diff --git a/dumper.go b/dumper.go
new file mode 100644
index 0000000..3e2ef65
--- /dev/null
+++ b/dumper.go
@@ -0,0 +1,26 @@
+package main
+
+import (
+	"fmt"
+
+	"github.com/z7zmey/php-parser/node"
+)
+
+type dumper struct {
+	indent string
+}
+
+func (d dumper) Visit(n node.Node) bool {
+	fmt.Printf("%v[%v]:\n", d.indent, n.Name())
+
+	return true
+}
+
+func (d dumper) Children(key string) node.Visitor {
+	fmt.Printf("%v%v:\n", d.indent+". ", key)
+	return dumper{d.indent + ". . "}
+}
+
+func (d dumper) Scalar(key string, value interface{}) {
+	fmt.Printf("%v%v: %v\n", d.indent+". ", key, value)
+}
diff --git a/main.go b/main.go
index d3a1c72..959f6e6 100644
--- a/main.go
+++ b/main.go
@@ -1,7 +1,6 @@
 package main
 
 import (
-	"bytes"
 	"flag"
 	"fmt"
 	"log"
@@ -17,14 +16,12 @@ func main() {
 	for _, path := range flag.Args() {
 		real, err := realpath.Realpath(path)
 		checkErr(err)
-		fmt.Printf("\n==> %s", real)
+		fmt.Printf("==> %s\n", real)
 
 		src, _ := os.Open(string(real))
 		rootnode := parser.Parse(src, real)
 
-		buf := new(bytes.Buffer)
-		rootnode.Print(buf, "")
-		fmt.Println(buf.String())
+		rootnode.Walk(dumper{"  | "})
 	}
 }
 
diff --git a/node/argument.go b/node/argument.go
index 6102d97..e50dc82 100644
--- a/node/argument.go
+++ b/node/argument.go
@@ -1,10 +1,5 @@
 package node
 
-import (
-	"fmt"
-	"io"
-)
-
 type Argument struct {
 	name     string
 	expr     Node
@@ -23,12 +18,13 @@ func NewArgument(expression Node, variadic bool) Node {
 	}
 }
 
-func (n Argument) Print(out io.Writer, indent string) {
-	fmt.Fprintf(out, "\n%v%v [- -]", indent, n.name)
-	fmt.Fprintf(out, "\n%vvariadic: %t", indent+"  ", n.variadic)
+func (n Argument) Walk(v Visitor) {
+	if v.Visit(n) == false {
+		return
+	}
 
 	if n.expr != nil {
-		fmt.Fprintf(out, "\n%vexpr:", indent+"  ")
-		n.expr.Print(out, indent+"    ")
+		vv := v.Children("expr")
+		n.expr.Walk(vv)
 	}
 }
diff --git a/node/expr/array.go b/node/expr/array.go
index 883f487..773de1d 100644
--- a/node/expr/array.go
+++ b/node/expr/array.go
@@ -1,9 +1,6 @@
 package expr
 
 import (
-	"fmt"
-	"io"
-
 	"github.com/z7zmey/php-parser/node"
 	"github.com/z7zmey/php-parser/token"
 )
@@ -28,13 +25,15 @@ func NewArray(opentToken token.Token, closeToken token.Token, items []node.Node)
 	}
 }
 
-func (n Array) Print(out io.Writer, indent string) {
-	fmt.Fprintf(out, "\n%v%v [%d %d]", indent, n.name, n.opentToken.StartLine, n.closeToken.EndLine)
+func (n Array) Walk(v node.Visitor) {
+	if v.Visit(n) == false {
+		return
+	}
 
 	if n.items != nil {
-		fmt.Fprintf(out, "\n%vitems:", indent+"  ")
+		vv := v.Children("items")
 		for _, nn := range n.items {
-			nn.Print(out, indent+"    ")
+			nn.Walk(vv)
 		}
 	}
 }
diff --git a/node/expr/array_dim_fetch.go b/node/expr/array_dim_fetch.go
index e79f0cc..34d9dfc 100644
--- a/node/expr/array_dim_fetch.go
+++ b/node/expr/array_dim_fetch.go
@@ -1,9 +1,6 @@
 package expr
 
 import (
-	"fmt"
-	"io"
-
 	"github.com/z7zmey/php-parser/node"
 )
 
@@ -25,16 +22,18 @@ func NewArrayDimFetch(variable node.Node, dim node.Node) node.Node {
 	}
 }
 
-func (n ArrayDimFetch) Print(out io.Writer, indent string) {
-	fmt.Fprintf(out, "\n%v%v [- -]", indent, n.Name)
+func (n ArrayDimFetch) Walk(v node.Visitor) {
+	if v.Visit(n) == false {
+		return
+	}
 
 	if n.variable != nil {
-		fmt.Fprintf(out, "\n%vvariable:", indent+"  ")
-		n.variable.Print(out, indent+"    ")
+		vv := v.Children("variable")
+		n.variable.Walk(vv)
 	}
 
 	if n.dim != nil {
-		fmt.Fprintf(out, "\n%vdim:", indent+"  ")
-		n.dim.Print(out, indent+"    ")
+		vv := v.Children("dim")
+		n.dim.Walk(vv)
 	}
 }
diff --git a/node/expr/array_item.go b/node/expr/array_item.go
index 9b20b7e..9073be9 100644
--- a/node/expr/array_item.go
+++ b/node/expr/array_item.go
@@ -1,9 +1,6 @@
 package expr
 
 import (
-	"fmt"
-	"io"
-
 	"github.com/z7zmey/php-parser/node"
 )
 
@@ -27,17 +24,18 @@ func NewArrayItem(key node.Node, val node.Node, byRef bool) node.Node {
 	}
 }
 
-func (n ArrayItem) Print(out io.Writer, indent string) {
-	fmt.Fprintf(out, "\n%v%v [- -]", indent, n.name)
-	fmt.Fprintf(out, "\n%vbyRef: %t", indent+"  ", n.byRef)
+func (n ArrayItem) Walk(v node.Visitor) {
+	if v.Visit(n) == false {
+		return
+	}
 
 	if n.key != nil {
-		fmt.Fprintf(out, "\n%vkey:", indent+"  ")
-		n.key.Print(out, indent+"    ")
+		vv := v.Children("key")
+		n.key.Walk(vv)
 	}
 
 	if n.val != nil {
-		fmt.Fprintf(out, "\n%vval:", indent+"  ")
-		n.val.Print(out, indent+"    ")
+		vv := v.Children("val")
+		n.val.Walk(vv)
 	}
 }
diff --git a/node/expr/assign_op/assign.go b/node/expr/assign_op/assign.go
index 977a8d1..b8da9f1 100644
--- a/node/expr/assign_op/assign.go
+++ b/node/expr/assign_op/assign.go
@@ -21,3 +21,19 @@ func NewAssign(variable node.Node, expression node.Node) node.Node {
 		},
 	}
 }
+
+func (n Assign) Walk(v node.Visitor) {
+	if v.Visit(n) == false {
+		return
+	}
+
+	if n.variable != nil {
+		vv := v.Children("variable")
+		n.variable.Walk(vv)
+	}
+
+	if n.expression != nil {
+		vv := v.Children("expression")
+		n.expression.Walk(vv)
+	}
+}
diff --git a/node/expr/assign_op/assign_op.go b/node/expr/assign_op/assign_op.go
index 55d9629..a0da3f7 100644
--- a/node/expr/assign_op/assign_op.go
+++ b/node/expr/assign_op/assign_op.go
@@ -1,9 +1,6 @@
 package assign_op
 
 import (
-	"fmt"
-	"io"
-
 	"github.com/z7zmey/php-parser/node"
 )
 
@@ -12,17 +9,3 @@ type AssignOp struct {
 	variable   node.Node
 	expression node.Node
 }
-
-func (n AssignOp) Print(out io.Writer, indent string) {
-	fmt.Fprintf(out, "\n%v%v [- -]", indent, n.name)
-
-	if n.variable != nil {
-		fmt.Fprintf(out, "\n%vvariable:", indent+"  ")
-		n.variable.Print(out, indent+"    ")
-	}
-
-	if n.expression != nil {
-		fmt.Fprintf(out, "\n%vexpression:", indent+"  ")
-		n.expression.Print(out, indent+"    ")
-	}
-}
diff --git a/node/expr/assign_op/assign_ref.go b/node/expr/assign_op/assign_ref.go
index b719616..b1e7810 100644
--- a/node/expr/assign_op/assign_ref.go
+++ b/node/expr/assign_op/assign_ref.go
@@ -21,3 +21,19 @@ func NewAssignRef(variable node.Node, expression node.Node) node.Node {
 		},
 	}
 }
+
+func (n AssignRef) Walk(v node.Visitor) {
+	if v.Visit(n) == false {
+		return
+	}
+
+	if n.variable != nil {
+		vv := v.Children("variable")
+		n.variable.Walk(vv)
+	}
+
+	if n.expression != nil {
+		vv := v.Children("expression")
+		n.expression.Walk(vv)
+	}
+}
diff --git a/node/expr/assign_op/bitwise_and.go b/node/expr/assign_op/bitwise_and.go
index 93ce1ca..3878e58 100644
--- a/node/expr/assign_op/bitwise_and.go
+++ b/node/expr/assign_op/bitwise_and.go
@@ -21,3 +21,19 @@ func NewBitwiseAnd(variable node.Node, expression node.Node) node.Node {
 		},
 	}
 }
+
+func (n BitwiseAnd) Walk(v node.Visitor) {
+	if v.Visit(n) == false {
+		return
+	}
+
+	if n.variable != nil {
+		vv := v.Children("variable")
+		n.variable.Walk(vv)
+	}
+
+	if n.expression != nil {
+		vv := v.Children("expression")
+		n.expression.Walk(vv)
+	}
+}
diff --git a/node/expr/assign_op/bitwise_or.go b/node/expr/assign_op/bitwise_or.go
index 1901349..55f3e59 100644
--- a/node/expr/assign_op/bitwise_or.go
+++ b/node/expr/assign_op/bitwise_or.go
@@ -21,3 +21,19 @@ func NewBitwiseOr(variable node.Node, expression node.Node) node.Node {
 		},
 	}
 }
+
+func (n BitwiseOr) Walk(v node.Visitor) {
+	if v.Visit(n) == false {
+		return
+	}
+
+	if n.variable != nil {
+		vv := v.Children("variable")
+		n.variable.Walk(vv)
+	}
+
+	if n.expression != nil {
+		vv := v.Children("expression")
+		n.expression.Walk(vv)
+	}
+}
diff --git a/node/expr/assign_op/bitwise_xor.go b/node/expr/assign_op/bitwise_xor.go
index 71e48b5..d0e1927 100644
--- a/node/expr/assign_op/bitwise_xor.go
+++ b/node/expr/assign_op/bitwise_xor.go
@@ -21,3 +21,19 @@ func NewBitwiseXor(variable node.Node, expression node.Node) node.Node {
 func (n BitwiseXor) Name() string {
 	return "BitwiseXor"
 }
+
+func (n BitwiseXor) Walk(v node.Visitor) {
+	if v.Visit(n) == false {
+		return
+	}
+
+	if n.variable != nil {
+		vv := v.Children("variable")
+		n.variable.Walk(vv)
+	}
+
+	if n.expression != nil {
+		vv := v.Children("expression")
+		n.expression.Walk(vv)
+	}
+}
diff --git a/node/expr/assign_op/concat.go b/node/expr/assign_op/concat.go
index 7b5c652..bd9621e 100644
--- a/node/expr/assign_op/concat.go
+++ b/node/expr/assign_op/concat.go
@@ -21,3 +21,19 @@ func NewConcat(variable node.Node, expression node.Node) node.Node {
 		},
 	}
 }
+
+func (n Concat) Walk(v node.Visitor) {
+	if v.Visit(n) == false {
+		return
+	}
+
+	if n.variable != nil {
+		vv := v.Children("variable")
+		n.variable.Walk(vv)
+	}
+
+	if n.expression != nil {
+		vv := v.Children("expression")
+		n.expression.Walk(vv)
+	}
+}
diff --git a/node/expr/assign_op/div.go b/node/expr/assign_op/div.go
index 8504fa3..b9b6716 100644
--- a/node/expr/assign_op/div.go
+++ b/node/expr/assign_op/div.go
@@ -21,3 +21,19 @@ func NewDiv(variable node.Node, expression node.Node) node.Node {
 		},
 	}
 }
+
+func (n Div) Walk(v node.Visitor) {
+	if v.Visit(n) == false {
+		return
+	}
+
+	if n.variable != nil {
+		vv := v.Children("variable")
+		n.variable.Walk(vv)
+	}
+
+	if n.expression != nil {
+		vv := v.Children("expression")
+		n.expression.Walk(vv)
+	}
+}
diff --git a/node/expr/assign_op/minus.go b/node/expr/assign_op/minus.go
index fadbbc5..47b9ef8 100644
--- a/node/expr/assign_op/minus.go
+++ b/node/expr/assign_op/minus.go
@@ -21,3 +21,19 @@ func NewMinus(variable node.Node, expression node.Node) node.Node {
 		},
 	}
 }
+
+func (n Minus) Walk(v node.Visitor) {
+	if v.Visit(n) == false {
+		return
+	}
+
+	if n.variable != nil {
+		vv := v.Children("variable")
+		n.variable.Walk(vv)
+	}
+
+	if n.expression != nil {
+		vv := v.Children("expression")
+		n.expression.Walk(vv)
+	}
+}
diff --git a/node/expr/assign_op/mod.go b/node/expr/assign_op/mod.go
index a068144..ab2163e 100644
--- a/node/expr/assign_op/mod.go
+++ b/node/expr/assign_op/mod.go
@@ -21,3 +21,19 @@ func NewMod(variable node.Node, expression node.Node) node.Node {
 		},
 	}
 }
+
+func (n Mod) Walk(v node.Visitor) {
+	if v.Visit(n) == false {
+		return
+	}
+
+	if n.variable != nil {
+		vv := v.Children("variable")
+		n.variable.Walk(vv)
+	}
+
+	if n.expression != nil {
+		vv := v.Children("expression")
+		n.expression.Walk(vv)
+	}
+}
diff --git a/node/expr/assign_op/mul.go b/node/expr/assign_op/mul.go
index 6d400fa..cd0b5d8 100644
--- a/node/expr/assign_op/mul.go
+++ b/node/expr/assign_op/mul.go
@@ -21,3 +21,19 @@ func NewMul(variable node.Node, expression node.Node) node.Node {
 		},
 	}
 }
+
+func (n Mul) Walk(v node.Visitor) {
+	if v.Visit(n) == false {
+		return
+	}
+
+	if n.variable != nil {
+		vv := v.Children("variable")
+		n.variable.Walk(vv)
+	}
+
+	if n.expression != nil {
+		vv := v.Children("expression")
+		n.expression.Walk(vv)
+	}
+}
diff --git a/node/expr/assign_op/plus.go b/node/expr/assign_op/plus.go
index 7ab0e01..ca3375f 100644
--- a/node/expr/assign_op/plus.go
+++ b/node/expr/assign_op/plus.go
@@ -21,3 +21,19 @@ func NewPlus(variable node.Node, expression node.Node) node.Node {
 		},
 	}
 }
+
+func (n Plus) Walk(v node.Visitor) {
+	if v.Visit(n) == false {
+		return
+	}
+
+	if n.variable != nil {
+		vv := v.Children("variable")
+		n.variable.Walk(vv)
+	}
+
+	if n.expression != nil {
+		vv := v.Children("expression")
+		n.expression.Walk(vv)
+	}
+}
diff --git a/node/expr/assign_op/pow.go b/node/expr/assign_op/pow.go
index 47d606d..790f359 100644
--- a/node/expr/assign_op/pow.go
+++ b/node/expr/assign_op/pow.go
@@ -21,3 +21,19 @@ func NewPow(variable node.Node, expression node.Node) node.Node {
 		},
 	}
 }
+
+func (n Pow) Walk(v node.Visitor) {
+	if v.Visit(n) == false {
+		return
+	}
+
+	if n.variable != nil {
+		vv := v.Children("variable")
+		n.variable.Walk(vv)
+	}
+
+	if n.expression != nil {
+		vv := v.Children("expression")
+		n.expression.Walk(vv)
+	}
+}
diff --git a/node/expr/assign_op/shift_left.go b/node/expr/assign_op/shift_left.go
index 1a25f58..13a1aeb 100644
--- a/node/expr/assign_op/shift_left.go
+++ b/node/expr/assign_op/shift_left.go
@@ -21,3 +21,19 @@ func NewShiftLeft(variable node.Node, expression node.Node) node.Node {
 		},
 	}
 }
+
+func (n ShiftLeft) Walk(v node.Visitor) {
+	if v.Visit(n) == false {
+		return
+	}
+
+	if n.variable != nil {
+		vv := v.Children("variable")
+		n.variable.Walk(vv)
+	}
+
+	if n.expression != nil {
+		vv := v.Children("expression")
+		n.expression.Walk(vv)
+	}
+}
diff --git a/node/expr/assign_op/shift_right.go b/node/expr/assign_op/shift_right.go
index 16b2e4f..03b153b 100644
--- a/node/expr/assign_op/shift_right.go
+++ b/node/expr/assign_op/shift_right.go
@@ -21,3 +21,19 @@ func NewShiftRight(variable node.Node, expression node.Node) node.Node {
 		},
 	}
 }
+
+func (n ShiftRight) Walk(v node.Visitor) {
+	if v.Visit(n) == false {
+		return
+	}
+
+	if n.variable != nil {
+		vv := v.Children("variable")
+		n.variable.Walk(vv)
+	}
+
+	if n.expression != nil {
+		vv := v.Children("expression")
+		n.expression.Walk(vv)
+	}
+}
diff --git a/node/expr/binary_op/binary_op.go b/node/expr/binary_op/binary_op.go
index 7f2a9b0..167c819 100644
--- a/node/expr/binary_op/binary_op.go
+++ b/node/expr/binary_op/binary_op.go
@@ -1,9 +1,6 @@
 package binary_op
 
 import (
-	"fmt"
-	"io"
-
 	"github.com/z7zmey/php-parser/node"
 )
 
@@ -12,17 +9,3 @@ type BinaryOp struct {
 	left  node.Node
 	right node.Node
 }
-
-func (n BinaryOp) Print(out io.Writer, indent string) {
-	fmt.Fprintf(out, "\n%v%v [- -]", indent, n.name)
-
-	if n.left != nil {
-		fmt.Fprintf(out, "\n%vleft:", indent+"  ")
-		n.left.Print(out, indent+"    ")
-	}
-
-	if n.right != nil {
-		fmt.Fprintf(out, "\n%vright:", indent+"  ")
-		n.right.Print(out, indent+"    ")
-	}
-}
diff --git a/node/expr/binary_op/bitwise_and.go b/node/expr/binary_op/bitwise_and.go
index 194ac80..bbeb817 100644
--- a/node/expr/binary_op/bitwise_and.go
+++ b/node/expr/binary_op/bitwise_and.go
@@ -21,3 +21,19 @@ func NewBitwiseAnd(variable node.Node, expression node.Node) node.Node {
 		},
 	}
 }
+
+func (n BitwiseAnd) Walk(v node.Visitor) {
+	if v.Visit(n) == false {
+		return
+	}
+
+	if n.left != nil {
+		vv := v.Children("left")
+		n.left.Walk(vv)
+	}
+
+	if n.right != nil {
+		vv := v.Children("right")
+		n.right.Walk(vv)
+	}
+}
diff --git a/node/expr/binary_op/bitwise_or.go b/node/expr/binary_op/bitwise_or.go
index 00affb6..93650bf 100644
--- a/node/expr/binary_op/bitwise_or.go
+++ b/node/expr/binary_op/bitwise_or.go
@@ -21,3 +21,19 @@ func NewBitwiseOr(variable node.Node, expression node.Node) node.Node {
 func (n BitwiseOr) Name() string {
 	return "BitwiseOr"
 }
+
+func (n BitwiseOr) Walk(v node.Visitor) {
+	if v.Visit(n) == false {
+		return
+	}
+
+	if n.left != nil {
+		vv := v.Children("left")
+		n.left.Walk(vv)
+	}
+
+	if n.right != nil {
+		vv := v.Children("right")
+		n.right.Walk(vv)
+	}
+}
diff --git a/node/expr/binary_op/bitwise_xor.go b/node/expr/binary_op/bitwise_xor.go
index d5bc094..2d68ed7 100644
--- a/node/expr/binary_op/bitwise_xor.go
+++ b/node/expr/binary_op/bitwise_xor.go
@@ -21,3 +21,19 @@ func NewBitwiseXor(variable node.Node, expression node.Node) node.Node {
 func (n BitwiseXor) Name() string {
 	return "BitwiseXor"
 }
+
+func (n BitwiseXor) Walk(v node.Visitor) {
+	if v.Visit(n) == false {
+		return
+	}
+
+	if n.left != nil {
+		vv := v.Children("left")
+		n.left.Walk(vv)
+	}
+
+	if n.right != nil {
+		vv := v.Children("right")
+		n.right.Walk(vv)
+	}
+}
diff --git a/node/expr/binary_op/boolean_and.go b/node/expr/binary_op/boolean_and.go
index b7eff32..422be6a 100644
--- a/node/expr/binary_op/boolean_and.go
+++ b/node/expr/binary_op/boolean_and.go
@@ -21,3 +21,19 @@ func NewBooleanAnd(variable node.Node, expression node.Node) node.Node {
 		},
 	}
 }
+
+func (n BooleanAnd) Walk(v node.Visitor) {
+	if v.Visit(n) == false {
+		return
+	}
+
+	if n.left != nil {
+		vv := v.Children("left")
+		n.left.Walk(vv)
+	}
+
+	if n.right != nil {
+		vv := v.Children("right")
+		n.right.Walk(vv)
+	}
+}
diff --git a/node/expr/binary_op/boolean_or.go b/node/expr/binary_op/boolean_or.go
index 0e5885c..35c56d6 100644
--- a/node/expr/binary_op/boolean_or.go
+++ b/node/expr/binary_op/boolean_or.go
@@ -21,3 +21,19 @@ func NewBooleanOr(variable node.Node, expression node.Node) node.Node {
 		},
 	}
 }
+
+func (n BooleanOr) Walk(v node.Visitor) {
+	if v.Visit(n) == false {
+		return
+	}
+
+	if n.left != nil {
+		vv := v.Children("left")
+		n.left.Walk(vv)
+	}
+
+	if n.right != nil {
+		vv := v.Children("right")
+		n.right.Walk(vv)
+	}
+}
diff --git a/node/expr/binary_op/coalesce.go b/node/expr/binary_op/coalesce.go
index 180f9d1..f0a2b4a 100644
--- a/node/expr/binary_op/coalesce.go
+++ b/node/expr/binary_op/coalesce.go
@@ -21,3 +21,19 @@ func NewCoalesce(variable node.Node, expression node.Node) node.Node {
 		},
 	}
 }
+
+func (n Coalesce) Walk(v node.Visitor) {
+	if v.Visit(n) == false {
+		return
+	}
+
+	if n.left != nil {
+		vv := v.Children("left")
+		n.left.Walk(vv)
+	}
+
+	if n.right != nil {
+		vv := v.Children("right")
+		n.right.Walk(vv)
+	}
+}
diff --git a/node/expr/binary_op/concat.go b/node/expr/binary_op/concat.go
index 4349778..ac1183d 100644
--- a/node/expr/binary_op/concat.go
+++ b/node/expr/binary_op/concat.go
@@ -21,3 +21,19 @@ func NewConcat(variable node.Node, expression node.Node) node.Node {
 		},
 	}
 }
+
+func (n Concat) Walk(v node.Visitor) {
+	if v.Visit(n) == false {
+		return
+	}
+
+	if n.left != nil {
+		vv := v.Children("left")
+		n.left.Walk(vv)
+	}
+
+	if n.right != nil {
+		vv := v.Children("right")
+		n.right.Walk(vv)
+	}
+}
diff --git a/node/expr/binary_op/div.go b/node/expr/binary_op/div.go
index a9785fc..bec6627 100644
--- a/node/expr/binary_op/div.go
+++ b/node/expr/binary_op/div.go
@@ -21,3 +21,19 @@ func NewDiv(variable node.Node, expression node.Node) node.Node {
 		},
 	}
 }
+
+func (n Div) Walk(v node.Visitor) {
+	if v.Visit(n) == false {
+		return
+	}
+
+	if n.left != nil {
+		vv := v.Children("left")
+		n.left.Walk(vv)
+	}
+
+	if n.right != nil {
+		vv := v.Children("right")
+		n.right.Walk(vv)
+	}
+}
diff --git a/node/expr/binary_op/equal.go b/node/expr/binary_op/equal.go
index d9346f6..cef0055 100644
--- a/node/expr/binary_op/equal.go
+++ b/node/expr/binary_op/equal.go
@@ -21,3 +21,19 @@ func NewEqual(variable node.Node, expression node.Node) node.Node {
 		},
 	}
 }
+
+func (n Equal) Walk(v node.Visitor) {
+	if v.Visit(n) == false {
+		return
+	}
+
+	if n.left != nil {
+		vv := v.Children("left")
+		n.left.Walk(vv)
+	}
+
+	if n.right != nil {
+		vv := v.Children("right")
+		n.right.Walk(vv)
+	}
+}
diff --git a/node/expr/binary_op/greater.go b/node/expr/binary_op/greater.go
index 2e4276f..cd9ec50 100644
--- a/node/expr/binary_op/greater.go
+++ b/node/expr/binary_op/greater.go
@@ -21,3 +21,19 @@ func NewGreater(variable node.Node, expression node.Node) node.Node {
 		},
 	}
 }
+
+func (n Greater) Walk(v node.Visitor) {
+	if v.Visit(n) == false {
+		return
+	}
+
+	if n.left != nil {
+		vv := v.Children("left")
+		n.left.Walk(vv)
+	}
+
+	if n.right != nil {
+		vv := v.Children("right")
+		n.right.Walk(vv)
+	}
+}
diff --git a/node/expr/binary_op/greater_or_equal.go b/node/expr/binary_op/greater_or_equal.go
index 689ebdf..8e7f52f 100644
--- a/node/expr/binary_op/greater_or_equal.go
+++ b/node/expr/binary_op/greater_or_equal.go
@@ -21,3 +21,19 @@ func NewGreaterOrEqual(variable node.Node, expression node.Node) node.Node {
 		},
 	}
 }
+
+func (n GreaterOrEqual) Walk(v node.Visitor) {
+	if v.Visit(n) == false {
+		return
+	}
+
+	if n.left != nil {
+		vv := v.Children("left")
+		n.left.Walk(vv)
+	}
+
+	if n.right != nil {
+		vv := v.Children("right")
+		n.right.Walk(vv)
+	}
+}
diff --git a/node/expr/binary_op/identical.go b/node/expr/binary_op/identical.go
index f566423..c5e5094 100644
--- a/node/expr/binary_op/identical.go
+++ b/node/expr/binary_op/identical.go
@@ -21,3 +21,19 @@ func NewIdentical(variable node.Node, expression node.Node) node.Node {
 		},
 	}
 }
+
+func (n Identical) Walk(v node.Visitor) {
+	if v.Visit(n) == false {
+		return
+	}
+
+	if n.left != nil {
+		vv := v.Children("left")
+		n.left.Walk(vv)
+	}
+
+	if n.right != nil {
+		vv := v.Children("right")
+		n.right.Walk(vv)
+	}
+}
diff --git a/node/expr/binary_op/logical_and.go b/node/expr/binary_op/logical_and.go
index 59341d7..31edd78 100644
--- a/node/expr/binary_op/logical_and.go
+++ b/node/expr/binary_op/logical_and.go
@@ -21,3 +21,19 @@ func NewLogicalAnd(variable node.Node, expression node.Node) node.Node {
 		},
 	}
 }
+
+func (n LogicalAnd) Walk(v node.Visitor) {
+	if v.Visit(n) == false {
+		return
+	}
+
+	if n.left != nil {
+		vv := v.Children("left")
+		n.left.Walk(vv)
+	}
+
+	if n.right != nil {
+		vv := v.Children("right")
+		n.right.Walk(vv)
+	}
+}
diff --git a/node/expr/binary_op/logical_or.go b/node/expr/binary_op/logical_or.go
index e9c4a0a..7be1e49 100644
--- a/node/expr/binary_op/logical_or.go
+++ b/node/expr/binary_op/logical_or.go
@@ -21,3 +21,19 @@ func NewLogicalOr(variable node.Node, expression node.Node) node.Node {
 		},
 	}
 }
+
+func (n LogicalOr) Walk(v node.Visitor) {
+	if v.Visit(n) == false {
+		return
+	}
+
+	if n.left != nil {
+		vv := v.Children("left")
+		n.left.Walk(vv)
+	}
+
+	if n.right != nil {
+		vv := v.Children("right")
+		n.right.Walk(vv)
+	}
+}
diff --git a/node/expr/binary_op/logical_xor.go b/node/expr/binary_op/logical_xor.go
index e0213d6..c1960b6 100644
--- a/node/expr/binary_op/logical_xor.go
+++ b/node/expr/binary_op/logical_xor.go
@@ -21,3 +21,19 @@ func NewLogicalXor(variable node.Node, expression node.Node) node.Node {
 		},
 	}
 }
+
+func (n LogicalXor) Walk(v node.Visitor) {
+	if v.Visit(n) == false {
+		return
+	}
+
+	if n.left != nil {
+		vv := v.Children("left")
+		n.left.Walk(vv)
+	}
+
+	if n.right != nil {
+		vv := v.Children("right")
+		n.right.Walk(vv)
+	}
+}
diff --git a/node/expr/binary_op/minus.go b/node/expr/binary_op/minus.go
index 00cfedc..e7924b3 100644
--- a/node/expr/binary_op/minus.go
+++ b/node/expr/binary_op/minus.go
@@ -21,3 +21,19 @@ func NewMinus(variable node.Node, expression node.Node) node.Node {
 		},
 	}
 }
+
+func (n Minus) Walk(v node.Visitor) {
+	if v.Visit(n) == false {
+		return
+	}
+
+	if n.left != nil {
+		vv := v.Children("left")
+		n.left.Walk(vv)
+	}
+
+	if n.right != nil {
+		vv := v.Children("right")
+		n.right.Walk(vv)
+	}
+}
diff --git a/node/expr/binary_op/mod.go b/node/expr/binary_op/mod.go
index a99409a..da9da7c 100644
--- a/node/expr/binary_op/mod.go
+++ b/node/expr/binary_op/mod.go
@@ -4,7 +4,7 @@ import (
 	"github.com/z7zmey/php-parser/node"
 )
 
-func(n Mod) Name() string {
+func (n Mod) Name() string {
 	return "Mod"
 }
 
@@ -21,3 +21,19 @@ func NewMod(variable node.Node, expression node.Node) node.Node {
 		},
 	}
 }
+
+func (n Mod) Walk(v node.Visitor) {
+	if v.Visit(n) == false {
+		return
+	}
+
+	if n.left != nil {
+		vv := v.Children("left")
+		n.left.Walk(vv)
+	}
+
+	if n.right != nil {
+		vv := v.Children("right")
+		n.right.Walk(vv)
+	}
+}
diff --git a/node/expr/binary_op/mul.go b/node/expr/binary_op/mul.go
index 8b6dff0..e5ef893 100644
--- a/node/expr/binary_op/mul.go
+++ b/node/expr/binary_op/mul.go
@@ -4,7 +4,7 @@ import (
 	"github.com/z7zmey/php-parser/node"
 )
 
-func(n Mul) Name() string {
+func (n Mul) Name() string {
 	return "Mul"
 }
 
@@ -21,3 +21,19 @@ func NewMul(variable node.Node, expression node.Node) node.Node {
 		},
 	}
 }
+
+func (n Mul) Walk(v node.Visitor) {
+	if v.Visit(n) == false {
+		return
+	}
+
+	if n.left != nil {
+		vv := v.Children("left")
+		n.left.Walk(vv)
+	}
+
+	if n.right != nil {
+		vv := v.Children("right")
+		n.right.Walk(vv)
+	}
+}
diff --git a/node/expr/binary_op/not_equal.go b/node/expr/binary_op/not_equal.go
index a5c3271..fdee617 100644
--- a/node/expr/binary_op/not_equal.go
+++ b/node/expr/binary_op/not_equal.go
@@ -4,7 +4,7 @@ import (
 	"github.com/z7zmey/php-parser/node"
 )
 
-func(n NotEqual) Name() string {
+func (n NotEqual) Name() string {
 	return "NotEqual"
 }
 
@@ -21,3 +21,19 @@ func NewNotEqual(variable node.Node, expression node.Node) node.Node {
 		},
 	}
 }
+
+func (n NotEqual) Walk(v node.Visitor) {
+	if v.Visit(n) == false {
+		return
+	}
+
+	if n.left != nil {
+		vv := v.Children("left")
+		n.left.Walk(vv)
+	}
+
+	if n.right != nil {
+		vv := v.Children("right")
+		n.right.Walk(vv)
+	}
+}
diff --git a/node/expr/binary_op/not_identical.go b/node/expr/binary_op/not_identical.go
index f9ee000..6a2deb8 100644
--- a/node/expr/binary_op/not_identical.go
+++ b/node/expr/binary_op/not_identical.go
@@ -4,7 +4,7 @@ import (
 	"github.com/z7zmey/php-parser/node"
 )
 
-func(n NotIdentical) Name() string {
+func (n NotIdentical) Name() string {
 	return "NotIdentical"
 }
 
@@ -21,3 +21,19 @@ func NewNotIdentical(variable node.Node, expression node.Node) node.Node {
 		},
 	}
 }
+
+func (n NotIdentical) Walk(v node.Visitor) {
+	if v.Visit(n) == false {
+		return
+	}
+
+	if n.left != nil {
+		vv := v.Children("left")
+		n.left.Walk(vv)
+	}
+
+	if n.right != nil {
+		vv := v.Children("right")
+		n.right.Walk(vv)
+	}
+}
diff --git a/node/expr/binary_op/plus.go b/node/expr/binary_op/plus.go
index ab9a967..c7a805f 100644
--- a/node/expr/binary_op/plus.go
+++ b/node/expr/binary_op/plus.go
@@ -4,7 +4,7 @@ import (
 	"github.com/z7zmey/php-parser/node"
 )
 
-func(n Plus) Name() string {
+func (n Plus) Name() string {
 	return "Plus"
 }
 
@@ -21,3 +21,19 @@ func NewPlus(variable node.Node, expression node.Node) node.Node {
 		},
 	}
 }
+
+func (n Plus) Walk(v node.Visitor) {
+	if v.Visit(n) == false {
+		return
+	}
+
+	if n.left != nil {
+		vv := v.Children("left")
+		n.left.Walk(vv)
+	}
+
+	if n.right != nil {
+		vv := v.Children("right")
+		n.right.Walk(vv)
+	}
+}
diff --git a/node/expr/binary_op/pow.go b/node/expr/binary_op/pow.go
index 9a6fdbb..5f28094 100644
--- a/node/expr/binary_op/pow.go
+++ b/node/expr/binary_op/pow.go
@@ -4,7 +4,7 @@ import (
 	"github.com/z7zmey/php-parser/node"
 )
 
-func(n Pow) Name() string {
+func (n Pow) Name() string {
 	return "Pow"
 }
 
@@ -21,3 +21,19 @@ func NewPow(variable node.Node, expression node.Node) node.Node {
 		},
 	}
 }
+
+func (n Pow) Walk(v node.Visitor) {
+	if v.Visit(n) == false {
+		return
+	}
+
+	if n.left != nil {
+		vv := v.Children("left")
+		n.left.Walk(vv)
+	}
+
+	if n.right != nil {
+		vv := v.Children("right")
+		n.right.Walk(vv)
+	}
+}
diff --git a/node/expr/binary_op/shift_left.go b/node/expr/binary_op/shift_left.go
index 4638f0f..7be8148 100644
--- a/node/expr/binary_op/shift_left.go
+++ b/node/expr/binary_op/shift_left.go
@@ -4,7 +4,7 @@ import (
 	"github.com/z7zmey/php-parser/node"
 )
 
-func(n ShiftLeft) Name() string {
+func (n ShiftLeft) Name() string {
 	return "ShiftLeft"
 }
 
@@ -21,3 +21,19 @@ func NewShiftLeft(variable node.Node, expression node.Node) node.Node {
 		},
 	}
 }
+
+func (n ShiftLeft) Walk(v node.Visitor) {
+	if v.Visit(n) == false {
+		return
+	}
+
+	if n.left != nil {
+		vv := v.Children("left")
+		n.left.Walk(vv)
+	}
+
+	if n.right != nil {
+		vv := v.Children("right")
+		n.right.Walk(vv)
+	}
+}
diff --git a/node/expr/binary_op/shift_right.go b/node/expr/binary_op/shift_right.go
index d078d41..6110ddd 100644
--- a/node/expr/binary_op/shift_right.go
+++ b/node/expr/binary_op/shift_right.go
@@ -4,7 +4,7 @@ import (
 	"github.com/z7zmey/php-parser/node"
 )
 
-func(n ShiftRight) Name() string {
+func (n ShiftRight) Name() string {
 	return "ShiftRight"
 }
 
@@ -21,3 +21,19 @@ func NewShiftRight(variable node.Node, expression node.Node) node.Node {
 		},
 	}
 }
+
+func (n ShiftRight) Walk(v node.Visitor) {
+	if v.Visit(n) == false {
+		return
+	}
+
+	if n.left != nil {
+		vv := v.Children("left")
+		n.left.Walk(vv)
+	}
+
+	if n.right != nil {
+		vv := v.Children("right")
+		n.right.Walk(vv)
+	}
+}
diff --git a/node/expr/binary_op/smaller.go b/node/expr/binary_op/smaller.go
index 8557506..ee98050 100644
--- a/node/expr/binary_op/smaller.go
+++ b/node/expr/binary_op/smaller.go
@@ -4,7 +4,7 @@ import (
 	"github.com/z7zmey/php-parser/node"
 )
 
-func(n Smaller) Name() string {
+func (n Smaller) Name() string {
 	return "Smaller"
 }
 
@@ -21,3 +21,19 @@ func NewSmaller(variable node.Node, expression node.Node) node.Node {
 		},
 	}
 }
+
+func (n Smaller) Walk(v node.Visitor) {
+	if v.Visit(n) == false {
+		return
+	}
+
+	if n.left != nil {
+		vv := v.Children("left")
+		n.left.Walk(vv)
+	}
+
+	if n.right != nil {
+		vv := v.Children("right")
+		n.right.Walk(vv)
+	}
+}
diff --git a/node/expr/binary_op/smaller_or_equal.go b/node/expr/binary_op/smaller_or_equal.go
index f390416..934d0e8 100644
--- a/node/expr/binary_op/smaller_or_equal.go
+++ b/node/expr/binary_op/smaller_or_equal.go
@@ -4,7 +4,7 @@ import (
 	"github.com/z7zmey/php-parser/node"
 )
 
-func(n SmallerOrEqual) Name() string {
+func (n SmallerOrEqual) Name() string {
 	return "SmallerOrEqual"
 }
 
@@ -21,3 +21,19 @@ func NewSmallerOrEqual(variable node.Node, expression node.Node) node.Node {
 		},
 	}
 }
+
+func (n SmallerOrEqual) Walk(v node.Visitor) {
+	if v.Visit(n) == false {
+		return
+	}
+
+	if n.left != nil {
+		vv := v.Children("left")
+		n.left.Walk(vv)
+	}
+
+	if n.right != nil {
+		vv := v.Children("right")
+		n.right.Walk(vv)
+	}
+}
diff --git a/node/expr/binary_op/spaceship.go b/node/expr/binary_op/spaceship.go
index 0799d7c..a2ff825 100644
--- a/node/expr/binary_op/spaceship.go
+++ b/node/expr/binary_op/spaceship.go
@@ -4,7 +4,7 @@ import (
 	"github.com/z7zmey/php-parser/node"
 )
 
-func(n Spaceship) Name() string {
+func (n Spaceship) Name() string {
 	return "Spaceship"
 }
 
@@ -21,3 +21,19 @@ func NewSpaceship(variable node.Node, expression node.Node) node.Node {
 		},
 	}
 }
+
+func (n Spaceship) Walk(v node.Visitor) {
+	if v.Visit(n) == false {
+		return
+	}
+
+	if n.left != nil {
+		vv := v.Children("left")
+		n.left.Walk(vv)
+	}
+
+	if n.right != nil {
+		vv := v.Children("right")
+		n.right.Walk(vv)
+	}
+}
diff --git a/node/expr/bitwise_not.go b/node/expr/bitwise_not.go
index a1ac956..ea7dcf5 100644
--- a/node/expr/bitwise_not.go
+++ b/node/expr/bitwise_not.go
@@ -1,9 +1,6 @@
 package expr
 
 import (
-	"fmt"
-	"io"
-
 	"github.com/z7zmey/php-parser/node"
 )
 
@@ -23,11 +20,13 @@ func NewBitwiseNot(expression node.Node) node.Node {
 	}
 }
 
-func (n BitwiseNot) Print(out io.Writer, indent string) {
-	fmt.Fprintf(out, "\n%v%v [- -]", indent, n.name)
+func (n BitwiseNot) Walk(v node.Visitor) {
+	if v.Visit(n) == false {
+		return
+	}
 
 	if n.expr != nil {
-		fmt.Fprintf(out, "\n%vexpr:", indent+"  ")
-		n.expr.Print(out, indent+"    ")
+		vv := v.Children("expr")
+		n.expr.Walk(vv)
 	}
 }
diff --git a/node/expr/boolean_not.go b/node/expr/boolean_not.go
index 1de96dd..f6d2210 100644
--- a/node/expr/boolean_not.go
+++ b/node/expr/boolean_not.go
@@ -1,9 +1,6 @@
 package expr
 
 import (
-	"fmt"
-	"io"
-
 	"github.com/z7zmey/php-parser/node"
 )
 
@@ -23,11 +20,13 @@ func NewBooleanNot(expression node.Node) node.Node {
 	}
 }
 
-func (n BooleanNot) Print(out io.Writer, indent string) {
-	fmt.Fprintf(out, "\n%v%v [- -]", indent, n.name)
+func (n BooleanNot) Walk(v node.Visitor) {
+	if v.Visit(n) == false {
+		return
+	}
 
 	if n.expr != nil {
-		fmt.Fprintf(out, "\n%vexpr:", indent+"  ")
-		n.expr.Print(out, indent+"    ")
+		vv := v.Children("expr")
+		n.expr.Walk(vv)
 	}
 }
diff --git a/node/expr/cast/cast.go b/node/expr/cast/cast.go
index 75853f7..abaeb94 100644
--- a/node/expr/cast/cast.go
+++ b/node/expr/cast/cast.go
@@ -1,9 +1,6 @@
 package cast
 
 import (
-	"fmt"
-	"io"
-
 	"github.com/z7zmey/php-parser/node"
 )
 
@@ -11,12 +8,3 @@ type Cast struct {
 	name string
 	expr node.Node
 }
-
-func (n Cast) Print(out io.Writer, indent string) {
-	fmt.Fprintf(out, "\n%v%v [- -]", indent, n.name)
-
-	if n.expr != nil {
-		fmt.Fprintf(out, "\n%vexpr:", indent+"  ")
-		n.expr.Print(out, indent+"    ")
-	}
-}
diff --git a/node/expr/cast/cast_array.go b/node/expr/cast/cast_array.go
index 01d6375..2ad6a65 100644
--- a/node/expr/cast/cast_array.go
+++ b/node/expr/cast/cast_array.go
@@ -20,3 +20,14 @@ func NewCastArray(expr node.Node) node.Node {
 		},
 	}
 }
+
+func (n CastArray) Walk(v node.Visitor) {
+	if v.Visit(n) == false {
+		return
+	}
+
+	if n.expr != nil {
+		vv := v.Children("expr")
+		n.expr.Walk(vv)
+	}
+}
diff --git a/node/expr/cast/cast_bool.go b/node/expr/cast/cast_bool.go
index 48468d1..c5b47a3 100644
--- a/node/expr/cast/cast_bool.go
+++ b/node/expr/cast/cast_bool.go
@@ -20,3 +20,14 @@ func NewCastBool(expr node.Node) node.Node {
 		},
 	}
 }
+
+func (n CastBool) Walk(v node.Visitor) {
+	if v.Visit(n) == false {
+		return
+	}
+
+	if n.expr != nil {
+		vv := v.Children("expr")
+		n.expr.Walk(vv)
+	}
+}
diff --git a/node/expr/cast/cast_double.go b/node/expr/cast/cast_double.go
index 044dbd8..2ec2a8e 100644
--- a/node/expr/cast/cast_double.go
+++ b/node/expr/cast/cast_double.go
@@ -20,3 +20,14 @@ func NewCastDouble(expr node.Node) node.Node {
 		},
 	}
 }
+
+func (n CastDouble) Walk(v node.Visitor) {
+	if v.Visit(n) == false {
+		return
+	}
+
+	if n.expr != nil {
+		vv := v.Children("expr")
+		n.expr.Walk(vv)
+	}
+}
diff --git a/node/expr/cast/cast_int.go b/node/expr/cast/cast_int.go
index 7690e00..28495f0 100644
--- a/node/expr/cast/cast_int.go
+++ b/node/expr/cast/cast_int.go
@@ -20,3 +20,14 @@ func NewCastInt(expr node.Node) node.Node {
 		},
 	}
 }
+
+func (n CastInt) Walk(v node.Visitor) {
+	if v.Visit(n) == false {
+		return
+	}
+
+	if n.expr != nil {
+		vv := v.Children("expr")
+		n.expr.Walk(vv)
+	}
+}
diff --git a/node/expr/cast/cast_object.go b/node/expr/cast/cast_object.go
index dad301f..2985726 100644
--- a/node/expr/cast/cast_object.go
+++ b/node/expr/cast/cast_object.go
@@ -20,3 +20,14 @@ func NewCastObject(expr node.Node) node.Node {
 		},
 	}
 }
+
+func (n CastObject) Walk(v node.Visitor) {
+	if v.Visit(n) == false {
+		return
+	}
+
+	if n.expr != nil {
+		vv := v.Children("expr")
+		n.expr.Walk(vv)
+	}
+}
diff --git a/node/expr/cast/cast_string.go b/node/expr/cast/cast_string.go
index 915357c..993aa4d 100644
--- a/node/expr/cast/cast_string.go
+++ b/node/expr/cast/cast_string.go
@@ -20,3 +20,14 @@ func NewCastString(expr node.Node) node.Node {
 		},
 	}
 }
+
+func (n CastString) Walk(v node.Visitor) {
+	if v.Visit(n) == false {
+		return
+	}
+
+	if n.expr != nil {
+		vv := v.Children("expr")
+		n.expr.Walk(vv)
+	}
+}
diff --git a/node/expr/cast/cast_unset.go b/node/expr/cast/cast_unset.go
index a1f8e01..b9359c7 100644
--- a/node/expr/cast/cast_unset.go
+++ b/node/expr/cast/cast_unset.go
@@ -20,3 +20,14 @@ func NewCastUnset(expr node.Node) node.Node {
 		},
 	}
 }
+
+func (n CastUnset) Walk(v node.Visitor) {
+	if v.Visit(n) == false {
+		return
+	}
+
+	if n.expr != nil {
+		vv := v.Children("expr")
+		n.expr.Walk(vv)
+	}
+}
diff --git a/node/expr/class_const_fetch.go b/node/expr/class_const_fetch.go
index ad7e778..8926c37 100644
--- a/node/expr/class_const_fetch.go
+++ b/node/expr/class_const_fetch.go
@@ -1,9 +1,6 @@
 package expr
 
 import (
-	"fmt"
-	"io"
-
 	"github.com/z7zmey/php-parser/node"
 	"github.com/z7zmey/php-parser/token"
 )
@@ -18,6 +15,7 @@ type ClassConstFetch struct {
 	constant token.Token
 }
 
+// TODO: constant must be identifier
 func NewClassConstFetch(class node.Node, constant token.Token) node.Node {
 	return ClassConstFetch{
 		"ClassConstFetch",
@@ -26,12 +24,15 @@ func NewClassConstFetch(class node.Node, constant token.Token) node.Node {
 	}
 }
 
-func (n ClassConstFetch) Print(out io.Writer, indent string) {
-	fmt.Fprintf(out, "\n%v%v [- -]", indent, n.name)
-	fmt.Fprintf(out, "\n%vname: %q", indent+"  ", n.constant.Value)
+func (n ClassConstFetch) Walk(v node.Visitor) {
+	if v.Visit(n) == false {
+		return
+	}
+
+	v.Scalar("constant", n.constant.Value)
 
 	if n.class != nil {
-		fmt.Fprintf(out, "\n%vclass:", indent+"  ")
-		n.class.Print(out, indent+"    ")
+		vv := v.Children("class")
+		n.class.Walk(vv)
 	}
 }
diff --git a/node/expr/clone.go b/node/expr/clone.go
index 027892d..21ec935 100644
--- a/node/expr/clone.go
+++ b/node/expr/clone.go
@@ -1,9 +1,6 @@
 package expr
 
 import (
-	"fmt"
-	"io"
-
 	"github.com/z7zmey/php-parser/node"
 )
 
@@ -23,11 +20,13 @@ func NewClone(expression node.Node) node.Node {
 	}
 }
 
-func (n Clone) Print(out io.Writer, indent string) {
-	fmt.Fprintf(out, "\n%v%v [- -]", indent, n.name)
+func (n Clone) Walk(v node.Visitor) {
+	if v.Visit(n) == false {
+		return
+	}
 
 	if n.expr != nil {
-		fmt.Fprintf(out, "\n%vexpr:", indent+"  ")
-		n.expr.Print(out, indent+"    ")
+		vv := v.Children("expr")
+		n.expr.Walk(vv)
 	}
 }
diff --git a/node/expr/closure.go b/node/expr/closure.go
index fd31671..6d47ebe 100644
--- a/node/expr/closure.go
+++ b/node/expr/closure.go
@@ -1,9 +1,6 @@
 package expr
 
 import (
-	"fmt"
-	"io"
-
 	"github.com/z7zmey/php-parser/node"
 )
 
@@ -33,35 +30,37 @@ func NewClosure(params []node.Node, uses []node.Node, returnType node.Node, stmt
 	}
 }
 
-func (n Closure) Print(out io.Writer, indent string) {
-	fmt.Fprintf(out, "\n%v%v [- -]", indent, n.name)
+func (n Closure) Walk(v node.Visitor) {
+	if v.Visit(n) == false {
+		return
+	}
 
-	fmt.Fprintf(out, "\n%vis static: %t", indent+"  ", n.isStatic)
-	fmt.Fprintf(out, "\n%vis return ref: %t", indent+"  ", n.isReturnRef)
+	v.Scalar("isStatic", n.isStatic)
+	v.Scalar("isReturnRef", n.isReturnRef)
 
 	if n.params != nil {
-		fmt.Fprintf(out, "\n%vparams:", indent+"  ")
+		vv := v.Children("params")
 		for _, nn := range n.params {
-			nn.Print(out, indent+"    ")
+			nn.Walk(vv)
 		}
 	}
 
 	if n.uses != nil {
-		fmt.Fprintf(out, "\n%vuses:", indent+"  ")
+		vv := v.Children("uses")
 		for _, nn := range n.uses {
-			nn.Print(out, indent+"    ")
+			nn.Walk(vv)
 		}
 	}
 
 	if n.returnType != nil {
-		fmt.Fprintf(out, "\n%vreturn type:", indent+"  ")
-		n.returnType.Print(out, indent+"    ")
+		vv := v.Children("returnType")
+		n.returnType.Walk(vv)
 	}
 
 	if n.stmts != nil {
-		fmt.Fprintf(out, "\n%vstmts:", indent+"  ")
+		vv := v.Children("stmts")
 		for _, nn := range n.stmts {
-			nn.Print(out, indent+"    ")
+			nn.Walk(vv)
 		}
 	}
 }
diff --git a/node/expr/closure_use.go b/node/expr/closure_use.go
index b05ed2f..4e48da6 100644
--- a/node/expr/closure_use.go
+++ b/node/expr/closure_use.go
@@ -1,9 +1,6 @@
 package expr
 
 import (
-	"fmt"
-	"io"
-
 	"github.com/z7zmey/php-parser/node"
 )
 
@@ -25,12 +22,15 @@ func NewClusureUse(variable node.Node, byRef bool) node.Node {
 	}
 }
 
-func (n ClusureUse) Print(out io.Writer, indent string) {
-	fmt.Fprintf(out, "\n%v%v [- -]", indent, n.name)
-	fmt.Fprintf(out, "\n%vby ref: %t", indent+"  ", n.byRef)
+func (n ClusureUse) Walk(v node.Visitor) {
+	if v.Visit(n) == false {
+		return
+	}
+
+	v.Scalar("byRef", n.byRef)
 
 	if n.variable != nil {
-		fmt.Fprintf(out, "\n%vvariable:", indent+"  ")
-		n.variable.Print(out, indent+"    ")
+		vv := v.Children("variable")
+		n.variable.Walk(vv)
 	}
 }
diff --git a/node/expr/const_fetch.go b/node/expr/const_fetch.go
index 1b2b7ec..3607ba8 100644
--- a/node/expr/const_fetch.go
+++ b/node/expr/const_fetch.go
@@ -1,9 +1,6 @@
 package expr
 
 import (
-	"fmt"
-	"io"
-
 	"github.com/z7zmey/php-parser/node"
 )
 
@@ -23,11 +20,13 @@ func NewConstFetch(constant node.Node) node.Node {
 	}
 }
 
-func (n ConstFetch) Print(out io.Writer, indent string) {
-	fmt.Fprintf(out, "\n%v%v [- -]", indent, n.name)
+func (n ConstFetch) Walk(v node.Visitor) {
+	if v.Visit(n) == false {
+		return
+	}
 
 	if n.constant != nil {
-		fmt.Fprintf(out, "\n%vconstant:", indent+"  ")
-		n.constant.Print(out, indent+"    ")
+		vv := v.Children("constant")
+		n.constant.Walk(vv)
 	}
 }
diff --git a/node/expr/empty.go b/node/expr/empty.go
index f07ac29..3546c99 100644
--- a/node/expr/empty.go
+++ b/node/expr/empty.go
@@ -1,9 +1,6 @@
 package expr
 
 import (
-	"fmt"
-	"io"
-
 	"github.com/z7zmey/php-parser/node"
 )
 
@@ -23,11 +20,13 @@ func NewEmpty(expression node.Node) node.Node {
 	}
 }
 
-func (n Empty) Print(out io.Writer, indent string) {
-	fmt.Fprintf(out, "\n%v%v [- -]", indent, n.name)
+func (n Empty) Walk(v node.Visitor) {
+	if v.Visit(n) == false {
+		return
+	}
 
 	if n.expr != nil {
-		fmt.Fprintf(out, "\n%vexpr:", indent+"  ")
-		n.expr.Print(out, indent+"    ")
+		vv := v.Children("expr")
+		n.expr.Walk(vv)
 	}
 }
diff --git a/node/expr/error_suppress.go b/node/expr/error_suppress.go
index 0484eec..4bbd76f 100644
--- a/node/expr/error_suppress.go
+++ b/node/expr/error_suppress.go
@@ -1,9 +1,6 @@
 package expr
 
 import (
-	"fmt"
-	"io"
-
 	"github.com/z7zmey/php-parser/node"
 )
 
@@ -23,11 +20,13 @@ func NewErrorSuppress(expression node.Node) node.Node {
 	}
 }
 
-func (n ErrorSuppress) Print(out io.Writer, indent string) {
-	fmt.Fprintf(out, "\n%v%v [- -]", indent, n.name)
+func (n ErrorSuppress) Walk(v node.Visitor) {
+	if v.Visit(n) == false {
+		return
+	}
 
 	if n.expr != nil {
-		fmt.Fprintf(out, "\n%vexpr:", indent+"  ")
-		n.expr.Print(out, indent+"    ")
+		vv := v.Children("expr")
+		n.expr.Walk(vv)
 	}
 }
diff --git a/node/expr/eval.go b/node/expr/eval.go
index a7c50d1..08dcca3 100644
--- a/node/expr/eval.go
+++ b/node/expr/eval.go
@@ -1,9 +1,6 @@
 package expr
 
 import (
-	"fmt"
-	"io"
-
 	"github.com/z7zmey/php-parser/node"
 )
 
@@ -23,11 +20,13 @@ func NewEval(expression node.Node) node.Node {
 	}
 }
 
-func (n Eval) Print(out io.Writer, indent string) {
-	fmt.Fprintf(out, "\n%v%v [- -]", indent, n.name)
+func (n Eval) Walk(v node.Visitor) {
+	if v.Visit(n) == false {
+		return
+	}
 
 	if n.expr != nil {
-		fmt.Fprintf(out, "\n%vexpr:", indent+"  ")
-		n.expr.Print(out, indent+"    ")
+		vv := v.Children("expr")
+		n.expr.Walk(vv)
 	}
 }
diff --git a/node/expr/exit.go b/node/expr/exit.go
index 238770c..50248df 100644
--- a/node/expr/exit.go
+++ b/node/expr/exit.go
@@ -1,9 +1,6 @@
 package expr
 
 import (
-	"fmt"
-	"io"
-
 	"github.com/z7zmey/php-parser/node"
 )
 
@@ -25,12 +22,13 @@ func NewExit(expr node.Node, isDie bool) node.Node {
 	}
 }
 
-func (n Exit) Print(out io.Writer, indent string) {
-	fmt.Fprintf(out, "\n%v%v [- -]", indent, n.name)
-	fmt.Fprintf(out, "\n%vis die: %t", indent+"  ", n.isDie)
+func (n Exit) Walk(v node.Visitor) {
+	if v.Visit(n) == false {
+		return
+	}
 
 	if n.expr != nil {
-		fmt.Fprintf(out, "\n%vexpr:", indent+"  ")
-		n.expr.Print(out, indent+"    ")
+		vv := v.Children("expr")
+		n.expr.Walk(vv)
 	}
 }
diff --git a/node/expr/function_call.go b/node/expr/function_call.go
index 77878f4..90a8fe1 100644
--- a/node/expr/function_call.go
+++ b/node/expr/function_call.go
@@ -1,9 +1,6 @@
 package expr
 
 import (
-	"fmt"
-	"io"
-
 	"github.com/z7zmey/php-parser/node"
 )
 
@@ -25,18 +22,20 @@ func NewFunctionCall(function node.Node, arguments []node.Node) node.Node {
 	}
 }
 
-func (n FunctionCall) Print(out io.Writer, indent string) {
-	fmt.Fprintf(out, "\n%v%v [- -]", indent, n.name)
+func (n FunctionCall) Walk(v node.Visitor) {
+	if v.Visit(n) == false {
+		return
+	}
 
 	if n.function != nil {
-		fmt.Fprintf(out, "\n%vfunction:", indent+"  ")
-		n.function.Print(out, indent+"    ")
+		vv := v.Children("function")
+		n.function.Walk(vv)
 	}
 
 	if n.arguments != nil {
-		fmt.Fprintf(out, "\n%varguments:", indent+"  ")
+		vv := v.Children("arguments")
 		for _, nn := range n.arguments {
-			nn.Print(out, indent+"    ")
+			nn.Walk(vv)
 		}
 	}
 }
diff --git a/node/expr/include.go b/node/expr/include.go
index 9987af7..634e797 100644
--- a/node/expr/include.go
+++ b/node/expr/include.go
@@ -1,9 +1,6 @@
 package expr
 
 import (
-	"fmt"
-	"io"
-
 	"github.com/z7zmey/php-parser/node"
 )
 
@@ -23,11 +20,13 @@ func NewInclude(expression node.Node) node.Node {
 	}
 }
 
-func (n Include) Print(out io.Writer, indent string) {
-	fmt.Fprintf(out, "\n%v%v [- -]", indent, n.name)
+func (n Include) Walk(v node.Visitor) {
+	if v.Visit(n) == false {
+		return
+	}
 
 	if n.expr != nil {
-		fmt.Fprintf(out, "\n%vexpr:", indent+"  ")
-		n.expr.Print(out, indent+"    ")
+		vv := v.Children("expr")
+		n.expr.Walk(vv)
 	}
 }
diff --git a/node/expr/include_once.go b/node/expr/include_once.go
index 47962b2..8c564bb 100644
--- a/node/expr/include_once.go
+++ b/node/expr/include_once.go
@@ -1,9 +1,6 @@
 package expr
 
 import (
-	"fmt"
-	"io"
-
 	"github.com/z7zmey/php-parser/node"
 )
 
@@ -23,11 +20,13 @@ func NewIncludeOnce(expression node.Node) node.Node {
 	}
 }
 
-func (n IncludeOnce) Print(out io.Writer, indent string) {
-	fmt.Fprintf(out, "\n%v%v [- -]", indent, n.name)
+func (n IncludeOnce) Walk(v node.Visitor) {
+	if v.Visit(n) == false {
+		return
+	}
 
 	if n.expr != nil {
-		fmt.Fprintf(out, "\n%vexpr:", indent+"  ")
-		n.expr.Print(out, indent+"    ")
+		vv := v.Children("expr")
+		n.expr.Walk(vv)
 	}
 }
diff --git a/node/expr/instance_of.go b/node/expr/instance_of.go
index 324ddb3..94a1e27 100644
--- a/node/expr/instance_of.go
+++ b/node/expr/instance_of.go
@@ -1,9 +1,6 @@
 package expr
 
 import (
-	"fmt"
-	"io"
-
 	"github.com/z7zmey/php-parser/node"
 )
 
@@ -25,16 +22,18 @@ func NewInstanceOf(expr node.Node, class node.Node) node.Node {
 	}
 }
 
-func (n InstanceOf) Print(out io.Writer, indent string) {
-	fmt.Fprintf(out, "\n%v%v [- -]", indent, n.name)
+func (n InstanceOf) Walk(v node.Visitor) {
+	if v.Visit(n) == false {
+		return
+	}
 
 	if n.expr != nil {
-		fmt.Fprintf(out, "\n%vexpr:", indent+"  ")
-		n.expr.Print(out, indent+"    ")
+		vv := v.Children("expr")
+		n.expr.Walk(vv)
 	}
 
 	if n.class != nil {
-		fmt.Fprintf(out, "\n%vclass:", indent+"  ")
-		n.class.Print(out, indent+"    ")
+		vv := v.Children("class")
+		n.class.Walk(vv)
 	}
 }
diff --git a/node/expr/isset.go b/node/expr/isset.go
index 5df82d4..f17c74e 100644
--- a/node/expr/isset.go
+++ b/node/expr/isset.go
@@ -1,9 +1,6 @@
 package expr
 
 import (
-	"fmt"
-	"io"
-
 	"github.com/z7zmey/php-parser/node"
 )
 
@@ -23,13 +20,15 @@ func NewIsset(variables []node.Node) node.Node {
 	}
 }
 
-func (n Isset) Print(out io.Writer, indent string) {
-	fmt.Fprintf(out, "\n%v%v [- -]", indent, n.name)
+func (n Isset) Walk(v node.Visitor) {
+	if v.Visit(n) == false {
+		return
+	}
 
 	if n.variables != nil {
-		fmt.Fprintf(out, "\n%vvariables:", indent+"  ")
+		vv := v.Children("variables")
 		for _, nn := range n.variables {
-			nn.Print(out, indent+"    ")
+			nn.Walk(vv)
 		}
 	}
 }
diff --git a/node/expr/list.go b/node/expr/list.go
index 733e6bc..d9c9f34 100644
--- a/node/expr/list.go
+++ b/node/expr/list.go
@@ -1,9 +1,6 @@
 package expr
 
 import (
-	"fmt"
-	"io"
-
 	"github.com/z7zmey/php-parser/node"
 )
 
@@ -23,13 +20,15 @@ func NewList(items []node.Node) node.Node {
 	}
 }
 
-func (n List) Print(out io.Writer, indent string) {
-	fmt.Fprintf(out, "\n%v%v [- -]", indent, n.name)
+func (n List) Walk(v node.Visitor) {
+	if v.Visit(n) == false {
+		return
+	}
 
 	if n.items != nil {
-		fmt.Fprintf(out, "\n%vitems:", indent+"  ")
+		vv := v.Children("items")
 		for _, nn := range n.items {
-			nn.Print(out, indent+"    ")
+			nn.Walk(vv)
 		}
 	}
 }
diff --git a/node/expr/method_call.go b/node/expr/method_call.go
index cb3ff6d..1cbb154 100644
--- a/node/expr/method_call.go
+++ b/node/expr/method_call.go
@@ -1,9 +1,6 @@
 package expr
 
 import (
-	"fmt"
-	"io"
-
 	"github.com/z7zmey/php-parser/node"
 )
 
@@ -27,23 +24,25 @@ func NewMethodCall(variable node.Node, method node.Node, arguments []node.Node)
 	}
 }
 
-func (n MethodCall) Print(out io.Writer, indent string) {
-	fmt.Fprintf(out, "\n%v%v [- -]", indent, n.name)
+func (n MethodCall) Walk(v node.Visitor) {
+	if v.Visit(n) == false {
+		return
+	}
 
 	if n.variable != nil {
-		fmt.Fprintf(out, "\n%vvariable:", indent+"  ")
-		n.variable.Print(out, indent+"    ")
+		vv := v.Children("variable")
+		n.variable.Walk(vv)
 	}
 
 	if n.method != nil {
-		fmt.Fprintf(out, "\n%vmethod:", indent+"  ")
-		n.method.Print(out, indent+"    ")
+		vv := v.Children("method")
+		n.method.Walk(vv)
 	}
 
 	if n.arguments != nil {
-		fmt.Fprintf(out, "\n%varguments:", indent+"  ")
+		vv := v.Children("arguments")
 		for _, nn := range n.arguments {
-			nn.Print(out, indent+"    ")
+			nn.Walk(vv)
 		}
 	}
 }
diff --git a/node/expr/new.go b/node/expr/new.go
index ecd1b56..311cc17 100644
--- a/node/expr/new.go
+++ b/node/expr/new.go
@@ -1,9 +1,6 @@
 package expr
 
 import (
-	"fmt"
-	"io"
-
 	"github.com/z7zmey/php-parser/node"
 )
 
@@ -25,18 +22,20 @@ func NewNew(class node.Node, arguments []node.Node) node.Node {
 	}
 }
 
-func (n New) Print(out io.Writer, indent string) {
-	fmt.Fprintf(out, "\n%v%v [- -]", indent, n.name)
+func (n New) Walk(v node.Visitor) {
+	if v.Visit(n) == false {
+		return
+	}
 
 	if n.class != nil {
-		fmt.Fprintf(out, "\n%vclass:", indent+"  ")
-		n.class.Print(out, indent+"    ")
+		vv := v.Children("class")
+		n.class.Walk(vv)
 	}
 
 	if n.arguments != nil {
-		fmt.Fprintf(out, "\n%varguments:", indent+"  ")
+		vv := v.Children("arguments")
 		for _, nn := range n.arguments {
-			nn.Print(out, indent+"    ")
+			nn.Walk(vv)
 		}
 	}
 }
diff --git a/node/expr/post_dec.go b/node/expr/post_dec.go
index deb27d1..25d9dc6 100644
--- a/node/expr/post_dec.go
+++ b/node/expr/post_dec.go
@@ -1,9 +1,6 @@
 package expr
 
 import (
-	"fmt"
-	"io"
-
 	"github.com/z7zmey/php-parser/node"
 )
 
@@ -23,11 +20,13 @@ func NewPostDec(variableession node.Node) node.Node {
 	}
 }
 
-func (n PostDec) Print(out io.Writer, indent string) {
-	fmt.Fprintf(out, "\n%v%v [- -]", indent, n.name)
+func (n PostDec) Walk(v node.Visitor) {
+	if v.Visit(n) == false {
+		return
+	}
 
 	if n.variable != nil {
-		fmt.Fprintf(out, "\n%vvariable:", indent+"  ")
-		n.variable.Print(out, indent+"    ")
+		vv := v.Children("variable")
+		n.variable.Walk(vv)
 	}
 }
diff --git a/node/expr/post_inc.go b/node/expr/post_inc.go
index d036f4e..be9cccc 100644
--- a/node/expr/post_inc.go
+++ b/node/expr/post_inc.go
@@ -1,9 +1,6 @@
 package expr
 
 import (
-	"fmt"
-	"io"
-
 	"github.com/z7zmey/php-parser/node"
 )
 
@@ -23,11 +20,13 @@ func NewPostInc(variableession node.Node) node.Node {
 	}
 }
 
-func (n PostInc) Print(out io.Writer, indent string) {
-	fmt.Fprintf(out, "\n%v%v [- -]", indent, n.name)
+func (n PostInc) Walk(v node.Visitor) {
+	if v.Visit(n) == false {
+		return
+	}
 
 	if n.variable != nil {
-		fmt.Fprintf(out, "\n%vvariable:", indent+"  ")
-		n.variable.Print(out, indent+"    ")
+		vv := v.Children("variable")
+		n.variable.Walk(vv)
 	}
 }
diff --git a/node/expr/pre_dec.go b/node/expr/pre_dec.go
index 0b3d89d..2036ae6 100644
--- a/node/expr/pre_dec.go
+++ b/node/expr/pre_dec.go
@@ -1,9 +1,6 @@
 package expr
 
 import (
-	"fmt"
-	"io"
-
 	"github.com/z7zmey/php-parser/node"
 )
 
@@ -23,11 +20,13 @@ func NewPreDec(variableession node.Node) node.Node {
 	}
 }
 
-func (n PreDec) Print(out io.Writer, indent string) {
-	fmt.Fprintf(out, "\n%v%v [- -]", indent, n.name)
+func (n PreDec) Walk(v node.Visitor) {
+	if v.Visit(n) == false {
+		return
+	}
 
 	if n.variable != nil {
-		fmt.Fprintf(out, "\n%vvariable:", indent+"  ")
-		n.variable.Print(out, indent+"    ")
+		vv := v.Children("variable")
+		n.variable.Walk(vv)
 	}
 }
diff --git a/node/expr/pre_inc.go b/node/expr/pre_inc.go
index ca048da..3ddc59e 100644
--- a/node/expr/pre_inc.go
+++ b/node/expr/pre_inc.go
@@ -1,9 +1,6 @@
 package expr
 
 import (
-	"fmt"
-	"io"
-
 	"github.com/z7zmey/php-parser/node"
 )
 
@@ -23,11 +20,13 @@ func NewPreInc(variableession node.Node) node.Node {
 	}
 }
 
-func (n PreInc) Print(out io.Writer, indent string) {
-	fmt.Fprintf(out, "\n%v%v [- -]", indent, n.name)
+func (n PreInc) Walk(v node.Visitor) {
+	if v.Visit(n) == false {
+		return
+	}
 
 	if n.variable != nil {
-		fmt.Fprintf(out, "\n%vvariable:", indent+"  ")
-		n.variable.Print(out, indent+"    ")
+		vv := v.Children("variable")
+		n.variable.Walk(vv)
 	}
 }
diff --git a/node/expr/print.go b/node/expr/print.go
index ab2438f..6adcd5f 100644
--- a/node/expr/print.go
+++ b/node/expr/print.go
@@ -1,9 +1,6 @@
 package expr
 
 import (
-	"fmt"
-	"io"
-
 	"github.com/z7zmey/php-parser/node"
 )
 
@@ -23,11 +20,13 @@ func NewPrint(expression node.Node) node.Node {
 	}
 }
 
-func (n Print) Print(out io.Writer, indent string) {
-	fmt.Fprintf(out, "\n%v%v [- -]", indent, n.name)
+func (n Print) Walk(v node.Visitor) {
+	if v.Visit(n) == false {
+		return
+	}
 
 	if n.expr != nil {
-		fmt.Fprintf(out, "\n%vexpr:", indent+"  ")
-		n.expr.Print(out, indent+"    ")
+		vv := v.Children("expr")
+		n.expr.Walk(vv)
 	}
 }
diff --git a/node/expr/property_fetch.go b/node/expr/property_fetch.go
index 774823d..6469ba4 100644
--- a/node/expr/property_fetch.go
+++ b/node/expr/property_fetch.go
@@ -1,9 +1,6 @@
 package expr
 
 import (
-	"fmt"
-	"io"
-
 	"github.com/z7zmey/php-parser/node"
 )
 
@@ -25,16 +22,18 @@ func NewPropertyFetch(variable node.Node, property node.Node) node.Node {
 	}
 }
 
-func (n PropertyFetch) Print(out io.Writer, indent string) {
-	fmt.Fprintf(out, "\n%v%v [- -]", indent, n.name)
+func (n PropertyFetch) Walk(v node.Visitor) {
+	if v.Visit(n) == false {
+		return
+	}
 
 	if n.variable != nil {
-		fmt.Fprintf(out, "\n%vvariable:", indent+"  ")
-		n.variable.Print(out, indent+"    ")
+		vv := v.Children("variable")
+		n.variable.Walk(vv)
 	}
 
 	if n.property != nil {
-		fmt.Fprintf(out, "\n%vproperty:", indent+"  ")
-		n.property.Print(out, indent+"    ")
+		vv := v.Children("property")
+		n.property.Walk(vv)
 	}
 }
diff --git a/node/expr/require.go b/node/expr/require.go
index 2d13a17..0e6d7be 100644
--- a/node/expr/require.go
+++ b/node/expr/require.go
@@ -1,13 +1,10 @@
 package expr
 
 import (
-	"fmt"
-	"io"
-
 	"github.com/z7zmey/php-parser/node"
 )
 
-func(n Require) Name() string {
+func (n Require) Name() string {
 	return "Require"
 }
 
@@ -23,11 +20,13 @@ func NewRequire(expression node.Node) node.Node {
 	}
 }
 
-func (n Require) Print(out io.Writer, indent string) {
-	fmt.Fprintf(out, "\n%v%v [- -]", indent, n.name)
+func (n Require) Walk(v node.Visitor) {
+	if v.Visit(n) == false {
+		return
+	}
 
 	if n.expr != nil {
-		fmt.Fprintf(out, "\n%vexpr:", indent+"  ")
-		n.expr.Print(out, indent+"    ")
+		vv := v.Children("expr")
+		n.expr.Walk(vv)
 	}
 }
diff --git a/node/expr/require_once.go b/node/expr/require_once.go
index af2bf4d..491fa54 100644
--- a/node/expr/require_once.go
+++ b/node/expr/require_once.go
@@ -1,9 +1,6 @@
 package expr
 
 import (
-	"fmt"
-	"io"
-
 	"github.com/z7zmey/php-parser/node"
 )
 
@@ -23,11 +20,13 @@ func NewRequireOnce(expression node.Node) node.Node {
 	}
 }
 
-func (n RequireOnce) Print(out io.Writer, indent string) {
-	fmt.Fprintf(out, "\n%v%v [- -]", indent, n.name)
+func (n RequireOnce) Walk(v node.Visitor) {
+	if v.Visit(n) == false {
+		return
+	}
 
 	if n.expr != nil {
-		fmt.Fprintf(out, "\n%vexpr:", indent+"  ")
-		n.expr.Print(out, indent+"    ")
+		vv := v.Children("expr")
+		n.expr.Walk(vv)
 	}
 }
diff --git a/node/expr/shell_exec.go b/node/expr/shell_exec.go
index 69b31a2..4b7bb6a 100644
--- a/node/expr/shell_exec.go
+++ b/node/expr/shell_exec.go
@@ -1,9 +1,6 @@
 package expr
 
 import (
-	"fmt"
-	"io"
-
 	"github.com/z7zmey/php-parser/node"
 )
 
@@ -23,13 +20,15 @@ func NewShellExec(parts []node.Node) node.Node {
 	}
 }
 
-func (n ShellExec) Print(out io.Writer, indent string) {
-	fmt.Fprintf(out, "\n%v%v [- -]", indent, n.name)
+func (n ShellExec) Walk(v node.Visitor) {
+	if v.Visit(n) == false {
+		return
+	}
 
 	if n.parts != nil {
-		fmt.Fprintf(out, "\n%vparts:", indent+"  ")
+		vv := v.Children("parts")
 		for _, nn := range n.parts {
-			nn.Print(out, indent+"    ")
+			nn.Walk(vv)
 		}
 	}
 }
diff --git a/node/expr/short_array.go b/node/expr/short_array.go
index 2d73efe..0f4b2e2 100644
--- a/node/expr/short_array.go
+++ b/node/expr/short_array.go
@@ -1,9 +1,6 @@
 package expr
 
 import (
-	"fmt"
-	"io"
-
 	"github.com/z7zmey/php-parser/node"
 	"github.com/z7zmey/php-parser/token"
 )
@@ -28,13 +25,15 @@ func NewShortArray(opentToken token.Token, closeToken token.Token, items []node.
 	}
 }
 
-func (n ShortArray) Print(out io.Writer, indent string) {
-	fmt.Fprintf(out, "\n%v%v [%d %d]", indent, n.name, n.opentToken.StartLine, n.closeToken.EndLine)
+func (n ShortArray) Walk(v node.Visitor) {
+	if v.Visit(n) == false {
+		return
+	}
 
 	if n.items != nil {
-		fmt.Fprintf(out, "\n%vitems:", indent+"  ")
+		vv := v.Children("items")
 		for _, nn := range n.items {
-			nn.Print(out, indent+"    ")
+			nn.Walk(vv)
 		}
 	}
 }
diff --git a/node/expr/short_list.go b/node/expr/short_list.go
index 3efbe46..d7c3ac3 100644
--- a/node/expr/short_list.go
+++ b/node/expr/short_list.go
@@ -1,9 +1,6 @@
 package expr
 
 import (
-	"fmt"
-	"io"
-
 	"github.com/z7zmey/php-parser/node"
 )
 
@@ -23,13 +20,15 @@ func NewShortList(items []node.Node) node.Node {
 	}
 }
 
-func (n ShortList) Print(out io.Writer, indent string) {
-	fmt.Fprintf(out, "\n%v%v [- -]", indent, n.name)
+func (n ShortList) Walk(v node.Visitor) {
+	if v.Visit(n) == false {
+		return
+	}
 
 	if n.items != nil {
-		fmt.Fprintf(out, "\n%vitems:", indent+"  ")
+		vv := v.Children("items")
 		for _, nn := range n.items {
-			nn.Print(out, indent+"    ")
+			nn.Walk(vv)
 		}
 	}
 }
diff --git a/node/expr/static_call.go b/node/expr/static_call.go
index b21f657..41ddce1 100644
--- a/node/expr/static_call.go
+++ b/node/expr/static_call.go
@@ -1,9 +1,6 @@
 package expr
 
 import (
-	"fmt"
-	"io"
-
 	"github.com/z7zmey/php-parser/node"
 )
 
@@ -27,23 +24,25 @@ func NewStaticCall(class node.Node, call node.Node, arguments []node.Node) node.
 	}
 }
 
-func (n StaticCall) Print(out io.Writer, indent string) {
-	fmt.Fprintf(out, "\n%v%v [- -]", indent, n.name)
+func (n StaticCall) Walk(v node.Visitor) {
+	if v.Visit(n) == false {
+		return
+	}
 
 	if n.class != nil {
-		fmt.Fprintf(out, "\n%vclass:", indent+"  ")
-		n.class.Print(out, indent+"    ")
+		vv := v.Children("class")
+		n.class.Walk(vv)
 	}
 
 	if n.call != nil {
-		fmt.Fprintf(out, "\n%vcall:", indent+"  ")
-		n.call.Print(out, indent+"    ")
+		vv := v.Children("call")
+		n.call.Walk(vv)
 	}
 
 	if n.arguments != nil {
-		fmt.Fprintf(out, "\n%varguments:", indent+"  ")
+		vv := v.Children("arguments")
 		for _, nn := range n.arguments {
-			nn.Print(out, indent+"    ")
+			nn.Walk(vv)
 		}
 	}
 }
diff --git a/node/expr/static_property_fetch.go b/node/expr/static_property_fetch.go
index 7163c3e..4a67fd4 100644
--- a/node/expr/static_property_fetch.go
+++ b/node/expr/static_property_fetch.go
@@ -1,9 +1,6 @@
 package expr
 
 import (
-	"fmt"
-	"io"
-
 	"github.com/z7zmey/php-parser/node"
 )
 
@@ -25,16 +22,18 @@ func NewStaticPropertyFetch(class node.Node, property node.Node) node.Node {
 	}
 }
 
-func (n StaticPropertyFetch) Print(out io.Writer, indent string) {
-	fmt.Fprintf(out, "\n%v%v [- -]", indent, n.name)
+func (n StaticPropertyFetch) Walk(v node.Visitor) {
+	if v.Visit(n) == false {
+		return
+	}
 
 	if n.class != nil {
-		fmt.Fprintf(out, "\n%vclass:", indent+"  ")
-		n.class.Print(out, indent+"    ")
+		vv := v.Children("class")
+		n.class.Walk(vv)
 	}
 
 	if n.property != nil {
-		fmt.Fprintf(out, "\n%vproperty:", indent+"  ")
-		n.property.Print(out, indent+"    ")
+		vv := v.Children("property")
+		n.property.Walk(vv)
 	}
 }
diff --git a/node/expr/ternary.go b/node/expr/ternary.go
index 8b6768e..9296c14 100644
--- a/node/expr/ternary.go
+++ b/node/expr/ternary.go
@@ -1,9 +1,6 @@
 package expr
 
 import (
-	"fmt"
-	"io"
-
 	"github.com/z7zmey/php-parser/node"
 )
 
@@ -27,21 +24,23 @@ func NewTernary(condition node.Node, ifTrue node.Node, ifFalse node.Node) node.N
 	}
 }
 
-func (n Ternary) Print(out io.Writer, indent string) {
-	fmt.Fprintf(out, "\n%v%v [- -]", indent, n.name)
+func (n Ternary) Walk(v node.Visitor) {
+	if v.Visit(n) == false {
+		return
+	}
 
 	if n.condition != nil {
-		fmt.Fprintf(out, "\n%vcondition:", indent+"  ")
-		n.condition.Print(out, indent+"    ")
+		vv := v.Children("condition")
+		n.condition.Walk(vv)
 	}
 
 	if n.ifTrue != nil {
-		fmt.Fprintf(out, "\n%vifTrue:", indent+"  ")
-		n.ifTrue.Print(out, indent+"    ")
+		vv := v.Children("ifTrue")
+		n.ifTrue.Walk(vv)
 	}
 
 	if n.ifFalse != nil {
-		fmt.Fprintf(out, "\n%vifFalse:", indent+"  ")
-		n.ifFalse.Print(out, indent+"    ")
+		vv := v.Children("ifFalse")
+		n.ifFalse.Walk(vv)
 	}
 }
diff --git a/node/expr/unary_minus.go b/node/expr/unary_minus.go
index f0cdc7c..4ecb90c 100644
--- a/node/expr/unary_minus.go
+++ b/node/expr/unary_minus.go
@@ -1,9 +1,6 @@
 package expr
 
 import (
-	"fmt"
-	"io"
-
 	"github.com/z7zmey/php-parser/node"
 )
 
@@ -23,11 +20,13 @@ func NewUnaryMinus(expression node.Node) node.Node {
 	}
 }
 
-func (n UnaryMinus) Print(out io.Writer, indent string) {
-	fmt.Fprintf(out, "\n%v%v [- -]", indent, n.name)
+func (n UnaryMinus) Walk(v node.Visitor) {
+	if v.Visit(n) == false {
+		return
+	}
 
 	if n.expr != nil {
-		fmt.Fprintf(out, "\n%vexpr:", indent+"  ")
-		n.expr.Print(out, indent+"    ")
+		vv := v.Children("expr")
+		n.expr.Walk(vv)
 	}
 }
diff --git a/node/expr/unary_plus.go b/node/expr/unary_plus.go
index aff43d3..c0bb60d 100644
--- a/node/expr/unary_plus.go
+++ b/node/expr/unary_plus.go
@@ -1,9 +1,6 @@
 package expr
 
 import (
-	"fmt"
-	"io"
-
 	"github.com/z7zmey/php-parser/node"
 )
 
@@ -23,11 +20,13 @@ func NewUnaryPlus(expression node.Node) node.Node {
 	}
 }
 
-func (n UnaryPlus) Print(out io.Writer, indent string) {
-	fmt.Fprintf(out, "\n%v%v [- -]", indent, n.name)
+func (n UnaryPlus) Walk(v node.Visitor) {
+	if v.Visit(n) == false {
+		return
+	}
 
 	if n.expr != nil {
-		fmt.Fprintf(out, "\n%vexpr:", indent+"  ")
-		n.expr.Print(out, indent+"    ")
+		vv := v.Children("expr")
+		n.expr.Walk(vv)
 	}
 }
diff --git a/node/expr/variable.go b/node/expr/variable.go
index 3213d05..3d0e787 100644
--- a/node/expr/variable.go
+++ b/node/expr/variable.go
@@ -1,9 +1,6 @@
 package expr
 
 import (
-	"fmt"
-	"io"
-
 	"github.com/z7zmey/php-parser/node"
 )
 
@@ -12,22 +9,24 @@ func (n Variable) Name() string {
 }
 
 type Variable struct {
-	name     string
-	variable node.Node
+	name    string
+	varName node.Node
 }
 
-func NewVariable(variable node.Node) node.Node {
+func NewVariable(varName node.Node) node.Node {
 	return Variable{
 		"Variable",
-		variable,
+		varName,
 	}
 }
 
-func (n Variable) Print(out io.Writer, indent string) {
-	fmt.Fprintf(out, "\n%v%v [- -]", indent, n.name)
+func (n Variable) Walk(v node.Visitor) {
+	if v.Visit(n) == false {
+		return
+	}
 
-	if n.variable != nil {
-		fmt.Fprintf(out, "\n%vvariable:", indent+"  ")
-		n.variable.Print(out, indent+"    ")
+	if n.varName != nil {
+		vv := v.Children("varName")
+		n.varName.Walk(vv)
 	}
 }
diff --git a/node/expr/yield.go b/node/expr/yield.go
index 4de1c01..470aceb 100644
--- a/node/expr/yield.go
+++ b/node/expr/yield.go
@@ -1,9 +1,6 @@
 package expr
 
 import (
-	"fmt"
-	"io"
-
 	"github.com/z7zmey/php-parser/node"
 )
 
@@ -25,16 +22,18 @@ func NewYield(key node.Node, value node.Node) node.Node {
 	}
 }
 
-func (n Yield) Print(out io.Writer, indent string) {
-	fmt.Fprintf(out, "\n%v%v [- -]", indent, n.name)
+func (n Yield) Walk(v node.Visitor) {
+	if v.Visit(n) == false {
+		return
+	}
 
 	if n.key != nil {
-		fmt.Fprintf(out, "\n%vkey:", indent+"  ")
-		n.key.Print(out, indent+"    ")
+		vv := v.Children("key")
+		n.key.Walk(vv)
 	}
 
 	if n.value != nil {
-		fmt.Fprintf(out, "\n%vvalue:", indent+"  ")
-		n.value.Print(out, indent+"    ")
+		vv := v.Children("value")
+		n.value.Walk(vv)
 	}
 }
diff --git a/node/expr/yield_from.go b/node/expr/yield_from.go
index 95006a0..78f6a7f 100644
--- a/node/expr/yield_from.go
+++ b/node/expr/yield_from.go
@@ -1,9 +1,6 @@
 package expr
 
 import (
-	"fmt"
-	"io"
-
 	"github.com/z7zmey/php-parser/node"
 )
 
@@ -23,11 +20,13 @@ func NewYieldFrom(expression node.Node) node.Node {
 	}
 }
 
-func (n YieldFrom) Print(out io.Writer, indent string) {
-	fmt.Fprintf(out, "\n%v%v [- -]", indent, n.name)
+func (n YieldFrom) Walk(v node.Visitor) {
+	if v.Visit(n) == false {
+		return
+	}
 
 	if n.expr != nil {
-		fmt.Fprintf(out, "\n%vexpr:", indent+"  ")
-		n.expr.Print(out, indent+"    ")
+		vv := v.Children("expr")
+		n.expr.Walk(vv)
 	}
 }
diff --git a/node/identifier.go b/node/identifier.go
index 45b6b15..4d38366 100644
--- a/node/identifier.go
+++ b/node/identifier.go
@@ -1,9 +1,6 @@
 package node
 
 import (
-	"fmt"
-	"io"
-
 	"github.com/z7zmey/php-parser/token"
 )
 
@@ -23,7 +20,10 @@ func NewIdentifier(token token.Token) Node {
 	}
 }
 
-func (n Identifier) Print(out io.Writer, indent string) {
-	fmt.Fprintf(out, "\n%v%v [- -]", indent, n.name)
-	fmt.Fprintf(out, "\n%vname: %q", indent+"  ", n.token.Value)
+func (n Identifier) Walk(v Visitor) {
+	if v.Visit(n) == false {
+		return
+	}
+
+	v.Scalar("token", n.token.Value)
 }
diff --git a/node/name/name.go b/node/name/name.go
index bd2dcbd..30c5eb6 100644
--- a/node/name/name.go
+++ b/node/name/name.go
@@ -1,9 +1,6 @@
 package name
 
 import (
-	"fmt"
-	"io"
-
 	"github.com/z7zmey/php-parser/node"
 )
 
@@ -23,13 +20,15 @@ func NewName(parts []node.Node) node.Node {
 	}
 }
 
-func (n NameNode) Print(out io.Writer, indent string) {
-	fmt.Fprintf(out, "\n%v%v", indent, n.name)
+func (n NameNode) Walk(v node.Visitor) {
+	if v.Visit(n) == false {
+		return
+	}
 
 	if n.parts != nil {
-		fmt.Fprintf(out, "\n%vparts:", indent+"  ")
+		vv := v.Children("parts")
 		for _, nn := range n.parts {
-			nn.Print(out, indent+"    ")
+			nn.Walk(vv)
 		}
 	}
 }
diff --git a/node/name/name_part.go b/node/name/name_part.go
index e5c59c5..56f35d8 100644
--- a/node/name/name_part.go
+++ b/node/name/name_part.go
@@ -1,14 +1,11 @@
 package name
 
 import (
-	"fmt"
-	"io"
-
 	"github.com/z7zmey/php-parser/node"
 	"github.com/z7zmey/php-parser/token"
 )
 
-func(n NamePart) Name() string {
+func (n NamePart) Name() string {
 	return "NamePart"
 }
 
@@ -24,6 +21,10 @@ func NewNamePart(token token.Token) node.Node {
 	}
 }
 
-func (n NamePart) Print(out io.Writer, indent string) {
-	fmt.Fprintf(out, "\n%v%v [%d %d] %q", indent, n.name, n.token.StartLine, n.token.EndLine, n.token.Value)
+func (n NamePart) Walk(v node.Visitor) {
+	if v.Visit(n) == false {
+		return
+	}
+
+	v.Scalar("token", n.token.Value)
 }
diff --git a/node/node.go b/node/node.go
index 6be4d59..0dca0ac 100644
--- a/node/node.go
+++ b/node/node.go
@@ -1,10 +1,6 @@
 package node
 
-import (
-	"io"
-)
-
 type Node interface {
 	Name() string
-	Print(out io.Writer, indent string)
+	Walk(v Visitor)
 }
diff --git a/node/nullable.go b/node/nullable.go
index e08e787..da751c3 100644
--- a/node/nullable.go
+++ b/node/nullable.go
@@ -1,10 +1,5 @@
 package node
 
-import (
-	"fmt"
-	"io"
-)
-
 type Nullable struct {
 	name string
 	expr Node
@@ -21,11 +16,13 @@ func NewNullable(expression Node) Node {
 	}
 }
 
-func (n Nullable) Print(out io.Writer, indent string) {
-	fmt.Fprintf(out, "\n%v%v [- -]", indent, n.name)
+func (n Nullable) Walk(v Visitor) {
+	if v.Visit(n) == false {
+		return
+	}
 
 	if n.expr != nil {
-		fmt.Fprintf(out, "\n%vexpr:", indent+"  ")
-		n.expr.Print(out, indent+"    ")
+		vv := v.Children("expr")
+		n.expr.Walk(vv)
 	}
 }
diff --git a/node/parameter.go b/node/parameter.go
index 2c0514f..90e35e1 100644
--- a/node/parameter.go
+++ b/node/parameter.go
@@ -1,10 +1,5 @@
 package node
 
-import (
-	"fmt"
-	"io"
-)
-
 type Parameter struct {
 	name         string
 	variableType Node
@@ -29,24 +24,26 @@ func NewParameter(variableType Node, variable Node, defaultValue Node, byRef boo
 	}
 }
 
-func (n Parameter) Print(out io.Writer, indent string) {
-	fmt.Fprintf(out, "\n%v%v [- -]", indent, n.name)
-	fmt.Fprintf(out, "\n%vbyRef: %t", indent+"  ", n.byRef)
-	fmt.Fprintf(out, "\n%vvariadic: %t", indent+"  ", n.variadic)
+func (n Parameter) Walk(v Visitor) {
+	if v.Visit(n) == false {
+		return
+	}
+
+	v.Scalar("byRef", n.byRef)
+	v.Scalar("variadic", n.variadic)
 
 	if n.variableType != nil {
-		fmt.Fprintf(out, "\n%vvariableType:", indent+"  ")
-		n.variableType.Print(out, indent+"    ")
+		vv := v.Children("variableType")
+		n.variableType.Walk(vv)
 	}
 
 	if n.variable != nil {
-		fmt.Fprintf(out, "\n%vvariable:", indent+"  ")
-		n.variable.Print(out, indent+"    ")
+		vv := v.Children("variable")
+		n.variable.Walk(vv)
 	}
 
 	if n.defaultValue != nil {
-		fmt.Fprintf(out, "\n%vdefaultValue:", indent+"  ")
-		n.defaultValue.Print(out, indent+"    ")
+		vv := v.Children("defaultValue")
+		n.defaultValue.Walk(vv)
 	}
-
 }
diff --git a/node/scalar/dnumber.go b/node/scalar/dnumber.go
index 1169782..5c8bd96 100644
--- a/node/scalar/dnumber.go
+++ b/node/scalar/dnumber.go
@@ -1,14 +1,11 @@
 package scalar
 
 import (
-	"fmt"
-	"io"
-
 	"github.com/z7zmey/php-parser/node"
 	"github.com/z7zmey/php-parser/token"
 )
 
-func(n Dnumber) Name() string {
+func (n Dnumber) Name() string {
 	return "Dnumber"
 }
 
@@ -24,6 +21,10 @@ func NewDnumber(token token.Token) node.Node {
 	}
 }
 
-func (n Dnumber) Print(out io.Writer, indent string) {
-	fmt.Fprintf(out, "\n%v%v [%d %d] %q", indent, n.name, n.token.StartLine, n.token.EndLine, n.token.Value)
+func (n Dnumber) Walk(v node.Visitor) {
+	if v.Visit(n) == false {
+		return
+	}
+
+	v.Scalar("token", n.token.Value)
 }
diff --git a/node/scalar/encapsed.go b/node/scalar/encapsed.go
index 26c3361..6ebeaf8 100644
--- a/node/scalar/encapsed.go
+++ b/node/scalar/encapsed.go
@@ -1,14 +1,11 @@
 package scalar
 
 import (
-	"fmt"
-	"io"
-
 	"github.com/z7zmey/php-parser/node"
 	"github.com/z7zmey/php-parser/token"
 )
 
-func(n Encapsed) Name() string {
+func (n Encapsed) Name() string {
 	return "Encapsed"
 }
 
@@ -28,13 +25,15 @@ func NewEncapsed(startToken token.Token, parts []node.Node, endToken token.Token
 	}
 }
 
-func (n Encapsed) Print(out io.Writer, indent string) {
-	fmt.Fprintf(out, "\n%v%v [%d %d]", indent, n.name, n.startToken.StartLine, n.endToken.EndLine)
+func (n Encapsed) Walk(v node.Visitor) {
+	if v.Visit(n) == false {
+		return
+	}
 
 	if n.parts != nil {
-		fmt.Fprintf(out, "\n%vparts:", indent+"  ")
+		vv := v.Children("parts")
 		for _, nn := range n.parts {
-			nn.Print(out, indent+"    ")
+			nn.Walk(vv)
 		}
 	}
 }
diff --git a/node/scalar/encapsed_string_part.go b/node/scalar/encapsed_string_part.go
index 0c8f77b..41ea6cf 100644
--- a/node/scalar/encapsed_string_part.go
+++ b/node/scalar/encapsed_string_part.go
@@ -1,14 +1,11 @@
 package scalar
 
 import (
-	"fmt"
-	"io"
-
 	"github.com/z7zmey/php-parser/node"
 	"github.com/z7zmey/php-parser/token"
 )
 
-func(n EncapsedStringPart) Name() string {
+func (n EncapsedStringPart) Name() string {
 	return "EncapsedStringPart"
 }
 
@@ -24,6 +21,10 @@ func NewEncapsedStringPart(t token.Token) node.Node {
 	}
 }
 
-func (n EncapsedStringPart) Print(out io.Writer, indent string) {
-	fmt.Fprintf(out, "\n%v%v [%d %d] %q", indent, n.name, n.token.StartLine, n.token.EndLine, n.token.Value)
+func (n EncapsedStringPart) Walk(v node.Visitor) {
+	if v.Visit(n) == false {
+		return
+	}
+
+	v.Scalar("token", n.token.Value)
 }
diff --git a/node/scalar/lnumber.go b/node/scalar/lnumber.go
index 47c65df..68cb21d 100644
--- a/node/scalar/lnumber.go
+++ b/node/scalar/lnumber.go
@@ -1,14 +1,11 @@
 package scalar
 
 import (
-	"fmt"
-	"io"
-
 	"github.com/z7zmey/php-parser/node"
 	"github.com/z7zmey/php-parser/token"
 )
 
-func(n Lnumber) Name() string {
+func (n Lnumber) Name() string {
 	return "Lnumber"
 }
 
@@ -24,6 +21,10 @@ func NewLnumber(token token.Token) node.Node {
 	}
 }
 
-func (n Lnumber) Print(out io.Writer, indent string) {
-	fmt.Fprintf(out, "\n%v%v [%d %d] %q", indent, n.name, n.token.StartLine, n.token.EndLine, n.token.Value)
+func (n Lnumber) Walk(v node.Visitor) {
+	if v.Visit(n) == false {
+		return
+	}
+
+	v.Scalar("token", n.token.Value)
 }
diff --git a/node/scalar/magic_constant.go b/node/scalar/magic_constant.go
index 6dfaf9c..0993927 100644
--- a/node/scalar/magic_constant.go
+++ b/node/scalar/magic_constant.go
@@ -1,14 +1,11 @@
 package scalar
 
 import (
-	"fmt"
-	"io"
-
 	"github.com/z7zmey/php-parser/node"
 	"github.com/z7zmey/php-parser/token"
 )
 
-func(n MagicConstant) Name() string {
+func (n MagicConstant) Name() string {
 	return "MagicConstant"
 }
 
@@ -24,6 +21,10 @@ func NewMagicConstant(token token.Token) node.Node {
 	}
 }
 
-func (n MagicConstant) Print(out io.Writer, indent string) {
-	fmt.Fprintf(out, "\n%v%v [%d %d] %q", indent, n.name, n.token.StartLine, n.token.EndLine, n.token.Value)
+func (n MagicConstant) Walk(v node.Visitor) {
+	if v.Visit(n) == false {
+		return
+	}
+
+	v.Scalar("token", n.token.Value)
 }
diff --git a/node/scalar/string.go b/node/scalar/string.go
index 400825a..82784e0 100644
--- a/node/scalar/string.go
+++ b/node/scalar/string.go
@@ -1,14 +1,11 @@
 package scalar
 
 import (
-	"fmt"
-	"io"
-
 	"github.com/z7zmey/php-parser/node"
 	"github.com/z7zmey/php-parser/token"
 )
 
-func(n String) Name() string {
+func (n String) Name() string {
 	return "String"
 }
 
@@ -24,6 +21,10 @@ func NewString(token token.Token) node.Node {
 	}
 }
 
-func (n String) Print(out io.Writer, indent string) {
-	fmt.Fprintf(out, "\n%v%v [%d %d] %q", indent, n.name, n.token.StartLine, n.token.EndLine, n.token.Value)
+func (n String) Walk(v node.Visitor) {
+	if v.Visit(n) == false {
+		return
+	}
+
+	v.Scalar("token", n.token.Value)
 }
diff --git a/node/stmt/alt_else.go b/node/stmt/alt_else.go
index 65bce03..4e5d768 100644
--- a/node/stmt/alt_else.go
+++ b/node/stmt/alt_else.go
@@ -1,14 +1,11 @@
 package stmt
 
 import (
-	"fmt"
-	"io"
-
 	"github.com/z7zmey/php-parser/node"
 	"github.com/z7zmey/php-parser/token"
 )
 
-func(n AltElse) Name() string {
+func (n AltElse) Name() string {
 	return "AltElse"
 }
 
@@ -26,11 +23,13 @@ func NewAltElse(token token.Token, stmt node.Node) node.Node {
 	}
 }
 
-func (n AltElse) Print(out io.Writer, indent string) {
-	fmt.Fprintf(out, "\n%v%v [%d %d] %q", indent, n.name, n.token.StartLine, n.token.EndLine, n.token.Value)
+func (n AltElse) Walk(v node.Visitor) {
+	if v.Visit(n) == false {
+		return
+	}
 
 	if n.stmt != nil {
-		fmt.Fprintf(out, "\n%vstmt:", indent+"  ")
-		n.stmt.Print(out, indent+"    ")
+		vv := v.Children("stmt")
+		n.stmt.Walk(vv)
 	}
 }
diff --git a/node/stmt/alt_else_if.go b/node/stmt/alt_else_if.go
index 9826698..c88cbfa 100644
--- a/node/stmt/alt_else_if.go
+++ b/node/stmt/alt_else_if.go
@@ -1,14 +1,11 @@
 package stmt
 
 import (
-	"fmt"
-	"io"
-
 	"github.com/z7zmey/php-parser/node"
 	"github.com/z7zmey/php-parser/token"
 )
 
-func(n AltElseIf) Name() string {
+func (n AltElseIf) Name() string {
 	return "AltElseIf"
 }
 
@@ -28,16 +25,18 @@ func NewAltElseIf(token token.Token, cond node.Node, stmt node.Node) node.Node {
 	}
 }
 
-func (n AltElseIf) Print(out io.Writer, indent string) {
-	fmt.Fprintf(out, "\n%v%v [%d %d] %q", indent, n.name, n.token.StartLine, n.token.EndLine, n.token.Value)
+func (n AltElseIf) Walk(v node.Visitor) {
+	if v.Visit(n) == false {
+		return
+	}
 
 	if n.cond != nil {
-		fmt.Fprintf(out, "\n%vcond:", indent+"  ")
-		n.cond.Print(out, indent+"    ")
+		vv := v.Children("cond")
+		n.cond.Walk(vv)
 	}
 
 	if n.stmt != nil {
-		fmt.Fprintf(out, "\n%vstmt:", indent+"  ")
-		n.stmt.Print(out, indent+"    ")
+		vv := v.Children("stmt")
+		n.stmt.Walk(vv)
 	}
 }
diff --git a/node/stmt/alt_if.go b/node/stmt/alt_if.go
index ab58dd5..7deca96 100644
--- a/node/stmt/alt_if.go
+++ b/node/stmt/alt_if.go
@@ -1,24 +1,21 @@
 package stmt
 
 import (
-	"fmt"
-	"io"
-
 	"github.com/z7zmey/php-parser/node"
 	"github.com/z7zmey/php-parser/token"
 )
 
-func(n AltIf) Name() string {
+func (n AltIf) Name() string {
 	return "AltIf"
 }
 
 type AltIf struct {
-	name      string
-	token     token.Token
-	cond      node.Node
-	stmt      node.Node
-	elseAltIf []node.Node
-	_else     node.Node
+	name   string
+	token  token.Token
+	cond   node.Node
+	stmt   node.Node
+	elseIf []node.Node
+	_else  node.Node
 }
 
 func NewAltIf(token token.Token, cond node.Node, stmt node.Node) node.Node {
@@ -32,12 +29,12 @@ func NewAltIf(token token.Token, cond node.Node, stmt node.Node) node.Node {
 	}
 }
 
-func (n AltIf) AddElseIf(elseAltIf node.Node) node.Node {
-	if n.elseAltIf == nil {
-		n.elseAltIf = make([]node.Node, 0)
+func (n AltIf) AddElseIf(elseIf node.Node) node.Node {
+	if n.elseIf == nil {
+		n.elseIf = make([]node.Node, 0)
 	}
 
-	n.elseAltIf = append(n.elseAltIf, elseAltIf)
+	n.elseIf = append(n.elseIf, elseIf)
 
 	return n
 }
@@ -48,27 +45,30 @@ func (n AltIf) SetElse(_else node.Node) node.Node {
 	return n
 }
 
-func (n AltIf) Print(out io.Writer, indent string) {
-	fmt.Fprintf(out, "\n%v%v [%d %d] %q", indent, n.name, n.token.StartLine, n.token.EndLine, n.token.Value)
+func (n AltIf) Walk(v node.Visitor) {
+	if v.Visit(n) == false {
+		return
+	}
 
 	if n.cond != nil {
-		fmt.Fprintf(out, "\n%vcond:", indent+"  ")
-		n.cond.Print(out, indent+"    ")
+		vv := v.Children("cond")
+		n.cond.Walk(vv)
 	}
 
 	if n.stmt != nil {
-		fmt.Fprintf(out, "\n%vstmt:", indent+"  ")
-		n.stmt.Print(out, indent+"    ")
+		vv := v.Children("stmt")
+		n.stmt.Walk(vv)
 	}
 
-	if n.elseAltIf != nil {
-		fmt.Fprintf(out, "\n%velseAltIfs:", indent+"  ")
-		for _, nn := range n.elseAltIf {
-			nn.Print(out, indent+"    ")
+	if n.elseIf != nil {
+		vv := v.Children("elseIf")
+		for _, nn := range n.elseIf {
+			nn.Walk(vv)
 		}
 	}
+
 	if n._else != nil {
-		fmt.Fprintf(out, "\n%velse:", indent+"  ")
-		n._else.Print(out, indent+"    ")
+		vv := v.Children("else")
+		n._else.Walk(vv)
 	}
 }
diff --git a/node/stmt/break.go b/node/stmt/break.go
index 1a72f55..9749b15 100644
--- a/node/stmt/break.go
+++ b/node/stmt/break.go
@@ -1,14 +1,11 @@
 package stmt
 
 import (
-	"fmt"
-	"io"
-
 	"github.com/z7zmey/php-parser/node"
 	"github.com/z7zmey/php-parser/token"
 )
 
-func(n Break) Name() string {
+func (n Break) Name() string {
 	return "Break"
 }
 
@@ -26,11 +23,13 @@ func NewBreak(token token.Token, expr node.Node) node.Node {
 	}
 }
 
-func (n Break) Print(out io.Writer, indent string) {
-	fmt.Fprintf(out, "\n%v%v [%d %d] %q", indent, n.name, n.token.StartLine, n.token.EndLine, n.token.Value)
+func (n Break) Walk(v node.Visitor) {
+	if v.Visit(n) == false {
+		return
+	}
 
 	if n.expr != nil {
-		fmt.Fprintf(out, "\n%vexpr:", indent+"  ")
-		n.expr.Print(out, indent+"    ")
+		vv := v.Children("expr")
+		n.expr.Walk(vv)
 	}
 }
diff --git a/node/stmt/case.go b/node/stmt/case.go
index ca1069e..05f9326 100644
--- a/node/stmt/case.go
+++ b/node/stmt/case.go
@@ -1,14 +1,11 @@
 package stmt
 
 import (
-	"fmt"
-	"io"
-
 	"github.com/z7zmey/php-parser/node"
 	"github.com/z7zmey/php-parser/token"
 )
 
-func(n Case) Name() string {
+func (n Case) Name() string {
 	return "Case"
 }
 
@@ -28,16 +25,20 @@ func NewCase(token token.Token, cond node.Node, stmts []node.Node) node.Node {
 	}
 }
 
-func (n Case) Print(out io.Writer, indent string) {
-	fmt.Fprintf(out, "\n%v%v [%d %d] %q", indent, n.name, n.token.StartLine, n.token.EndLine, n.token.Value)
+func (n Case) Walk(v node.Visitor) {
+	if v.Visit(n) == false {
+		return
+	}
 
-	fmt.Fprintf(out, "\n%vcond:", indent+"  ")
-	n.cond.Print(out, indent+"    ")
+	if n.cond != nil {
+		vv := v.Children("cond")
+		n.cond.Walk(vv)
+	}
 
 	if n.stmts != nil {
-		fmt.Fprintf(out, "\n%vstmts:", indent+"  ")
+		vv := v.Children("stmts")
 		for _, nn := range n.stmts {
-			nn.Print(out, indent+"    ")
+			nn.Walk(vv)
 		}
 	}
 }
diff --git a/node/stmt/catch.go b/node/stmt/catch.go
index d4d541f..1444786 100644
--- a/node/stmt/catch.go
+++ b/node/stmt/catch.go
@@ -1,14 +1,11 @@
 package stmt
 
 import (
-	"fmt"
-	"io"
-
 	"github.com/z7zmey/php-parser/node"
 	"github.com/z7zmey/php-parser/token"
 )
 
-func(n Catch) Name() string {
+func (n Catch) Name() string {
 	return "Catch"
 }
 
@@ -30,21 +27,22 @@ func NewCatch(token token.Token, types []node.Node, variable node.Node, stmts []
 	}
 }
 
-func (n Catch) Print(out io.Writer, indent string) {
-	fmt.Fprintf(out, "\n%v%v [%d %d] %q", indent, n.name, n.token.StartLine, n.token.EndLine, n.token.Value)
-
-	fmt.Fprintf(out, "\n%vtypes:", indent+"  ")
-	for _, nn := range n.types {
-		nn.Print(out, indent+"    ")
+func (n Catch) Walk(v node.Visitor) {
+	if v.Visit(n) == false {
+		return
 	}
 
-	fmt.Fprintf(out, "\n%vvariable:", indent+"  ")
-	n.variable.Print(out, indent+"    ")
+	if n.types != nil {
+		vv := v.Children("types")
+		for _, nn := range n.types {
+			nn.Walk(vv)
+		}
+	}
 
 	if n.stmts != nil {
-		fmt.Fprintf(out, "\n%vstmts:", indent+"  ")
+		vv := v.Children("stmts")
 		for _, nn := range n.stmts {
-			nn.Print(out, indent+"    ")
+			nn.Walk(vv)
 		}
 	}
 }
diff --git a/node/stmt/class.go b/node/stmt/class.go
index 4f4ba53..cf32ea8 100644
--- a/node/stmt/class.go
+++ b/node/stmt/class.go
@@ -1,14 +1,11 @@
 package stmt
 
 import (
-	"fmt"
-	"io"
-
 	"github.com/z7zmey/php-parser/node"
 	"github.com/z7zmey/php-parser/token"
 )
 
-func(n Class) Name() string {
+func (n Class) Name() string {
 	return "Class"
 }
 
@@ -34,39 +31,43 @@ func NewClass(token token.Token, modifiers []node.Node, args []node.Node, extend
 	}
 }
 
-func (n Class) Print(out io.Writer, indent string) {
-	fmt.Fprintf(out, "\n%v%v [%d %d] %q", indent, n.name, n.token.StartLine, n.token.EndLine, n.token.Value)
+func (n Class) Walk(v node.Visitor) {
+	if v.Visit(n) == false {
+		return
+	}
+
+	v.Scalar("token", n.token.Value)
 
 	if n.modifiers != nil {
-		fmt.Fprintf(out, "\n%vmotifiers:", indent+"  ")
+		vv := v.Children("modifiers")
 		for _, nn := range n.modifiers {
-			nn.Print(out, indent+"    ")
+			nn.Walk(vv)
 		}
 	}
 
 	if n.args != nil {
-		fmt.Fprintf(out, "\n%vargs:", indent+"  ")
+		vv := v.Children("args")
 		for _, nn := range n.args {
-			nn.Print(out, indent+"    ")
+			nn.Walk(vv)
 		}
 	}
 
 	if n.extends != nil {
-		fmt.Fprintf(out, "\n%vextends:", indent+"  ")
-		n.extends.Print(out, indent+"    ")
+		vv := v.Children("extends")
+		n.extends.Walk(vv)
 	}
 
 	if n.implements != nil {
-		fmt.Fprintf(out, "\n%vimplements:", indent+"  ")
+		vv := v.Children("implements")
 		for _, nn := range n.implements {
-			nn.Print(out, indent+"    ")
+			nn.Walk(vv)
 		}
 	}
 
 	if n.stmts != nil {
-		fmt.Fprintf(out, "\n%vstmts:", indent+"  ")
+		vv := v.Children("stmts")
 		for _, nn := range n.stmts {
-			nn.Print(out, indent+"    ")
+			nn.Walk(vv)
 		}
 	}
 }
diff --git a/node/stmt/class_const_list.go b/node/stmt/class_const_list.go
index 91e7153..20e08f6 100644
--- a/node/stmt/class_const_list.go
+++ b/node/stmt/class_const_list.go
@@ -1,14 +1,11 @@
 package stmt
 
 import (
-	"fmt"
-	"io"
-
 	"github.com/z7zmey/php-parser/node"
 	"github.com/z7zmey/php-parser/token"
 )
 
-func(n ClassConstList) Name() string {
+func (n ClassConstList) Name() string {
 	return "ClassConstList"
 }
 
@@ -28,20 +25,22 @@ func NewClassConstList(token token.Token, modifiers []node.Node, consts []node.N
 	}
 }
 
-func (n ClassConstList) Print(out io.Writer, indent string) {
-	fmt.Fprintf(out, "\n%v%v [%d %d] %q", indent, n.name, n.token.StartLine, n.token.EndLine, n.token.Value)
+func (n ClassConstList) Walk(v node.Visitor) {
+	if v.Visit(n) == false {
+		return
+	}
 
 	if n.modifiers != nil {
-		fmt.Fprintf(out, "\n%vmotifiers:", indent+"  ")
+		vv := v.Children("modifiers")
 		for _, nn := range n.modifiers {
-			nn.Print(out, indent+"    ")
+			nn.Walk(vv)
 		}
 	}
 
 	if n.consts != nil {
-		fmt.Fprintf(out, "\n%vconsts:", indent+"  ")
+		vv := v.Children("consts")
 		for _, nn := range n.consts {
-			nn.Print(out, indent+"    ")
+			nn.Walk(vv)
 		}
 	}
 }
diff --git a/node/stmt/class_method.go b/node/stmt/class_method.go
index 3f1dca3..c3a429c 100644
--- a/node/stmt/class_method.go
+++ b/node/stmt/class_method.go
@@ -1,14 +1,11 @@
 package stmt
 
 import (
-	"fmt"
-	"io"
-
 	"github.com/z7zmey/php-parser/node"
 	"github.com/z7zmey/php-parser/token"
 )
 
-func(n ClassMethod) Name() string {
+func (n ClassMethod) Name() string {
 	return "ClassMethod"
 }
 
@@ -34,34 +31,37 @@ func NewClassMethod(token token.Token, modifiers []node.Node, isReturnRef bool,
 	}
 }
 
-func (n ClassMethod) Print(out io.Writer, indent string) {
-	fmt.Fprintf(out, "\n%v%v [%d %d] %q", indent, n.name, n.token.StartLine, n.token.EndLine, n.token.Value)
+func (n ClassMethod) Walk(v node.Visitor) {
+	if v.Visit(n) == false {
+		return
+	}
+
+	v.Scalar("token", n.token.Value)
+	v.Scalar("isReturnRef", n.isReturnRef)
 
 	if n.modifiers != nil {
-		fmt.Fprintf(out, "\n%vmodifiers:", indent+"  ")
+		vv := v.Children("modifiers")
 		for _, nn := range n.modifiers {
-			nn.Print(out, indent+"    ")
+			nn.Walk(vv)
 		}
 	}
 
-	fmt.Fprintf(out, "\n%vreturn ref: %t", indent+"  ", n.isReturnRef)
-
 	if n.params != nil {
-		fmt.Fprintf(out, "\n%vparams:", indent+"  ")
+		vv := v.Children("params")
 		for _, nn := range n.params {
-			nn.Print(out, indent+"    ")
+			nn.Walk(vv)
 		}
 	}
 
 	if n.returnType != nil {
-		fmt.Fprintf(out, "\n%vreturn type:", indent+"  ")
-		n.returnType.Print(out, indent+"    ")
+		vv := v.Children("returnType")
+		n.returnType.Walk(vv)
 	}
 
 	if n.stmts != nil {
-		fmt.Fprintf(out, "\n%vstmts:", indent+"  ")
+		vv := v.Children("stmts")
 		for _, nn := range n.stmts {
-			nn.Print(out, indent+"    ")
+			nn.Walk(vv)
 		}
 	}
 }
diff --git a/node/stmt/const_list.go b/node/stmt/const_list.go
index bf6cec3..f27daff 100644
--- a/node/stmt/const_list.go
+++ b/node/stmt/const_list.go
@@ -1,14 +1,11 @@
 package stmt
 
 import (
-	"fmt"
-	"io"
-
 	"github.com/z7zmey/php-parser/node"
 	"github.com/z7zmey/php-parser/token"
 )
 
-func(n ConstList) Name() string {
+func (n ConstList) Name() string {
 	return "ConstList"
 }
 
@@ -26,13 +23,15 @@ func NewConstList(token token.Token, consts []node.Node) node.Node {
 	}
 }
 
-func (n ConstList) Print(out io.Writer, indent string) {
-	fmt.Fprintf(out, "\n%v%v [%d %d] %q", indent, n.name, n.token.StartLine, n.token.EndLine, n.token.Value)
+func (n ConstList) Walk(v node.Visitor) {
+	if v.Visit(n) == false {
+		return
+	}
 
 	if n.consts != nil {
-		fmt.Fprintf(out, "\n%vconsts:", indent+"  ")
+		vv := v.Children("consts")
 		for _, nn := range n.consts {
-			nn.Print(out, indent+"    ")
+			nn.Walk(vv)
 		}
 	}
 }
diff --git a/node/stmt/constant.go b/node/stmt/constant.go
index 9567040..05bcb84 100644
--- a/node/stmt/constant.go
+++ b/node/stmt/constant.go
@@ -1,14 +1,11 @@
 package stmt
 
 import (
-	"fmt"
-	"io"
-
 	"github.com/z7zmey/php-parser/node"
 	"github.com/z7zmey/php-parser/token"
 )
 
-func(n Constant) Name() string {
+func (n Constant) Name() string {
 	return "Constant"
 }
 
@@ -26,9 +23,15 @@ func NewConstant(token token.Token, expr node.Node) node.Node {
 	}
 }
 
-func (n Constant) Print(out io.Writer, indent string) {
-	fmt.Fprintf(out, "\n%v%v [%d %d] %q", indent, n.name, n.token.StartLine, n.token.EndLine, n.token.Value)
+func (n Constant) Walk(v node.Visitor) {
+	if v.Visit(n) == false {
+		return
+	}
 
-	fmt.Fprintf(out, "\n%vexpr:", indent+"  ")
-	n.expr.Print(out, indent+"    ")
+	v.Scalar("token", n.token.Value)
+
+	if n.expr != nil {
+		vv := v.Children("expr")
+		n.expr.Walk(vv)
+	}
 }
diff --git a/node/stmt/continue.go b/node/stmt/continue.go
index e5a02fc..d240bee 100644
--- a/node/stmt/continue.go
+++ b/node/stmt/continue.go
@@ -1,14 +1,11 @@
 package stmt
 
 import (
-	"fmt"
-	"io"
-
 	"github.com/z7zmey/php-parser/node"
 	"github.com/z7zmey/php-parser/token"
 )
 
-func(n Continue) Name() string {
+func (n Continue) Name() string {
 	return "Continue"
 }
 
@@ -26,11 +23,13 @@ func NewContinue(token token.Token, expr node.Node) node.Node {
 	}
 }
 
-func (n Continue) Print(out io.Writer, indent string) {
-	fmt.Fprintf(out, "\n%v%v [%d %d] %q", indent, n.name, n.token.StartLine, n.token.EndLine, n.token.Value)
+func (n Continue) Walk(v node.Visitor) {
+	if v.Visit(n) == false {
+		return
+	}
 
 	if n.expr != nil {
-		fmt.Fprintf(out, "\n%vexpr:", indent+"  ")
-		n.expr.Print(out, indent+"    ")
+		vv := v.Children("expr")
+		n.expr.Walk(vv)
 	}
 }
diff --git a/node/stmt/declare.go b/node/stmt/declare.go
index 9d453e4..12c0a68 100644
--- a/node/stmt/declare.go
+++ b/node/stmt/declare.go
@@ -1,14 +1,11 @@
 package stmt
 
 import (
-	"fmt"
-	"io"
-
 	"github.com/z7zmey/php-parser/node"
 	"github.com/z7zmey/php-parser/token"
 )
 
-func(n Declare) Name() string {
+func (n Declare) Name() string {
 	return "Declare"
 }
 
@@ -28,18 +25,20 @@ func NewDeclare(token token.Token, consts []node.Node, stmt node.Node) node.Node
 	}
 }
 
-func (n Declare) Print(out io.Writer, indent string) {
-	fmt.Fprintf(out, "\n%v%v [%d %d] %q", indent, n.name, n.token.StartLine, n.token.EndLine, n.token.Value)
+func (n Declare) Walk(v node.Visitor) {
+	if v.Visit(n) == false {
+		return
+	}
 
 	if n.consts != nil {
-		fmt.Fprintf(out, "\n%vconsts:", indent+"  ")
+		vv := v.Children("consts")
 		for _, nn := range n.consts {
-			nn.Print(out, indent+"    ")
+			nn.Walk(vv)
 		}
 	}
 
 	if n.stmt != nil {
-		fmt.Fprintf(out, "\n%vstmt:", indent+"  ")
-		n.stmt.Print(out, indent+"    ")
+		vv := v.Children("stmt")
+		n.stmt.Walk(vv)
 	}
 }
diff --git a/node/stmt/default.go b/node/stmt/default.go
index 6e3fb47..f54bcae 100644
--- a/node/stmt/default.go
+++ b/node/stmt/default.go
@@ -1,14 +1,11 @@
 package stmt
 
 import (
-	"fmt"
-	"io"
-
 	"github.com/z7zmey/php-parser/node"
 	"github.com/z7zmey/php-parser/token"
 )
 
-func(n Default) Name() string {
+func (n Default) Name() string {
 	return "Default"
 }
 
@@ -26,13 +23,15 @@ func NewDefault(token token.Token, stmts []node.Node) node.Node {
 	}
 }
 
-func (n Default) Print(out io.Writer, indent string) {
-	fmt.Fprintf(out, "\n%v%v [%d %d] %q", indent, n.name, n.token.StartLine, n.token.EndLine, n.token.Value)
+func (n Default) Walk(v node.Visitor) {
+	if v.Visit(n) == false {
+		return
+	}
 
 	if n.stmts != nil {
-		fmt.Fprintf(out, "\n%vstmts:", indent+"  ")
+		vv := v.Children("stmts")
 		for _, nn := range n.stmts {
-			nn.Print(out, indent+"    ")
+			nn.Walk(vv)
 		}
 	}
 }
diff --git a/node/stmt/do.go b/node/stmt/do.go
index 3fd920b..f9b6776 100644
--- a/node/stmt/do.go
+++ b/node/stmt/do.go
@@ -1,14 +1,11 @@
 package stmt
 
 import (
-	"fmt"
-	"io"
-
 	"github.com/z7zmey/php-parser/node"
 	"github.com/z7zmey/php-parser/token"
 )
 
-func(n Do) Name() string {
+func (n Do) Name() string {
 	return "Do"
 }
 
@@ -28,16 +25,18 @@ func NewDo(token token.Token, stmt node.Node, cond node.Node) node.Node {
 	}
 }
 
-func (n Do) Print(out io.Writer, indent string) {
-	fmt.Fprintf(out, "\n%v%v [%d %d] %q", indent, n.name, n.token.StartLine, n.token.EndLine, n.token.Value)
+func (n Do) Walk(v node.Visitor) {
+	if v.Visit(n) == false {
+		return
+	}
 
 	if n.cond != nil {
-		fmt.Fprintf(out, "\n%vcond:", indent+"  ")
-		n.cond.Print(out, indent+"    ")
+		vv := v.Children("cond")
+		n.cond.Walk(vv)
 	}
 
 	if n.stmt != nil {
-		fmt.Fprintf(out, "\n%vstmt:", indent+"  ")
-		n.stmt.Print(out, indent+"    ")
+		vv := v.Children("stmt")
+		n.stmt.Walk(vv)
 	}
 }
diff --git a/node/stmt/echo.go b/node/stmt/echo.go
index 9c8b097..0912614 100644
--- a/node/stmt/echo.go
+++ b/node/stmt/echo.go
@@ -1,14 +1,11 @@
 package stmt
 
 import (
-	"fmt"
-	"io"
-
 	"github.com/z7zmey/php-parser/node"
 	"github.com/z7zmey/php-parser/token"
 )
 
-func(n Echo) Name() string {
+func (n Echo) Name() string {
 	return "Echo"
 }
 
@@ -26,13 +23,15 @@ func NewEcho(token token.Token, exprs []node.Node) node.Node {
 	}
 }
 
-func (n Echo) Print(out io.Writer, indent string) {
-	fmt.Fprintf(out, "\n%v%v [%d %d] %q", indent, n.name, n.token.StartLine, n.token.EndLine, n.token.Value)
+func (n Echo) Walk(v node.Visitor) {
+	if v.Visit(n) == false {
+		return
+	}
 
 	if n.exprs != nil {
-		fmt.Fprintf(out, "\n%vexprs:", indent+"  ")
+		vv := v.Children("exprs")
 		for _, nn := range n.exprs {
-			nn.Print(out, indent+"    ")
+			nn.Walk(vv)
 		}
 	}
 }
diff --git a/node/stmt/else.go b/node/stmt/else.go
index 71d5a49..ab3f233 100644
--- a/node/stmt/else.go
+++ b/node/stmt/else.go
@@ -1,14 +1,11 @@
 package stmt
 
 import (
-	"fmt"
-	"io"
-
 	"github.com/z7zmey/php-parser/node"
 	"github.com/z7zmey/php-parser/token"
 )
 
-func(n Else) Name() string {
+func (n Else) Name() string {
 	return "Else"
 }
 
@@ -26,11 +23,13 @@ func NewElse(token token.Token, stmt node.Node) node.Node {
 	}
 }
 
-func (n Else) Print(out io.Writer, indent string) {
-	fmt.Fprintf(out, "\n%v%v [%d %d] %q", indent, n.name, n.token.StartLine, n.token.EndLine, n.token.Value)
+func (n Else) Walk(v node.Visitor) {
+	if v.Visit(n) == false {
+		return
+	}
 
 	if n.stmt != nil {
-		fmt.Fprintf(out, "\n%vstmt:", indent+"  ")
-		n.stmt.Print(out, indent+"    ")
+		vv := v.Children("stmt")
+		n.stmt.Walk(vv)
 	}
 }
diff --git a/node/stmt/else_if.go b/node/stmt/else_if.go
index 56b12a4..3a1f87a 100644
--- a/node/stmt/else_if.go
+++ b/node/stmt/else_if.go
@@ -1,14 +1,11 @@
 package stmt
 
 import (
-	"fmt"
-	"io"
-
 	"github.com/z7zmey/php-parser/node"
 	"github.com/z7zmey/php-parser/token"
 )
 
-func(n ElseIf) Name() string {
+func (n ElseIf) Name() string {
 	return "ElseIf"
 }
 
@@ -28,16 +25,18 @@ func NewElseIf(token token.Token, cond node.Node, stmt node.Node) node.Node {
 	}
 }
 
-func (n ElseIf) Print(out io.Writer, indent string) {
-	fmt.Fprintf(out, "\n%v%v [%d %d] %q", indent, n.name, n.token.StartLine, n.token.EndLine, n.token.Value)
+func (n ElseIf) Walk(v node.Visitor) {
+	if v.Visit(n) == false {
+		return
+	}
 
 	if n.cond != nil {
-		fmt.Fprintf(out, "\n%vcond:", indent+"  ")
-		n.cond.Print(out, indent+"    ")
+		vv := v.Children("cond")
+		n.cond.Walk(vv)
 	}
 
 	if n.stmt != nil {
-		fmt.Fprintf(out, "\n%vstmt:", indent+"  ")
-		n.stmt.Print(out, indent+"    ")
+		vv := v.Children("stmt")
+		n.stmt.Walk(vv)
 	}
 }
diff --git a/node/stmt/expression.go b/node/stmt/expression.go
index 1876636..410f8df 100644
--- a/node/stmt/expression.go
+++ b/node/stmt/expression.go
@@ -1,13 +1,10 @@
 package stmt
 
 import (
-	"fmt"
-	"io"
-
 	"github.com/z7zmey/php-parser/node"
 )
 
-func(n Expression) Name() string {
+func (n Expression) Name() string {
 	return "Expression"
 }
 
@@ -23,11 +20,13 @@ func NewExpression(expr node.Node) node.Node {
 	}
 }
 
-func (n Expression) Print(out io.Writer, indent string) {
-	fmt.Fprintf(out, "\n%v%v [- -]", indent, n.name)
+func (n Expression) Walk(v node.Visitor) {
+	if v.Visit(n) == false {
+		return
+	}
 
 	if n.expr != nil {
-		fmt.Fprintf(out, "\n%vexpr:", indent+"  ")
-		n.expr.Print(out, indent+"    ")
+		vv := v.Children("expr")
+		n.expr.Walk(vv)
 	}
 }
diff --git a/node/stmt/finally.go b/node/stmt/finally.go
index 7823205..918fa99 100644
--- a/node/stmt/finally.go
+++ b/node/stmt/finally.go
@@ -1,14 +1,11 @@
 package stmt
 
 import (
-	"fmt"
-	"io"
-
 	"github.com/z7zmey/php-parser/node"
 	"github.com/z7zmey/php-parser/token"
 )
 
-func(n Finally) Name() string {
+func (n Finally) Name() string {
 	return "Finally"
 }
 
@@ -26,13 +23,15 @@ func NewFinally(token token.Token, stmts []node.Node) node.Node {
 	}
 }
 
-func (n Finally) Print(out io.Writer, indent string) {
-	fmt.Fprintf(out, "\n%v%v [%d %d] %q", indent, n.name, n.token.StartLine, n.token.EndLine, n.token.Value)
+func (n Finally) Walk(v node.Visitor) {
+	if v.Visit(n) == false {
+		return
+	}
 
 	if n.stmts != nil {
-		fmt.Fprintf(out, "\n%vstmts:", indent+"  ")
+		vv := v.Children("stmts")
 		for _, nn := range n.stmts {
-			nn.Print(out, indent+"    ")
+			nn.Walk(vv)
 		}
 	}
 }
diff --git a/node/stmt/for.go b/node/stmt/for.go
index f572931..7458418 100644
--- a/node/stmt/for.go
+++ b/node/stmt/for.go
@@ -1,14 +1,11 @@
 package stmt
 
 import (
-	"fmt"
-	"io"
-
 	"github.com/z7zmey/php-parser/node"
 	"github.com/z7zmey/php-parser/token"
 )
 
-func(n For) Name() string {
+func (n For) Name() string {
 	return "For"
 }
 
@@ -32,32 +29,34 @@ func NewFor(token token.Token, init []node.Node, cond []node.Node, loop []node.N
 	}
 }
 
-func (n For) Print(out io.Writer, indent string) {
-	fmt.Fprintf(out, "\n%v%v [%d %d] %q", indent, n.name, n.token.StartLine, n.token.EndLine, n.token.Value)
+func (n For) Walk(v node.Visitor) {
+	if v.Visit(n) == false {
+		return
+	}
 
 	if n.init != nil {
-		fmt.Fprintf(out, "\n%vinit:", indent+"  ")
+		vv := v.Children("init")
 		for _, nn := range n.init {
-			nn.Print(out, indent+"    ")
+			nn.Walk(vv)
 		}
 	}
 
 	if n.cond != nil {
-		fmt.Fprintf(out, "\n%vcond:", indent+"  ")
+		vv := v.Children("cond")
 		for _, nn := range n.cond {
-			nn.Print(out, indent+"    ")
+			nn.Walk(vv)
 		}
 	}
 
 	if n.loop != nil {
-		fmt.Fprintf(out, "\n%vloop:", indent+"  ")
+		vv := v.Children("loop")
 		for _, nn := range n.loop {
-			nn.Print(out, indent+"    ")
+			nn.Walk(vv)
 		}
 	}
 
 	if n.stmt != nil {
-		fmt.Fprintf(out, "\n%vstmt:", indent+"  ")
-		n.stmt.Print(out, indent+"    ")
+		vv := v.Children("stmt")
+		n.stmt.Walk(vv)
 	}
 }
diff --git a/node/stmt/foreach.go b/node/stmt/foreach.go
index a1ef5c9..aed5fc2 100644
--- a/node/stmt/foreach.go
+++ b/node/stmt/foreach.go
@@ -1,14 +1,11 @@
 package stmt
 
 import (
-	"fmt"
-	"io"
-
 	"github.com/z7zmey/php-parser/node"
 	"github.com/z7zmey/php-parser/token"
 )
 
-func(n Foreach) Name() string {
+func (n Foreach) Name() string {
 	return "Foreach"
 }
 
@@ -34,26 +31,28 @@ func NewForeach(token token.Token, expr node.Node, key node.Node, variable node.
 	}
 }
 
-func (n Foreach) Print(out io.Writer, indent string) {
-	fmt.Fprintf(out, "\n%v%v [%d %d] %q", indent, n.name, n.token.StartLine, n.token.EndLine, n.token.Value)
+func (n Foreach) Walk(v node.Visitor) {
+	if v.Visit(n) == false {
+		return
+	}
 
 	if n.expr != nil {
-		fmt.Fprintf(out, "\n%vexpr:", indent+"  ")
-		n.expr.Print(out, indent+"    ")
+		vv := v.Children("expr")
+		n.expr.Walk(vv)
 	}
 
 	if n.key != nil {
-		fmt.Fprintf(out, "\n%vkey:", indent+"  ")
-		n.key.Print(out, indent+"    ")
+		vv := v.Children("key")
+		n.key.Walk(vv)
 	}
 
 	if n.variable != nil {
-		fmt.Fprintf(out, "\n%vvariable[byRef: %t]:", indent+"  ", n.byRef)
-		n.variable.Print(out, indent+"    ")
+		vv := v.Children("variable")
+		n.variable.Walk(vv)
 	}
 
 	if n.stmt != nil {
-		fmt.Fprintf(out, "\n%vstmt:", indent+"  ")
-		n.stmt.Print(out, indent+"    ")
+		vv := v.Children("stmt")
+		n.stmt.Walk(vv)
 	}
 }
diff --git a/node/stmt/function.go b/node/stmt/function.go
index 83b1a7f..9400d86 100644
--- a/node/stmt/function.go
+++ b/node/stmt/function.go
@@ -1,14 +1,11 @@
 package stmt
 
 import (
-	"fmt"
-	"io"
-
 	"github.com/z7zmey/php-parser/node"
 	"github.com/z7zmey/php-parser/token"
 )
 
-func(n Function) Name() string {
+func (n Function) Name() string {
 	return "Function"
 }
 
@@ -32,27 +29,30 @@ func NewFunction(token token.Token, isReturnRef bool, params []node.Node, return
 	}
 }
 
-func (n Function) Print(out io.Writer, indent string) {
-	fmt.Fprintf(out, "\n%v%v [%d %d] %q", indent, n.name, n.token.StartLine, n.token.EndLine, n.token.Value)
+func (n Function) Walk(v node.Visitor) {
+	if v.Visit(n) == false {
+		return
+	}
 
-	fmt.Fprintf(out, "\n%vreturn ref: %t", indent+"  ", n.isReturnRef)
+	v.Scalar("token", n.token.Value)
+	v.Scalar("isReturnRef", n.isReturnRef)
 
 	if n.params != nil {
-		fmt.Fprintf(out, "\n%vparams:", indent+"  ")
+		vv := v.Children("params")
 		for _, nn := range n.params {
-			nn.Print(out, indent+"    ")
+			nn.Walk(vv)
 		}
 	}
 
 	if n.returnType != nil {
-		fmt.Fprintf(out, "\n%vreturn type:", indent+"  ")
-		n.returnType.Print(out, indent+"    ")
+		vv := v.Children("returnType")
+		n.returnType.Walk(vv)
 	}
 
 	if n.stmts != nil {
-		fmt.Fprintf(out, "\n%vstmts:", indent+"  ")
+		vv := v.Children("stmts")
 		for _, nn := range n.stmts {
-			nn.Print(out, indent+"    ")
+			nn.Walk(vv)
 		}
 	}
 }
diff --git a/node/stmt/global.go b/node/stmt/global.go
index 84c25bb..50f11e8 100644
--- a/node/stmt/global.go
+++ b/node/stmt/global.go
@@ -1,14 +1,11 @@
 package stmt
 
 import (
-	"fmt"
-	"io"
-
 	"github.com/z7zmey/php-parser/node"
 	"github.com/z7zmey/php-parser/token"
 )
 
-func(n Global) Name() string {
+func (n Global) Name() string {
 	return "Global"
 }
 
@@ -26,13 +23,15 @@ func NewGlobal(token token.Token, vars []node.Node) node.Node {
 	}
 }
 
-func (n Global) Print(out io.Writer, indent string) {
-	fmt.Fprintf(out, "\n%v%v [%d %d] %q", indent, n.name, n.token.StartLine, n.token.EndLine, n.token.Value)
+func (n Global) Walk(v node.Visitor) {
+	if v.Visit(n) == false {
+		return
+	}
 
 	if n.vars != nil {
-		fmt.Fprintf(out, "\n%vvars:", indent+"  ")
+		vv := v.Children("vars")
 		for _, nn := range n.vars {
-			nn.Print(out, indent+"    ")
+			nn.Walk(vv)
 		}
 	}
 }
diff --git a/node/stmt/goto.go b/node/stmt/goto.go
index c3311f2..f66e84d 100644
--- a/node/stmt/goto.go
+++ b/node/stmt/goto.go
@@ -1,14 +1,11 @@
 package stmt
 
 import (
-	"fmt"
-	"io"
-
 	"github.com/z7zmey/php-parser/node"
 	"github.com/z7zmey/php-parser/token"
 )
 
-func(n Goto) Name() string {
+func (n Goto) Name() string {
 	return "Goto"
 }
 
@@ -18,14 +15,19 @@ type Goto struct {
 	label token.Token
 }
 
-func NewGoto(token token.Token, name token.Token) node.Node {
+// todl label must be identifier
+func NewGoto(token token.Token, label token.Token) node.Node {
 	return Goto{
 		"Goto",
 		token,
-		name,
+		label,
 	}
 }
 
-func (n Goto) Print(out io.Writer, indent string) {
-	fmt.Fprintf(out, "\n%v%v [%d %d] %q", indent, n.name, n.token.StartLine, n.label.EndLine, n.label.Value)
+func (n Goto) Walk(v node.Visitor) {
+	if v.Visit(n) == false {
+		return
+	}
+
+	v.Scalar("label", n.label.Value)
 }
diff --git a/node/stmt/group_use.go b/node/stmt/group_use.go
index 745cb85..cc3918b 100644
--- a/node/stmt/group_use.go
+++ b/node/stmt/group_use.go
@@ -1,14 +1,11 @@
 package stmt
 
 import (
-	"fmt"
-	"io"
-
 	"github.com/z7zmey/php-parser/node"
 	"github.com/z7zmey/php-parser/token"
 )
 
-func(n GroupUse) Name() string {
+func (n GroupUse) Name() string {
 	return "GroupUse"
 }
 
@@ -41,23 +38,25 @@ func (n GroupUse) SetUseType(useType node.Node) node.Node {
 	return n
 }
 
-func (n GroupUse) Print(out io.Writer, indent string) {
-	fmt.Fprintf(out, "\n%v%v [%d %d] %q", indent, n.name, n.token.GetStartLine(), n.token.GetEndLine(), n.token.GetValue())
+func (n GroupUse) Walk(v node.Visitor) {
+	if v.Visit(n) == false {
+		return
+	}
 
 	if n.useType != nil {
-		fmt.Fprintf(out, "\n%vuse type:", indent+"  ")
-		n.useType.Print(out, indent+"    ")
+		vv := v.Children("useType")
+		n.useType.Walk(vv)
 	}
 
 	if n.prefix != nil {
-		fmt.Fprintf(out, "\n%vprefix:", indent+"  ")
-		n.prefix.Print(out, indent+"    ")
+		vv := v.Children("prefix")
+		n.prefix.Walk(vv)
 	}
 
 	if n.useList != nil {
-		fmt.Fprintf(out, "\n%vuse list:", indent+"  ")
+		vv := v.Children("useList")
 		for _, nn := range n.useList {
-			nn.Print(out, indent+"    ")
+			nn.Walk(vv)
 		}
 	}
 }
diff --git a/node/stmt/halt_compiler.go b/node/stmt/halt_compiler.go
index 7636ead..9e0f66a 100644
--- a/node/stmt/halt_compiler.go
+++ b/node/stmt/halt_compiler.go
@@ -1,14 +1,11 @@
 package stmt
 
 import (
-	"fmt"
-	"io"
-
 	"github.com/z7zmey/php-parser/node"
 	"github.com/z7zmey/php-parser/token"
 )
 
-func(n HaltCompiler) Name() string {
+func (n HaltCompiler) Name() string {
 	return "HaltCompiler"
 }
 
@@ -24,6 +21,8 @@ func NewHaltCompiler(token token.Token) node.Node {
 	}
 }
 
-func (n HaltCompiler) Print(out io.Writer, indent string) {
-	fmt.Fprintf(out, "\n%v%v [%d %d] %q", indent, n.name, n.token.StartLine, n.token.EndLine, n.token.Value)
+func (n HaltCompiler) Walk(v node.Visitor) {
+	if v.Visit(n) == false {
+		return
+	}
 }
diff --git a/node/stmt/if.go b/node/stmt/if.go
index aeca4ff..4ae2293 100644
--- a/node/stmt/if.go
+++ b/node/stmt/if.go
@@ -1,14 +1,11 @@
 package stmt
 
 import (
-	"fmt"
-	"io"
-
 	"github.com/z7zmey/php-parser/node"
 	"github.com/z7zmey/php-parser/token"
 )
 
-func(n If) Name() string {
+func (n If) Name() string {
 	return "If"
 }
 
@@ -48,27 +45,30 @@ func (n If) SetElse(_else node.Node) node.Node {
 	return n
 }
 
-func (n If) Print(out io.Writer, indent string) {
-	fmt.Fprintf(out, "\n%v%v [%d %d] %q", indent, n.name, n.token.StartLine, n.token.EndLine, n.token.Value)
+func (n If) Walk(v node.Visitor) {
+	if v.Visit(n) == false {
+		return
+	}
 
 	if n.cond != nil {
-		fmt.Fprintf(out, "\n%vcond:", indent+"  ")
-		n.cond.Print(out, indent+"    ")
+		vv := v.Children("cond")
+		n.cond.Walk(vv)
 	}
 
 	if n.stmt != nil {
-		fmt.Fprintf(out, "\n%vstmt:", indent+"  ")
-		n.stmt.Print(out, indent+"    ")
+		vv := v.Children("stmt")
+		n.stmt.Walk(vv)
 	}
 
 	if n.elseIf != nil {
-		fmt.Fprintf(out, "\n%velseIfs:", indent+"  ")
+		vv := v.Children("elseIf")
 		for _, nn := range n.elseIf {
-			nn.Print(out, indent+"    ")
+			nn.Walk(vv)
 		}
 	}
+
 	if n._else != nil {
-		fmt.Fprintf(out, "\n%velse:", indent+"  ")
-		n._else.Print(out, indent+"    ")
+		vv := v.Children("else")
+		n._else.Walk(vv)
 	}
 }
diff --git a/node/stmt/inline_html.go b/node/stmt/inline_html.go
index 55e25aa..2dd05c2 100644
--- a/node/stmt/inline_html.go
+++ b/node/stmt/inline_html.go
@@ -1,14 +1,11 @@
 package stmt
 
 import (
-	"fmt"
-	"io"
-
 	"github.com/z7zmey/php-parser/node"
 	"github.com/z7zmey/php-parser/token"
 )
 
-func(n InlineHtml) Name() string {
+func (n InlineHtml) Name() string {
 	return "InlineHtml"
 }
 
@@ -24,6 +21,10 @@ func NewInlineHtml(token token.Token) node.Node {
 	}
 }
 
-func (n InlineHtml) Print(out io.Writer, indent string) {
-	fmt.Fprintf(out, "\n%v%v [%d %d] %q", indent, n.name, n.token.StartLine, n.token.EndLine, n.token.Value)
+func (n InlineHtml) Walk(v node.Visitor) {
+	if v.Visit(n) == false {
+		return
+	}
+
+	v.Scalar("token", n.token.Value)
 }
diff --git a/node/stmt/interface.go b/node/stmt/interface.go
index 79e253d..e70b3d3 100644
--- a/node/stmt/interface.go
+++ b/node/stmt/interface.go
@@ -1,23 +1,20 @@
 package stmt
 
 import (
-	"fmt"
-	"io"
-
 	"github.com/z7zmey/php-parser/node"
 	"github.com/z7zmey/php-parser/token"
 )
 
-func(n Interface) Name() string {
+func (n Interface) Name() string {
 	return "Interface"
 }
 
 type Interface struct {
-	name    string
-	token   token.Token
-	iName   token.Token
-	extends []node.Node
-	stmts   []node.Node
+	name          string
+	token         token.Token
+	interfaceName token.Token
+	extends       []node.Node
+	stmts         []node.Node
 }
 
 func NewInterface(token token.Token, name token.Token, extends []node.Node, stmts []node.Node) node.Node {
@@ -30,20 +27,24 @@ func NewInterface(token token.Token, name token.Token, extends []node.Node, stmt
 	}
 }
 
-func (n Interface) Print(out io.Writer, indent string) {
-	fmt.Fprintf(out, "\n%v%v [%d %d] %q", indent, n.name, n.token.StartLine, n.token.EndLine, n.iName.Value)
+func (n Interface) Walk(v node.Visitor) {
+	if v.Visit(n) == false {
+		return
+	}
+
+	v.Scalar("token", n.interfaceName.Value)
 
 	if n.extends != nil {
-		fmt.Fprintf(out, "\n%vextends:", indent+"  ")
+		vv := v.Children("extends")
 		for _, nn := range n.extends {
-			nn.Print(out, indent+"    ")
+			nn.Walk(vv)
 		}
 	}
 
 	if n.stmts != nil {
-		fmt.Fprintf(out, "\n%vstmts:", indent+"  ")
+		vv := v.Children("stmts")
 		for _, nn := range n.stmts {
-			nn.Print(out, indent+"    ")
+			nn.Walk(vv)
 		}
 	}
 }
diff --git a/node/stmt/label.go b/node/stmt/label.go
index a51741a..08e966e 100644
--- a/node/stmt/label.go
+++ b/node/stmt/label.go
@@ -1,14 +1,11 @@
 package stmt
 
 import (
-	"fmt"
-	"io"
-
 	"github.com/z7zmey/php-parser/node"
 	"github.com/z7zmey/php-parser/token"
 )
 
-func(n Label) Name() string {
+func (n Label) Name() string {
 	return "Label"
 }
 
@@ -24,6 +21,10 @@ func NewLabel(token token.Token) node.Node {
 	}
 }
 
-func (n Label) Print(out io.Writer, indent string) {
-	fmt.Fprintf(out, "\n%v%v [%d %d] %q", indent, n.name, n.token.StartLine, n.token.EndLine, n.token.Value)
+func (n Label) Walk(v node.Visitor) {
+	if v.Visit(n) == false {
+		return
+	}
+
+	v.Scalar("token", n.token.Value)
 }
diff --git a/node/stmt/namespace.go b/node/stmt/namespace.go
index 017454f..17b55ec 100644
--- a/node/stmt/namespace.go
+++ b/node/stmt/namespace.go
@@ -1,45 +1,44 @@
 package stmt
 
 import (
-	"fmt"
-	"io"
-
 	"github.com/z7zmey/php-parser/node"
 	"github.com/z7zmey/php-parser/token"
 )
 
-func(n Namespace) Name() string {
+func (n Namespace) Name() string {
 	return "Namespace"
 }
 
 type Namespace struct {
-	name  string
-	token token.Token
-	nName node.Node
-	stmts []node.Node
+	name          string
+	token         token.Token
+	namespaceName node.Node
+	stmts         []node.Node
 }
 
-func NewNamespace(token token.Token, name node.Node, stmts []node.Node) node.Node {
+func NewNamespace(token token.Token, namespaceName node.Node, stmts []node.Node) node.Node {
 	return Namespace{
 		"Namespace",
 		token,
-		name,
+		namespaceName,
 		stmts,
 	}
 }
 
-func (n Namespace) Print(out io.Writer, indent string) {
-	fmt.Fprintf(out, "\n%v%v [%d %d] %q", indent, n.name, n.token.StartLine, n.token.EndLine, n.token.Value)
+func (n Namespace) Walk(v node.Visitor) {
+	if v.Visit(n) == false {
+		return
+	}
 
-	if n.nName != nil {
-		fmt.Fprintf(out, "\n%vname:", indent+"  ")
-		n.nName.Print(out, indent+"    ")
+	if n.namespaceName != nil {
+		vv := v.Children("namespaceName")
+		n.namespaceName.Walk(vv)
 	}
 
 	if n.stmts != nil {
-		fmt.Fprintf(out, "\n%vstmts:", indent+"  ")
+		vv := v.Children("stmts")
 		for _, nn := range n.stmts {
-			nn.Print(out, indent+"    ")
+			nn.Walk(vv)
 		}
 	}
 }
diff --git a/node/stmt/nop.go b/node/stmt/nop.go
index c6f3210..78bef7b 100644
--- a/node/stmt/nop.go
+++ b/node/stmt/nop.go
@@ -8,7 +8,7 @@ import (
 	"github.com/z7zmey/php-parser/token"
 )
 
-func(n Nop) Name() string {
+func (n Nop) Name() string {
 	return "Nop"
 }
 
@@ -27,3 +27,11 @@ func NewNop(token token.Token) node.Node {
 func (n Nop) Print(out io.Writer, indent string) {
 	fmt.Fprintf(out, "\n%v%v [%d %d] %q", indent, n.name, n.token.StartLine, n.token.EndLine, n.token.Value)
 }
+
+func (n Nop) Walk(v node.Visitor) {
+	if v.Visit(n) == false {
+		return
+	}
+
+	v.Scalar("token", n.token.Value)
+}
diff --git a/node/stmt/property.go b/node/stmt/property.go
index 30529c5..577624a 100644
--- a/node/stmt/property.go
+++ b/node/stmt/property.go
@@ -1,14 +1,11 @@
 package stmt
 
 import (
-	"fmt"
-	"io"
-
 	"github.com/z7zmey/php-parser/node"
 	"github.com/z7zmey/php-parser/token"
 )
 
-func(n Property) Name() string {
+func (n Property) Name() string {
 	return "Property"
 }
 
@@ -26,11 +23,15 @@ func NewProperty(token token.Token, expr node.Node) node.Node {
 	}
 }
 
-func (n Property) Print(out io.Writer, indent string) {
-	fmt.Fprintf(out, "\n%v%v [%d %d] %q", indent, n.name, n.token.StartLine, n.token.EndLine, n.token.Value)
+func (n Property) Walk(v node.Visitor) {
+	if v.Visit(n) == false {
+		return
+	}
+
+	v.Scalar("token", n.token.Value)
 
 	if n.expr != nil {
-		fmt.Fprintf(out, "\n%vexpr:", indent+"  ")
-		n.expr.Print(out, indent+"    ")
+		vv := v.Children("expr")
+		n.expr.Walk(vv)
 	}
 }
diff --git a/node/stmt/property_list.go b/node/stmt/property_list.go
index 2864c54..8c3d04f 100644
--- a/node/stmt/property_list.go
+++ b/node/stmt/property_list.go
@@ -1,13 +1,10 @@
 package stmt
 
 import (
-	"fmt"
-	"io"
-
 	"github.com/z7zmey/php-parser/node"
 )
 
-func(n PropertyList) Name() string {
+func (n PropertyList) Name() string {
 	return "PropertyList"
 }
 
@@ -25,20 +22,22 @@ func NewPropertyList(modifiers []node.Node, properties []node.Node) node.Node {
 	}
 }
 
-func (n PropertyList) Print(out io.Writer, indent string) {
-	fmt.Fprintf(out, "\n%v%v [- -]", indent, n.name)
+func (n PropertyList) Walk(v node.Visitor) {
+	if v.Visit(n) == false {
+		return
+	}
 
 	if n.modifiers != nil {
-		fmt.Fprintf(out, "\n%vmodifiers:", indent+"  ")
+		vv := v.Children("modifiers")
 		for _, nn := range n.modifiers {
-			nn.Print(out, indent+"    ")
+			nn.Walk(vv)
 		}
 	}
 
 	if n.properties != nil {
-		fmt.Fprintf(out, "\n%vproperties:", indent+"  ")
+		vv := v.Children("properties")
 		for _, nn := range n.properties {
-			nn.Print(out, indent+"    ")
+			nn.Walk(vv)
 		}
 	}
 }
diff --git a/node/stmt/return.go b/node/stmt/return.go
index aed2d3e..79fd167 100644
--- a/node/stmt/return.go
+++ b/node/stmt/return.go
@@ -1,14 +1,11 @@
 package stmt
 
 import (
-	"fmt"
-	"io"
-
 	"github.com/z7zmey/php-parser/node"
 	"github.com/z7zmey/php-parser/token"
 )
 
-func(n Return) Name() string {
+func (n Return) Name() string {
 	return "Return"
 }
 
@@ -26,11 +23,13 @@ func NewReturn(token token.Token, expr node.Node) node.Node {
 	}
 }
 
-func (n Return) Print(out io.Writer, indent string) {
-	fmt.Fprintf(out, "\n%v%v [%d %d] %q", indent, n.name, n.token.StartLine, n.token.EndLine, n.token.Value)
+func (n Return) Walk(v node.Visitor) {
+	if v.Visit(n) == false {
+		return
+	}
 
 	if n.expr != nil {
-		fmt.Fprintf(out, "\n%vexpr:", indent+"  ")
-		n.expr.Print(out, indent+"    ")
+		vv := v.Children("expr")
+		n.expr.Walk(vv)
 	}
 }
diff --git a/node/stmt/static.go b/node/stmt/static.go
index 37a3207..a33984d 100644
--- a/node/stmt/static.go
+++ b/node/stmt/static.go
@@ -1,14 +1,11 @@
 package stmt
 
 import (
-	"fmt"
-	"io"
-
 	"github.com/z7zmey/php-parser/node"
 	"github.com/z7zmey/php-parser/token"
 )
 
-func(n Static) Name() string {
+func (n Static) Name() string {
 	return "Static"
 }
 
@@ -26,13 +23,15 @@ func NewStatic(token token.Token, vars []node.Node) node.Node {
 	}
 }
 
-func (n Static) Print(out io.Writer, indent string) {
-	fmt.Fprintf(out, "\n%v%v [%d %d] %q", indent, n.name, n.token.StartLine, n.token.EndLine, n.token.Value)
+func (n Static) Walk(v node.Visitor) {
+	if v.Visit(n) == false {
+		return
+	}
 
 	if n.vars != nil {
-		fmt.Fprintf(out, "\n%vvars:", indent+"  ")
+		vv := v.Children("vars")
 		for _, nn := range n.vars {
-			nn.Print(out, indent+"    ")
+			nn.Walk(vv)
 		}
 	}
 }
diff --git a/node/stmt/static_var.go b/node/stmt/static_var.go
index 17ab3ba..15aa864 100644
--- a/node/stmt/static_var.go
+++ b/node/stmt/static_var.go
@@ -1,14 +1,11 @@
 package stmt
 
 import (
-	"fmt"
-	"io"
-
 	"github.com/z7zmey/php-parser/node"
 	"github.com/z7zmey/php-parser/token"
 )
 
-func(n StaticVar) Name() string {
+func (n StaticVar) Name() string {
 	return "StaticVar"
 }
 
@@ -26,11 +23,13 @@ func NewStaticVar(token token.Token, expr node.Node) node.Node {
 	}
 }
 
-func (n StaticVar) Print(out io.Writer, indent string) {
-	fmt.Fprintf(out, "\n%v%v [%d %d] %q", indent, n.name, n.token.StartLine, n.token.EndLine, n.token.Value)
+func (n StaticVar) Walk(v node.Visitor) {
+	if v.Visit(n) == false {
+		return
+	}
 
 	if n.expr != nil {
-		fmt.Fprintf(out, "\n%vexpr:", indent+"  ")
-		n.expr.Print(out, indent+"    ")
+		vv := v.Children("expr")
+		n.expr.Walk(vv)
 	}
 }
diff --git a/node/stmt/stmt_list.go b/node/stmt/stmt_list.go
index d2d0dcb..ccbf237 100644
--- a/node/stmt/stmt_list.go
+++ b/node/stmt/stmt_list.go
@@ -1,13 +1,10 @@
 package stmt
 
 import (
-	"fmt"
-	"io"
-
 	"github.com/z7zmey/php-parser/node"
 )
 
-func(n StmtList) Name() string {
+func (n StmtList) Name() string {
 	return "StmtList"
 }
 
@@ -23,13 +20,15 @@ func NewStmtList(stmts []node.Node) node.Node {
 	}
 }
 
-func (n StmtList) Print(out io.Writer, indent string) {
-	fmt.Fprintf(out, "\n%v%v [- -]", indent, n.name)
+func (n StmtList) Walk(v node.Visitor) {
+	if v.Visit(n) == false {
+		return
+	}
 
 	if n.stmts != nil {
-		fmt.Fprintf(out, "\n%vstmts:", indent+"  ")
+		vv := v.Children("stmts")
 		for _, nn := range n.stmts {
-			nn.Print(out, indent+"    ")
+			nn.Walk(vv)
 		}
 	}
 }
diff --git a/node/stmt/switch.go b/node/stmt/switch.go
index 7e82755..278d74f 100644
--- a/node/stmt/switch.go
+++ b/node/stmt/switch.go
@@ -1,14 +1,11 @@
 package stmt
 
 import (
-	"fmt"
-	"io"
-
 	"github.com/z7zmey/php-parser/node"
 	"github.com/z7zmey/php-parser/token"
 )
 
-func(n Switch) Name() string {
+func (n Switch) Name() string {
 	return "Switch"
 }
 
@@ -28,18 +25,20 @@ func NewSwitch(token token.Token, cond node.Node, cases []node.Node) node.Node {
 	}
 }
 
-func (n Switch) Print(out io.Writer, indent string) {
-	fmt.Fprintf(out, "\n%v%v [%d %d] %q", indent, n.name, n.token.StartLine, n.token.EndLine, n.token.Value)
+func (n Switch) Walk(v node.Visitor) {
+	if v.Visit(n) == false {
+		return
+	}
 
 	if n.cond != nil {
-		fmt.Fprintf(out, "\n%vcond:", indent+"  ")
-		n.cond.Print(out, indent+"    ")
+		vv := v.Children("cond")
+		n.cond.Walk(vv)
 	}
 
 	if n.cases != nil {
-		fmt.Fprintf(out, "\n%vcases:", indent+"  ")
+		vv := v.Children("cases")
 		for _, nn := range n.cases {
-			nn.Print(out, indent+"    ")
+			nn.Walk(vv)
 		}
 	}
 }
diff --git a/node/stmt/throw.go b/node/stmt/throw.go
index 1da2d8d..05b8bd3 100644
--- a/node/stmt/throw.go
+++ b/node/stmt/throw.go
@@ -1,14 +1,11 @@
 package stmt
 
 import (
-	"fmt"
-	"io"
-
 	"github.com/z7zmey/php-parser/node"
 	"github.com/z7zmey/php-parser/token"
 )
 
-func(n Throw) Name() string {
+func (n Throw) Name() string {
 	return "Throw"
 }
 
@@ -26,11 +23,13 @@ func NewThrow(token token.Token, expr node.Node) node.Node {
 	}
 }
 
-func (n Throw) Print(out io.Writer, indent string) {
-	fmt.Fprintf(out, "\n%v%v [%d %d] %q", indent, n.name, n.token.StartLine, n.token.EndLine, n.token.Value)
+func (n Throw) Walk(v node.Visitor) {
+	if v.Visit(n) == false {
+		return
+	}
 
 	if n.expr != nil {
-		fmt.Fprintf(out, "\n%vexpr:", indent+"  ")
-		n.expr.Print(out, indent+"    ")
+		vv := v.Children("expr")
+		n.expr.Walk(vv)
 	}
 }
diff --git a/node/stmt/trait.go b/node/stmt/trait.go
index 25e036f..fa96fc5 100644
--- a/node/stmt/trait.go
+++ b/node/stmt/trait.go
@@ -1,14 +1,11 @@
 package stmt
 
 import (
-	"fmt"
-	"io"
-
 	"github.com/z7zmey/php-parser/node"
 	"github.com/z7zmey/php-parser/token"
 )
 
-func(n Trait) Name() string {
+func (n Trait) Name() string {
 	return "Trait"
 }
 
@@ -27,13 +24,17 @@ func NewTrait(token token.Token, stmts []node.Node) node.Node {
 	}
 }
 
-func (n Trait) Print(out io.Writer, indent string) {
-	fmt.Fprintf(out, "\n%v%v [%d %d] %q", indent, n.name, n.token.StartLine, n.token.EndLine, n.token.Value)
+func (n Trait) Walk(v node.Visitor) {
+	if v.Visit(n) == false {
+		return
+	}
+
+	v.Scalar("token", n.token.Value)
 
 	if n.stmts != nil {
-		fmt.Fprintf(out, "\n%vstmts:", indent+"  ")
+		vv := v.Children("stmts")
 		for _, nn := range n.stmts {
-			nn.Print(out, indent+"    ")
+			nn.Walk(vv)
 		}
 	}
 }
diff --git a/node/stmt/trait_method_ref.go b/node/stmt/trait_method_ref.go
index d694410..8fc2efd 100644
--- a/node/stmt/trait_method_ref.go
+++ b/node/stmt/trait_method_ref.go
@@ -1,14 +1,11 @@
 package stmt
 
 import (
-	"fmt"
-	"io"
-
 	"github.com/z7zmey/php-parser/node"
 	"github.com/z7zmey/php-parser/token"
 )
 
-func(n TraitMethodRef) Name() string {
+func (n TraitMethodRef) Name() string {
 	return "TraitMethodRef"
 }
 
@@ -18,6 +15,7 @@ type TraitMethodRef struct {
 	method token.Token
 }
 
+// TODO: method must be identifier
 func NewTraitMethodRef(trait node.Node, method token.Token) node.Node {
 	return TraitMethodRef{
 		"TraitMethodRef",
@@ -26,11 +24,15 @@ func NewTraitMethodRef(trait node.Node, method token.Token) node.Node {
 	}
 }
 
-func (n TraitMethodRef) Print(out io.Writer, indent string) {
-	fmt.Fprintf(out, "\n%v%v [- -] %q", indent, n.name, n.method.Value)
+func (n TraitMethodRef) Walk(v node.Visitor) {
+	if v.Visit(n) == false {
+		return
+	}
+
+	v.Scalar("method", n.method.Value)
 
 	if n.trait != nil {
-		fmt.Fprintf(out, "\n%vtrait", indent+"  ")
-		n.trait.Print(out, indent+"    ")
+		vv := v.Children("trait")
+		n.trait.Walk(vv)
 	}
 }
diff --git a/node/stmt/trait_use.go b/node/stmt/trait_use.go
index fcad08e..d4ca5c6 100644
--- a/node/stmt/trait_use.go
+++ b/node/stmt/trait_use.go
@@ -1,14 +1,11 @@
 package stmt
 
 import (
-	"fmt"
-	"io"
-
 	"github.com/z7zmey/php-parser/node"
 	"github.com/z7zmey/php-parser/token"
 )
 
-func(n TraitUse) Name() string {
+func (n TraitUse) Name() string {
 	return "TraitUse"
 }
 
@@ -29,20 +26,22 @@ func NewTraitUse(token token.Token, traits []node.Node, adaptations []node.Node)
 	}
 }
 
-func (n TraitUse) Print(out io.Writer, indent string) {
-	fmt.Fprintf(out, "\n%v%v [%d %d] %q", indent, n.name, n.token.StartLine, n.token.EndLine, n.token.Value)
+func (n TraitUse) Walk(v node.Visitor) {
+	if v.Visit(n) == false {
+		return
+	}
 
 	if n.traits != nil {
-		fmt.Fprintf(out, "\n%vtraits:", indent+"  ")
+		vv := v.Children("traits")
 		for _, nn := range n.traits {
-			nn.Print(out, indent+"    ")
+			nn.Walk(vv)
 		}
 	}
 
 	if n.adaptations != nil {
-		fmt.Fprintf(out, "\n%vadaptations:", indent+"  ")
+		vv := v.Children("adaptations")
 		for _, nn := range n.adaptations {
-			nn.Print(out, indent+"    ")
+			nn.Walk(vv)
 		}
 	}
 }
diff --git a/node/stmt/trait_use_alias.go b/node/stmt/trait_use_alias.go
index 4c67e37..137f848 100644
--- a/node/stmt/trait_use_alias.go
+++ b/node/stmt/trait_use_alias.go
@@ -1,14 +1,11 @@
 package stmt
 
 import (
-	"fmt"
-	"io"
-
 	"github.com/z7zmey/php-parser/node"
 	"github.com/z7zmey/php-parser/token"
 )
 
-func(n TraitUseAlias) Name() string {
+func (n TraitUseAlias) Name() string {
 	return "TraitUseAlias"
 }
 
@@ -28,20 +25,18 @@ func NewTraitUseAlias(ref node.Node, modifier node.Node, alias token.TokenInterf
 	}
 }
 
-func (n TraitUseAlias) Print(out io.Writer, indent string) {
-	fmt.Fprintf(out, "\n%v%v [- -]", indent, n.name)
-
-	if n.alias != nil {
-		fmt.Fprintf(out, "\n%valias: %q", indent+"  ", n.alias.GetValue())
+func (n TraitUseAlias) Walk(v node.Visitor) {
+	if v.Visit(n) == false {
+		return
 	}
 
 	if n.ref != nil {
-		fmt.Fprintf(out, "\n%vmethod", indent+"  ")
-		n.ref.Print(out, indent+"    ")
+		vv := v.Children("ref")
+		n.ref.Walk(vv)
 	}
 
 	if n.modifier != nil {
-		fmt.Fprintf(out, "\n%vmodifier:", indent+"  ")
-		n.modifier.Print(out, indent+"    ")
+		vv := v.Children("modifier")
+		n.modifier.Walk(vv)
 	}
 }
diff --git a/node/stmt/trait_use_precedence.go b/node/stmt/trait_use_precedence.go
index a711192..5d1bf9e 100644
--- a/node/stmt/trait_use_precedence.go
+++ b/node/stmt/trait_use_precedence.go
@@ -1,13 +1,10 @@
 package stmt
 
 import (
-	"fmt"
-	"io"
-
 	"github.com/z7zmey/php-parser/node"
 )
 
-func(n TraitUsePrecedence) Name() string {
+func (n TraitUsePrecedence) Name() string {
 	return "TraitUsePrecedence"
 }
 
@@ -25,16 +22,18 @@ func NewTraitUsePrecedence(ref node.Node, insteadof node.Node) node.Node {
 	}
 }
 
-func (n TraitUsePrecedence) Print(out io.Writer, indent string) {
-	fmt.Fprintf(out, "\n%v%v [- -]", indent, n.name)
+func (n TraitUsePrecedence) Walk(v node.Visitor) {
+	if v.Visit(n) == false {
+		return
+	}
 
 	if n.ref != nil {
-		fmt.Fprintf(out, "\n%vmethod", indent+"  ")
-		n.ref.Print(out, indent+"    ")
+		vv := v.Children("ref")
+		n.ref.Walk(vv)
 	}
 
 	if n.insteadof != nil {
-		fmt.Fprintf(out, "\n%vinsteadof:", indent+"  ")
-		n.insteadof.Print(out, indent+"    ")
+		vv := v.Children("insteadof")
+		n.insteadof.Walk(vv)
 	}
 }
diff --git a/node/stmt/try.go b/node/stmt/try.go
index 34cb02f..b0c4c11 100644
--- a/node/stmt/try.go
+++ b/node/stmt/try.go
@@ -1,14 +1,11 @@
 package stmt
 
 import (
-	"fmt"
-	"io"
-
 	"github.com/z7zmey/php-parser/node"
 	"github.com/z7zmey/php-parser/token"
 )
 
-func(n Try) Name() string {
+func (n Try) Name() string {
 	return "Try"
 }
 
@@ -30,25 +27,27 @@ func NewTry(token token.Token, stmts []node.Node, catches []node.Node, finally n
 	}
 }
 
-func (n Try) Print(out io.Writer, indent string) {
-	fmt.Fprintf(out, "\n%v%v [%d %d] %q", indent, n.name, n.token.StartLine, n.token.EndLine, n.token.Value)
+func (n Try) Walk(v node.Visitor) {
+	if v.Visit(n) == false {
+		return
+	}
 
 	if n.stmts != nil {
-		fmt.Fprintf(out, "\n%vstmts:", indent+"  ")
+		vv := v.Children("stmts")
 		for _, nn := range n.stmts {
-			nn.Print(out, indent+"    ")
+			nn.Walk(vv)
 		}
 	}
 
 	if n.catches != nil {
-		fmt.Fprintf(out, "\n%vcatches:", indent+"  ")
+		vv := v.Children("catches")
 		for _, nn := range n.catches {
-			nn.Print(out, indent+"    ")
+			nn.Walk(vv)
 		}
 	}
 
 	if n.finally != nil {
-		fmt.Fprintf(out, "\n%vfinally:", indent+"  ")
-		n.finally.Print(out, indent+"    ")
+		vv := v.Children("finally")
+		n.finally.Walk(vv)
 	}
 }
diff --git a/node/stmt/unset.go b/node/stmt/unset.go
index 54e878c..0035884 100644
--- a/node/stmt/unset.go
+++ b/node/stmt/unset.go
@@ -1,14 +1,11 @@
 package stmt
 
 import (
-	"fmt"
-	"io"
-
 	"github.com/z7zmey/php-parser/node"
 	"github.com/z7zmey/php-parser/token"
 )
 
-func(n Unset) Name() string {
+func (n Unset) Name() string {
 	return "Unset"
 }
 
@@ -26,13 +23,15 @@ func NewUnset(token token.Token, vars []node.Node) node.Node {
 	}
 }
 
-func (n Unset) Print(out io.Writer, indent string) {
-	fmt.Fprintf(out, "\n%v%v [%d %d] %q", indent, n.name, n.token.StartLine, n.token.EndLine, n.token.Value)
+func (n Unset) Walk(v node.Visitor) {
+	if v.Visit(n) == false {
+		return
+	}
 
 	if n.vars != nil {
-		fmt.Fprintf(out, "\n%vvars:", indent+"  ")
+		vv := v.Children("vars")
 		for _, nn := range n.vars {
-			nn.Print(out, indent+"    ")
+			nn.Walk(vv)
 		}
 	}
 }
diff --git a/node/stmt/use.go b/node/stmt/use.go
index c571aef..479eea5 100644
--- a/node/stmt/use.go
+++ b/node/stmt/use.go
@@ -1,17 +1,10 @@
 package stmt
 
 import (
-	"fmt"
-	"io"
-
 	"github.com/z7zmey/php-parser/node"
 	"github.com/z7zmey/php-parser/token"
 )
 
-func(n Use) Name() string {
-	return "Use"
-}
-
 type Use struct {
 	name    string
 	useType node.Node
@@ -28,25 +21,27 @@ func NewUse(useType node.Node, use node.Node, alias token.TokenInterface) node.N
 	}
 }
 
+func (n Use) Name() string {
+	return "Use"
+}
+
 func (n Use) SetType(useType node.Node) node.Node {
 	n.useType = useType
 	return n
 }
 
-func (n Use) Print(out io.Writer, indent string) {
-	fmt.Fprintf(out, "\n%v%v [- -]", indent, n.name)
+func (n Use) Walk(v node.Visitor) {
+	if v.Visit(n) == false {
+		return
+	}
 
 	if n.useType != nil {
-		fmt.Fprintf(out, "\n%vtype:", indent+"  ")
-		n.useType.Print(out, indent+"    ")
+		vv := v.Children("useType")
+		n.useType.Walk(vv)
 	}
 
 	if n.use != nil {
-		fmt.Fprintf(out, "\n%vuse:", indent+"  ")
-		n.use.Print(out, indent+"    ")
-	}
-
-	if n.alias != nil {
-		fmt.Fprintf(out, "\n%valias: %q", indent+"  ", n.alias.GetValue())
+		vv := v.Children("use")
+		n.use.Walk(vv)
 	}
 }
diff --git a/node/stmt/use_list.go b/node/stmt/use_list.go
index 7a5adc9..3621a62 100644
--- a/node/stmt/use_list.go
+++ b/node/stmt/use_list.go
@@ -1,14 +1,11 @@
 package stmt
 
 import (
-	"fmt"
-	"io"
-
 	"github.com/z7zmey/php-parser/node"
 	"github.com/z7zmey/php-parser/token"
 )
 
-func(n UseList) Name() string {
+func (n UseList) Name() string {
 	return "UseList"
 }
 
@@ -28,18 +25,20 @@ func NewUseList(token token.Token, useType node.Node, uses []node.Node) node.Nod
 	}
 }
 
-func (n UseList) Print(out io.Writer, indent string) {
-	fmt.Fprintf(out, "\n%v%v [%d %d] %q", indent, n.name, n.token.StartLine, n.token.EndLine, n.token.Value)
+func (n UseList) Walk(v node.Visitor) {
+	if v.Visit(n) == false {
+		return
+	}
 
 	if n.useType != nil {
-		fmt.Fprintf(out, "\n%vtype:", indent+"  ")
-		n.useType.Print(out, indent+"    ")
+		vv := v.Children("useType")
+		n.useType.Walk(vv)
 	}
 
 	if n.uses != nil {
-		fmt.Fprintf(out, "\n%vuses:", indent+"  ")
+		vv := v.Children("uses")
 		for _, nn := range n.uses {
-			nn.Print(out, indent+"    ")
+			nn.Walk(vv)
 		}
 	}
 }
diff --git a/node/stmt/while.go b/node/stmt/while.go
index 259df64..c708b1d 100644
--- a/node/stmt/while.go
+++ b/node/stmt/while.go
@@ -1,17 +1,10 @@
 package stmt
 
 import (
-	"fmt"
-	"io"
-
 	"github.com/z7zmey/php-parser/node"
 	"github.com/z7zmey/php-parser/token"
 )
 
-func(n While) Name() string {
-	return "While"
-}
-
 type While struct {
 	name  string
 	token token.Token
@@ -28,16 +21,22 @@ func NewWhile(token token.Token, cond node.Node, stmt node.Node) node.Node {
 	}
 }
 
-func (n While) Print(out io.Writer, indent string) {
-	fmt.Fprintf(out, "\n%v%v [%d %d] %q", indent, n.name, n.token.StartLine, n.token.EndLine, n.token.Value)
+func (n While) Name() string {
+	return "While"
+}
+
+func (n While) Walk(v node.Visitor) {
+	if v.Visit(n) == false {
+		return
+	}
 
 	if n.cond != nil {
-		fmt.Fprintf(out, "\n%vcond:", indent+"  ")
-		n.cond.Print(out, indent+"    ")
+		vv := v.Children("cond")
+		n.cond.Walk(vv)
 	}
 
 	if n.stmt != nil {
-		fmt.Fprintf(out, "\n%vstmt:", indent+"  ")
-		n.stmt.Print(out, indent+"    ")
+		vv := v.Children("stmt")
+		n.stmt.Walk(vv)
 	}
 }
diff --git a/node/visitor.go b/node/visitor.go
new file mode 100644
index 0000000..3659f03
--- /dev/null
+++ b/node/visitor.go
@@ -0,0 +1,7 @@
+package node
+
+type Visitor interface {
+	Visit(node Node) bool
+	Children(key string) Visitor
+	Scalar(key string, value interface{})
+}