Hex.hs

-- This Source Code Form is subject to the terms of the Mozilla Public
-- License, v. 2.0. If a copy of the MPL was not distributed with this
-- file, You can obtain one at http://mozilla.org/MPL/2.0/.

{-# LANGUAGE GeneralizedNewtypeDeriving #-}
{-# LANGUAGE OverloadedStrings          #-}

module Data.ByteString.From.Hex where

import Control.Applicative
import Data.Attoparsec.ByteString
import Data.Attoparsec.ByteString.Char8 (signed, hexadecimal)
import Data.ByteString.From
import Data.Bits (Bits)
import Data.ByteString (elem)
import Prelude hiding (elem)
import Text.Printf (PrintfArg)

-- | Newtype wrapper to parse integral numbers in hexadecimal
-- format, optionally with a @0x@ or @0X@ prefix.
newtype Hex a = Hex { fromHex :: a }
    deriving ( Eq
             , Ord
             , Num
             , Read
             , Show
             , Bounded
             , Integral
             , Bits
             , PrintfArg
             , Enum
             , Real )

instance (Integral a, Bits a) => FromByteString (Hex a) where
    parser = Hex <$> signed (optional prefix *> hexadecimal)
      where
        prefix = word8 0x30 *> satisfy (`elem` "xX")