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{-# language TypeFamilies, FunctionalDependencies, GADTs, DataKinds, TypeOperators, ScopedTypeVariables, FlexibleInstances , UndecidableInstances, PartialTypeSignatures #-}
module T17024 where
infixr 6 :::
data HList xs where
HNil :: HList '[]
(:::) :: a -> HList as -> HList (a ': as)
class AppHList ts o f | ts f -> o, ts o -> f where
appHList :: f -> HList ts -> o
instance AppHList '[] o o where
appHList x HNil = x
instance AppHList ts o f => AppHList (t : ts) o (t -> f) where
appHList f (x ::: xs) = appHList (f x) xs
foo :: (a -> b -> c) -> HList '[a, b] -> _
foo = appHList
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