You do realize that the example you gave is just as general as all the tutorials. Here is an example I was working, but it gives a *segmentation fault* for some reason: example.h typedef struct { unsigned char a; unsigned char b; unsigned char c; unsigned char d; } IP; IP* shiftIP(IP* addr); example.c #include "example.h" IP* shiftIP(IP* addr){ unsigned char t; t = addr->a; addr->a = addr->b; addr->b = addr->c; addr->c = addr->d; addr->d = t; } Example.hsc {-# OPTIONS -ffi -fglasgow-exts #-} module Example where import Foreign import Foreign.C.Types import Control.Monad #include "buzz.h" data MyIP = MyIP { a :: CUChar , b :: CUChar , c :: CUChar , d :: CUChar } deriving (Show) instance Storable MyIP where sizeOf _ = #{size IP} -- 4 alignment _ = alignment (undefined :: CUChar) -- 1 peek p = return MyIP `ap` (#{peek IP, a} p) `ap` (#{peek IP, b} p) `ap` (#{peek IP, c} p) `ap` (#{peek IP, d} p) poke p ip = do #{poke IP, a} p $ a ip #{poke IP, b} p $ b ip #{poke IP, c} p $ c ip #{poke IP, d} p $ d ip foreign import ccall safe "static buzzlib.h shiftIP" shiftIP :: Ptr MyIP -> Ptr MyIP shiftMyIP :: MyIP -> MyIP shiftMyIP ip = unsafePerformIO . alloca $ \ptr -> poke ptr ip >> peek (shiftIP ptr)