symbol.java

package java_cup ;


/**
 * This abstract class serves as the base class for grammar symbols (i.e., both
 * terminals and non-terminals). Each symbol has a name string, and a string
 * giving the type of object that the symbol will be represented by on the
 * runtime parse stack. In addition, each symbol maintains a use count in order
 * to detect symbols that are declared but never used, and an index number that
 * indicates where it appears in parse tables (index numbers are unique within
 * terminals or non terminals, but not across both).
 * 
 * @see java_cup.terminal
 * @see java_cup.non_terminal
 * @version last updated: 7/3/96
 * @author Frank Flannery
 */
public abstract class symbol
{
  /*-----------------------------------------------------------*/
  /*--- Constructor(s) ----------------------------------------*/
  /*-----------------------------------------------------------*/
  /**
   * Full constructor.
   * 
   * @param nm the name of the symbol.
   * @param tp a string with the type name.
   */
  public symbol ( String nm , String tp )
  {
    /* sanity check */
    if ( nm == null ) nm = "" ;
    /* apply default if no type given */
    if ( tp == null ) tp = "Object" ;
    _name = nm ;
    _stack_type = tp ;
  }


  /* . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . */
  /**
   * Constructor with default type.
   * 
   * @param nm the name of the symbol.
   */
  public symbol ( String nm )
  {
    this ( nm , null ) ;
  }


  /*-----------------------------------------------------------*/
  /*--- (Access to) Instance Variables ------------------------*/
  /*-----------------------------------------------------------*/
  /** String for the human readable name of the symbol. */
  protected String _name ;


  /** String for the human readable name of the symbol. */
  public String name ( )
  {
    return _name ;
  }


  /* . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . */
  /** String for the type of object used for the symbol on the parse stack. */
  protected String _stack_type ;


  /** String for the type of object used for the symbol on the parse stack. */
  public String stack_type ( )
  {
    return _stack_type ;
  }


  /* . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . */
  /** Count of how many times the symbol appears in productions. */
  protected int _use_count = 0 ;


  /** Count of how many times the symbol appears in productions. */
  public int use_count ( )
  {
    return _use_count ;
  }


  /** Increment the use count. */
  public void note_use ( )
  {
    _use_count ++ ;
  }


  /* . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . */
  /**
   * Index of this symbol (terminal or non terminal) in the parse tables. Note:
   * indexes are unique among terminals and unique among non terminals, however,
   * a terminal may have the same index as a non-terminal, etc.
   */
  protected int _index ;


  /**
   * Index of this symbol (terminal or non terminal) in the parse tables. Note:
   * indexes are unique among terminals and unique among non terminals, however,
   * a terminal may have the same index as a non-terminal, etc.
   */
  public int index ( )
  {
    return _index ;
  }


  /* . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . */
  /**
   * Indicate if this is a non-terminal. Here in the base class we don't know,
   * so this is abstract.
   */
  public abstract boolean is_non_term ( ) ;


  /* . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . */
  /** Convert to a string. */
  public String toString ( )
  {
    return name ( ) ;
  }
  /*-----------------------------------------------------------*/
}