Tree

- Correct visitation stratergy

source/niknaks/containers.d

@@ -666,27 +666,47 @@ public class Tree(T)
         TouchStratergy!(T) touch = toDelegate(&Nothing!(T))
     )
     {
-        T[] collected;
-        foreach(Tree!(T) child; this.children)
+        version(unittest)
         {
-            if(strat(child))
+            writeln("dfs entry: ", this);
+        }
+        
+        T[] collected;
+        scope(exit)
+        {
+            version(unittest)
             {
-                // Touch
-                touch(child);
-
-                // Visit
-                collected ~= child.dfs(strat);
+                writeln("leaving node ", this, " with collected ", collected);
             }
         }
 
-        if(strat(this))
-        {
-            // Touch
-            touch(this);
+        // Touch
+        touch(this); // root[x]
 
-            // "Visit"
-            collected ~= this.value;
+        foreach(Tree!(T) child; this.children) // subtree[x], 
+        {
+            if(strat(child))
+            {
+                version(unittest)
+                {
+                    writeln("dfs, strat good for child: ", child);
+                }
+
+                // Visit
+                collected ~= child.dfs(strat, touch);
+            }
+            else
+            {
+                version(unittest)
+                {
+                    writeln("dfs, strat ignored for child: ", child);
+                }
+            }
         }
+
+        // "Visit"
+        collected ~= this.value;
+        
         
         return collected;
     }
@@ -727,4 +747,56 @@ unittest
 
     string[] result = treeOfStrings.dfs(strat, touch);
     writeln("dfs: ", result);
+}
+
+public class VisitationTree(T) : Tree!(T)
+{
+    private bool visisted;    
+
+    this(T value)
+    {
+        super(value);
+    }
+
+    public T[] linearize()
+    {
+        return dfs(toDelegate(&_shouldVisit), toDelegate(&_touch));
+    }
+
+    private static bool _shouldVisit(Tree!(T) tnode)
+    {
+        VisitationTree!(T) vnode = cast(VisitationTree!(T))tnode;
+        return vnode && !vnode.isVisited();
+    }
+
+    private static void _touch(Tree!(T) tnode)
+    {
+        VisitationTree!(T) vnode = cast(VisitationTree!(T))tnode;
+        if(vnode)
+        {
+            vnode.mark();
+        }
+    }
+
+    private void mark()
+    {
+        this.visisted = true;
+    }
+    
+    private bool isVisited()
+    {
+        return this.visisted;
+    }
+}
+
+unittest
+{
+    VisitationTree!(string) root = new VisitationTree!(string)("root");
+
+    VisitationTree!(string) thing = new VisitationTree!(string)("subtree");
+    root.appendNode(thing);
+    thing.appendNode(root);
+
+    writeln(root.linearize());
+
 }