diff --git a/function/function.go b/function/function.go
index 3356c6d..85fc6e9 100644
--- a/function/function.go
+++ b/function/function.go
@@ -58,6 +58,15 @@ func Regist(name string, fn Func) error {
 	return nil
 }
 
+// Registered returns all registered functions or operators
+func Registered() []string {
+	ss := make([]string, 0, len(functions))
+	for k, _ := range functions {
+		ss = append(ss, k)
+	}
+	return ss
+}
+
 // MustRegist is same as Regist but may overide if function with name existed
 func MustRegist(name string, fn Func) {
 	functions[name] = fn
diff --git a/function/function_test.go b/function/function_test.go
index 35728a6..d1a2146 100644
--- a/function/function_test.go
+++ b/function/function_test.go
@@ -1,6 +1,8 @@
 package function
 
-import "testing"
+import (
+	"testing"
+)
 
 func TestGet(t *testing.T) {
 	if err := Regist("foo", foo); err != nil {
@@ -23,7 +25,7 @@ func TestGet(t *testing.T) {
 	if _, err := Get("fooooo"); err != ErrNotFound {
 		t.Error("should not found")
 	}
-
+	_ = Registered()
 }
 
 var foo = func(params ...interface{}) (interface{}, error) {