(
#comment
(let config (DataSource 'config))
(let world (Configure! world config 'PureDataSource 'yt))

(let res_sink (DataSink 'result))
(let udf (Udf 'SimpleUdf.EchoWithPrefix))
(let x (String 'aaa))
(let y (String 'bbb))
(let data (Apply udf x))
(let world (Write! world res_sink (Key) data '()))
(let data (Apply udf x y))
(let world (Write! world res_sink (Key) data '()))
(let world (Commit! world res_sink))
(return world)
)