diff --git a/CanonSharp.Common/Abstractions/ISourceReader.cs b/CanonSharp.Common/Abstractions/ISourceReader.cs
new file mode 100644
index 0000000..c53fa2f
--- /dev/null
+++ b/CanonSharp.Common/Abstractions/ISourceReader.cs
@@ -0,0 +1,17 @@
+namespace CanonSharp.Common.Abstractions;
+
+public interface ISourceReader
+{
+    /// <summary>
+    /// 偷看一下下一个字符
+    /// </summary>
+    /// <param name="c">看到的下一个字符</param>
+    /// <returns></returns>
+    public bool TryPeek(out char c);
+
+    /// <summary>
+    /// 读取下一个字符
+    /// </summary>
+    /// <returns></returns>
+    public char Read();
+}
diff --git a/CanonSharp.Common/LexicalAnalyzer/DeterministicFiniteAutomation.cs b/CanonSharp.Common/LexicalAnalyzer/DeterministicFiniteAutomation.cs
index 6d52008..eaf844f 100644
--- a/CanonSharp.Common/LexicalAnalyzer/DeterministicFiniteAutomation.cs
+++ b/CanonSharp.Common/LexicalAnalyzer/DeterministicFiniteAutomation.cs
@@ -1,11 +1,13 @@
 namespace CanonSharp.Common.LexicalAnalyzer;
 
-public class DeterministicState : IEquatable<DeterministicState>
+public class DeterministicState(HashSet<NondeterministicState> closure) : IEquatable<DeterministicState>
 {
     public Guid Id { get; } = Guid.NewGuid();
 
     public Dictionary<char, DeterministicState> Transaction { get; } = [];
 
+    public HashSet<NondeterministicState> Closure { get; } = closure;
+
     public bool Equals(DeterministicState? other) => other is not null && Id.Equals(other.Id);
 
     public override bool Equals(object? obj) => obj is DeterministicState other && Equals(other);
@@ -35,7 +37,7 @@ public class DeterministicFiniteAutomation
         HashSet<DeterministicState> finalStates = [];
 
         HashSet<NondeterministicState> startClosure = nfa.Start.CalculateEmptyClosure();
-        DeterministicState start = new();
+        DeterministicState start = new(startClosure);
         map.Add(new NondeterministicStateSet(startClosure), start);
         queue.Enqueue(new Pair(startClosure, start));
 
@@ -50,7 +52,7 @@ public class DeterministicFiniteAutomation
 
             foreach (NondeterministicState state in pair.States)
             {
-                foreach (KeyValuePair<EmptyChar,HashSet<NondeterministicState>> transaction in
+                foreach (KeyValuePair<EmptyChar, HashSet<NondeterministicState>> transaction in
                          state.Transactions.Where(p => !p.Key.IsEmpty))
                 {
                     HashSet<NondeterministicState> closure = [];
@@ -64,16 +66,19 @@ public class DeterministicFiniteAutomation
                     {
                         n.UnionWith(closure);
                     }
-                    next.Add(transaction.Key.Char, closure);
+                    else
+                    {
+                        next.Add(transaction.Key.Char, closure);
+                    }
                 }
             }
 
-            foreach (KeyValuePair<char,HashSet<NondeterministicState>> transaction in next)
+            foreach (KeyValuePair<char, HashSet<NondeterministicState>> transaction in next)
             {
                 NondeterministicStateSet set = new(transaction.Value);
                 if (!map.TryGetValue(set, out DeterministicState? nextState))
                 {
-                    nextState = new DeterministicState();
+                    nextState = new DeterministicState(transaction.Value);
                     map.Add(set, nextState);
                 }
 
diff --git a/CanonSharp.Common/LexicalAnalyzer/LexicalScanner.cs b/CanonSharp.Common/LexicalAnalyzer/LexicalScanner.cs
new file mode 100644
index 0000000..caa8c2b
--- /dev/null
+++ b/CanonSharp.Common/LexicalAnalyzer/LexicalScanner.cs
@@ -0,0 +1,92 @@
+using System.Diagnostics.CodeAnalysis;
+using CanonSharp.Common.Abstractions;
+
+namespace CanonSharp.Common.LexicalAnalyzer;
+
+public class LexicalScanner(
+    DeterministicState startState,
+    Dictionary<DeterministicState, LexicalToken> finalStateMap,
+    HashSet<LexicalToken> skippedTokens,
+    ISourceReader reader)
+{
+    private readonly DeterministicState _startState = startState;
+
+    private readonly List<char> _readHistory = [];
+
+    private DeterministicState _currentState = startState;
+
+    public bool TryRead([NotNullWhen(true)] out LexicalToken? token)
+    {
+        while (TryReadInternal(out token))
+        {
+            if (!skippedTokens.Contains(token))
+            {
+                return true;
+            }
+        }
+
+        return false;
+    }
+
+    private bool TryReadInternal([NotNullWhen(true)] out LexicalToken? token)
+    {
+        while (reader.TryPeek(out char c))
+        {
+            if (_currentState.Transaction.TryGetValue(c, out DeterministicState? nextState))
+            {
+                // 可以迁移到下一个状态
+                _currentState = nextState;
+                _readHistory.Add(reader.Read());
+            }
+            else
+            {
+                // 无法迁移到下一个状态
+                if (!finalStateMap.TryGetValue(_currentState, out LexicalToken? possibleToken))
+                {
+                    throw new InvalidOperationException();
+                }
+
+                // 当前状态是终止状态
+                token = new LexicalToken(possibleToken, new string(_readHistory.ToArray()));
+
+                // 重置状态
+                _readHistory.Clear();
+                _currentState = _startState;
+                return true;
+            }
+        }
+
+        // 当前状态是终止状态
+        if (finalStateMap.TryGetValue(_currentState, out LexicalToken? possibleToken2))
+        {
+            token = new LexicalToken(possibleToken2, new string(_readHistory.ToArray()));
+
+            _readHistory.Clear();
+            _currentState = _startState;
+            return true;
+        }
+
+        if (!_currentState.Equals(_startState))
+        {
+            throw new InvalidOperationException();
+        }
+
+        token = null;
+        return false;
+    }
+
+    public static LexicalScannerBuilder CreateDefaultBuilder()
+    {
+        LexicalScannerBuilder builder = new();
+
+        builder.DefineToken(LexicalToken.LineBreaker);
+        builder.DefineToken(LexicalToken.WhiteSpace);
+
+        builder.AddSkippedToken(LexicalToken.LineBreaker);
+        builder.AddSkippedToken(LexicalToken.WhiteSpace);
+
+        return builder;
+    }
+
+    public static LexicalScannerBuilder CreateEmptyBuilder() => new();
+}
diff --git a/CanonSharp.Common/LexicalAnalyzer/LexicalScannerBuilder.cs b/CanonSharp.Common/LexicalAnalyzer/LexicalScannerBuilder.cs
new file mode 100644
index 0000000..5cdf402
--- /dev/null
+++ b/CanonSharp.Common/LexicalAnalyzer/LexicalScannerBuilder.cs
@@ -0,0 +1,62 @@
+using CanonSharp.Common.Abstractions;
+
+namespace CanonSharp.Common.LexicalAnalyzer;
+
+public class LexicalScannerBuilder
+{
+    private readonly Dictionary<NondeterministicState, LexicalToken> _finalStateMap = [];
+    private readonly List<NondeterministicFiniteAutomation> _nondeterministicFiniteAutomations = [];
+    private readonly HashSet<LexicalToken> _skippedTokens = [];
+
+    internal LexicalScannerBuilder()
+    {
+
+    }
+
+    public void DefineToken(LexicalToken token)
+    {
+        NondeterministicFiniteAutomation automation = token.Expression.Convert2Nfa();
+        _nondeterministicFiniteAutomations.Add(automation);
+
+        foreach (NondeterministicState state in automation.FinalStates)
+        {
+            _finalStateMap.Add(state, token);
+        }
+    }
+
+    public void AddSkippedToken(LexicalToken token) => _skippedTokens.Add(token);
+
+    public LexicalScanner Build(ISourceReader reader)
+    {
+        NondeterministicFiniteAutomation finaAutomation = Combine();
+        DeterministicFiniteAutomation deterministicFiniteAutomation =
+            DeterministicFiniteAutomation.Create(finaAutomation);
+
+        Dictionary<DeterministicState, LexicalToken> finalTokenMap = [];
+
+        foreach (DeterministicState state in deterministicFiniteAutomation.FinalStates)
+        {
+            finalTokenMap.Add(state, state.Closure
+                .Where(s => _finalStateMap.ContainsKey(s))
+                .Select(s => _finalStateMap[s])
+                .OrderByDescending(t => t.Priority)
+                .First());
+        }
+
+        return new LexicalScanner(deterministicFiniteAutomation.Start, finalTokenMap, _skippedTokens, reader);
+    }
+
+    private NondeterministicFiniteAutomation Combine()
+    {
+        NondeterministicState head = new();
+        NondeterministicFiniteAutomation result = new(head, []);
+
+        foreach (NondeterministicFiniteAutomation automation in _nondeterministicFiniteAutomations)
+        {
+            head.AddTransaction(EmptyChar.Empty, automation.Start);
+            result.FinalStates.UnionWith(automation.FinalStates);
+        }
+
+        return result;
+    }
+}
diff --git a/CanonSharp.Common/LexicalAnalyzer/LexicalToken.cs b/CanonSharp.Common/LexicalAnalyzer/LexicalToken.cs
new file mode 100644
index 0000000..e6be9eb
--- /dev/null
+++ b/CanonSharp.Common/LexicalAnalyzer/LexicalToken.cs
@@ -0,0 +1,56 @@
+using System.Globalization;
+
+namespace CanonSharp.Common.LexicalAnalyzer;
+
+public class LexicalToken : IEquatable<LexicalToken>
+{
+    private readonly Guid _tokenId;
+
+    public RegularExpression Expression { get; }
+
+    public int Priority { get; }
+
+    public LexicalToken(RegularExpression expression, int priority)
+    {
+        _tokenId = Guid.NewGuid();
+        Expression = expression;
+        Priority = priority;
+        LiteralValue = string.Empty;
+    }
+
+    internal LexicalToken(LexicalToken definition, string literalValue)
+    {
+        _tokenId = definition._tokenId;
+        Expression = definition.Expression;
+        Priority = definition.Priority;
+        LiteralValue = literalValue;
+    }
+
+    public string LiteralValue { get; }
+
+    public bool Equals(LexicalToken? other) => other is not null && _tokenId == other._tokenId;
+
+    public override bool Equals(object? obj) => obj is LexicalToken other && Equals(other);
+
+    public override int GetHashCode() => _tokenId.GetHashCode();
+
+    public static bool operator ==(LexicalToken a, LexicalToken b) => a.Equals(b);
+
+    public static bool operator !=(LexicalToken a, LexicalToken b) => !(a == b);
+
+    /// <summary>
+    /// 匹配所有的空白字符
+    /// </summary>
+    public static readonly LexicalToken WhiteSpace = new(
+        RegularExpression.Alternate(
+            RegularExpression.CharSetOf(c => char.GetUnicodeCategory(c) == UnicodeCategory.SpaceSeparator),
+            RegularExpression.CharSetOf("\u0009\u000B\u000C")), int.MinValue);
+
+    /// <summary>
+    /// 匹配所有的换行符
+    /// </summary>
+    public static readonly LexicalToken LineBreaker = new(
+        RegularExpression.Alternate(
+            RegularExpression.CharSetOf("\u000D\u000A\u0085\u2028\u2029"),
+            RegularExpression.String("\r\n")), int.MinValue);
+}
diff --git a/CanonSharp.Common/LexicalAnalyzer/RegularExpression.cs b/CanonSharp.Common/LexicalAnalyzer/RegularExpression.cs
index e051535..79a98d8 100644
--- a/CanonSharp.Common/LexicalAnalyzer/RegularExpression.cs
+++ b/CanonSharp.Common/LexicalAnalyzer/RegularExpression.cs
@@ -4,17 +4,76 @@ public abstract class RegularExpression
 {
     public abstract NondeterministicFiniteAutomation Convert2Nfa();
 
+    /// <summary>
+    /// 匹配空字符串
+    /// </summary>
     public static RegularExpression Empty => new EmptyExpression();
 
+    /// <summary>
+    /// 匹配单个字符
+    /// c
+    /// </summary>
+    /// <param name="c"></param>
+    /// <returns></returns>
     public static RegularExpression Single(char c) => new SymbolExpression(c);
 
+    /// <summary>
+    /// left|right
+    /// </summary>
+    /// <param name="left"></param>
+    /// <param name="right"></param>
+    /// <returns></returns>
     public static RegularExpression Alternate(RegularExpression left, RegularExpression right) =>
         new AlternationExpression(left, right);
 
+    /// <summary>
+    /// left-right
+    /// </summary>
+    /// <param name="first"></param>
+    /// <param name="second"></param>
+    /// <returns></returns>
     public static RegularExpression Concatenate(RegularExpression first, RegularExpression second) =>
         new ConcatenationExpression(first, second);
 
+    /// <summary>
+    /// inner*
+    /// </summary>
+    /// <param name="inner"></param>
+    /// <returns></returns>
     public static RegularExpression Kleene(RegularExpression inner) => new KleeneExpression(inner);
+
+    /// <summary>
+    /// value
+    /// </summary>
+    /// <param name="value"></param>
+    /// <returns></returns>
+    public static RegularExpression String(string value) => new StringExpression(value);
+
+    public static RegularExpression CharSetOf(string value) => new CharSetExpression(value.ToCharArray());
+
+    public static RegularExpression CharSetOf(Func<char, bool> predicate)
+        => new CharSetExpression(Iterate(char.MinValue, char.MaxValue).Where(predicate).ToArray());
+
+    /// <summary>
+    /// [a-b]
+    /// </summary>
+    /// <param name="a"></param>
+    /// <param name="b"></param>
+    /// <returns></returns>
+    public static RegularExpression Range(char a, char b) => new CharSetExpression(Iterate(a, b).ToArray());
+
+    private static IEnumerable<char> Iterate(char a, char b)
+    {
+        for (char c = a; c <= b; c++)
+        {
+            if (c == char.MaxValue)
+            {
+                yield break;
+            }
+
+            yield return c;
+        }
+    }
 }
 
 public class EmptyExpression : RegularExpression
@@ -107,3 +166,59 @@ public class KleeneExpression(RegularExpression inner) : RegularExpression
         return new NondeterministicFiniteAutomation(final, [final]);
     }
 }
+
+public class CharSetExpression : RegularExpression
+{
+    public char[] Set { get; }
+
+    public CharSetExpression(Span<char> set)
+    {
+        if (set.Length == 0)
+        {
+            throw new InvalidOperationException();
+        }
+
+        Set = set.ToArray();
+    }
+
+    public override NondeterministicFiniteAutomation Convert2Nfa()
+    {
+        NondeterministicState start = new();
+        NondeterministicState final = new();
+
+        foreach (char c in Set)
+        {
+            start.AddTransaction(new EmptyChar(c), final);
+        }
+
+        return new NondeterministicFiniteAutomation(start, [final]);
+    }
+}
+
+public class StringExpression : RegularExpression
+{
+    public string Word { get; }
+
+    public StringExpression(string word)
+    {
+        if (string.IsNullOrEmpty(word))
+        {
+            throw new InvalidOperationException();
+        }
+
+        Word = word;
+    }
+
+    public override NondeterministicFiniteAutomation Convert2Nfa()
+    {
+        NondeterministicState start = new();
+        NondeterministicState final = Word.Aggregate(start, (state, c) =>
+        {
+            NondeterministicState next = new();
+            state.AddTransaction(new EmptyChar(c), next);
+            return next;
+        });
+
+        return new NondeterministicFiniteAutomation(start, [final]);
+    }
+}
diff --git a/CanonSharp.Common/Reader/SourceReader.cs b/CanonSharp.Common/Reader/SourceReader.cs
new file mode 100644
index 0000000..0c2b818
--- /dev/null
+++ b/CanonSharp.Common/Reader/SourceReader.cs
@@ -0,0 +1,78 @@
+using CanonSharp.Common.Abstractions;
+
+namespace CanonSharp.Common.Reader;
+
+public class SourceReader : ISourceReader
+{
+    private readonly StreamReader _reader;
+    private char? _lookAhead;
+
+    public SourceReader(string filename)
+    {
+        FileInfo source = new(filename);
+
+        if (!source.Exists)
+        {
+            throw new InvalidOperationException();
+        }
+
+        _reader = new StreamReader(filename);
+    }
+
+    public char Read()
+    {
+        if (_lookAhead.HasValue)
+        {
+            char result = _lookAhead.Value;
+            _lookAhead = null;
+            return result;
+        }
+
+        if (!TryFetchChar(out char c))
+        {
+            throw new InvalidOperationException();
+        }
+
+        return c;
+    }
+
+    public bool TryPeek(out char c)
+    {
+        if (_lookAhead.HasValue)
+        {
+            c = _lookAhead.Value;
+            return true;
+        }
+
+        if (!TryFetchChar(out c))
+        {
+            return false;
+        }
+
+        _lookAhead = c;
+        return true;
+    }
+
+    private readonly char[] _buffer = new char[1024];
+    private int _length;
+    private int _count;
+
+    private bool TryFetchChar(out char c)
+    {
+        if (_length == _count)
+        {
+            _length = _reader.Read(_buffer);
+            _count = 0;
+        }
+
+        if (_length == 0)
+        {
+            c = char.MinValue;
+            return false;
+        }
+
+        c = _buffer[_count];
+        _count += 1;
+        return true;
+    }
+}
diff --git a/CanonSharp.Common/Reader/StringReader.cs b/CanonSharp.Common/Reader/StringReader.cs
new file mode 100644
index 0000000..e7493ef
--- /dev/null
+++ b/CanonSharp.Common/Reader/StringReader.cs
@@ -0,0 +1,33 @@
+using CanonSharp.Common.Abstractions;
+
+namespace CanonSharp.Common.Reader;
+
+public class StringReader(string source) : ISourceReader
+{
+    private int _pos;
+
+    public char Read()
+    {
+        if (_pos >= source.Length)
+        {
+            throw new InvalidOperationException();
+        }
+
+        char result = source[_pos];
+        _pos += 1;
+        return result;
+
+    }
+
+    public bool TryPeek(out char c)
+    {
+        if (_pos < source.Length)
+        {
+            c = source[_pos];
+            return true;
+        }
+
+        c = char.MinValue;
+        return false;
+    }
+}
diff --git a/CanonSharp.Tests/LexicalAnalyzerTests/ReaderTests.cs b/CanonSharp.Tests/LexicalAnalyzerTests/ReaderTests.cs
new file mode 100644
index 0000000..01b6df7
--- /dev/null
+++ b/CanonSharp.Tests/LexicalAnalyzerTests/ReaderTests.cs
@@ -0,0 +1,25 @@
+using CanonSharp.Common.Abstractions;
+using StringReader = CanonSharp.Common.Reader.StringReader;
+
+namespace CanonSharp.Tests.LexicalAnalyzerTests;
+
+public class ReaderTests
+{
+    [Fact]
+    public void StringReaderTest()
+    {
+        StringReader reader = new("ab");
+
+        Assert.True(reader.TryPeek(out char c));
+        Assert.Equal('a', c);
+        Assert.True(reader.TryPeek(out c));
+        Assert.Equal('a', c);
+        Assert.Equal('a', reader.Read());
+        Assert.True(reader.TryPeek(out c));
+        Assert.Equal('b', c);
+        Assert.True(reader.TryPeek(out c));
+        Assert.Equal('b', c);
+        Assert.Equal('b', reader.Read());
+        Assert.False(reader.TryPeek(out c));
+    }
+}
diff --git a/CanonSharp.Tests/LexicalAnalyzerTests/RegularExpressionTests.cs b/CanonSharp.Tests/LexicalAnalyzerTests/RegularExpressionTests.cs
index 8fb8820..da1b49e 100644
--- a/CanonSharp.Tests/LexicalAnalyzerTests/RegularExpressionTests.cs
+++ b/CanonSharp.Tests/LexicalAnalyzerTests/RegularExpressionTests.cs
@@ -43,6 +43,15 @@ public class RegularExpressionTests
             s => s.Transactions.ContainsKey(new EmptyChar('a')));
     }
 
+    [Fact]
+    public void RangeTest()
+    {
+        RegularExpression expression = RegularExpression.Range('a', 'z');
+        NondeterministicFiniteAutomation nfa = expression.Convert2Nfa();
+
+        Assert.Equal(26, nfa.Start.Transactions.Count);
+    }
+
     [Fact]
     public void ConvertTest()
     {
@@ -74,4 +83,22 @@ public class RegularExpressionTests
 
         Assert.Equal('a', map[new NondeterministicStateSet([key2, key1])]);
     }
+
+    [Fact]
+    public void PrefixConvertTest()
+    {
+        RegularExpression expression = RegularExpression.Alternate(
+            RegularExpression.String("string"),
+            RegularExpression.String("string1"));
+
+        NondeterministicFiniteAutomation nfa = expression.Convert2Nfa();
+        DeterministicFiniteAutomation.Create(nfa);
+    }
+
+    [Fact]
+    public void WhiteSpaceConvertTest()
+    {
+        NondeterministicFiniteAutomation nfa = LexicalToken.WhiteSpace.Expression.Convert2Nfa();
+        DeterministicFiniteAutomation.Create(nfa);
+    }
 }
diff --git a/CanonSharp.Tests/LexicalAnalyzerTests/ScanTests.cs b/CanonSharp.Tests/LexicalAnalyzerTests/ScanTests.cs
new file mode 100644
index 0000000..a929b90
--- /dev/null
+++ b/CanonSharp.Tests/LexicalAnalyzerTests/ScanTests.cs
@@ -0,0 +1,71 @@
+using CanonSharp.Common.LexicalAnalyzer;
+using StringReader = CanonSharp.Common.Reader.StringReader;
+
+namespace CanonSharp.Tests.LexicalAnalyzerTests;
+
+public class ScanTests
+{
+    [Fact]
+    public void ScanTest1()
+    {
+        LexicalScannerBuilder builder = LexicalScanner.CreateEmptyBuilder();
+
+        LexicalToken token1 = new(RegularExpression.String("ab"), 1);
+        builder.DefineToken(token1);
+
+        StringReader reader = new("ab");
+        LexicalScanner scanner = builder.Build(reader);
+
+        Assert.True(scanner.TryRead(out LexicalToken? result));
+        Assert.Equal(token1, result);
+        Assert.Equal("ab", result.LiteralValue);
+    }
+
+    [Fact]
+    public void ScanTest2()
+    {
+        LexicalScannerBuilder builder = LexicalScanner.CreateDefaultBuilder();
+
+        LexicalToken stringKeyword = new(RegularExpression.String("string"), 100);
+        LexicalToken periodDelimiter = new(RegularExpression.Single('.'), 100);
+        LexicalToken semiColonDelimiter = new(RegularExpression.Single(';'), 100);
+        LexicalToken identifier = new(RegularExpression.Concatenate(RegularExpression.Range('a', 'z'),
+            RegularExpression.Kleene(RegularExpression.Range('a', 'z'))), 0);
+        LexicalToken assigner = new(RegularExpression.String(":="), 100);
+        builder.DefineToken(stringKeyword);
+        builder.DefineToken(periodDelimiter);
+        builder.DefineToken(semiColonDelimiter);
+        builder.DefineToken(identifier);
+        builder.DefineToken(assigner);
+
+        StringReader reader = new("""
+                                  string value := origin;
+                                  string abc := value.
+                                  """);
+        LexicalScanner scanner = builder.Build(reader);
+        Validate(scanner, [
+            stringKeyword,
+            identifier,
+            assigner,
+            identifier,
+            semiColonDelimiter,
+            stringKeyword,
+            identifier,
+            assigner,
+            identifier,
+            periodDelimiter
+        ]);
+
+        Assert.False(scanner.TryRead(out _));
+    }
+
+    private static void Validate(LexicalScanner scanner, IEnumerable<LexicalToken> expectedTokens)
+    {
+        foreach (LexicalToken token in expectedTokens)
+        {
+            Assert.True(scanner.TryRead(out LexicalToken? outToken));
+            Assert.NotNull(outToken);
+            Assert.Equal(token, outToken);
+        }
+    }
+}