content: /*
   * Copyright 1999-2012 Alibaba Group.
   *  
   * 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.
   */
  /**
   * (created at 2012-8-2)
   */
  package com.alibaba.cobar.parser.ast.expression;
  
  import java.util.ArrayList;
  import java.util.List;
  import java.util.Map;
  
  /**
   * an operator with arity of n<br/>
   * associative and commutative<br/>
   * non-polyadic operator with same precedence is not exist
   * 
   * @author <a href="mailto:shuo.qius@alibaba-inc.com">QIU Shuo</a>
   */
  public abstract class PolyadicOperatorExpression extends AbstractExpression {
      protected List<Expression> operands;
      protected final int precedence;
  
      public PolyadicOperatorExpression(int precedence) {
          this(precedence, true);
      }
  
      public PolyadicOperatorExpression(int precedence, boolean leftCombine) {
          this(precedence, 4);
      }
  
      public PolyadicOperatorExpression(int precedence, int initArity) {
          this.precedence = precedence;
          this.operands = new ArrayList<Expression>(initArity);
      }
  
      /**
       * @return this
       */
      public PolyadicOperatorExpression appendOperand(Expression operand) {
          if (operand == null)
              return this;
          if (getClass().isAssignableFrom(operand.getClass())) {
              PolyadicOperatorExpression sub = (PolyadicOperatorExpression) operand;
              operands.addAll(sub.operands);
          } else {
              operands.add(operand);
          }
          return this;
      }
  
      /**
       * @param index start from 0
       */
      public Expression getOperand(int index) {
          if (index >= operands.size()) {
              throw new IllegalArgumentException("only contains " + operands.size() + " operands," + index
                      + " is out of bound");
          }
          return operands.get(index);
      }
  
      public int getArity() {
          return operands.size();
      }
  
      @Override
      public int getPrecedence() {
          return precedence;
      }
  
      public abstract String getOperator();
  
      @Override
      protected Object evaluationInternal(Map<? extends Object, ? extends Object> parameters) {
          return UNEVALUATABLE;
      }
  }
  