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-- Sven Panne found this example; a mistake in typechecking
-- lazy patterns made functions too strict in a version of
-- GHC 6.7
module Main where
import Foreign
-- Strangely enough, this works if newtype is used...
data Elem a = Elem a
instance Storable a => Storable (Elem a) where
sizeOf ~(Elem r) = 3 * sizeOf r
alignment ~(Elem r) = alignment r
peek ptr = do r <- peekElemOff (castPtr ptr) 0; return (Elem r)
poke ptr (Elem r) = poke (castPtr ptr) r
main :: IO ()
main = do
putStrLn "*** main 1"
allocaBytes 100 $ \buf -> do
poke buf (Elem 12345)
putStrLn "*** main 2"
Elem x <- peekElemOff buf 0
print (x :: Int)
putStrLn "*** main 3"
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