[Haskell-cafe] Review request for my encoding function

[Ivan Lazar Miljenovic]

On 8 January 2011 16:27, C K Kashyap <ckkashyap at gmail.com> wrote:
> Hi,
> I've written a function to encode a color value of type (Int,Int,Int)
> into 8,16 or 32 byte ByteString depending on the value of bits per
> pixel. This is for my VNC server implementation.
> I'd appreciate some feedback on the Haskellism of the implementation.
>
> import Data.Bits
> import Data.ByteString.Lazy
> import Data.Binary.Put
> import Data.Word
>
> type Red = Int
> type Green = Int
> type Blue = Int
> type Color = (Red,Green,Blue)
>
>
>
> encode :: Color -> Int-> Int-> Int-> Int-> Int-> Int-> Int -> ByteString
> encode (r,g,b) bitsPerPixel redMax greenMax blueMax redShift
> greenShift blueShift = runPut $ do
>        case bitsPerPixel of
>                8       -> putWord8 z8
>                16      -> putWord16be z16
>                32      -> putWord32be z32
>        where
>                z8  = (fromIntegral $ nr + ng + nb) :: Word8
>                z16 = (fromIntegral $ nr + ng + nb) :: Word16
>                z32 = (fromIntegral $ nr + ng + nb) :: Word32
>                nr = scale r redMax redShift
>                ng = scale g greenMax greenShift
>                nb = scale b blueMax blueShift
>                scale c cm cs = (c * cm `div` 255) `shift` cs

The more "Haskellian" approach would be to use a dedicated datatype to
specify the number of bits, not to have a partial function on Int.
Possibly even encode the RGB triple such that it specifies the number
of bits rather than separating each value.

-- 
Ivan Lazar Miljenovic
Ivan.Miljenovic at gmail.com
IvanMiljenovic.wordpress.com