diff --git a/Data/Karakuri.hs b/Data/Karakuri.hs
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--- /dev/null
+++ b/Data/Karakuri.hs
@@ -0,0 +1,63 @@
+{-# LANGUAGE ExistentialQuantification, Rank2Types #-}
+
+module Data.Karakuri (
+    Karakuri(..)
+    , Karakuri'
+    , step
+    , transKarakuri
+    , stateful
+    , stateful'
+    , effective
+    ) where
+
+import Control.Monad.Trans.State
+import Control.Applicative
+import Control.Comonad
+import Data.Functor.Identity
+import Control.Monad
+
+-- | Karakuri means automaton in Japanese.
+data Karakuri m a = forall s. Karakuri (s -> m s) (s -> a) s
+
+-- | Run a 'Karakuri'.
+step :: Monad m => Karakuri m a -> m (Karakuri m a)
+step (Karakuri m f s) = Karakuri m f `liftM` m s
+
+instance Functor (Karakuri m) where
+    fmap f (Karakuri m g s) = Karakuri m (f . g) s
+    {-# INLINE fmap #-}
+
+instance Monad m => Applicative (Karakuri m) where
+    pure a = Karakuri return (const a) ()
+    {-# INLINE pure #-}
+    Karakuri m f s <*> Karakuri n g t = Karakuri
+        (\(a, b) -> m a >>= \r -> n b >>= \s -> return (r, s))
+        (\(x, y) -> f x (g y))
+        (s, t)
+
+instance Comonad (Karakuri m) where
+    extract (Karakuri _ f s) = f s
+    {-# INLINE extract #-}
+    extend k (Karakuri m f s) = Karakuri m (k . Karakuri m f) s
+    {-# INLINE extend #-}
+
+instance Monad m => ComonadApply (Karakuri m) where
+    (<@>) = (<*>)
+    {-# INLINE (<@>) #-}
+
+transKarakuri :: (forall s. m s -> n s) -> Karakuri m a -> Karakuri n a
+transKarakuri t (Karakuri f e s) = Karakuri (t . f) e s
+
+-- | Create a 'Karakuri' from the stateful action.
+stateful :: Monad m => StateT s m () -> s -> Karakuri m s
+stateful m s = Karakuri (execStateT m) id s
+
+type Karakuri' = Karakuri Identity
+
+-- | Create a 'Karakuri' from the stateful action.
+stateful' :: Monad m => State s () -> s -> Karakuri m s
+stateful' m s = Karakuri (return . execState m) id s
+
+-- | Create a 'Karakuri' that performs the given action every time.
+effective :: Monad m => a -> m a -> Karakuri m a
+effective a m = Karakuri (const m) id a
diff --git a/LICENSE b/LICENSE
new file mode 100644
--- /dev/null
+++ b/LICENSE
@@ -0,0 +1,30 @@
+Copyright (c) 2013, Fumiaki Kinoshita
+
+All rights reserved.
+
+Redistribution and use in source and binary forms, with or without
+modification, are permitted provided that the following conditions are met:
+
+    * Redistributions of source code must retain the above copyright
+      notice, this list of conditions and the following disclaimer.
+
+    * Redistributions in binary form must reproduce the above
+      copyright notice, this list of conditions and the following
+      disclaimer in the documentation and/or other materials provided
+      with the distribution.
+
+    * Neither the name of Fumiaki Kinoshita nor the names of other
+      contributors may be used to endorse or promote products derived
+      from this software without specific prior written permission.
+
+THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+"AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+(INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
diff --git a/Setup.hs b/Setup.hs
new file mode 100644
--- /dev/null
+++ b/Setup.hs
@@ -0,0 +1,2 @@
+import Distribution.Simple
+main = defaultMain
diff --git a/karakuri.cabal b/karakuri.cabal
new file mode 100644
--- /dev/null
+++ b/karakuri.cabal
@@ -0,0 +1,22 @@
+name:                karakuri
+version:             0.1
+synopsis:            Good stateful automata 
+-- description:         
+homepage:            https://github.com/fumieval/karakuri
+license:             BSD3
+license-file:        LICENSE
+author:              Fumiaki Kinoshita
+maintainer:          fumiexcel@gmail.com
+copyright:           Copyright (C) 2013 Fumiaki Kinoshita
+category:            Data
+build-type:          Simple
+-- extra-source-files:  
+cabal-version:       >=1.10
+
+library
+  exposed-modules:     Data.Karakuri
+  -- other-modules:       
+  other-extensions:    ExistentialQuantification, Rank2Types
+  build-depends:       base == 4.*, transformers >=0.3 && <0.4, comonad == 3.*
+  -- hs-source-dirs:      
+  default-language:    Haskell2010