feat: call function without argument

builtin/function.go

@@ -1,15 +1,23 @@
 package builtin
 
 import (
+	"crypto/md5"
+	"encoding/hex"
 	"math"
 	"math/rand"
 	"time"
 )
 
 var Functions = map[string]interface{}{
+	"get_timestamp":     getTimestamp,    // call without arguments
 	"sleep":             sleep,           // call with one argument
 	"gen_random_string": genRandomString, // call with one argument
 	"max":               math.Max,        // call with two arguments
+	"md5":               MD5,
+}
+
+func getTimestamp() int64 {
+	return time.Now().UnixNano() / int64(time.Millisecond)
 }
 
 func sleep(nSecs int) {
@@ -26,3 +34,9 @@ func genRandomString(n int) string {
 	}
 	return string(b)
 }
+
+func MD5(str string) string {
+	hasher := md5.New()
+	hasher.Write([]byte(str))
+	return hex.EncodeToString(hasher.Sum(nil))
+}