I actually don't need a pure function, IO is OK. I'll try something in these lines. It doesn't build yet, with an error message I'll probably take a few months to understand: Couldn't match expected type `forall a. (Storable a) => a -> IO a' against inferred type `a -> IO a' Thanks, Maurício ----- import Control.Monad ; import Foreign ; import Foreign.C ; type CUInt16 = CUShort ; type CUInt8 = CChar ; littleEndianToHost,hostToLittleEndian :: forall a. (Storable a ) => a -> IO a ; (littleEndianToHost,hostToLittleEndian) = (f,f) where { f :: forall a. ( Storable a ) => a -> IO a ; f a = with ( 0x0102 :: CUInt16 ) $ \p -> do { firstByte <- peek ( castPtr p :: Ptr CUInt8 ) ; littleEndian <- return $ firstByte == 0x02 ; halfSize <- return $ div ( alignment a ) 2; reverse <- with a $ \val -> zipWithM (swapByte (castPtr val :: Ptr CUInt8)) [0..halfSize-1] [halfSize..2*halfSize-1] >> peek val ; return $ if littleEndian then a else reverse ; } ; swapByte p n1 n2 = do { v1 <- peekElemOff p n1 ; v2 <- peekElemOff p n2 ; pokeElemOff p n1 v2 ; pokeElemOff p n2 v1 } >> return () } -----
On Thursday 18 December 2008 13:40:47 Ryan Ingram wrote:
Actually, this is probably safer:
import Foreign.Marshal.Alloc import Foreign.Ptr import Foreign.Storable import Data.Word import System.IO.Unsafe
endianCheck = unsafePerformIO $ alloca $ \p -> poke p (0x01020304 :: Word32) >> peek (castPtr p :: Ptr Word8)
littleEndian = endianCheck == 4 bigEndian = endianCheck == 1
(...)