src/Rel8/Query/Null.hs · rel8

on da76712 help sign in

38 lines 897 B history raw

1{-# language FlexibleContexts #-}

3module Rel8.Query.Null

4 ( catNull

5 , catNullTable

6 )

7where

9-- base

10import Prelude

12-- rel8

13import Rel8.Expr ( Expr )

14import Rel8.Expr.Null ( isNonNull, unsafeUnnullify )

15import Rel8.Table ( Table )

16import Rel8.Table.Null ( NullTable, isNonNullTable, unsafeUnnullifyTable )

17import Rel8.Query ( Query )

18import Rel8.Query.Filter ( where_ )

21-- | Filter a 'Query' that might return @null@ to a 'Query' without any

22-- @null@s.

24-- Corresponds to 'Data.Maybe.catMaybes'.

25catNull :: Expr (Maybe a) -> Query (Expr a)

26catNull a = do

27 where_ $ isNonNull a

28 pure $ unsafeUnnullify a

31-- | Filter a 'Query' that might return @nullTable@ to a 'Query' without any

32-- @nullTable@s.

34-- Corresponds to 'Data.Maybe.catMaybes'.

35catNullTable :: Table Expr a => NullTable Expr a -> Query a

36catNullTable a = do

37 where_ $ isNonNullTable a

38 pure $ unsafeUnnullifyTable a