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Add piMaybeFlatten.

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This commit is contained in:
Kei Hibino 2013-05-23 14:26:55 +09:00
parent 3db40de6c7
commit 28b0987ea8
1 changed files with 10 additions and 4 deletions
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14
relational-join/src/Database/Relational/Query/ProjectableExtended.hs
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@ -4,6 +4,8 @@
module Database.Relational.Query.ProjectableExtended (
ProjectableFlattenMaybe (flatten),
piMaybeFlatten,
(!), (!?), (!??),
@ -36,10 +38,14 @@ p ! pi' = project $ Projection.pi p pi'
=> Projection (Maybe a) -> Pi a b -> p (Maybe b)
p !? pi' = project $ Projection.piMaybe p pi'
(!??) :: (PersistableWidth b, Projectable p, ProjectableMaybe p,
ProjectableFlattenMaybe c (Maybe a))
=> Projection c -> Pi a b -> p (Maybe b)
p !?? pi' = project $ Projection.piMaybe (flatten p) pi'
piMaybeFlatten :: (PersistableWidth b, ProjectableFlattenMaybe c (Maybe a))
=> Projection c -> Pi a b -> Projection (Maybe b)
piMaybeFlatten = Projection.piMaybe . flatten
(!??) :: (PersistableWidth b, ProjectableFlattenMaybe c (Maybe a),
Projectable p, ProjectableMaybe p)
=> Projection c -> Pi a b -> p (Maybe b)
p !?? pi' = project $ piMaybeFlatten p pi'
class ProjectableGeneralizedZip a b c where
generalizedZip :: ProjectableZip p => p a -> p b -> p c