[Haskell-cafe] bytestring vs. uvector

[Manlio Perillo]

Don Stewart ha scritto:
> [...]
>> You also have to add instance for UIO:
>>
>>     instance (RealFloat a, UIO a) => UIO (Complex a) where
>>         hPutU h (UAComplex arr) = hPutU h arr
>>         hGetU h                 = do arr <- hGetU h
>>                                      return (UAComplex arr)
>>
>>
>> With Storable, this should not be required; you just have to write an  
>> instance for the Storable class.
>> 
> 
> Though you get no IO operations with Storable... UIO is entirely
> separate.
> 

Yes, but using Storable and Foreign.Ptr, IO is rather simple.
 From storablevector package:

-- | Outputs a 'Vector' to the specified 'Handle'.
hPut :: (Storable a) => Handle -> Vector a -> IO ()
hPut h v =
    if null v
      then return ()
      else
        let (fptr, s, l) = toForeignPtr v
        in  withForeignPtr fptr $ \ ptr ->
               let ptrS = advancePtr ptr s
                   ptrE = advancePtr ptrS l
                   -- use advancePtr and minusPtr in order to respect
                   -- alignment
               in  hPutBuf h ptrS (minusPtr ptrE ptrS)

-- | Read a 'Vector' directly from the specified 'Handle'.  This
-- is far more efficient than reading the characters into a list
-- and then using 'pack'.
--
hGet :: (Storable a) => Handle -> Int -> IO (Vector a)
hGet _ 0 = return empty
hGet h i =
    createAndTrim i $ \p ->
       let elemType :: Ptr a -> a
           elemType _ = undefined
           sizeOfElem = sizeOf (elemType p)
       in  fmap (flip div sizeOfElem) $
           hGetBuf h p (i * sizeOfElem)


Regards  Manlio