Thanks Brandon,

data Endian = Big | Little
data Size = Eight | Sixteen | ThirtyTwo | SixtyFour
type EncTuple = (Int,Size,Endian)

My requirement is to write encode :: [EncTuple] -> ByteString
I'd like to use it with just the libraries that are part of the platform - and I am not a fan of using the internal stuff :)
I'd appreciate it very much if you could give me a sample. 

And thank you very much for http://research.microsoft.com/en-us/um/people/simonpj/papers/unboxed-values.ps.Z

Regards,
Kashyap