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