diff --git a/Katheryne/DefaultChatRobot.cs b/Katheryne/DefaultChatRobot.cs
index 7cac34b..f473e8a 100644
--- a/Katheryne/DefaultChatRobot.cs
+++ b/Katheryne/DefaultChatRobot.cs
@@ -12,15 +12,16 @@ public class DefaultChatRobot : IChatRobot
         _logger = logger;
     }
     
-    public string RobotName => "凯瑟琳";
+    public string RobotName => "Default";
     
     public IEnumerable<string> OnChatStart()
     {
         _logger.LogDebug("Start default chat robot.");
         return new[]
         {
-            "向着星辰与深渊！",
-            "欢迎来到冒险家协会。"
+            "坏了，被你发现默认机器人了。",
+            "使用这个粪机器人，怎么能得高分呢？",
+            "必须要出重拳！"
         };
     }
 
@@ -29,7 +30,7 @@ public class DefaultChatRobot : IChatRobot
         _logger.LogDebug("End default chat robot.");
         return new[]
         {
-            "再见，感谢您对协会做出的贡献，冒险家。"
+            "我不到啊。"
         };
     }
 
@@ -38,7 +39,7 @@ public class DefaultChatRobot : IChatRobot
         _logger.LogDebug("Robot receive message: \"{}\".", input);
         return new[]
         {
-            "暂时不支持该功能，请联系维护人员。"
+            "啊对对对。"
         };
     }
 }
\ No newline at end of file
diff --git a/Katheryne/Exceptions/GrammarException.cs b/Katheryne/Exceptions/GrammarException.cs
new file mode 100644
index 0000000..e4b9ab7
--- /dev/null
+++ b/Katheryne/Exceptions/GrammarException.cs
@@ -0,0 +1,22 @@
+namespace Katheryne.Exceptions;
+
+/// <summary>
+/// 语法中存在的错误
+/// </summary>
+public class GrammarException : Exception
+{
+    public GrammarException() : base()
+    {
+        
+    }
+
+    public GrammarException(string message) : base(message)
+    {
+        
+    }
+
+    public GrammarException(string message, Exception innerException) : base(message, innerException)
+    {
+        
+    }
+}
\ No newline at end of file
diff --git a/Katheryne/KatheryneChatRobot.cs b/Katheryne/KatheryneChatRobot.cs
new file mode 100644
index 0000000..c84e5f3
--- /dev/null
+++ b/Katheryne/KatheryneChatRobot.cs
@@ -0,0 +1,54 @@
+using Katheryne.Abstractions;
+using Katheryne.Models;
+using Katheryne.Services;
+using Microsoft.Extensions.Logging;
+using YamlDotNet.Serialization;
+
+namespace Katheryne;
+
+public class KatheryneChatRobot : IChatRobot
+{
+    private readonly ILogger<KatheryneChatRobot> _logger;
+    private readonly GrammarTree _grammarTree;
+
+    private string _currentStage;
+
+    public KatheryneChatRobot(GrammarTree grammarTree, ILogger<KatheryneChatRobot> logger, 
+        string beginStage, string robotName)
+    {
+        _logger = logger;
+
+        _grammarTree = grammarTree;
+        _currentStage = beginStage;
+        RobotName = robotName;
+    }
+    
+    public string RobotName { get; }
+    public IEnumerable<string> OnChatStart()
+    {
+        return new[]
+        {
+            _grammarTree[_currentStage]
+        };
+    }
+
+    public IEnumerable<string> OnChatStop()
+    {
+        return new[]
+        {
+            "再见。"
+        };
+    }
+
+    public IEnumerable<string> ChatNext(string input)
+    {
+        _logger.LogDebug("Receive input {} on stage {}.", input, _currentStage);
+        (_currentStage, string answer) = _grammarTree.NextStage(_currentStage, input);
+        _logger.LogDebug("Change stage to {}.", _currentStage);
+
+        return new[]
+        {
+            answer
+        };
+    }
+}
\ No newline at end of file
diff --git a/Katheryne/Models/GrammarTree.cs b/Katheryne/Models/GrammarTree.cs
new file mode 100644
index 0000000..c76d694
--- /dev/null
+++ b/Katheryne/Models/GrammarTree.cs
@@ -0,0 +1,109 @@
+using System.Text.RegularExpressions;
+using Katheryne.Exceptions;
+
+namespace Katheryne.Models;
+
+public class GrammarTree
+{
+    private readonly Dictionary<string, InnerStage> _stages = new();
+
+    public GrammarTree(LexicalModel model)
+    {
+        foreach (Stage stage in model.Stages)
+        {
+            _stages[stage.Name] = new InnerStage(stage);
+        }
+
+        if (!Validate(model))
+        {
+            throw new GrammarException("使用了未声明的阶段名");
+        }
+    }
+
+    /// <summary>
+    /// 获得下一个阶段
+    /// </summary>
+    /// <param name="currentStage">当前所在阶段</param>
+    /// <param name="input">用户输入</param>
+    /// <returns>元组，第一个参数是下一个阶段名称 第二个参数是机器人回答</returns>
+    /// <exception cref="GrammarException"></exception>
+    public (string, string) NextStage(string currentStage, string input)
+    {
+        List<InnerTransformer> transformers = _stages[currentStage].Transformers;
+
+        foreach (InnerTransformer transformer in transformers)
+        {
+            Match match = transformer.Pattern.Match(input);
+
+            if (match.Success)
+            {
+                return (_stages[transformer.NextStage].Name,
+                    _stages[transformer.NextStage].Answer);
+            }
+        }
+
+        throw new GrammarException("Failed to get next stage.");
+    }
+
+    public string this[string index] => _stages[index].Answer;
+
+    /// <summary>
+    /// 主要验证语法的两个特点
+    /// 1. 起始阶段是否被定义
+    /// 2. 每个Transformer的下一个阶段是否被定义
+    /// </summary>
+    /// <returns></returns>
+    private bool Validate(LexicalModel model)
+    {
+        if (!_stages.ContainsKey(model.BeginStageName))
+        {
+            return false;
+        }
+
+        return model.Stages.All((stage) =>
+        {
+            return stage.Transformers.All(t => _stages.ContainsKey(t.NextStageName));
+        });
+    }
+    
+    private class InnerStage
+    {
+        public string Name { get; }
+
+        public List<InnerTransformer> Transformers { get; } = new();
+        
+        public string Answer { get; }
+
+        public InnerStage(Stage stage)
+        {
+            Name = stage.Name;
+            Answer = stage.Answer;
+
+            foreach (Transformer transformer in stage.Transformers)
+            {
+                Transformers.Add(new InnerTransformer(transformer));
+            }
+        }
+    }
+    
+    private class InnerTransformer
+    {
+        public Regex Pattern { get; }
+        
+        public string NextStage { get; }
+
+        public InnerTransformer(Transformer transformer)
+        {
+            NextStage = transformer.NextStageName;
+
+            try
+            {
+                Pattern = new Regex(transformer.Pattern);
+            }
+            catch (ArgumentException e)
+            {
+                throw new GrammarException($"Failed to Parse regex:{transformer.Pattern}.", e);
+            }
+        }
+    }
+}
\ No newline at end of file
diff --git a/Katheryne/ServiceCollectionExtensions.cs b/Katheryne/ServiceCollectionExtensions.cs
new file mode 100644
index 0000000..5ad2dd0
--- /dev/null
+++ b/Katheryne/ServiceCollectionExtensions.cs
@@ -0,0 +1,14 @@
+using Katheryne.Services;
+using Microsoft.Extensions.DependencyInjection;
+
+namespace Katheryne;
+
+public static class ServiceCollectionExtensions
+{
+    public static void AddYamlDeserializerFactory(this IServiceCollection collection)
+    {
+        collection.AddSingleton<YamlDeserializerFactory>();
+        collection.AddSingleton<DefaultChatRobot>();
+        collection.AddScoped<KatheryneChatRobotFactory>();
+    }
+}
\ No newline at end of file
diff --git a/Katheryne/Services/KatheryneChatRobotFactory.cs b/Katheryne/Services/KatheryneChatRobotFactory.cs
new file mode 100644
index 0000000..dcfedd3
--- /dev/null
+++ b/Katheryne/Services/KatheryneChatRobotFactory.cs
@@ -0,0 +1,51 @@
+using Katheryne.Abstractions;
+using Katheryne.Models;
+using Microsoft.Extensions.Logging;
+using YamlDotNet.Serialization;
+
+namespace Katheryne.Services;
+
+public class KatheryneChatRobotFactory
+{
+    private readonly YamlDeserializerFactory _deserializerFactory;
+    private readonly ILogger<KatheryneChatRobotFactory> _factoryLogger;
+    private readonly ILogger<KatheryneChatRobot> _robotLogger;
+    private readonly DefaultChatRobot _defaultChatRobot;
+
+    private Grammar? _grammar;
+
+    public KatheryneChatRobotFactory(YamlDeserializerFactory deserializerFactory,
+        ILogger<KatheryneChatRobotFactory> factoryLogger,
+        ILogger<KatheryneChatRobot> robotLogger,
+        DefaultChatRobot defaultChatRobot)
+    {
+        _deserializerFactory = deserializerFactory;
+        _factoryLogger = factoryLogger;
+        _robotLogger = robotLogger;
+        _defaultChatRobot = defaultChatRobot;
+    }
+
+    public void SetGrammar(string grammarText)
+    {
+        _factoryLogger.LogInformation("Receive new grammar: {}.", grammarText);
+        IDeserializer deserializer = _deserializerFactory.GetDeserializer();
+
+        LexicalModel model = deserializer.Deserialize<LexicalModel>(grammarText);
+        _grammar = new Grammar(new GrammarTree(model), model.RobotName, model.BeginStageName);
+    }
+
+    public IChatRobot GetRobot()
+    {
+        if (_grammar is null)
+        {
+            _factoryLogger.LogDebug("Get default chat robot.");
+            return _defaultChatRobot;
+        }
+
+        _factoryLogger.LogDebug("Get chat robot: {}.", _grammar.RobotName);
+        return new KatheryneChatRobot(_grammar.GrammarTree, _robotLogger,
+            _grammar.BeginStage, _grammar.RobotName);
+    }
+
+    private record Grammar(GrammarTree GrammarTree, string RobotName, string BeginStage);
+}
\ No newline at end of file