[Haskell-cafe] Writing binary files?

[Glynn Clements]

Ron de Bruijn wrote:

> Basically, I just want to have a function, that
> converts a list with zeros and ones to a binary file
> and the other way around. 
> 
> If I write 11111111 to a file, it would take 8 bytes.
> But I want it to take 8 bits. 

	import Char (digitToInt, chr)
	import Word (Word8)
	import System.IO (openBinaryFile)
	import IO (IOMode(..), hPutStr, hClose)
	
	bitsToOctet :: [Char] -> Word8
	bitsToOctet ds = fromIntegral $ sum $ zipWith (*) powers digits
		where	powers = [2^n | n <- [7,6..0]]
			digits = map digitToInt ds
	
	octetToChar :: Word8 -> Char
	octetToChar = chr . fromIntegral
	
	bits :: [[Char]]
	bits =	[ "01101000" -- 0x68 'h'
		, "01100101" -- 0x65 'e'
		, "01101100" -- 0x6c 'l'
		, "01101100" -- 0x6c 'l'
		, "01101111" -- 0x6f 'o'
		, "00001010" -- 0x0a '\n'
		]
	
	main :: IO ()
	main = do
		h <- openBinaryFile "out.dat" WriteMode
		hPutStr h $ map (octetToChar . bitsToOctet) bits
		hClose h

-- 
Glynn Clements <glynn.clements at virgin.net>