diff --git a/ast/NodeChoose.go b/ast/NodeChoose.go
index 0447e38..2a1aaab 100644
--- a/ast/NodeChoose.go
+++ b/ast/NodeChoose.go
@@ -21,7 +21,7 @@ func (it *NodeChoose) Eval(env map[string]interface{}, arg_array *[]interface{},
 		if e != nil {
 			return nil, e
 		}
-		if r != nil {
+		if v.Type() == NWhen && r != nil {
 			return r, nil
 		}
 	}