A-M baby

Task/LZW-compression/Haskell/lzw-compression-1.hs

@@ -0,0 +1,20 @@
+import Data.List
+import Data.Char
+import Data.Maybe
+import Control.Monad
+import Control.Arrow
+
+take2 = filter((==2).length). map (take 2). tails
+
+doLZW _ [] = []
+doLZW as (x:xs) =  lzw (map return as) [x] xs
+   where lzw a w [] = [fromJust $ elemIndex w a]
+         lzw a w (x:xs)  | w' `elem` a = lzw a w' xs
+                         | otherwise   = fromJust (elemIndex w a) : lzw (a++[w']) [x] xs
+              where w' = w++[x]
+
+undoLZW _ [] = []
+undoLZW a cs =
+  ((cs >>=).(!!)) $
+  foldl (liftM2 (.) (++) (((return. liftM2 (++) head (take 1. last)).). map. (!!)))
+  (map return a) (take2 cs)

Task/LZW-compression/Haskell/lzw-compression-2.hs

@@ -0,0 +1,5 @@
+*Main> doLZW ['\0'..'\255'] "TOBEORNOTTOBEORTOBEORNOT"
+[84,79,66,69,79,82,78,79,84,256,258,260,265,259,261,263]
+
+*Main> undoLZW ['\0'..'\255'] [84,79,66,69,79,82,78,79,84,256,258,260,265,259,261,263]
+"TOBEORNOTTOBEORTOBEORNOT"

Task/LZW-compression/Haskell/lzw-compression-3.hs

@@ -0,0 +1,2 @@
+*Main> (ap (==) . liftM2 (.) undoLZW doLZW) ['\0'..'\255'] "TOBEORNOTTOBEORTOBEORNOT"
+True