Handy error handling combinators

Error.hs

data Error = Timeout
           | Exception SomeException

liftST.hs

import Control.Exception
import System.Timeout

liftST :: Int -> (a -> IO b) -> a -> IO (Either Error b)
liftST n f = liftM conv . try . timeout n . f
  where
    conv :: Either SomeException (Maybe a) -> Either Error a
    conv (Left e)         = Left (Exception e)
    conv (Right Nothing)  = Left Timeout
    conv (Right (Just r)) = Right r

safeDL.hs

import Network.HTTP

type HttpResponse = Network.Stream.Result (Response String)

dl :: String -> IO HttpResponse
dl = simpleHTTP . getRequest

safeDL :: Int -> String -> IO (Either Error HttpResponse)
safeDL n = liftST n dl