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Document Rel8.Table.These

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Ollie Charles 2021-06-18 11:29:52 +01:00
parent 7568c75e03
commit 1a3c3c139d
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src/Rel8/Table/These.hs
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@ -78,6 +78,13 @@ import Data.Functor.Bind ( Bind, (>>-) )
import Data.These ( These )
-- | @TheseTable a b@ is a Rel8 table that contains either the table @a@, the
-- table @b@, or both tables @a@ and @b@. You can construct @TheseTable@s using
-- 'thisTable', 'thatTable' and 'thoseTable'. @TheseTable@s can be
-- eliminated/pattern matched using 'theseTable'.
--
-- @TheseTable@ is operationally the same as Haskell's 'These' type, but
-- adapted to work with Rel8.
type TheseTable :: Type -> Type -> Type
data TheseTable a b = TheseTable
{ here :: MaybeTable a
@ -180,46 +187,57 @@ toThereTag :: Tag "isJust" a -> Tag "hasThere" a
toThereTag Tag {..} = Tag {..}
-- | Test if a 'TheseTable' was constructed with 'thisTable'.
isThisTable :: TheseTable a b -> Expr Bool
isThisTable a = hasHereTable a &&. not_ (hasThereTable a)
-- | Test if a 'TheseTable' was constructed with 'thatTable'.
isThatTable :: TheseTable a b -> Expr Bool
isThatTable a = not_ (hasHereTable a) &&. hasThereTable a
-- | Test if a 'TheseTable' was constructed with 'thoseTable'.
isThoseTable :: TheseTable a b -> Expr Bool
isThoseTable a = hasHereTable a &&. hasThereTable a
-- | Test if the @a@ table of @TheseTable a b@ is present.
hasHereTable :: TheseTable a b -> Expr Bool
hasHereTable TheseTable {here} = isJustTable here
-- | Test if the @b@ table of @TheseTable a b@ is present.
hasThereTable :: TheseTable a b -> Expr Bool
hasThereTable TheseTable {there} = isJustTable there
-- | Attempt to project out the @a@ table of a @TheseTable a b@.
justHereTable :: TheseTable a b -> MaybeTable a
justHereTable = here
-- | Attempt to project out the @b@ table of a @TheseTable a b@.
justThereTable :: TheseTable a b -> MaybeTable b
justThereTable = there
-- | Construct a @TheseTable@. Corresponds to 'This'.
thisTable :: Table Expr b => a -> TheseTable a b
thisTable a = TheseTable (justTable a) nothingTable
-- | Construct a @TheseTable@. Corresponds to 'That'.
thatTable :: Table Expr a => b -> TheseTable a b
thatTable b = TheseTable nothingTable (justTable b)
-- | Construct a @TheseTable@. Corresponds to 'These'.
thoseTable :: a -> b -> TheseTable a b
thoseTable a b = TheseTable (justTable a) (justTable b)
-- | Pattern match on a 'TheseTable'.
theseTable :: Table Expr c
=> (a -> c) -> (b -> c) -> (a -> b -> c) -> TheseTable a b -> c
theseTable f g h TheseTable {here, there} =