
package java_cup;

/**
 * This class represents a shift action within the parse table. The action
 * simply stores the state that it shifts to and responds to queries about its
 * type.
 *
 * @version last updated: 11/25/95
 * @author Scott Hudson
 */
public class shift_action extends parse_action {

  /*-----------------------------------------------------------*/
  /*--- Constructor(s) ----------------------------------------*/
  /*-----------------------------------------------------------*/

  /**
   * Simple constructor.
   * 
   * @param shft_to the state that this action shifts to.
   */
  public shift_action(lalr_state shft_to) throws internal_error {
    /* sanity check */
    if (shft_to == null)
      throw new internal_error("Attempt to create a shift_action to a null state");

    _shift_to = shft_to;
  }

  /*-----------------------------------------------------------*/
  /*--- (Access to) Instance Variables ------------------------*/
  /*-----------------------------------------------------------*/

  /** The state we shift to. */
  protected lalr_state _shift_to;

  /** The state we shift to. */
  public lalr_state shift_to() {
    return _shift_to;
  }

  /*-----------------------------------------------------------*/
  /*--- General Methods ---------------------------------------*/
  /*-----------------------------------------------------------*/

  /** Quick access to type of action. */
  @Override
  public int kind() {
    return SHIFT;
  }

  /* . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . */

  /** Equality test. */
  public boolean equals(shift_action other) {
    return other != null && other.shift_to() == shift_to();
  }

  /* . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . */

  /** Generic equality test. */
  @Override
  public boolean equals(Object other) {
    if (other instanceof shift_action)
      return equals((shift_action) other);
    else
      return false;
  }

  /* . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . */

  /** Compute a hash code. */
  @Override
  public int hashCode() {
    /* use the hash code of the state we are shifting to */
    return shift_to().hashCode();
  }

  /* . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . */

  /** Convert to a string. */
  @Override
  public String toString() {
    return "SHIFT(to state " + shift_to().index() + ")";
  }

  /*-----------------------------------------------------------*/

}
