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Java Lookahead Parser Generator. Generator produces LALR(k) parsers. Grammar rules are entered using annotations. Rule annotation can be attached to reducer method, which keeps rule and it's action together.
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/*
 * Copyright (C) 2012 Timo Vesalainen
 *
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program.  If not, see .
 */
package org.vesalainen.grammar.state;

import java.util.ArrayDeque;
import java.util.Collection;
import java.util.Deque;
import java.util.HashMap;
import java.util.Map;

    /**
 * DiGraph class implements the digraph algorithm described in FRANK DeREMER and 
 * THOMAS PENNELLO: Efficient Computation of LALR(1) Look-Ahead Sets
 * @see 
 * FRANK DeREMER and 
 * THOMAS PENNELLO: Efficient Computation of LALR(1) Look-Ahead Sets
 * 
 * 
 * @author Timo Vesalainen
 */
public class DiGraph
{
    private Deque stack = new ArrayDeque<>();
    private Map indexMap = new HashMap<>();
    private static final int INFINITY = 9999999;

    /**
     * This algorithm traverses all vertices and all edges once.
     * @param allX 
     */
    public void traverse(Collection allX)
    {
        reset();
        for (X x : allX)
        {
            if (indexOf(x) == 0)
            {
                traverse(x);
            }
        }
    }
    public void traverse(X x)
    {
        enter(x);
        stack.push(x);

        int d = stack.size();
        setIndexOf(x, d);

        int depth = traversedCount();
        Collection c = x.edges();
        for (X s : c)
        {
            edge(x, s);
            if (indexOf(s) == 0)
            {
                traverse(s);
            }
            setIndexOf(x, Math.min(indexOf(x), indexOf(s)));
        }
        if (indexOf(x) == d)
        {
            branch(x);
            X s = stack.peek();
            while (!s.equals(x))
            {
                pop(s);
                stack.pop();
                setIndexOf(s, INFINITY);
                s = stack.peek();
            }
            setIndexOf(x, INFINITY);
            stack.pop();
        }
        exit(x, traversedCount() - depth);
    }
    
    protected void enter(X x)
    {
    }

    protected void edge(X from, X to)
    {
    }

    protected void branch(X x)
    {
    }

    protected void pop(X s)
    {
    }

    protected void exit(X x, int depth)
    {
    }

    private void setIndexOf(X state, int index)
    {
        indexMap.put(state, index);
    }
    
    public boolean traversed(X x)
    {
        return indexMap.containsKey(x);
    }
    
    public int traversedCount()
    {
        return indexMap.size();
    }

    public int stackDepth()
    {
        return stack.size();
    }
    
    private int indexOf(X state)
    {
        Integer i = indexMap.get(state);
        if (i == null)
        {
            return 0;
        }
        else
        {
            return i;
        }
    }
    public void reset()
    {
        indexMap.clear();
        stack.clear();
    }
    /**
     * @param args the command line arguments
    public static void main(String[] args)    
    {
        try
        {
            DFA dfa = Regex.createDFA("c(abd)*");
            DiGraph> d = new DiGraph<>();
            d.traverse(dfa);
            //dfa.dump(System.err);
        }
        catch (Exception ex)
        {
            ex.printStackTrace();
        }
    }
     */

}