Compress 2

gistfile1.hs

import Data.List
import Control.Arrow

-- "aaabbbbcc"
-- ["aaa", "bbbb", "cc"]
f1 :: String -> [String]
f1 str = group str

-- "aaa"
-- -> ("a", "3")
f2 :: [Char] -> (Char, String)
f2 xs = (head &&& (show . length)) xs

-- ("a", "13")
-- -> "a13"
f3 :: (Char, String) -> String
f3 (a, b) = uncurry (:) (a, b)

-- "aaaa"
-- "a4"
f23 :: [Char] -> String
f23 xs = f3 $ f2 xs

f4 :: (String -> String) -> [String] -> String
f4 f xs = concat $ map f xs

compress :: String -> String
compress s = f4 f23 $ f1 s