Util.hs

{-
  Copyright (C) 2009 John Millikin <jmillikin@gmail.com>
  
  This program is free software: you can redistribute it and/or modify
  it under the terms of the GNU General Public License as published by
  the Free Software Foundation, either version 3 of the License, or
  any later version.
  
  This program is distributed in the hope that it will be useful,
  but WITHOUT ANY WARRANTY; without even the implied warranty of
  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  GNU General Public License for more details.
  
  You should have received a copy of the GNU General Public License
  along with this program.  If not, see <http://www.gnu.org/licenses/>.
-}

module DBus.Util where
import Text.Parsec (Parsec, parse)
import Data.Char (digitToInt)

checkLength :: Int -> String -> Maybe String
checkLength length' s | length s <= length' = Just s
checkLength _ _ = Nothing

parseMaybe :: Parsec String () a -> String -> Maybe a
parseMaybe p = either (const Nothing) Just . parse p ""

mkUnsafe :: Show a => String -> (a -> Maybe b) -> a -> b
mkUnsafe label f x = case f x of
        Just x' -> x'
        Nothing -> error $ "Invalid " ++ label ++ ": " ++ show x

hexToInt :: String -> Int
hexToInt = foldl ((+) . (16 *)) 0 . map digitToInt

eitherToMaybe :: Either a b -> Maybe b
eitherToMaybe (Left  _) = Nothing
eitherToMaybe (Right x) = Just x

fromRight :: Either a b -> b
fromRight (Right x) = x
fromRight _ = error "DBus.Util.fromRight: Left"

maybeIndex :: [a] -> Int -> Maybe a
maybeIndex (x:_ ) 0         = Just x
maybeIndex (_:xs) n | n > 0 = maybeIndex xs (n - 1)
maybeIndex _ _ = Nothing