diff --git a/avl/avl_test.go b/avl/avl_test.go
index e2680d3..07f145b 100644
--- a/avl/avl_test.go
+++ b/avl/avl_test.go
@@ -80,7 +80,7 @@ func TestIterator(t *testing.T) {
 	// 			   └── 1`
 
 	iter := avl.Iterator() // root start point
-
+	t.Error(iter.cur, spew.Sdump(iter.tstack))
 	l := []int{14, 15, 20, 21, 30}
 
 	for i := 0; iter.Prev(); i++ {
@@ -95,7 +95,7 @@ func TestIterator(t *testing.T) {
 	}
 
 	l = []int{21, 20, 15, 14, 7, 7, 6, 5, 4, 3, 2, 1}
-	t.Error(iter.cur, iter.tstack)
+	t.Error(iter.cur, spew.Sdump(iter.tstack))
 	for i := 0; iter.Next(); i++ { // cur is 30 next is 21
 		if iter.Value().(int) != l[i] {
 			t.Error(iter.Value())
diff --git a/avl/iterator.go b/avl/iterator.go
index a0a834d..d20e993 100644
--- a/avl/iterator.go
+++ b/avl/iterator.go
@@ -3,6 +3,8 @@ package avl
 import (
 	"log"
 
+	"github.com/davecgh/go-spew/spew"
+
 	"474420502.top/eson/structure/lastack"
 )
 
@@ -186,7 +188,7 @@ func (iter *Iterator) curPushNextStack(cur *Node) {
 	next := cur.children[0] // 当前的左然后向右找, 找到最大, 就是最接近cur 并且小于cur的值
 
 	if next != nil {
-		log.Println(iter.tstack)
+		log.Println(spew.Sdump(iter.tstack))
 		iter.tstack.Push(next)
 		for next.children[1] != nil {
 			next = next.children[1]
diff --git a/lastack/lastack.go b/lastack/lastack.go
index 65c2b2c..196dc5a 100644
--- a/lastack/lastack.go
+++ b/lastack/lastack.go
@@ -62,7 +62,7 @@ func New() *Stack {
 
 func (as *Stack) Clear() {
 	as.size = 0
-	as.top = nil
+	as.top = &Node{elements: make([]interface{}, 8, 8), cur: -1}
 	as.cache = nil
 }