RLE

gistfile1.hs

tails :: String -> [String]
tails [] = []
tails (x:[]) = [[x]]
tails (x:xs) = (x:xs) : tails xs

isDigit :: Char -> Bool
isDigit x =  '0' < x && x < '9'

f :: String -> String -> String
f (xs) (y:[])       = xs
f (x:xs) (y1:y2:ys) = if y1 == y2
                      then if isDigit x
                           then (show (1 + (read (x:""))::Int)) ++ xs
                           else '2' : x : xs
                      else
                         y2 : x : xs

rle :: String -> String
rle (x:xs) = reverse $ foldl f [x] $ tails (x:xs)