content: /* 
   * Kodkod -- Copyright (c) 2005-present, Emina Torlak
   *
   * Permission is hereby granted, free of charge, to any person obtaining a copy
   * of this software and associated documentation files (the "Software"), to deal
   * in the Software without restriction, including without limitation the rights
   * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
   * copies of the Software, and to permit persons to whom the Software is
   * furnished to do so, subject to the following conditions:
   *
   * The above copyright notice and this permission notice shall be included in
   * all copies or substantial portions of the Software.
   *
   * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
   * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
   * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
   * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
   * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
   * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
   * THE SOFTWARE.
   */
  package kodkod.ast;
  
  import kodkod.ast.operator.ExprOperator;
  import kodkod.ast.visitor.ReturnVisitor;
  import kodkod.ast.visitor.VoidVisitor;
  
  
  /** 
   * A relational {@link kodkod.ast.Expression expression} with two children.
   * 
   * @specfield left: Expression
   * @specfield right: Expression
   * @specfield op: ExprOperator
   * @specfield op.binary()
   * @invariant children = 0->left + 1->right
   * @author Emina Torlak 
   */
  public final class BinaryExpression extends Expression {
  	private final ExprOperator op;
  	private final Expression left;
  	private final Expression right;
  	private final int arity;
  
  	/**  
  	 * Constructs a new binary expression: left op right
  	 * 
  	 * @ensures this.left' = left && this.right' = right && this.op' = op
  	 * @throws NullPointerException  left = null || right = null || op = null
  	 * @throws IllegalArgumentException  left and right cannot be combined with the specified operator.
  	 */
  	BinaryExpression(final Expression left, final ExprOperator op, final Expression right) {
  		switch(op) { 
  		case UNION : case INTERSECTION : case DIFFERENCE : case OVERRIDE :
  			this.arity = left.arity();
  			if (arity!=right.arity())
  				throw new IllegalArgumentException("Incompatible arities: " + left + " and " + right);
  			break;
  		case JOIN : 
  			this.arity = left.arity() + right.arity() - 2;
  			if (arity < 1)
  				throw new IllegalArgumentException("Incompatible arities: " + left + " and " + right);
  			break;
  		case PRODUCT : 
  			this.arity = left.arity() + right.arity();
  			break;
  		default : 
  			throw new IllegalArgumentException("Not a binary operator: " + op);
  		}
  		
  		this.op = op;
  		this.left = left;
  		this.right = right;
  		
  	}
  
  	/**
  	 * Returns the arity of this binary expression.
  	 * @return this.arity
  	 * @see kodkod.ast.Expression#arity()
  	 */
  	public int arity() {
  		return arity;
  	}
  
  	/**
  	 * Returns this.op.
  	 * @return this.op
  	 */
  	public ExprOperator op() { return op ; }
  	/**
  	 * Returns the left child of this.
  	 * @return this.left
  	 */
  	public Expression left() {return left;}
  
  	/**
  	 * Returns the right child of this.
  	 * @return this.right
  	 */
  	public Expression right() {return right;}
  
  	/**
  	 * {@inheritDoc}
  	 * @see kodkod.ast.Expression#accept(kodkod.ast.visitor.ReturnVisitor)
  	 */
  	public <E, F, D, I> E accept(ReturnVisitor<E, F, D, I> visitor) {
  		return visitor.visit(this);
  	}
  
  	/**
  	 * {@inheritDoc}
  	 * @see kodkod.ast.Node#accept(kodkod.ast.visitor.VoidVisitor)
  	 */
  	public void accept(VoidVisitor visitor) {
  		visitor.visit(this);
  	}
  
  	/**
  	 * {@inheritDoc}
  	 * @see kodkod.ast.Node#toString()
  	 */
  	public String toString() {
  		return "(" + left + " " + op + " " + right + ")";
  	}
  }
  