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{-# LANGUAGE GADTs, EmptyDataDecls, ScopedTypeVariables, TypeFamilies #-}
module T4093b where
data C
data O
type family EitherCO e a b :: *
type instance EitherCO C a b = a
type instance EitherCO O a b = b
data MaybeC ex t where
JustC :: t -> MaybeC C t
NothingC :: MaybeC O t
data Block (n :: * -> * -> *) e x
blockToNodeList ::
forall n e x. (EitherCO e (A C O n) (A O O n) ~ A e O n,
EitherCO x (A C C n) (A C O n) ~ A C x n) =>
Block n e x -> A e x n
type A e x n = (MaybeC e (n C O), MaybeC x (n O C))
blockToNodeList b = foldBlockNodesF (f, l) b z
where
z :: EitherCO e (EitherCO e (A C O n) (A O O n)) (EitherCO e (A C O n) (A O O n))
z = undefined
f :: n C O -> EitherCO e (A C O n) (A O O n) -> EitherCO e (A C O n) (A O O n)
f n _ = (JustC n, NothingC)
l :: n O C -> EitherCO e (A C O n) (A O O n) -> EitherCO e (A C C n) (A O C n)
l _ = undefined
foldBlockNodesF :: forall n a b c e x .
( n C O -> a -> b
, n O C -> b -> c)
-> (Block n e x -> EitherCO e a b -> EitherCO x c b)
foldBlockNodesF _ = undefined
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