fix errors in interpreter. add a enumerator for tree. working on tree optimizer

StgSharp.RegularAnalysis/Abstraction/ISyntaxNode.cs

@@ -1,9 +1,9 @@
-//-----------------------------------------------------------------------
+//-----------------------------------------------------------------------
 // -----------------------------------------------------------------------
 // file="ISyntaxNode"
 // Project: StgSharp
-// AuthorGroup: Nitload Space
-// Copyright (c) Nitload Space. All rights reserved.
+// AuthorGroup: Nitload
+// Copyright (c) Nitload. All rights reserved.
 //     
 // Permission is hereby granted, free of charge, to any person obtaining a copy
 // of this software and associated documentation files (the "Software"), to deal
@@ -31,11 +31,13 @@ using System;
 using System.Collections;
 using System.Collections.Generic;
 using System.Reflection;
+using System.Runtime.CompilerServices;
 using System.Text;
 
 namespace StgSharp.RegularAnalysis.Abstraction
 {
-    public interface ISyntaxNode<TNode, TLabel> where TNode: ISyntaxNode<TNode, TLabel> where TLabel: unmanaged
+    public interface ISyntaxNode<TNode, TLabel> where TNode : ISyntaxNode<TNode, TLabel>
+        where TLabel : unmanaged
     {
 
         long NodeFlag { get; }
@@ -60,9 +62,21 @@ namespace StgSharp.RegularAnalysis.Abstraction
 
         protected internal int EnumState { get; set; }
 
-        void AppendNode(TNode nextToken);
+        void AppendNode(
+             TNode nextToken
+        );
 
-        void PrependNode(TNode previousNode);
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        public static virtual bool IsNullOrEmpty(
+                                   TNode node
+        )
+        {
+            return node is null || node.Equals(TNode.Empty);
+        }
+
+        void PrependNode(
+             TNode previousNode
+        );
 
     }
 }