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{-# LANGUAGE BangPatterns, FlexibleInstances, MultiParamTypeClasses #-}
module T23012 where
import Data.Kind (Type)
class Vector v a where
nothing :: v a
just :: a -> v a
data Proxy (a :: Type) = P
instance Vector Proxy a where
nothing = P
just _ = P
step :: Maybe a
step = Nothing
{-# INLINE[0] step #-}
stream :: Vector v a => v a
stream = case step of
Nothing -> nothing
Just !x -> just x
{-# INLINE[1] stream #-}
data Id a = MkId a
f :: (Proxy (Id a), Proxy a)
f = (stream, stream)
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