feat: Parser Combinator库和词法分析器 (#2)

Reviewed-on: https://git.bupt-hpc.cn/jackfiled/CanonSharp/pulls/2
Co-authored-by: jackfiled <xcrenchangjun@outlook.com>
Co-committed-by: jackfiled <xcrenchangjun@outlook.com>

CanonSharp.Combinator/Extensions/ReadStateExtensions.cs

@@ -0,0 +1,18 @@
+using CanonSharp.Combinator.Abstractions;
+
+namespace CanonSharp.Combinator.Extensions;
+
+public static class ReadStateExtensions
+{
+    public static IEnumerable<TState> AsEnumerable<TToken, TState>(this TState source)
+        where TState : IReadState<TToken, TState>
+    {
+        TState current = source;
+
+        while (current.HasValue)
+        {
+            yield return current;
+            current = current.Next;
+        }
+    }
+}