Add LLama2 Chat Session example with a custom templator

LLama.Examples/ExampleRunner.cs

@@ -6,6 +6,7 @@ public class ExampleRunner
     private static readonly Dictionary<string, Func<Task>> Examples = new()
     {
         { "Chat Session: LLama3", LLama3ChatSession.Run },
+        { "Chat Session: LLama2", LLama2ChatSession.Run },
         { "Chat Session: History", ChatSessionWithHistory.Run },
         { "Chat Session: Role names", ChatSessionWithRoleName.Run },
         { "Chat Session: Role names stripped", ChatSessionStripRoleName.Run },

LLama.Examples/Examples/LLama2ChatSession.cs

@@ -0,0 +1,141 @@
+using LLama.Abstractions;
+using LLama.Common;
+using LLama.Sampling;
+using System.Text;
+
+namespace LLama.Examples.Examples;
+
+/// <summary>
+/// This sample shows a simple chatbot
+/// It's configured to use custom prompt template as provided by llama.cpp and supports
+/// models such as LLama 2 and Mistral Instruct
+/// </summary>
+public class LLama2ChatSession
+{
+    public static async Task Run()
+    {
+        var modelPath = UserSettings.GetModelPath();
+        var parameters = new ModelParams(modelPath)
+        {
+            Seed = 1337,
+            GpuLayerCount = 10
+        };
+
+        using var model = LLamaWeights.LoadFromFile(parameters);
+        using var context = model.CreateContext(parameters);
+        var executor = new InteractiveExecutor(context);
+
+        var chatHistoryJson = File.ReadAllText("Assets/chat-with-bob.json");
+        var chatHistory = ChatHistory.FromJson(chatHistoryJson) ?? new ChatHistory();
+
+        ChatSession session = new(executor, chatHistory);
+
+        // add custom templator 
+        session.WithHistoryTransform(new Llama2HistoryTransformer());
+
+        session.WithOutputTransform(new LLamaTransforms.KeywordTextOutputStreamTransform(
+            [model.Tokens.EndOfTurnToken ?? "User:", "�"],
+            redundancyLength: 5));
+
+        var inferenceParams = new InferenceParams
+        {
+            SamplingPipeline = new DefaultSamplingPipeline
+            {
+                Temperature = 0.6f
+            },
+
+            MaxTokens = -1, // keep generating tokens until the anti prompt is encountered
+            AntiPrompts = [model.Tokens.EndOfTurnToken ?? "User:"] // model specific end of turn string (or default)
+        };
+
+        Console.ForegroundColor = ConsoleColor.Yellow;
+        Console.WriteLine("The chat session has started.");
+
+        // show the prompt
+        Console.ForegroundColor = ConsoleColor.Green;
+        Console.Write("User> ");
+        var userInput = Console.ReadLine() ?? "";
+
+        while (userInput != "exit")
+        {
+            Console.ForegroundColor = ConsoleColor.White;
+            Console.Write("Assistant> ");
+
+            // as each token (partial or whole word is streamed back) print it to the console, stream to web client, etc
+            await foreach (
+                var text
+                in session.ChatAsync(
+                    new ChatHistory.Message(AuthorRole.User, userInput),
+                    inferenceParams))
+            {
+                Console.ForegroundColor = ConsoleColor.White;
+                Console.Write(text);
+            }
+            Console.WriteLine();
+
+            Console.ForegroundColor = ConsoleColor.Green;
+            Console.Write("User> ");
+            userInput = Console.ReadLine() ?? "";
+        }
+    }
+
+    /// <summary>
+    /// Chat History transformer for Llama 2 family.
+    /// https://huggingface.co/blog/llama2#how-to-prompt-llama-2
+    /// </summary>
+    public class Llama2HistoryTransformer : IHistoryTransform
+    {
+        public string Name => "Llama2";
+
+        /// <inheritdoc/>
+        public IHistoryTransform Clone()
+        {
+            return new Llama2HistoryTransformer();
+        }
+
+        /// <inheritdoc/>
+        public string HistoryToText(ChatHistory history)
+        {
+            //More info on template format for llama2 https://huggingface.co/blog/llama2#how-to-prompt-llama-2
+            //We don't have to insert <BOS> token for the first message, as it's done automatically by LLamaSharp.InteractExecutor and LLama.cpp
+            //See more in https://github.com/ggerganov/llama.cpp/pull/7107
+            if (history.Messages.Count == 0)
+                return string.Empty;
+
+            var builder = new StringBuilder(64 * history.Messages.Count);
+
+            int i = 0;
+            if (history.Messages[i].AuthorRole == AuthorRole.System)
+            {
+                builder.Append($"[INST] <<SYS>>\n").Append(history.Messages[0].Content.Trim()).Append("\n<</SYS>>\n");
+                i++;
+
+                if (history.Messages.Count > 1)
+                {
+                    builder.Append(history.Messages[1].Content.Trim()).Append(" [/INST]");
+                    i++;
+                }
+            }
+
+            for (; i < history.Messages.Count; i++)
+            {
+                if (history.Messages[i].AuthorRole == AuthorRole.User)
+                {
+                    builder.Append(i == 0 ? "[INST] " : "<s>[INST] ").Append(history.Messages[i].Content.Trim()).Append(" [/INST]");
+                }
+                else
+                {
+                    builder.Append(' ').Append(history.Messages[i].Content.Trim()).Append(" </s>");
+                }
+            }
+
+            return builder.ToString();
+        }
+
+        /// <inheritdoc/>
+        public ChatHistory TextToHistory(AuthorRole role, string text)
+        {
+            return new ChatHistory([new ChatHistory.Message(role, text)]);
+        }
+    }
+}

LLama.Examples/Examples/LLama3ChatSession.cs

@@ -7,7 +7,7 @@ namespace LLama.Examples.Examples;
 /// <summary>
 /// This sample shows a simple chatbot
 /// It's configured to use the default prompt template as provided by llama.cpp and supports
-/// models such as llama3, llama2, phi3, qwen1.5, etc.
+/// models such as llama3, phi3, qwen1.5, etc.
 /// </summary>
 public class LLama3ChatSession
 {
@@ -35,7 +35,7 @@ public static async Task Run()
 
         // Add a transformer to eliminate printing the end of turn tokens, llama 3 specifically has an odd LF that gets printed sometimes
         session.WithOutputTransform(new LLamaTransforms.KeywordTextOutputStreamTransform(
-            [model.Tokens.EndOfTurnToken!, "�"],
+            [model.Tokens.EndOfTurnToken ?? "User:", "�"],
             redundancyLength: 5));
 
         var inferenceParams = new InferenceParams
@@ -46,7 +46,7 @@ public static async Task Run()
             },
 
             MaxTokens = -1, // keep generating tokens until the anti prompt is encountered
-            AntiPrompts = [model.Tokens.EndOfTurnToken!] // model specific end of turn string
+            AntiPrompts = [model.Tokens.EndOfTurnToken ?? "User:"] // model specific end of turn string (or default)
         };
 
         Console.ForegroundColor = ConsoleColor.Yellow;

LLama/ChatSession.cs

@@ -428,7 +428,7 @@
         if (state.IsPromptRun)
         {
             // If the session history was added as part of new chat session history,
-            // convert the complete history includsing system message and manually added history
+            // convert the complete history including system message and manually added history
             // to a prompt that adhere to the prompt template specified in the HistoryTransform class implementation.
             prompt = HistoryTransform.HistoryToText(History);
         }
@@ -779,7 +779,7 @@
 
         return new SessionState(
             contextState,
             executorState,
             history,
             inputTransforms.ToList(),
             outputTransform,