(
#comment
(let config (DataSource 'config))

(let res_sink (DataSink 'result))
(let s (AsStruct
  '('a (String 'aaa))
  '('b (Just (Uint32 '4)))
  '('c (Nothing (OptionalType (DataType 'Uint32)))))
)

(let js (Just s))
(let n (Nothing (TypeOf js)))

(let world (Write! world res_sink (Key) (Member s 'a) '()))
(let world (Write! world res_sink (Key) (Member js 'a) '()))
(let world (Write! world res_sink (Key) (Member js 'b) '()))
(let world (Write! world res_sink (Key) (Member js 'c) '()))
(let world (Write! world res_sink (Key) (Member n 'a) '()))
(let world (Write! world res_sink (Key) (Member n 'c) '()))

(let world (Commit! world res_sink))
(return world)
)