parse_action_row.java

我开发的一个用java语言实现的编译器,内含词法分析器,语法分析器,而且可以实现中间代码生成.用到了SLR算法和LR(1)算法

package java_cup;

/** This class represents one row (corresponding to one machine state) of the 
 *  parse action table.
 */
public class parse_action_row {

  /*-----------------------------------------------------------*/
  /*--- Constructor(s) ----------------------------------------*/
  /*-----------------------------------------------------------*/
	       
  /** Simple constructor.  Note: this should not be used until the number of
   *  terminals in the grammar has been established.
   */
  public parse_action_row()
    {
      /* make sure the size is set */
      if (_size <= 0 )  _size = terminal.number();

      /* allocate the array */
      under_term = new parse_action[size()];

      /* set each element to an error action */
      for (int i=0; i<_size; i++)
	under_term[i] = new parse_action();
    }

  /*-----------------------------------------------------------*/
  /*--- (Access to) Static (Class) Variables ------------------*/
  /*-----------------------------------------------------------*/

  /** Number of columns (terminals) in every row. */
  protected static int _size = 0;

  /** Number of columns (terminals) in every row. */
  public static int size() {return _size;}

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

  /** Table of reduction counts (reused by compute_default()). */
  protected static int reduction_count[] = null;

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

  /** Actual action entries for the row. */
  public parse_action under_term[];

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

  /** Default (reduce) action for this row.  -1 will represent default 
   *  of error. 
   */
  public int default_reduce;

  /*-----------------------------------------------------------*/
  /*--- General Methods ---------------------------------------*/
  /*-----------------------------------------------------------*/
	
  /** Compute the default (reduce) action for this row and store it in 
   *  default_reduce.  In the case of non-zero default we will have the 
   *  effect of replacing all errors by that reduction.  This may cause 
   *  us to do erroneous reduces, but will never cause us to shift past 
   *  the point of the error and never cause an incorrect parse.  -1 will 
   *  be used to encode the fact that no reduction can be used as a 
   *  default (in which case error will be used).
   */
  public void compute_default()
    {
      int i, prod, max_prod, max_red;

      /* if we haven't allocated the count table, do so now */
      if (reduction_count == null) 
	reduction_count = new int[production.number()];

      /* clear the reduction count table and maximums */
      for (i = 0; i < production.number(); i++)
	reduction_count[i] = 0;
      max_prod = -1;
      max_red = 0;
     
      /* walk down the row and look at the reduces */
      for (i = 0; i < size(); i++)
	if (under_term[i].kind() == parse_action.REDUCE)
	  {
	    /* count the reduce in the proper production slot and keep the 
	       max up to date */
	    prod = ((reduce_action)under_term[i]).reduce_with().index();
	    reduction_count[prod]++;
	    if (reduction_count[prod] > max_red)
	      {
		max_red = reduction_count[prod];
		max_prod = prod;
	      }
	  }

       /* record the max as the default (or -1 for not found) */
       default_reduce = max_prod;
    }

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

}