ydb/yql/essentials/tests/s-expressions/suites/InMem/FoldMap.yqls

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

(let res_sink (DataSink 'result))
(let list (AsList
'((Uint32 '1) (String 'b))
'((Uint32 '2) (String 'o))
'((Uint32 '1) (String 'm))
'((Uint32 '3) (String 'b))))

(let init_state '((Uint32 '0) (String '"")))

(let update (lambda '(item state) (block '(
    (let key (Nth item '0))
    (let val (Nth item '1))
    (let skey (Nth state '0))
    (let sval (Nth state '1))
    (let skey (+ skey key))
    (let sval (Concat sval val))
    (let new_item '(key val skey sval))
    (let new_state '(skey sval))
    (return '(new_item new_state)
)))))

(let result (FoldMap list init_state update))

(let world (Write! world res_sink (Key) result '('('type))))
(let world (Commit! world res_sink))
(return world)
)