diff --git a/binary-file.cabal b/binary-file.cabal
--- a/binary-file.cabal
+++ b/binary-file.cabal
@@ -2,7 +2,7 @@
 cabal-version:	>= 1.8
 
 name:		binary-file
-version:	0.15.11
+version:	0.15.13
 stability:	experimental
 author:		Yoshikuni Jujo <PAF01143@nifty.ne.jp>
 maintainer:	Yoshikuni Jujo <PAF01143@nifty.ne.jp>
@@ -90,7 +90,7 @@
 source-repository	this
     type:	git
     location:	git://github.com/YoshikuniJujo/binary-file.git
-    tag:	0.15.11
+    tag:	0.15.13
 
 library
     hs-source-dirs:	src
diff --git a/src/File/Binary/Classes.hs b/src/File/Binary/Classes.hs
--- a/src/File/Binary/Classes.hs
+++ b/src/File/Binary/Classes.hs
@@ -1,10 +1,12 @@
-{-# LANGUAGE TypeFamilies, TupleSections #-}
+{-# LANGUAGE TypeFamilies, TupleSections, OverloadedStrings #-}
 
 module File.Binary.Classes (Field(..), Binary(..), pop, push) where
 
-import Data.ByteString.Lazy (ByteString, unpack, singleton)
+import Data.ByteString.Lazy (ByteString, unpack, singleton, cons)
+import qualified Data.ByteString.Lazy.Char8 as BSLC ()
 import Data.Bits ((.&.), (.|.), shiftL, shiftR)
 import Data.Monoid (Monoid, mappend, mempty)
+import Data.Word
 import Control.Arrow (first, second)
 import Control.Applicative
 
@@ -44,4 +46,19 @@
 
 class (Eq b, Monoid b) => Binary b where
 	getBytes :: Int -> b -> (ByteString, b)
+	spanBytes :: (Word8 -> Bool) -> b -> (ByteString, b)
+	unconsByte :: b -> (Word8, b)
 	makeBinary :: ByteString -> b
+
+	getBytes 0 b = ("", b)
+	getBytes n b = let
+		(h, t) = unconsByte b
+		(r, b') = getBytes (n - 1) t in
+		(h `cons` r, b')
+
+	spanBytes p b
+		| b == makeBinary "" = ("", b)
+		| p h = let (ret, rest) = spanBytes p t in (h `cons` ret, rest)
+		| otherwise = ("", b)
+		where
+		(h, t) = unconsByte b
diff --git a/src/File/Binary/Instances.hs b/src/File/Binary/Instances.hs
--- a/src/File/Binary/Instances.hs
+++ b/src/File/Binary/Instances.hs
@@ -1,19 +1,28 @@
-{-# LANGUAGE TypeFamilies, TypeSynonymInstances, FlexibleInstances, PackageImports #-}
+{-# LANGUAGE
+	TypeFamilies,
+	TypeSynonymInstances,
+	FlexibleInstances,
+	PackageImports,
+	OverloadedStrings #-}
 {-# OPTIONS_GHC -fno-warn-orphans #-}
 
 module File.Binary.Instances () where
 
-import Prelude hiding (take, drop)
+import Prelude hiding (take, drop, span)
 import File.Binary.Classes (Field(..), Binary(..))
 import Data.Word (Word8)
-import Data.ByteString.Lazy (ByteString, take, drop, toChunks, fromChunks, pack, unpack)
+import Data.ByteString.Lazy
+	(ByteString, take, drop, toChunks, fromChunks, pack, unpack, uncons, span)
 import qualified Data.ByteString.Lazy.Char8 as BSLC (pack, unpack)
-import qualified Data.ByteString as BS (ByteString, take, drop, concat)
+import qualified Data.ByteString as BS (ByteString, take, drop, concat, uncons, span)
+import qualified Data.ByteString.Char8 ()
 import Control.Monad (replicateM)
 import "monads-tf" Control.Monad.State (StateT(..), gets)
 import Control.Applicative ((<$>), (<*>))
 import Control.Arrow (first, (&&&))
 import Data.Monoid (mempty)
+import Data.Char
+import Data.Maybe
 
 --------------------------------------------------------------------------------
 
@@ -56,12 +65,17 @@
 
 instance Binary String where
 	getBytes n = first BSLC.pack . splitAt n
+	unconsByte = fromIntegral . ord . head &&& tail
 	makeBinary = BSLC.unpack
 
 instance Binary ByteString where
 	getBytes n = take (fromIntegral n) &&& drop (fromIntegral n)
+	spanBytes = span
+	unconsByte = fromMaybe (0, "") . uncons
 	makeBinary = id
 
 instance Binary BS.ByteString where
 	getBytes n = fromChunks . (: []) . BS.take n &&& BS.drop n
+	spanBytes p = first (fromChunks . (: [])) . BS.span p
+	unconsByte = fromMaybe (0, "") . BS.uncons
 	makeBinary = BS.concat . toChunks
diff --git a/src/File/Binary/Instances/BigEndian.hs b/src/File/Binary/Instances/BigEndian.hs
--- a/src/File/Binary/Instances/BigEndian.hs
+++ b/src/File/Binary/Instances/BigEndian.hs
@@ -26,7 +26,7 @@
 	fromBinary n = return . first (wordsToInt . unpack) . getBytes n
 	toBinary n = makeBinary . pack . intToWords n
 
-wordsToInt :: Bits i => [Word8] -> i
+wordsToInt :: (Num i, Bits i) => [Word8] -> i
 wordsToInt = foldl (\i w -> i `shiftL` 8 .|. fromIntegral w) 0
 
 intToWords :: (Bits i, Integral i) => Int -> i -> [Word8]
diff --git a/src/File/Binary/Instances/LittleEndian.hs b/src/File/Binary/Instances/LittleEndian.hs
--- a/src/File/Binary/Instances/LittleEndian.hs
+++ b/src/File/Binary/Instances/LittleEndian.hs
@@ -25,7 +25,7 @@
 	fromBinary n = return . first (wordsToInt . unpack) . getBytes n
 	toBinary n = makeBinary . pack . intToWords n
 
-wordsToInt :: Bits i => [Word8] -> i
+wordsToInt :: (Num i, Bits i) => [Word8] -> i
 wordsToInt = foldr (\w i -> fromIntegral w .|. i `shiftL` 8) 0
 
 intToWords :: (Bits i, Integral i) => Int -> i -> [Word8]