Working on tree optimizer

StgSharp.RegularAnalysis/TextRegex/RegexInterpreter.cs

@@ -174,24 +174,37 @@ namespace StgSharp.RegularAnalysis.TextRegex
         {
             // phase0: scan container and remove no parent nodes
             _tree.AllNodes.RemoveWhere(node => node.Parent == null && node != _tree.Root);
-            HashSet<RegexAstNode>.Enumerator enumerator = _tree.AllNodes.GetEnumerator();
+            TreeEnumerator<RegexAstNode, RegexElementLabel> enumerator = new TreeEnumerator<RegexAstNode, RegexElementLabel>(_tree.Root);
+            RegexAstNode current;
 
             // phase1: ALT flatten
+            // phase2: CONCAT normalize
             while (enumerator.MoveNext())
             {
-                RegexAstNode node = enumerator.Current;
-                if ((RegexElementLabel)node.NodeFlag == RegexElementLabel.ALT)
+                current = enumerator.Current;
+                if (current.EqualityTypeConvert == RegexElementLabel.ALT)
                 {
-                    RegexAstNode list = FlattenAlt(node);
-                    node.Left = list;
-                    node.Right = RegexAstNode.Empty;
+                    RegexAstNode union = FlattenAlt(current);
+                    current.Right = union;
+                    current.Left = RegexAstNode.Empty;
+                } else if (current.EqualityTypeConvert == RegexElementLabel.CONCAT) {
+                    RotateConcat(current);
                 }
             }
 
-            // phase2: ALT merge
-
-
             // phase3: CONCAT merge
+            enumerator.Reset();
+            while (enumerator.MoveNext())
+            {
+                // suppose all concat is now in normalized form,
+                // we can merge adjacent unit nodes into a single unit node with string value
+                current = enumerator.Current;
+                if (current.EqualityTypeConvert == RegexElementLabel.CONCAT) {
+                    MergeConcat(current);
+                }
+            }
+
+            // phase4: ALT union
         }
 
         private void ProcessOperator(