Time for an 2014 update…

Task/Gray-code/Haskell/gray-code.hs

@@ -1,28 +1,18 @@
-module Main where
+import Data.Bits
+import Data.Char
+import Numeric
+import Text.Printf
 
-main = mapM_ (putStrLn . flip grayconvstr 5) [0..31]
+-- Conversion to and from traditional binary and Gray code
+grayToBin :: (Integral t, Bits t) => t -> t
+grayToBin 0 = 0
+grayToBin g = g `xor` (grayToBin $ g `shiftR` 1)
 
--- Convert number to bit list, MSB first.  Second argument is minimum width.
-num2bin :: (Integral t) => t -> t -> [t]
-num2bin n w = num2bin' n w [] where
-  num2bin' n w acc | n <= 0 && w <= 0 = acc
-                   | otherwise = num2bin' m (w-1) (b:acc)
-    where (m, b) = divMod n 2
+binToGray :: (Integral t, Bits t) => t -> t
+binToGray b = b `xor` (b `shiftR` 1)
 
-xor2 :: (Integral t) => t -> t -> t
-xor2 x y = (x + y) `mod` 2
-
-bin2gray :: (Integral t) => [t] -> [t]
-bin2gray [] = []
-bin2gray (x:xs) = x : zipWith xor2 xs (x:xs)
-
-gray2bin :: (Integral t) => [t] -> [t]
-gray2bin = scanl1 xor2
-
--- Prettyprinting, since it is in the task description...
-grayconvstr :: (Integral t, Show t) => t -> t -> String
-grayconvstr n w = (show n) ++ ": " ++ (show b) ++ " => " ++ (show g) ++ " => " ++ (show u)
-  where
-    b = num2bin n w
-    g = bin2gray b
-    u = gray2bin g
+-- Print the first 32 Gray codes alongside their decimal and binary equivalences.
+main = flip mapM_ (take 32 [0,1..] :: [Int]) (\num -> do
+	let bin  = showIntAtBase 2 intToDigit num ""
+	    gray = showIntAtBase 2 intToDigit (binToGray num) ""
+	printf "int: %2d -> bin: %5s -> gray: %5s\n" num bin gray)