RuleDriver {
  
    /**
     * Gets the rule queue.
     */
    RuleQueue getRuleQueue();
  
    /**
     * Applies rules.
     */
    void drive();
  
    /**
     * Callback when new RelNodes are added into RelSet.
     *
     * @param rel the new RelNode
     * @param subset subset to add
     */
    void onProduce(RelNode rel, RelSubset subset);
  
    /**
     * Callback when RelSets are merged.
     *
     * @param set the merged result set
     */
    void onSetMerged(RelSet set);
  
    /**
     * Clears this RuleDriver.
     */
    void clear();
  }
  