Haskell code to convert decimal numbers to a digital representation ([Digital]) and vice versa.

dec2bin2dec.hs

-- Dec2Bin
--

data Digital = D1 | D0

instance Show Digital where
    show D1 = "1"
    show D0 = "0"

instance Eq Digital where
    D1 == D1 = True
    D0 == D0 = True
    _  == _  = False

dec2bin :: Integer -> [Digital]
dec2bin n = fragmentDec n $ smallestPowerOf2ToFit n

fragmentDec :: Integer -> Integer -> [Digital]
fragmentDec _ (-1) = []
fragmentDec n p = (getDig matches):(fragmentDec (if matches then n-digval else n) (p-1))
    where matches = ((fromIntegral n)/(2^p)) >= 1
	  getDig b
		| b == True  = D1
		| b == False = D0
	  digval = 2^p

smallestPowerOf2ToFit :: Integer -> Integer
smallestPowerOf2ToFit n = sPO2TF n 0
    where sPO2TF n p = if ((fromIntegral n)/(fromIntegral $ 2^p)) >= 1
		       then sPO2TF n (p+1)
		       else p-1

-- Bin2Dec

bin2dec :: [Digital] -> Integer
bin2dec [] = 0
bin2dec l@(x:xs)
	| x == D1 = 2^(len-1) + bin2dec xs
	| x == D0 = bin2dec xs
    where len = length l