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// PLEASE DO NOT EDIT WITHOUT THE EXPLICIT CONSENT OF THE AUTHOR! \\
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using System.Collections;
using Ilog.Language.Util;

namespace Ilog.Language.Syntax
{
  /**
   * This the class of objects stored in the path table of a nonterminal.
   * It consists of a sequence of rule paths between a pair of nonterminals,
   * and a set of terminals, which is the union of all the FIRST sets of
   * these paths.  It also contains the start and end nonterminals.
   *
   * @version     Last modified on Sat May 21 20:22:00 2005 by hak
   * @author      <a href="mailto:hak@ilog.fr">Hassan A&iuml;t-Kaci</a>
   * @copyright   &copy; 2000 <a href="http://www.ilog.fr/">ILOG, S.A.</a>
   */
  internal class RulePaths
    {
      /**
       * The nonterminal at the origin of the paths.
       */
      private NonTerminal start;
      internal NonTerminal Start
        {
	  get { return start; }
	}

      /**
       * The nonterminal at the end of the paths.
       */
      private NonTerminal end;
      internal NonTerminal End
        {
	  get { return end; }
	}

      /**
       * The arrayList of paths.
       */
      private ArrayList paths;
      internal ArrayList Paths
        {
	  get { return paths; }
	}

      /**
       * The FIRST set; it is the union of all paths between Start and End.
       */
      private SetOf first;
      internal SetOf First
        {
	  get { return first; }
	}

      /**
       * This is <tt>true</tt> whenever one of the paths in this derives
       * the EMPTY symbol.
       */
      private bool isNullable;
      internal bool IsNullable
        {
	  get { return isNullable; }
	}

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      /**
       * Constructs a new Paths object with the given rule path.
       */
      internal RulePaths (RulePath path)
        {
	  (paths = new ArrayList()).Add(path);
	  start = path.Start;
	  end = path.End;
	  first = new SetOf(path.First);
	  start.Paths.Add(path);
	  isNullable = path.IsNullable;
	}

      /**
       * Adds the given path to this Paths object, and returns <tt>true</tt>
       * iff the given path contributes to the FIRST union or empty derivation.
       */
      internal bool Add (RulePath path)
        {
	  if ((path.First <= first) && (isNullable || !path.IsNullable))
	    return false;

	  paths.Add(path);
	  path.Start.Paths.Add(path);

	  first.Union(path.First);
	  isNullable |= path.IsNullable;

	  return true;
	}
  }
}