Some of the basics of the grammar API

LLama/Native/LLamaGrammarElement.cs

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+using System.Runtime.InteropServices;
+
+namespace LLama.Native
+{
+    /// <summary>
+    /// grammar element type
+    /// </summary>
+    public enum LLamaGrammarElementType
+    {
+        /// <summary>
+        /// end of rule definition
+        /// </summary>
+        END = 0,
+
+        /// <summary>
+        /// start of alternate definition for rule
+        /// </summary>
+        ALT = 1,
+
+        /// <summary>
+        /// non-terminal element: reference to rule
+        /// </summary>
+        RULE_REF = 2,
+
+        /// <summary>
+        /// terminal element: character (code point)
+        /// </summary>
+        CHAR = 3,
+
+        /// <summary>
+        /// inverse char(s) ([^a], [^a-b] [^abc])
+        /// </summary>
+        CHAR_NOT = 4,
+
+        /// <summary>
+        /// modifies a preceding LLAMA_GRETYPE_CHAR or LLAMA_GRETYPE_CHAR_ALT to
+        /// be an inclusive range ([a-z])
+        /// </summary>
+        CHAR_RNG_UPPER = 5,
+
+        /// <summary>
+        /// modifies a preceding LLAMA_GRETYPE_CHAR or
+        /// LLAMA_GRETYPE_CHAR_RNG_UPPER to add an alternate char to match ([ab], [a-zA])
+        /// </summary>
+        CHAR_ALT = 6,
+    };
+
+    /// <summary>
+    /// An element of a grammar
+    /// </summary>
+    [StructLayout(LayoutKind.Sequential)]
+    public struct LLamaGrammarElement
+    {
+        /// <summary>
+        /// The type of this element
+        /// </summary>
+        public LLamaGrammarElementType Type;
+
+        /// <summary>
+        /// Unicode code point or rule ID
+        /// </summary>
+        public uint Value;
+    }
+}

LLama/Native/NativeApi.Grammar.cs

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+using System;
+using System.Runtime.InteropServices;
+
+namespace LLama.Native
+{
+    using llama_token = Int32;
+
+	public unsafe partial class NativeApi
+    {
+		//todo: LLAMA_API struct llama_grammar * llama_grammar_init(const llama_grammar_element** rules, size_t n_rules,size_t start_rule_index);
+
+		/// <summary>
+		/// Free all memory from the given SafeLLamaGrammarHandle
+		/// </summary>
+		/// <param name="grammar"></param>
+		[DllImport(libraryName, CallingConvention = CallingConvention.Cdecl)]
+		public static extern void llama_grammar_free(IntPtr grammar);
+
+		/// <summary>
+		/// Apply constraints from grammar
+		/// </summary>
+		/// <param name="ctx"></param>
+		/// <param name="candidates"></param>
+		/// <param name="grammar"></param>
+		[DllImport(libraryName, CallingConvention = CallingConvention.Cdecl)]
+        public static extern void llama_sample_grammar(SafeLLamaContextHandle ctx, ref LLamaTokenDataArrayNative candidates, SafeLLamaGrammarHandle grammar);
+
+		/// <summary>
+		/// Accepts the sampled token into the grammar
+		/// </summary>
+		/// <param name="ctx"></param>
+		/// <param name="grammar"></param>
+		/// <param name="token"></param>
+		[DllImport(libraryName, CallingConvention = CallingConvention.Cdecl)]
+        public static extern void llama_grammar_accept_token(SafeLLamaContextHandle ctx, SafeLLamaGrammarHandle grammar, llama_token token);
+	}
+}

LLama/Native/SafeLLamaGrammarHandle.cs

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+using System;
+
+namespace LLama.Native
+{
+    /// <summary>
+    /// A safe reference to a `llama_grammar`
+    /// </summary>
+    public class SafeLLamaGrammarHandle
+        : SafeLLamaHandleBase
+    {
+        internal SafeLLamaGrammarHandle(IntPtr handle)
+            : base(handle)
+        {
+        }
+
+        /// <inheritdoc />
+        protected override bool ReleaseHandle()
+        {
+            NativeApi.llama_grammar_free(handle);
+            SetHandle(IntPtr.Zero);
+            return true;
+        }
+    }
+}