diff --git a/bytable.cabal b/bytable.cabal
--- a/bytable.cabal
+++ b/bytable.cabal
@@ -2,7 +2,7 @@
 build-type:	Simple
 
 name:		bytable
-version:	0.0.0.0
+version:	0.0.0.1
 stability:	Experimental
 author:		Yoshikuni Jujo <PAF01143@nifty.ne.jp>
 maintainer:	Yoshikuni Jujo <PAF01143@nifty.ne.jp>
@@ -28,7 +28,7 @@
 source-repository	this
     type:	git
     location:	git://github.com/YoshikuniJujo/forest
-    tag:	bytable-0.0.0.0
+    tag:	bytable-0.0.0.1
 
 library
     hs-source-dirs:	src
diff --git a/src/Codec/Bytable.hs b/src/Codec/Bytable.hs
--- a/src/Codec/Bytable.hs
+++ b/src/Codec/Bytable.hs
@@ -1,6 +1,10 @@
 {-# LANGUAGE TupleSections #-}
 
-module Codec.Bytable (BytableM(..), Bytable(..), head, take, null) where
+module Codec.Bytable (
+	Bytable(..),
+	BytableM(..), evalBytableM, execBytableM,
+	head, take, null
+) where
 
 import Prelude hiding (take, head, null)
 import Control.Applicative(Applicative(..), (<$>))
@@ -10,6 +14,12 @@
 
 data BytableM a = BytableM {
 	runBytableM :: BS.ByteString -> Either String (a, BS.ByteString) }
+
+evalBytableM :: BytableM a -> BS.ByteString -> Either String a
+evalBytableM m bs = fst <$> runBytableM m bs
+
+execBytableM :: BytableM a -> BS.ByteString -> Either String BS.ByteString
+execBytableM m bs = snd <$> runBytableM m bs
 
 instance Monad BytableM where
 	return x = BytableM $ \bs -> Right (x, bs)