M html.go → html.go

@@ -1100,7 +1100,7 @@ r.out(w, []byte{'\n'})
 	}
 }
 
-func (r *HTML) RenderNode(w io.Writer, node *Node, entering bool) {
+func (r *HTML) RenderNode(w io.Writer, node *Node, entering bool) WalkStatus {
 	attrs := []string{}
 	switch node.Type {
 	case Text:
@@ -1392,6 +1392,7 @@ }
 	default:
 		panic("Unknown node type " + node.Type.String())
 	}
+	return GoToNext
 }
 
 func (r *HTML) writeDocumentHeader(w *bytes.Buffer, sr *SPRenderer) {
@@ -1447,7 +1448,7 @@ //println("render_Blackfriday")
 	//dump(ast)
 	// Run Smartypants if it's enabled or simply escape text if not
 	sr := NewSmartypantsRenderer(r.extensions)
-	ast.Walk(func(node *Node, entering bool) {
+	ast.Walk(func(node *Node, entering bool) WalkStatus {
 		if node.Type == Text {
 			if r.extensions&Smartypants != 0 {
 				node.Literal = sr.Process(node.Literal)
@@ -1455,11 +1456,12 @@ } else {
 				node.Literal = esc(node.Literal, false)
 			}
 		}
+		return GoToNext
 	})
 	var buff bytes.Buffer
 	r.writeDocumentHeader(&buff, sr)
-	ast.Walk(func(node *Node, entering bool) {
-		r.RenderNode(&buff, node, entering)
+	ast.Walk(func(node *Node, entering bool) WalkStatus {
+		return r.RenderNode(&buff, node, entering)
 	})
 	r.writeDocumentFooter(&buff)
 	return buff.Bytes()

M markdown.go → markdown.go

@@ -452,12 +452,13 @@ for p.tip != nil {
 		p.finalize(p.tip)
 	}
 	// Walk the tree again and process inline markdown in each block
-	p.doc.Walk(func(node *Node, entering bool) {
+	p.doc.Walk(func(node *Node, entering bool) WalkStatus {
 		if node.Type == Paragraph || node.Type == Header || node.Type == TableCell {
 			p.currBlock = node
 			p.inline(node.content)
 			node.content = nil
 		}
+		return GoToNext
 	})
 	p.parseRefsToAST()
 	p.generateTOC()
@@ -477,7 +478,7 @@ var listNode *Node
 	var lastItem *Node
 	headerCount := 0
 	var currentLevel uint32
-	p.doc.Walk(func(node *Node, entering bool) {
+	p.doc.Walk(func(node *Node, entering bool) WalkStatus {
 		if entering && node.Type == Header {
 			if node.Level > currentLevel {
 				currentLevel++
@@ -504,6 +505,7 @@ anchorNode.Destination = []byte("#" + node.HeaderID)
 			lastItem.appendChild(anchorNode)
 			anchorNode.appendChild(text(node.FirstChild.Literal))
 		}
+		return GoToNext
 	})
 	firstChild := p.doc.FirstChild
 	// Insert TOC only if there is anything to insert
@@ -558,12 +560,13 @@ above := block.Parent
 	finalizeList(block)
 	p.tip = above
 	finalizeHtmlBlock(p.addBlock(HTMLBlock, []byte("</div>")))
-	block.Walk(func(node *Node, entering bool) {
+	block.Walk(func(node *Node, entering bool) WalkStatus {
 		if node.Type == Paragraph || node.Type == Header {
 			p.currBlock = node
 			p.inline(node.content)
 			node.content = nil
 		}
+		return GoToNext
 	})
 }
 

M node.go → node.go

@@ -230,17 +230,35 @@ }
 	return false
 }
 
+// WalkStatus allows NodeVisitor to have some control over the tree traversal.
+// It is returned from NodeVisitor and different values allow Node.Walk to
+// decide which node to go to next.
+type WalkStatus int
+
+const (
+	GoToNext     WalkStatus = iota // The default traversal of every node.
+	SkipChildren                   // Skips all children of current node.
+	Terminate                      // Terminates the traversal.
+)
+
 // NodeVisitor is a callback to be called when traversing the syntax tree.
 // Called twice for every node: once with entering=true when the branch is
 // first visited, then with entering=false after all the children are done.
-type NodeVisitor func(node *Node, entering bool)
+type NodeVisitor func(node *Node, entering bool) WalkStatus
 
 func (root *Node) Walk(visitor NodeVisitor) {
 	walker := NewNodeWalker(root)
 	node, entering := walker.next()
 	for node != nil {
-		visitor(node, entering)
-		node, entering = walker.next()
+		status := visitor(node, entering)
+		switch status {
+		case GoToNext:
+			node, entering = walker.next()
+		case SkipChildren:
+			node, entering = walker.resumeAt(node, false)
+		case Terminate:
+			return
+		}
 	}
 }
 
@@ -286,9 +304,10 @@ }
 	return nw.current, nw.entering
 }
 
-func (nw *NodeWalker) resumeAt(node *Node, entering bool) {
+func (nw *NodeWalker) resumeAt(node *Node, entering bool) (*Node, bool) {
 	nw.current = node
 	nw.entering = entering
+	return nw.next()
 }
 
 func dump(ast *Node) {