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Optimize <|>: implementation of Tabulation #178

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Jun 9, 2022
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Optimize <|>: implementation of Tabulation #178

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29 changes: 20 additions & 9 deletions src/Rel8/Tabulate.hs
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Original file line number Diff line number Diff line change
Expand Up @@ -58,7 +58,7 @@ import Data.Function ( on )
import Data.Functor.Contravariant ( Contravariant, (>$<), contramap )
import Data.Int ( Int64 )
import Data.Kind ( Type )
import Data.Maybe ( fromMaybe )
import Data.Maybe ( fromJust, fromMaybe )
import Prelude hiding ( lookup, zip, zipWith )

-- bifunctors
Expand Down Expand Up @@ -90,7 +90,6 @@ import Rel8.Order ( Order( Order ) )
import Rel8.Query ( Query )
import qualified Rel8.Query.Exists as Q ( exists, present, absent )
import Rel8.Query.Filter ( where_ )
import Rel8.Query.Limit ( limit )
import Rel8.Query.List ( catNonEmptyTable )
import qualified Rel8.Query.Maybe as Q ( optional )
import Rel8.Query.Opaleye ( mapOpaleye, unsafePeekQuery )
Expand Down Expand Up @@ -234,7 +233,13 @@ instance EqTable k => Monad (Tabulation k) where
-- | If @'Tabulation' k a@ is @Map k (NonEmpty a)@, then @(<|>:)@ is
-- @unionWith (<>)@.
instance EqTable k => AltTable (Tabulation k) where
as <|>: bs = catNonEmptyTable `through` ((<>) `on` some) as bs
tas <|>: tbs = do
eas <- peek tas
ebs <- peek tbs
case (eas, ebs) of
(Left as, Left bs) -> liftQuery $ as <|>: bs
(Right as, Right bs) -> fromQuery $ as <|>: bs
_ -> catNonEmptyTable `through` ((<>) `on` some) tas tbs


instance EqTable k => AlternativeTable (Tabulation k) where
Expand Down Expand Up @@ -343,12 +348,8 @@ aggregate (Tabulation f) = Tabulation $
-- \"first\" value it encounters for each key, but note that \"first\" is
-- undefined unless you first call 'order'.
distinct :: EqTable k => Tabulation k a -> Tabulation k a
distinct (Tabulation f) = Tabulation $ \p ->
-- workaround for https://github.com/tomjaguarpaw/haskell-opaleye/pull/518
case fst (unsafePeekQuery (f p)) of
Nothing -> limit 1 (f p)
Just _ ->
mapOpaleye (Opaleye.distinctOnExplicit (key unpackspec) fst) (f p)
distinct (Tabulation f) = Tabulation $
mapOpaleye (Opaleye.distinctOnExplicit (key unpackspec) fst) . f


-- | 'order' orders the /values/ of a 'Tabulation' within their
Expand Down Expand Up @@ -626,3 +627,13 @@ similarity a b = a <* present b
-- @do@-notation.
difference :: EqTable k => Tabulation k a -> Tabulation k b -> Tabulation k a
difference a b = a <* absent b


-- | 'Tabulation's can be produced with either 'fromQuery' or 'liftQuery', and
-- in some cases we might want to treat these differently. 'peek' uses
-- 'unsafePeekQuery' to determine which type of 'Tabulation' we have.
peek :: Tabulation k a -> Tabulation k (Either (Query a) (Query (k, a)))
peek (Tabulation f) = Tabulation $ \p ->
pure $ (empty,) $ case unsafePeekQuery (f p) of
(Nothing, _) -> Left $ fmap snd (f p)
(Just _, _) -> Right $ fmap (first fromJust) (f p)