--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/Implab/Parsing/DFABuilder.cs	Sun Jun 15 19:39:11 2014 +0400
@@ -0,0 +1,182 @@
+using Implab;
+using System;
+using System.Collections.Generic;
+using System.Diagnostics;
+using System.Linq;
+using System.Text;
+using System.Threading.Tasks;
+
+namespace Implab.Parsing {
+    /// <summary>
+    /// Используется для построения ДКА по регулярному выражению, сначала обходит
+    /// регулярное выражение и вычисляет followpos, затем используется метод
+    /// <see cref="BuildDFA(IDFADefinition)"/> для построения автомата.
+    /// </summary>
+    public class DFABuilder : IVisitor {
+        int m_idx = 0;
+        Token m_root;
+        HashSet<int> m_firstpos;
+        HashSet<int> m_lastpos;
+
+        Dictionary<int, HashSet<int>> m_followpos = new Dictionary<int, HashSet<int>>();
+        Dictionary<int, int> m_indexes = new Dictionary<int, int>();
+        Dictionary<int, int> m_ends = new Dictionary<int, int>();
+
+        public Dictionary<int, HashSet<int>> FollowposMap {
+            get { return m_followpos; }
+        }
+
+        public HashSet<int> Followpos(int pos) {
+            HashSet<int> set;
+            if (m_followpos.TryGetValue(pos, out set))
+                return set;
+            return m_followpos[pos] = new HashSet<int>();
+        }
+
+        bool Nullable(object n) {
+            if (n is EmptyToken || n is StarToken)
+                return true;
+            if (n is AltToken)
+                return Nullable(((AltToken)n).Left) || Nullable(((AltToken)n).Right);
+            if (n is CatToken)
+                return Nullable(((CatToken)n).Left) && Nullable(((CatToken)n).Right);
+            return false;
+        }
+
+
+        public void Visit(AltToken token) {
+            if (m_root == null)
+                m_root = token;
+            var firtspos = new HashSet<int>();
+            var lastpos = new HashSet<int>();
+
+            token.Left.Accept(this);
+            firtspos.UnionWith(m_firstpos);
+            lastpos.UnionWith(m_lastpos);
+
+            token.Right.Accept(this);
+            firtspos.UnionWith(m_firstpos);
+            lastpos.UnionWith(m_lastpos);
+
+            m_firstpos = firtspos;
+            m_lastpos = lastpos;
+        }
+
+        public void Visit(StarToken token) {
+            if (m_root == null)
+                m_root = token;
+            token.Token.Accept(this);
+
+            foreach (var i in m_lastpos)
+                Followpos(i).UnionWith(m_firstpos);
+        }
+
+        public void Visit(CatToken token) {
+            if (m_root == null)
+                m_root = token;
+
+            var firtspos = new HashSet<int>();
+            var lastpos = new HashSet<int>();
+            token.Left.Accept(this);
+            firtspos.UnionWith(m_firstpos);
+            var leftLastpos = m_lastpos;
+
+            token.Right.Accept(this);
+            lastpos.UnionWith(m_lastpos);
+            var rightFirstpos = m_firstpos;
+
+            if (Nullable(token.Left))
+                firtspos.UnionWith(rightFirstpos);
+
+            if (Nullable(token.Right))
+                lastpos.UnionWith(leftLastpos);
+
+            m_firstpos = firtspos;
+            m_lastpos = lastpos;
+
+            foreach (var i in leftLastpos)
+                Followpos(i).UnionWith(rightFirstpos);
+
+        }
+
+        public void Visit(EmptyToken token) {
+            if (m_root == null)
+                m_root = token;
+            ;
+        }
+
+        public void Visit(SymbolToken token) {
+            if (m_root == null)
+                m_root = token;
+            m_idx++;
+            m_indexes[m_idx] = token.Value;
+            m_firstpos = new HashSet<int>(new[] { m_idx });
+            m_lastpos = new HashSet<int>(new[] { m_idx });
+        }
+
+        public void Visit(EndToken token) {
+            if (m_root == null)
+                m_root = token;
+            m_idx++;
+            m_indexes[m_idx] = Alphabet.UNCLASSIFIED;
+            m_firstpos = new HashSet<int>(new[] { m_idx });
+            m_lastpos = new HashSet<int>(new[] { m_idx });
+            Followpos(m_idx);
+            m_ends.Add(m_idx, token.Tag);
+        }
+
+        public void BuildDFA(IDFADefinition dfa) {
+            Safe.ArgumentNotNull(dfa,"dfa");
+            
+            var stateMap = new Dictionary<HashSet<int>, int>(new CustomEqualityComparer<HashSet<int>>(
+                (x, y) => x.SetEquals(y),
+                (x) => x.Sum(n => n.GetHashCode())
+            ));
+            
+            stateMap[m_firstpos] = DefineState( dfa, m_firstpos);
+            Debug.Assert(stateMap[m_firstpos] == DFADefinitionBase.INITIAL_STATE);
+
+            var queue = new Queue<HashSet<int>>();
+
+            queue.Enqueue(m_firstpos);
+
+            while (queue.Count > 0) {
+                var state = queue.Dequeue();
+                var s1 = stateMap[state];
+
+                for (int a = 0; a < dfa.AlphabetSize; a++) {
+                    var next = new HashSet<int>();
+                    foreach (var p in state) {
+                        if (m_indexes[p] == a) {
+                            next.UnionWith(Followpos(p));
+                        }
+                    }
+                    if (next.Count > 0) {
+                        int s2;
+                        if (!stateMap.TryGetValue(next, out s2)) {
+                            stateMap[next] = s2 = DefineState(dfa, next);
+                            queue.Enqueue(next);
+                        }
+                        dfa.DefineTransition(s1, s2, a);
+                    }
+                }
+
+            }
+        }
+
+        int[] GetStateTags(HashSet<int> state) {
+            Debug.Assert(state != null);
+            return state.Where(pos => m_ends.ContainsKey(pos)).Select(pos => m_ends[pos]).ToArray();
+        }
+
+        int DefineState(IDFADefinition automa, HashSet<int> state) {
+            Debug.Assert(automa != null);
+            Debug.Assert(state != null);
+
+            var tags = GetStateTags(state);
+         
+            return tags.Length > 0 ? automa.AddState(tags) : automa.AddState();
+        }
+
+    }
+}