feat: 添加语法分析基类抽象 (#8)

增加语法分析基类和状态转换接口抽象，为直接生成语法分析器做准备，同时也提前释放一些大对象，降低内存消耗。

Reviewed-on: PostGuard/Canon#8

Canon.Core/Abstractions/GrammarParseBase.cs

@@ -0,0 +1,70 @@
+using Canon.Core.GrammarParser;
+using Canon.Core.LexicalParser;
+
+namespace Canon.Core.Abstractions;
+
+/// <summary>
+/// 语法分析器接口
+/// </summary>
+public abstract class GrammarParserBase
+{
+    public abstract ITransformer BeginTransformer { get; }
+
+    public abstract NonTerminator Begin { get; }
+
+    public SyntaxNode Analyse(IEnumerable<SemanticToken> tokens)
+    {
+        Stack<AnalyseState> stack = [];
+        stack.Push(new AnalyseState(BeginTransformer, new SyntaxNode(SemanticToken.End)));
+
+        using IEnumerator<SemanticToken> enumerator = tokens.GetEnumerator();
+        if (!enumerator.MoveNext())
+        {
+            throw new InvalidOperationException("Input token list is empty");
+        }
+
+        while (true)
+        {
+            AnalyseState top = stack.Peek();
+
+            // 首先尝试进行归约
+            if (top.State.ReduceTable.TryGetValue(enumerator.Current, out ReduceInformation? information))
+            {
+                if (information.Left == Begin)
+                {
+                    // 如果是归约到起始符
+                    // 那么就直接返回不继续进行归约
+                    return top.Node;
+                }
+
+                SyntaxNode newNode = new(information.Left.Type);
+                for (int i = 0; i < information.Length; i++)
+                {
+                    newNode.Children.Add(stack.Pop().Node);
+                }
+
+                stack.Push(new AnalyseState(stack.Peek().State.ShiftTable[information.Left],
+                    newNode));
+                continue;
+            }
+
+            // 如果没有成功归约就进行移进
+            if (top.State.ShiftTable.TryGetValue(enumerator.Current, out ITransformer? next))
+            {
+                stack.Push(new AnalyseState(next, new SyntaxNode(enumerator.Current)));
+                if (enumerator.MoveNext())
+                {
+                    continue;
+                }
+                else
+                {
+                    throw new InvalidOperationException("Run out of token but not accept");
+                }
+            }
+
+            throw new InvalidOperationException("Failed to analyse input grammar");
+        }
+    }
+
+    private record AnalyseState(ITransformer State, SyntaxNode Node);
+}

Canon.Core/Abstractions/ITransformer.cs

@@ -0,0 +1,26 @@
+using Canon.Core.GrammarParser;
+
+namespace Canon.Core.Abstractions;
+
+/// <summary>
+/// 进行归约需要的信息
+/// </summary>
+/// <param name="Length">归约的长度</param>
+/// <param name="Left">归约得到的左部符号</param>
+public record ReduceInformation(int Length, NonTerminator Left);
+
+/// <summary>
+/// 状态的各种迁移信息
+/// </summary>
+public interface ITransformer
+{
+    /// <summary>
+    /// 进行移进的信息
+    /// </summary>
+    public IDictionary<TerminatorBase, ITransformer> ShiftTable { get; }
+
+    /// <summary>
+    /// 进行归约的信息
+    /// </summary>
+    public IDictionary<Terminator, ReduceInformation> ReduceTable { get; }
+}