src/Rel8/Query/List.hs · rel8

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1{-# language FlexibleContexts #-}

3module Rel8.Query.List

4 ( many, some

5 )

6where

8-- base

9import Prelude

11-- rel8

12import Rel8.Expr ( Expr )

13import Rel8.Query ( Query )

14import Rel8.Query.Aggregate ( aggregate )

15import Rel8.Query.Maybe ( optional )

16import Rel8.Table ( Table )

17import Rel8.Table.Aggregate ( listAgg, nonEmptyAgg )

18import Rel8.Table.List ( ListTable )

19import Rel8.Table.Maybe ( maybeTable )

20import Rel8.Table.NonEmpty ( NonEmptyTable )

23-- | Aggregate a 'Query' into a 'NonEmptyTable'. If the supplied query returns

24-- 0 rows, this function will produce a 'Query' that is empty - that is, will

25-- produce zero @NonEmptyTable@s. If the supplied @Query@ does return rows,

26-- @some@ will return exactly one row, with a @NonEmptyTable@ collecting all

27-- returned rows.

29-- @some@ is analogous to 'Control.Applicative.some' from

30-- @Control.Applicative@.

31some :: Table Expr a => Query a -> Query (NonEmptyTable a)

32some = aggregate . fmap nonEmptyAgg

35-- | Aggregate a 'Query' into a 'ListTable'. If the supplied query returns 0

36-- rows, this function will produce a 'Query' that returns one row containing

37-- the empty @ListTable@. If the supplied @Query@ does return rows, @many@ will

38-- return exactly one row, with a @ListTable@ collecting all returned rows.

39--

40-- @many@ is analogous to 'Control.Applicative.many' from

41-- @Control.Applicative@.

42many :: Table Expr a => Query a -> Query (ListTable a)

43many = fmap (maybeTable mempty id) . optional . aggregate . fmap listAgg