--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/Implab/Automaton/RegularExpressions/RegularExpressionVisitor.cs	Mon Mar 14 01:19:38 2016 +0300
@@ -0,0 +1,184 @@
+using Implab;
+using System;
+using System.Collections.Generic;
+using System.Diagnostics;
+using System.Linq;
+
+namespace Implab.Automaton.RegularExpressions {
+    /// <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 RegularExpressionVisitor<TTag> : IVisitor<TTag> {
+        int m_idx;
+        Token<TTag> m_root;
+        HashSet<int> m_firstpos;
+        HashSet<int> m_lastpos;
+
+        readonly Dictionary<int, HashSet<int>> m_followpos = new Dictionary<int, HashSet<int>>();
+        readonly Dictionary<int, int> m_indexes = new Dictionary<int, int>();
+        readonly Dictionary<int, TTag> m_ends = new Dictionary<int, TTag>();
+
+        public Dictionary<int, HashSet<int>> FollowposMap {
+            get { return m_followpos; }
+        }
+
+        public HashSet<int> Followpos(int pos) {
+            HashSet<int> set;
+            return m_followpos.TryGetValue(pos, out set) ? set : m_followpos[pos] = new HashSet<int>();
+        }
+
+        bool Nullable(object n) {
+            if (n is EmptyToken<TTag> || n is StarToken<TTag>)
+                return true;
+            var altToken = n as AltToken<TTag>;
+            if (altToken != null)
+                return Nullable(altToken.Left) || Nullable(altToken.Right);
+            var catToken = n as CatToken<TTag>;
+            if (catToken != null)
+                return Nullable(catToken.Left) && Nullable(catToken.Right);
+            return false;
+        }
+
+
+        public void Visit(AltToken<TTag> 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<TTag> 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<TTag> 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<TTag> token) {
+            if (m_root == null)
+                m_root = token;
+        }
+
+        public void Visit(SymbolToken<TTag> 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<TTag> token) {
+            if (m_root == null)
+                m_root = token;
+            m_idx++;
+            m_indexes[m_idx] = DFAConst.UNCLASSIFIED_INPUT;
+            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(ITaggedDFABuilder<TTag> dfa) {
+            Safe.ArgumentNotNull(dfa,"dfa");
+
+            var states = new MapAlphabet<HashSet<int>>(
+                             false,
+                             new CustomEqualityComparer<HashSet<int>>(
+                                 (x, y) => x.SetEquals(y),
+                                 x => x.Sum(n => n.GetHashCode())
+                             ));
+
+            var initialState = states.DefineSymbol(m_firstpos);
+            dfa.SetInitialState(initialState);
+
+            var tags = GetStateTags(m_firstpos);
+            if (tags != null && tags.Length > 0)
+                dfa.MarkFinalState(initialState, tags);
+
+            var inputMax = m_indexes.Values.Max();
+            var queue = new Queue<HashSet<int>>();
+
+            queue.Enqueue(m_firstpos);
+
+            while (queue.Count > 0) {
+                var state = queue.Dequeue();
+                var s1 = states.Translate(state);
+                Debug.Assert(s1 != DFAConst.UNCLASSIFIED_INPUT);
+
+                for (int a = 0; a <= inputMax; 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 = states.Translate(next);
+                        if (s2 == DFAConst.UNCLASSIFIED_INPUT) {
+                            s2 = states.DefineSymbol(next);
+
+                            tags = GetStateTags(next);
+                            if (tags != null && tags.Length > 0) {
+                                dfa.MarkFinalState(s2);
+                                dfa.SetStateTag(s2, tags);
+                            }
+                            
+                            queue.Enqueue(next);
+                        }
+                        dfa.Add(new AutomatonTransition(s1, s2, a));
+                    }
+                }
+            }
+        }
+
+        TTag[] GetStateTags(IEnumerable<int> state) {
+            Debug.Assert(state != null);
+            return state.Where(m_ends.ContainsKey).Select(pos => m_ends[pos]).ToArray();
+        }
+
+    }
+}