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diff --git a/src/System/IO/MMap/Fixed.hs b/src/System/IO/MMap/Fixed.hs
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+-- TODO pprint
+-- TODO see if this IntervalMap is overkill: Interval dataty have 4 constrs
+-- TODO clarify lifetime in docs
+-- TODO use madvise
+-- TODO unmap selected interval
+-- TODO tests
+-- TODO benchmarks
+-- TODO unmap overlapped regions
+-- [A] TODO lazy mapping for 32 bit arch;
+--          we need tricky algorithm and a lot of perf tests
+-- TODO use memmove in write bytes
+-- TODO write elem, write byte, read byte
+-- |
+--   Copyright   :  (c) Sam T. 2013
+--   License     :  MIT
+--   Maintainer  :  pxqr.sta@gmail.com
+--   Stability   :  experimental
+--   Portability :  portable
+--
+--   This library provides mechanism to mmap files to fixed address
+--   with fine-grained control. Hovewer, instead of using MAP_FIXED we
+--   create our own address space upon virtual address space. If you
+--   would like you could call this space as "fixed address space".
+--
+--   This solves a few problems:
+--
+--     * Page already in use. If you mmap one file at 0..x addresses and
+--     want to map second file to x..y addresses using MAP_FIXED you
+--     can get in troubles: page might be mapped already. Raw call to
+--     mmap will silently unmap x..y addresses and then mmap our second
+--     file. So here we have extra unmap we would like to avoid.
+--
+--     * Page boundaries. If you mmap one file at x..x+1 you could
+--     not map next file to say addresses x+1..x+2.
+--
+--   Internally we make ordinary call to mmap to map a file and then
+--   using /interval map/ we map fixed address space to virtual
+--   address space. It takes TODO time in TODO cases.
+--
+--   Basically this library could be used when we need coalesce
+--   several files in arbitrary way. We could map at any position as
+--   long as offset + size fit in 'Int'.
+--
+--   For other details see:
+--
+--   > http://hackage.haskell.org/package/mmap
+--   > man mmap
+--
+module System.IO.MMap.Fixed
+       ( -- * Intervals
+         FixedOffset, FileOffset, FixedInterval, FileInterval
+       , interval, fileInterval
+
+         -- * Construction
+       , Fixed, Bytes
+       , System.IO.MMap.Fixed.empty, insertTo
+       , coalesceFiles
+
+         -- ** Specialized 'insertTo'
+       , mmapTo, mallocTo
+
+         -- * Query
+       , upperAddr
+
+         -- * Access
+       , viewBytes, readBytes, writeBytes
+       , readElem, writeElem
+       ) where
+
+import Data.ByteString.Lazy as Lazy
+import Data.ByteString.Lazy.Internal as Lazy
+import Data.ByteString.Internal as B
+import Data.List as L
+import Data.Int
+import Data.IntervalMap.Strict as M
+import Data.IntervalMap.Interval
+import System.IO.MMap
+import Foreign
+
+
+type FixedOffset = Int
+type FileOffset  = Int64
+type Size   = Int
+
+
+type FileInterval  = (FileOffset, Size)
+type FixedInterval = Interval FixedOffset
+
+
+interval :: FixedOffset -> Size -> FixedInterval
+interval off s = IntervalCO off (off + fromIntegral (max 0 s))
+{-# INLINE interval #-}
+
+fileInterval :: FileOffset -> Size -> FileInterval
+fileInterval off s = (off, s)
+{-# INLINE fileInterval #-}
+
+intervalSize :: FixedInterval -> Size
+intervalSize i = upperBound i - lowerBound i
+{-# INLINE intervalSize #-}
+
+
+type Bytes = (ForeignPtr Word8, Size)
+
+type FixedMap = IntervalMap FixedOffset Bytes
+
+newtype Fixed = Fixed { imap :: FixedMap }
+
+instance Show Fixed where
+  show = show . M.toList . imap
+
+
+mapIM :: (FixedMap -> FixedMap) -> Fixed -> Fixed
+mapIM f s = s { imap = f (imap s) }
+
+empty :: Fixed
+empty = Fixed M.empty
+
+coalesceFiles :: [(FilePath, Int)] -> IO Fixed
+coalesceFiles = go 0 System.IO.MMap.Fixed.empty
+  where
+    go _      s []       = return s
+    go offset s ((path, bsize) : xs) = do
+      s' <- mmapTo path (0, bsize) offset s
+      go (offset + bsize) s' xs
+
+upperAddr :: Fixed -> FixedOffset
+upperAddr = upperBound . fst . findLast . imap
+
+insertTo :: FixedInterval -> Bytes -> Fixed -> Fixed
+insertTo fi mm = mapIM (M.insert fi mm)
+{-# INLINE insertTo #-}
+
+mmapTo :: FilePath -> FileInterval -> FixedOffset -> Fixed -> IO Fixed
+mmapTo path mrange to s = do
+  (fptr, offset, fsize) <- mmapFileForeignPtr path ReadWriteEx (Just mrange)
+
+  let fixed  = interval to fsize
+  let mmaped = (fptr, offset)
+
+  return $ insertTo fixed mmaped s
+
+mallocTo :: FixedInterval -> Fixed -> IO Fixed
+mallocTo fi s = do
+  let bsize = intervalSize fi
+  fptr <- mallocForeignPtrBytes bsize
+  return (insertTo fi (fptr, 0) s)
+
+-- | Note: this is unsafe operation.
+viewBytes :: FixedInterval -> Fixed -> Lazy.ByteString
+viewBytes fi s = fromChunks $ L.map mk $ (imap s `intersecting` fi)
+  where
+   mk (i, (fptr, offset)) =
+     let dropB = max 0 (lowerBound fi - lowerBound i)
+         dropT = max 0 (upperBound i  - upperBound fi)
+         bsize = intervalSize i - (dropT + dropB)
+     in fromForeignPtr fptr (offset + dropB) bsize
+
+
+readBytes :: FixedInterval -> Fixed -> IO Lazy.ByteString
+readBytes fi s = let c = Lazy.copy (viewBytes fi s) in mkCopy c >> return c
+{-# INLINE readBytes #-}
+
+writeBytes :: FixedInterval -> Lazy.ByteString -> Fixed -> IO ()
+writeBytes fi bs s = bscpy (viewBytes fi s) bs
+{-# INLINE writeBytes #-}
+
+-- | Note: this operation takes O(log(files count)) time, if possible
+-- use readBytes.
+readElem :: Storable a => Fixed -> FixedOffset -> IO a
+readElem s offset = go undefined
+  where
+    go :: Storable a => a -> IO a
+    go dont_touch = do
+      let bsize = sizeOf dont_touch
+      let PS fptr off _ = Lazy.toStrict (viewBytes (interval offset bsize) s)
+      withForeignPtr fptr $ \ ptr -> peekByteOff ptr off
+
+writeElem :: Storable a => Fixed -> FixedOffset -> a -> IO ()
+writeElem s offset x = do
+  let bsize = sizeOf x
+  let PS fptr off _ = Lazy.toStrict (viewBytes (interval offset bsize) s)
+  withForeignPtr fptr $ \ptr -> pokeByteOff ptr off x
+
+
+mkCopy :: Lazy.ByteString -> IO ()
+mkCopy Empty = return ()
+mkCopy (Chunk _ x) = mkCopy x
+
+bscpy :: Lazy.ByteString -> Lazy.ByteString -> IO ()
+bscpy (PS _ _ 0 `Chunk` dest_rest) src                         = bscpy dest_rest src
+bscpy dest                         (PS _ _ 0 `Chunk` src_rest) = bscpy dest      src_rest
+bscpy (PS dest_fptr dest_off dest_size `Chunk` dest_rest)
+      (PS src_fptr  src_off  src_size  `Chunk` src_rest)
+  = do let csize = min dest_size src_size
+       withForeignPtr dest_fptr $ \dest_ptr ->
+         withForeignPtr src_fptr $ \src_ptr ->
+           memcpy (dest_ptr `advancePtr` dest_off)
+                  (src_ptr  `advancePtr` src_off)
+                  (fromIntegral csize) -- TODO memmove?
+       bscpy (PS dest_fptr (dest_off + csize) (dest_size - csize) `Chunk` dest_rest)
+             (PS src_fptr  (src_off  + csize) (src_size  - csize) `Chunk` src_rest)
+bscpy _ _ = return ()
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