diff --git a/operator-fraction.go b/operator-fraction.go
index f3e0c16..9802c7d 100644
--- a/operator-fraction.go
+++ b/operator-fraction.go
@@ -204,6 +204,10 @@ func (f *fraction) ToString(opt FmtOpt) string {
 	return sb.String()
 }
 
+func (f *fraction) TypeName() string {
+	return "fraction"
+}
+
 // -------- fraction term
 func newFractionTerm(tk *Token) *term {
 	return &term{