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rel8/src/Rel8/Query/Null.hs
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1module Rel8.Query.Null
2 ( catNull
3 )
4where
6-- base
7import Prelude
9-- rel8
10import Rel8.Expr ( Expr )
11import Rel8.Expr.Null ( isNonNull, unsafeUnnullify )
12import Rel8.Query ( Query )
13import Rel8.Query.Filter ( where_ )
16-- | Filter a 'Query' that might return @null@ to a 'Query' without any
17-- @null@s.
18--
19-- Corresponds to 'Data.Maybe.catMaybes'.
20catNull :: Expr (Maybe a) -> Query (Expr a)
21catNull a = do
22 where_ $ isNonNull a
23 pure $ unsafeUnnullify a