(
(let config (DataSource 'config))

# prepare python udf
(let ui64 (DataType 'Uint64))
(let str (DataType 'String))
(let funcType (CallableType '() '(ui64) '(ui64)))

(let udfType (CallableType '() '(funcType) '(ui64)))
(let udfScript (String '@@
def create_counter(start):
    def counter(step):
        v = counter.x
        counter.x += step
        return v

    counter.x = start
    return counter
@@))

(let udf (ScriptUdf 'Python3 'create_counter udfType udfScript))

# call udf
(let counter (Apply udf (Uint64 '1)))
(let result (AsList
    (Apply counter (Uint64 '1))
    (Apply counter (Uint64 '2))
    (Apply counter (Uint64 '3))
    (Apply counter (Uint64 '4))
))

# output result with type
(let res_sink (DataSink 'result))
(let world (Write! world res_sink (Key) result '( '('type) )))

# finish
(return (Commit! world res_sink))
)