Using unlifted types where lifted types are expected

unlifted_sneakiness.hs

{-# LANGUAGE MagicHash #-}
{-# LANGUAGE RankNTypes #-}
{-# LANGUAGE TypeInType #-}

import Data.Primitive
import Data.Primitive.UnliftedArray
import GHC.Types
import GHC.Exts

main :: IO ()
main = do
  a@(Array myArr) <- newArray 1 ("foo" :: String) >>= unsafeFreezeArray
  UnliftedArray myArrArr <- newUnliftedArray 1 a >>= unsafeFreezeUnliftedArray
  putStrLn (myFunc show (2 :: Integer)) 
  putStrLn (myFunc2 (\x -> show (Array x)) myArr) 
  putStrLn (myBigFunc (+1) show show (2 :: Integer)) 
  putStrLn (myBigFunc2 (\x -> array# (indexUnliftedArray (UnliftedArray x) 0 :: Array String)) (\x -> show (Array x)) (\x -> show (UnliftedArray x :: UnliftedArray (Array String))) myArrArr)

{-# NOINLINE myFunc #-}
myFunc :: (a -> String) -> a -> String
myFunc f a =
  let x = f a
   in x ++ x

myFunc2 :: forall (a :: TYPE 'UnliftedRep). (a -> String) -> a -> String
myFunc2 = unsafeCoerce# myFunc

{-# NOINLINE myBigFunc #-}
myBigFunc :: (a -> b) -> (b -> String) -> (a -> String) -> a -> String
myBigFunc f g h a =
  let y = f a
      x = g y
   in x ++ x ++ h a

myBigFunc2 :: forall (a :: TYPE 'UnliftedRep) (b :: TYPE 'UnliftedRep). (a -> b) -> (b -> String) -> (a -> String) -> a -> String
myBigFunc2 = unsafeCoerce# myBigFunc