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();
	}

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

}
