lalr_transition.java

package java_cup ;


/**
 * This class represents a transition in an LALR viable prefix recognition
 * machine. Transitions can be under terminals for non-terminals. They are
 * internally linked together into singly linked lists containing all the
 * transitions out of a single state via the _next field.
 * 
 * @see java_cup.lalr_state
 * @version last updated: 11/25/95
 * @author Scott Hudson
 */
public class lalr_transition
{
  /*-----------------------------------------------------------*/
  /*--- Constructor(s) ----------------------------------------*/
  /*-----------------------------------------------------------*/
  /**
   * Full constructor.
   * 
   * @param on_sym symbol we are transitioning on.
   * @param to_st state we transition to.
   * @param nxt next transition in linked list.
   */
  public lalr_transition ( symbol on_sym , lalr_state to_st ,
      lalr_transition nxt ) throws internal_error
  {
    /* sanity checks */
    if ( on_sym == null )
      throw new internal_error ( "Attempt to create transition on null symbol" ) ;
    if ( to_st == null )
      throw new internal_error ( "Attempt to create transition to null state" ) ;
    /* initialize */
    _on_symbol = on_sym ;
    _to_state = to_st ;
    _next = nxt ;
  }


  /* . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . */
  /**
   * Constructor with null next.
   * 
   * @param on_sym symbol we are transitioning on.
   * @param to_st state we transition to.
   */
  public lalr_transition ( symbol on_sym , lalr_state to_st )
      throws internal_error
  {
    this ( on_sym , to_st , null ) ;
  }


  /*-----------------------------------------------------------*/
  /*--- (Access to) Instance Variables ------------------------*/
  /*-----------------------------------------------------------*/
  /** The symbol we make the transition on. */
  protected symbol _on_symbol ;


  /** The symbol we make the transition on. */
  public symbol on_symbol ( )
  {
    return _on_symbol ;
  }


  /* . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . */
  /** The state we transition to. */
  protected lalr_state _to_state ;


  /** The state we transition to. */
  public lalr_state to_state ( )
  {
    return _to_state ;
  }


  /* . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . */
  /** Next transition in linked list of transitions out of a state */
  protected lalr_transition _next ;


  /** Next transition in linked list of transitions out of a state */
  public lalr_transition next ( )
  {
    return _next ;
  }


  /*-----------------------------------------------------------*/
  /*--- General Methods ---------------------------------------*/
  /*-----------------------------------------------------------*/
  /** Convert to a string. */
  public String toString ( )
  {
    String result ;
    result = "transition on " + on_symbol ( ).name ( ) + " to state [" ;
    result += _to_state.index ( ) ;
    result += "]" ;
    return result ;
  }
  /*-----------------------------------------------------------*/
}