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{-# LANGUAGE TemplateHaskell #-}
{-# LANGUAGE MagicHash #-}
import Language.Haskell.TH.Lib
import Data.Word
import Foreign.ForeignPtr
import Foreign.Marshal.Array
import GHC.Exts
import System.Mem
import Control.Monad.IO.Class
import GHC.CString
ptr :: Ptr ()
ptr = Ptr $(do
-- create a buffer containing the "Hello World!" string
let xs = [72,101,108,108,111,32,87,111,114,108,100,33] :: [Word8]
fp <- liftIO $ mallocForeignPtrArray 25
liftIO $ withForeignPtr fp $ \p -> do
pokeArray p xs
-- create a "Bytes" literal with an offset and size to only include "World"
let bys = mkBytes fp 6 5
liftIO performGC -- check that the GC doesn't release our buffer too early
litE (bytesPrimL bys))
main :: IO ()
main = do
let s = case ptr of Ptr addr -> unpackNBytes# addr 5#
putStrLn s
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