diff --git a/LICENSE b/LICENSE
new file mode 100644
--- /dev/null
+++ b/LICENSE
@@ -0,0 +1,30 @@
+Copyright KaiJia (c) 2016
+
+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 KaiJia 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
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--- /dev/null
+++ b/Setup.hs
@@ -0,0 +1,2 @@
+import Distribution.Simple
+main = defaultMain
diff --git a/snowflake-core.cabal b/snowflake-core.cabal
new file mode 100644
--- /dev/null
+++ b/snowflake-core.cabal
@@ -0,0 +1,35 @@
+name:                snowflake-core
+version:             0.1.0.0
+synopsis:            Initial project template from stack
+description:         Please see README.md
+homepage:            https://github.com/jiakai0419/snowflake#readme
+license:             BSD3
+license-file:        LICENSE
+author:              KaiJia
+maintainer:          jiakai0419@gmail.com
+copyright:           Copyright: (c) 2016 KaiJia
+category:            Demo
+build-type:          Simple
+-- extra-source-files:
+cabal-version:       >=1.10
+
+library
+  hs-source-dirs:      src
+  exposed-modules:     Snowflake
+  build-depends:       base >= 4.7 && < 5
+                     , time-exts
+  default-language:    Haskell2010
+
+test-suite snowflake-test
+  type:                exitcode-stdio-1.0
+  hs-source-dirs:      test
+  main-is:             Test.hs
+  build-depends:       base
+                     , snowflake-core
+                     , QuickCheck
+  ghc-options:         -threaded -rtsopts -with-rtsopts=-N
+  default-language:    Haskell2010
+
+source-repository head
+  type:     git
+  location: https://github.com/jiakai0419/snowflake
diff --git a/src/Snowflake.hs b/src/Snowflake.hs
new file mode 100644
--- /dev/null
+++ b/src/Snowflake.hs
@@ -0,0 +1,61 @@
+{-# LANGUAGE TemplateHaskell #-}
+module Snowflake
+  ( Timestamp
+  , Conf(..)
+  , IdWorker(..)
+  , defaultConf
+  , next
+  , nexts
+  ) where
+
+
+import Prelude hiding (sequence)
+import Data.Int (Int64)
+import Data.Maybe (Maybe, isNothing, fromJust)
+import Data.Bits ( (.|.)
+                 , shiftL
+                 )
+import Data.Time.Exts.Unix ( getCurrentUnixDateTimeMillis
+                           , UnixDateTimeMillis(..)
+                           )
+
+type Timestamp = Int64
+
+data Conf = Conf { _sequenceBits :: Int
+                 , _workerIdBits :: Int
+                 , _datacenterIdBits :: Int
+                 , _twepoch :: Timestamp  -- timestamp base-line
+                 } deriving (Show)
+
+data IdWorker = IdWorker { _sequence :: Int64
+                         , _workerId :: Int64
+                         , _datacenterId :: Int64
+                         , _timestamp :: Timestamp
+                         , _conf :: Conf
+                         } deriving (Show)
+
+defaultConf = Conf { _sequenceBits = 12
+                   , _workerIdBits = 5
+                   , _datacenterIdBits = 5
+                   , _twepoch = 1472733628921
+                   }
+
+next :: IdWorker -> Timestamp -> (Maybe Int64, IdWorker)
+next worker@(IdWorker lastSq wid did lastTs (Conf sBits wBits dBits twepoch)) ts
+  | lastTs == ts && lastSq == 2^sBits - 1 = (Nothing, worker)
+  | otherwise = (Just newId, worker {_sequence = newSq, _timestamp = ts})
+    where
+      newSq = if lastTs == ts then lastSq + 1 else 0
+      newId = tBit .|. dBit .|. wBit .|. newSq
+      wBit = wid `shiftL` sBits
+      dBit = did `shiftL` (sBits + wBits)
+      tBit = (ts - twepoch) `shiftL` (sBits + wBits + dBits)
+
+nexts :: IdWorker -> Int -> IO ([Int64], IdWorker)
+nexts worker 0 = return ([], worker)
+nexts worker n = do
+  timestamp <- _udt_mil_base <$> getCurrentUnixDateTimeMillis
+  let (maybeNewId, newWorker) = next worker timestamp in
+   if isNothing maybeNewId
+      then nexts worker n
+      else (\(ids, wk) -> (fromJust maybeNewId : ids, wk)) <$> nexts newWorker (n-1)
diff --git a/test/Test.hs b/test/Test.hs
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--- /dev/null
+++ b/test/Test.hs
@@ -0,0 +1,71 @@
+{-# LANGUAGE ScopedTypeVariables, TemplateHaskell #-}
+module Main where
+
+import Test.QuickCheck
+import Test.QuickCheck.All
+import Test.QuickCheck.Monadic
+import Snowflake
+import Data.Int (Int64)
+import Data.List (sort)
+
+--------------------------------------------------------------------------
+-- constant
+
+maxScale = 10^6
+
+--------------------------------------------------------------------------
+-- arbitrary instance
+
+instance Arbitrary IdWorker where
+  arbitrary = do
+    sequence     <- choose (0, 2^(_sequenceBits defaultConf) - 1) :: Gen Int64
+    workerId     <- choose (0, 2^(_workerIdBits defaultConf) - 1) :: Gen Int64
+    datacenterId <- choose (0, 2^(_datacenterIdBits defaultConf) - 1) :: Gen Int64
+    return IdWorker { _sequence = sequence
+                    , _workerId = workerId
+                    , _datacenterId = datacenterId
+                    , _timestamp = 0
+                    , _conf = defaultConf
+                    }
+
+--------------------------------------------------------------------------
+-- size consist with n
+
+prop_sc worker n = 0 <= n && n <= maxScale  ==> monadicIO $ do
+  (ids, _) <- run $ nexts worker n
+  assert $ length ids == n
+
+--------------------------------------------------------------------------
+-- strict ascending order
+
+isStrictAsc :: Ord a => [a] -> Bool
+isStrictAsc (x:y:xs)
+  | x < y = isStrictAsc (y:xs)
+  | otherwise = False
+isStrictAsc _ = True
+
+prop_asc worker n = 0 <= n && n <= maxScale  ==> monadicIO $ do
+  (ids, _) <- run $ nexts worker n
+  assert $ isStrictAsc ids
+
+--------------------------------------------------------------------------
+-- no-repeat
+
+isNoRepeat :: Ord a => [a] -> Bool
+isNoRepeat = isNoRepeat' . sort
+
+isNoRepeat' :: Eq a => [a] -> Bool
+isNoRepeat' (x:y:xs)
+  | x /= y = isNoRepeat' (y:xs)
+  | otherwise = False
+isNoRepeat' _ = True
+
+prop_np worker n = 0 <= n && n <= maxScale ==> monadicIO $ do
+  (ids, _) <- run $ nexts worker n
+  assert $ isNoRepeat ids
+
+--------------------------------------------------------------------------
+-- main
+
+return []
+main = $quickCheckAll