encodeurl.hs

import System.Environment

import qualified Data.ByteString as BS
import qualified Data.ByteString.UTF8 as UTF8

escapeURL :: String -> String
escapeURL = UTF8.toString . BS.concatMap (BS.pack . f) . UTF8.fromString
    where
        f c | alnum c || c `elem` [45,95,46,126] {- "-_.~" -} = [c]
            | otherwise = h c
        h c | c > 0xf   = let (a,b) = c `divMod` 16 in [37,i a,i b]
            | otherwise = [37,48,i c]     -- %,0
        i c | c >= 0xa  = 65 + c - 10
            | otherwise = 48 + c
        alnum c =  (48 <= c && c <= 57)   -- 0-9
                || (65 <= c && c <= 90)   -- A-Z
                || (97 <= c && c <= 122)  -- a-z

main = getArgs >>= mapM_ (putStrLn . escapeURL)