diff --git a/COPYING b/COPYING
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--- /dev/null
+++ b/COPYING
@@ -0,0 +1,29 @@
+Copyright (c) 2010, Taru Karttunen
+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 the Taru Karttunen; nor the names of its 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/Control/Monad/STLike/IO.hs b/Control/Monad/STLike/IO.hs
new file mode 100644
--- /dev/null
+++ b/Control/Monad/STLike/IO.hs
@@ -0,0 +1,59 @@
+module Control.Monad.STLike.IO
+    (-- * IOS monad
+     IOS, io, runIOS
+     -- * Regioned monad
+    ,Regioned, runRegion, region
+     -- * Utilities
+    ,rbsFromPtr,rbsToBS,withRbsPtr,rbsMapLookup
+    ) where
+
+import Control.Monad.STLike.Internal
+import Control.Monad.Trans
+import qualified Data.ByteString as B
+import qualified Data.ByteString.Unsafe as B
+import qualified Data.Map as M
+import Foreign
+
+
+-- | Monad for scoped IO computations
+-- The underlying monad must be strict here.
+type IOS s t = STLike IO s t
+instance STLikeImpl IO
+
+instance MonadIO (STLike IO s) where
+    liftIO x = io x
+
+-- | Lift IO computations into IOS. liftIO also works.
+io :: IO t -> IOS s t
+io x = STLike x
+
+-- | Run an IOS computation in the IO monad.
+runIOS :: (forall s. IOS s t) -> IO t
+runIOS x = let STLike v = x in v
+
+
+-- | Create a ByteString representing the pointer and length. 
+--   No copying done, O(1).
+rbsFromPtr :: Ptr a -> Int -> IOS s (Regioned s B.ByteString)
+rbsFromPtr ptr len = io $ fmap R $ B.unsafePackCStringLen (castPtr ptr,len)
+
+-- | Create a copy of a regioned ByteString as a normal ByteString. O(n).
+rbsToBS :: STLikeImpl m => Regioned s B.ByteString -> STLike m s B.ByteString
+rbsToBS (R b) = return $! B.copy b
+
+-- | Use a regioned ByteString as a pointer. O(1). 
+--   The pointer points to the region contents,
+--   so be cafeful with it.
+withRbsPtr :: Regioned s B.ByteString -> (Ptr any -> Int -> IOS s t) -> IOS s t
+--withRbsPtr (R b) act = io $ B.unsafeUseAsCStringLen b (\(p,l) -> unsafeSTToIO (act (castPtr p) l))
+withRbsPtr (R b) act = io $ B.unsafeUseAsCStringLen b (\(p,l) -> let STLike v = (act (castPtr p) l) in v)
+
+-- | Lookup inside a Map with a regioned ByteString.
+rbsMapLookup :: (STLikeImpl m, Ord key) => Regioned s key -> M.Map key value -> STLike m s (Maybe value)
+rbsMapLookup (R k) m = case M.lookup k m of
+                      Just x  -> return (Just x)
+                      Nothing -> return Nothing
+
+-- | Regions a value. Synonym for /return/.
+region :: t -> Regioned s t
+region = R
diff --git a/Control/Monad/STLike/Internal.hs b/Control/Monad/STLike/Internal.hs
new file mode 100644
--- /dev/null
+++ b/Control/Monad/STLike/Internal.hs
@@ -0,0 +1,80 @@
+module Control.Monad.STLike.Internal where
+
+import Control.DeepSeq
+import Control.Monad
+import Foreign
+
+-- | Regioned variables.
+-- A regioned variable is /safe/ i.e. no references to
+-- it may escape the current IOS.
+newtype Regioned s t = R t
+
+instance Monad (Regioned s) where
+    return      = R
+    _     >>  b = b
+    (R v) >>= f = f v
+instance Functor (Regioned s) where
+    fmap f (R v) = R (f v)
+
+-- | Run a computation on regioned data
+-- and return the result in a strict fashion.
+runRegion :: (NotShared ty, STLikeImpl m) => Regioned s ty -> STLike m s ty
+runRegion = runRegionImpl
+
+
+class NFData ty => NotShared ty where
+    runRegionImpl :: STLikeImpl m => Regioned s ty -> STLike m s ty
+    runRegionImpl (R v) = v `deepseq` return v
+
+instance NotShared Bool
+instance NotShared Char
+instance NotShared Double
+instance NotShared Float
+instance NotShared Int
+instance NotShared Int8
+instance NotShared Int16
+instance NotShared Int32
+instance NotShared Int64
+instance NotShared Integer
+instance NotShared Word
+instance NotShared Word8
+instance NotShared Word16
+instance NotShared Word32
+instance NotShared Word64
+instance NotShared ()
+--instance NotShared IntSet
+instance NotShared a => NotShared ([] a)
+--instance (Integral a, NotShared a) => NotShared (Ratio a)
+--instance (RealFloat a, NotShared a) => NotShared (Complex a)
+instance NotShared a => NotShared (Maybe a)
+--NotShared a => NotShared (IntMap a)
+--NotShared a => NotShared (Tree a)
+--NotShared a => NotShared (Set a)
+instance (NotShared a, NotShared b) => NotShared (Either a b)
+instance (NotShared a, NotShared b) => NotShared ((,) a b)
+--(Ix a, NotShared a, NotShared b) => NotShared (Array a b)
+--(NotShared k, NotShared a) => NotShared (Map k a)
+instance (NotShared a, NotShared b, NotShared c) => NotShared ((,,) a b c)
+instance (NotShared a, NotShared b, NotShared c, NotShared d) => NotShared ((,,,) a b c d)
+instance (NotShared a1, NotShared a2, NotShared a3, NotShared a4, NotShared a5) => NotShared ((,,,,) a1 a2 a3 a4 a5)
+--instance NotShared B.ByteString where
+--    runRegion (R bs) = return $! B.copy bs
+
+
+unsafeRemoveRegion :: STLikeImpl m => Regioned s r -> STLike m s r
+unsafeRemoveRegion (R x) = return x
+
+newtype STLike m s t = STLike (m t)
+
+class Monad m => STLikeImpl m
+
+instance STLikeImpl m => Monad (STLike m s) where
+    (STLike a) >> (STLike b)   = STLike (a >> b)
+    (STLike a) >>= b  = STLike $ do v <- a
+                                    let STLike r = b v
+                                    r
+    return x = STLike (return x)
+
+instance (STLikeImpl m) => Functor (STLike m s) where
+    fmap f (STLike m) = STLike (liftM f m)
+
diff --git a/Control/Monad/STLike/Unsafe.hs b/Control/Monad/STLike/Unsafe.hs
new file mode 100644
--- /dev/null
+++ b/Control/Monad/STLike/Unsafe.hs
@@ -0,0 +1,8 @@
+{-# OPTIONS_HADDOCK prune #-}
+-- | Unsafe intersafe for implementators.
+--   Purposefully not documented.
+module Control.Monad.STLike.Unsafe
+    (STLike(..), STLikeImpl, NotShared(..), unsafeRemoveRegion
+    ) where
+
+import Control.Monad.STLike.Internal
diff --git a/Setup.hs b/Setup.hs
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--- /dev/null
+++ b/Setup.hs
@@ -0,0 +1,3 @@
+#!/usr/bin/env runhaskell
+import Distribution.Simple
+main = defaultMain
diff --git a/monad-stlike-io.cabal b/monad-stlike-io.cabal
new file mode 100644
--- /dev/null
+++ b/monad-stlike-io.cabal
@@ -0,0 +1,17 @@
+Name:                monad-stlike-io
+Version:             0.1
+Synopsis:            ST-like monad capturing variables to regions and supporting IO.
+Description:         ST-like monad capturing variables to regions and supporting IO.
+License:             BSD3
+License-file:        COPYING
+Copyright:           Taru Karttunen <taruti@taruti.net>
+Author:              Taru Karttunen
+Category:            Regions, Monads
+Maintainer:          taruti@taruti.net
+Build-Depends:       base >= 4 && < 5, bytestring, containers, deepseq, transformers
+Exposed-modules:     Control.Monad.STLike.IO,
+		     Control.Monad.STLike.Unsafe
+Other-modules:       Control.Monad.STLike.Internal
+Extensions:          RankNTypes, FlexibleInstances
+GHC-Options:         -Wall
+Build-Type:	     Simple