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module TypeLevel.DatePart where
import Prelude hiding (break)
data a :/: b = a :/: b deriving (Eq, Ord)
infixr :/:
class Seq a x y where
break :: x -> (a, y)
build :: a -> y -> x
instance (Seq a x y, Seq b y z) => Seq (a :/: b) x z where
break x = let
(a, y) = break x :: (a, y)
(b, z) = break y :: (b, z)
in (a :/: b, z)
build (a :/: b) z = let
y = build b z :: y
x = build a y :: x
in x
data Foo = Foo Integer
instance Seq Foo Integer Bool where
break i | i >= 0 = (Foo $ abs i, True)
| otherwise = (Foo i, False)
build (Foo i) True = i
build (Foo i) False = negate i
data Bar = First | Second
instance Seq Bar Bool Bar where
break True = (First, First)
break False = (Second, Second)
build First _ = True
build Second _ = True
data Baz = Baz Bar
instance Seq Baz Bar () where
break b = (Baz b, ())
build (Baz b) _ = b
myBreak :: Integer -> (Foo :/: Bar :/: Baz)
myBreak = fst . break' where
break' = break :: Integer -> (Foo :/: Bar :/: Baz, ()) |