diff --git a/Data/StaticHash.hs b/Data/StaticHash.hs
new file mode 100644
--- /dev/null
+++ b/Data/StaticHash.hs
@@ -0,0 +1,68 @@
+{-|
+  Pure immutable hash whose lookup is O(1).
+-}
+
+module Data.StaticHash (
+    StaticHash
+  , fromList, lookup
+  ) where
+
+import Data.Array
+import Data.Hashable
+import Data.List (groupBy,sortBy)
+import Data.Numbers.Primes
+import qualified Prelude as P (lookup)
+import Prelude hiding (lookup)
+
+----------------------------------------------------------------
+
+{-|
+  Data type for immutable hashes.
+-}
+newtype StaticHash k v = StaticHash (Array Int (Maybe [(k,v)]))
+
+----------------------------------------------------------------
+
+{-| 
+  Creating 'StaticHash' from a list. A prime around the length of
+  the list x 2 is chosen for the size of array. This may prevent
+  collisions.
+-}
+
+fromList :: (Eq k,Hashable k) => [(k,v)] -> StaticHash k v
+fromList xs = StaticHash $ array (0,p-1) ls
+  where
+    len = length xs
+    threshold = len * 2 -- hoping collision free
+    p = head $ filter (>= threshold) primes
+    hs = map (\xy -> (fst xy `hashBy` p, xy)) xs
+    x <=> y = fst x`compare` fst y
+    x === y = fst x == fst y
+    gs = groupBy (===) $ sortBy (<=>) hs
+    unify ys = (fst (head ys), map snd ys)
+    ls = fil 0 p $ map unify gs
+
+fil :: Int -> Int -> [(Int, v)] -> [(Int, Maybe v)]
+fil i lim []
+  | i < lim   = (i,Nothing) : fil (i+1) lim []
+  | otherwise = []
+fil i lim kvs@((k,v):rest)
+  | i < k     = (i,Nothing) : fil (i+1) lim kvs
+  | otherwise = (k,Just v)  : fil (k+1) lim rest
+
+----------------------------------------------------------------
+
+{-|
+  Looking up 'StaticHash'.
+-}
+lookup :: (Eq k,Hashable k) => k -> StaticHash k v -> Maybe v
+lookup k (StaticHash hs) = hs ! i >>= P.lookup k
+  where
+    (_,p') = bounds hs
+    p = p' + 1
+    i = k `hashBy` p
+
+----------------------------------------------------------------
+
+hashBy :: Hashable k => k -> Int -> Int
+hashBy k p = hash k `mod` p
diff --git a/LICENSE b/LICENSE
new file mode 100644
--- /dev/null
+++ b/LICENSE
@@ -0,0 +1,29 @@
+Copyright (c) 2009, IIJ Innovation Institute Inc.
+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 copyright holders 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/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/static-hash.cabal b/static-hash.cabal
new file mode 100644
--- /dev/null
+++ b/static-hash.cabal
@@ -0,0 +1,21 @@
+Name:                   static-hash
+Version:                0.0.0
+Author:                 Kazu Yamamoto <kazu@iij.ad.jp>
+Maintainer:             Kazu Yamamoto <kazu@iij.ad.jp>
+License:                BSD3
+License-File:           LICENSE
+Synopsis:               Immutable hash
+Description:            Pure immutable hash whose lookup is O(1)
+Category:               Data Structures
+Cabal-Version:          >= 1.6
+Build-Type:             Simple
+library
+  if impl(ghc >= 6.12)
+    GHC-Options:        -Wall -fno-warn-unused-do-bind
+  else
+    GHC-Options:        -Wall
+  Exposed-Modules:      Data.StaticHash
+  Build-Depends:        base >= 4 && < 5, primes, hashable, array
+Source-Repository head
+  Type:                 git
+  Location:             git://github.com/kazu-yamamoto/static-hash.git