content: /* 
   * Kodkod -- Copyright (c) 2005-present, Emina Torlak
   * Pardinus -- Copyright (c) 2013-present, Nuno Macedo, INESC TEC
   *
   * 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.TemporalOperator;
  import kodkod.ast.visitor.ReturnVisitor;
  import kodkod.ast.visitor.VoidVisitor;
  
  /**
   * A temporal {@link kodkod.ast.Formula formula} with two children.
   * 
   * @specfield left: Formula
   * @specfield right: Formula
   * @specfield op: TemporalOperator
   * @invariant children = 0->left + 1->right
   * @author Eduardo Pessoa, Nuno Macedo // [HASLab] temporal model finding
   */
  public final class BinaryTempFormula extends Formula {
  	private final TemporalOperator op;
      private final Formula left;
      private final Formula right;
  
      /**  
       * Constructs a new temporal binary formula:  left op right
       * 
       * @ensures this.left' = left && this.right' = right &&  this.op' = op
       * @throws NullPointerException  left = null || right = null || op = null
       * @throws IllegalArgumentException  op.arity != 2
       */
      BinaryTempFormula(Formula left, TemporalOperator op, Formula right) {
          if (!op.binary()) {
              throw new IllegalArgumentException("Not a unary operator: " + op);
          }
          if (op == null || left == null || right == null) {
              throw new NullPointerException("null arg");
          }
          this.left = left;
          this.right = right;
          this.op = op;
      }
  
      /**
       * Returns the left child of this.
       * @return this.left
       */
      public Formula left() { return left; }
  
      /**
       * Returns the right child of this.
       * @return this.right
       */
      public Formula right() { return right; }
  
      /**
       * Returns the operator of this.
       * @return this.op
       */
      public TemporalOperator op() { return op; }
  
      /**
       * {@inheritDoc}
       * @see kodkod.ast.Formula#accept(kodkod.ast.visitor.ReturnVisitor)
       */
      public <E, F, D, I> F 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  "(" + this.left+" " + this.op + " "+ this.right + ")";
      }
  }
  