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{-# LANGUAGE ScopedTypeVariables, TypeApplications, RankNTypes, ImpredicativeTypes #-}
module ICFP20 where
import Control.Monad.ST( ST, runST )
type SId = forall a. a->a
choose :: a -> a -> a
choose x y = x
single :: a -> [a]
single x = [x]
auto'2 :: SId -> b -> b
auto'2 x = id @SId x
-- Fails, and should fail
auto'1 :: SId -> b -> b
auto'1 = id
-- Fails, and should do so
a6 = id auto'2
-- Fails, and should do so
a8 = choose id auto'2
-- Fails, and should do so
st2 :: forall a. (forall s. ST s a) -> a
st2 x = id runST x
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