diff --git a/parser/parser.go b/parser/parser.go
index 2b93e3a..15d0fe6 100644
--- a/parser/parser.go
+++ b/parser/parser.go
@@ -10,6 +10,11 @@ import (
 	"go/types"
 )
 
+// FieldFormatter transfers the field value to expected format
+type FieldFormatter interface {
+	Format(field *StructField) string
+}
+
 // StructField defines struct field
 type StructField struct {
 	Name       string
@@ -18,6 +23,7 @@ type StructField struct {
 	Comment    string
 	Doc        string
 	Tag        string
+	FormatFunc func(field *StructField) string
 }
 
 // Key returns the key of the field
@@ -32,7 +38,7 @@ func (sf *StructField) Value() interface{} {
 		return sf.NestedType.ToKV()
 	}
 
-	return ""
+	return sf.FormatFunc(sf)
 }
 
 // StructNode defines struct node
@@ -52,15 +58,16 @@ func (sn *StructNode) ToKV() map[string]interface{} {
 
 // StructParser parses structs in given file or string
 type StructParser struct {
-	MainStruct *StructNode
-	Info       types.Info
+	MainStruct     *StructNode
+	Info           types.Info
+	FieldFormatter FieldFormatter
 }
 
 // NewStructParser is the constructor of StructParser
 // filePath and src follow the same rule with go/parser.ParseFile
 // If src != nil, ParseFile parses the source from src and the filename is only used when recording position information. The type of the argument for the src parameter must be string, []byte, or io.Reader. If src == nil, ParseFile parses the file specified by filename.
 // rootStruct is the root struct we want to use
-func NewStructParser(filePath string, src interface{}, rootStruct string) (*StructParser, error) {
+func NewStructParser(filePath string, src interface{}, rootStruct string, formatter FieldFormatter) (*StructParser, error) {
 	fset := token.NewFileSet()
 	f, err := parser.ParseFile(fset, filePath, src, parser.ParseComments)
 	if err != nil {
@@ -80,8 +87,9 @@ func NewStructParser(filePath string, src interface{}, rootStruct string) (*Stru
 		return nil, err
 	}
 
-	cg := &StructParser{
-		Info: info,
+	sp := &StructParser{
+		FieldFormatter: formatter,
+		Info:           info,
 	}
 
 	ast.Inspect(f, func(n ast.Node) bool {
@@ -101,27 +109,27 @@ func NewStructParser(filePath string, src interface{}, rootStruct string) (*Stru
 			return true
 		}
 
-		cg.MainStruct = cg.ParseStruct(structName, s)
+		sp.MainStruct = sp.ParseStruct(structName, s)
 		return false
 	})
 
-	if cg.MainStruct == nil {
+	if sp.MainStruct == nil {
 		return nil, errors.New("non-exist root struct")
 	}
 
-	return cg, nil
+	return sp, nil
 }
 
-func (cg *StructParser) ToJSON() ([]byte, error) {
-	value := cg.MainStruct.ToKV()
+func (sp *StructParser) ToJSON() ([]byte, error) {
+	value := sp.MainStruct.ToKV()
 	return json.MarshalIndent(value, "", "  ")
 }
 
 // ParseField parses struct field in nested way
-func (cg *StructParser) ParseField(field *ast.Field) *StructField {
+func (sp *StructParser) ParseField(field *ast.Field) *StructField {
 	// ast.Print(nil, field)
 	fieldName := field.Names[0].Name
-	fieldType := cg.Info.TypeOf(field.Type)
+	fieldType := sp.Info.TypeOf(field.Type)
 
 	fieldTag := ""
 	if field.Tag != nil {
@@ -138,7 +146,7 @@ func (cg *StructParser) ParseField(field *ast.Field) *StructField {
 
 	var nestedStruct *StructNode
 	if s, isInlineStruct := field.Type.(*ast.StructType); isInlineStruct {
-		nestedStruct = cg.ParseStruct("", s)
+		nestedStruct = sp.ParseStruct("", s)
 	}
 
 	if _, isNamedStructorBasic := field.Type.(*ast.Ident); isNamedStructorBasic && field.Type.(*ast.Ident).Obj != nil {
@@ -151,7 +159,7 @@ func (cg *StructParser) ParseField(field *ast.Field) *StructField {
 		if !ok {
 			return nil
 		}
-		nestedStruct = cg.ParseStruct(ts.Name.Name, s)
+		nestedStruct = sp.ParseStruct(ts.Name.Name, s)
 	}
 	// fieldType.(*types.Basic) // basic type
 	// *ast.ArrayType:
@@ -165,14 +173,15 @@ func (cg *StructParser) ParseField(field *ast.Field) *StructField {
 		Comment:    fieldComment,
 		Doc:        fieldDoc,
 		NestedType: nestedStruct,
+		FormatFunc: sp.FieldFormatter.Format,
 	}
 }
 
 // ParseStruct parses struct in nested way
-func (cg *StructParser) ParseStruct(structName string, s *ast.StructType) *StructNode {
+func (sp *StructParser) ParseStruct(structName string, s *ast.StructType) *StructNode {
 	fields := []*StructField{}
 	for _, field := range s.Fields.List {
-		parsedField := cg.ParseField(field)
+		parsedField := sp.ParseField(field)
 		if parsedField != nil {
 			fields = append(fields, parsedField)
 		}
diff --git a/parser/parser_test.go b/parser/parser_test.go
index 4ba578a..9413765 100644
--- a/parser/parser_test.go
+++ b/parser/parser_test.go
@@ -5,6 +5,13 @@ import (
 	"log"
 )
 
+type sampleFormatter struct {
+}
+
+func (f *sampleFormatter) Format(field *StructField) string {
+	return ""
+}
+
 func ExampleStructParser() {
 	const src = `
 package p
@@ -28,14 +35,15 @@ type StructA struct {
 	Field6 func(int)
 	Field7 StructB
 }
-
 `
-	cg, err := NewStructParser("src.go", src, "StructA")
+	formatter := &sampleFormatter{}
+
+	sp, err := NewStructParser("src.go", src, "StructA", formatter)
 	if err != nil {
 		log.Fatal(err)
 	}
 
-	b, err := cg.ToJSON()
+	b, err := sp.ToJSON()
 	if err != nil {
 		log.Fatal(err)
 	}