diff --git a/hnix-store-core/src/System/Nix/Internal/Nar/Streamer.hs b/hnix-store-core/src/System/Nix/Internal/Nar/Streamer.hs
index 3cf21c9..25d9d1f 100644
--- a/hnix-store-core/src/System/Nix/Internal/Nar/Streamer.hs
+++ b/hnix-store-core/src/System/Nix/Internal/Nar/Streamer.hs
@@ -3,7 +3,10 @@
 {-# language ScopedTypeVariables #-}
 
 module System.Nix.Internal.Nar.Streamer
-  ( streamNarIO
+  ( NarSource
+  , dumpString
+  , dumpPath
+  , streamNarIO
   , IsExecutable(..)
   )
 where
@@ -19,22 +22,43 @@ import           System.FilePath                  ( (</>) )
 import qualified System.Nix.Internal.Nar.Effects as Nar
 
 
+-- | NarSource
+-- The source to provide nar to the handler `(ByteString -> m ())`.
+-- It is isomorphic to ByteString by Yoneda lemma
+-- if the result is meant to be m ().
+-- It is done in CPS style so IO can be chunks.
+type NarSource m =  (ByteString -> m ()) -> m ()
+
+
+-- | dumpString
+-- dump a string to nar in CPS style. The function takes in a `ByteString`,
+-- and build a `NarSource m`.
+dumpString
+  :: forall m. IO.MonadIO m
+  => ByteString -- ^ the string you want to dump
+  -> NarSource m -- ^ The nar result in CPS style
+dumpString text yield = traverse_ (yield . str)
+  ["nix-archive-1", "(", "type" , "regular", "contents", text, ")"]
+
+
+-- | dumpPath
+-- shorthand
+-- build a Source that turn file path to nar using the default narEffectsIO.
+dumpPath
+  :: forall m . IO.MonadIO m
+  => FilePath -- ^ path for the file you want to dump to nar
+  -> NarSource m -- ^ the nar result in CPS style
+dumpPath = streamNarIO Nar.narEffectsIO
+
+
 -- | This implementation of Nar encoding takes an arbitrary @yield@
 --   function from any streaming library, and repeatedly calls
 --   it while traversing the filesystem object to Nar encode
-streamNarIO
-  :: forall m
-   . (IO.MonadIO m)
-  => (ByteString -> m ())
-  -> Nar.NarEffects IO
-  -> FilePath
-  -> m ()
-streamNarIO yield effs basePath = do
+streamNarIO :: forall m . IO.MonadIO m => Nar.NarEffects IO -> FilePath -> NarSource m
+streamNarIO effs basePath yield = do
   yield $ str "nix-archive-1"
   parens $ go basePath
-
  where
-
   go :: FilePath -> m ()
   go path = do
     isDir     <- IO.liftIO $ Nar.narIsDir effs path
@@ -65,16 +89,6 @@ streamNarIO yield effs basePath = do
           yield $ strs ["name", Bytes.Char8.pack f, "node"]
           parens $ go fullName
 
-  str :: ByteString -> ByteString
-  str t =
-    let
-      len = Bytes.length t
-    in
-      int len <> padBS len t
-
-  padBS :: Int -> ByteString -> ByteString
-  padBS strSize bs = bs <> Bytes.replicate (padLen strSize) 0
-
   parens act = do
     yield $ str "("
     r <- act
@@ -87,13 +101,6 @@ streamNarIO yield effs basePath = do
     mapM_ yield . Bytes.Lazy.toChunks =<< IO.liftIO (Bytes.Lazy.readFile path)
     yield $ Bytes.replicate (padLen $ fromIntegral fsize) 0
 
-  strs :: [ByteString] -> ByteString
-  strs xs = Bytes.concat $ str <$> xs
-
-  int :: Integral a => a -> ByteString
-  int n = Serial.runPut $ Serial.putInt64le $ fromIntegral n
-
-
 data IsExecutable = NonExecutable | Executable
   deriving (Eq, Show)
 
@@ -107,3 +114,19 @@ isExecutable effs fp =
 -- | Distance to the next multiple of 8
 padLen :: Int -> Int
 padLen n = (8 - n) `mod` 8
+
+int :: Integral a => a -> ByteString
+int n = Serial.runPut $ Serial.putInt64le $ fromIntegral n
+
+str :: ByteString -> ByteString
+str t =
+  let
+    len = Bytes.length t
+  in
+    int len <> padBS len t
+
+padBS :: Int -> ByteString -> ByteString
+padBS strSize bs = bs <> Bytes.replicate (padLen strSize) 0
+
+strs :: [ByteString] -> ByteString
+strs xs = Bytes.concat $ str <$> xs
diff --git a/hnix-store-core/src/System/Nix/Nar.hs b/hnix-store-core/src/System/Nix/Nar.hs
index 8ea95bf..552823d 100644
--- a/hnix-store-core/src/System/Nix/Nar.hs
+++ b/hnix-store-core/src/System/Nix/Nar.hs
@@ -26,6 +26,11 @@ module System.Nix.Nar
   -- * Internal
   , Nar.streamNarIO
   , Nar.runParser
+  , Nar.dumpString
+  , Nar.dumpPath
+
+  -- * Type
+  , Nar.NarSource
   )
 where
 
@@ -52,9 +57,9 @@ buildNarIO
   -> IO ()
 buildNarIO effs basePath outHandle =
   Nar.streamNarIO
-    (\chunk -> BS.hPut outHandle chunk >> Concurrent.threadDelay 10)
     effs
     basePath
+    (\chunk -> BS.hPut outHandle chunk >> Concurrent.threadDelay 10)
 
 
 -- | Read NAR formatted bytes from the @IO.Handle@ and unpack them into
diff --git a/hnix-store-core/src/System/Nix/ReadonlyStore.hs b/hnix-store-core/src/System/Nix/ReadonlyStore.hs
index 491bf3a..d46f05c 100644
--- a/hnix-store-core/src/System/Nix/ReadonlyStore.hs
+++ b/hnix-store-core/src/System/Nix/ReadonlyStore.hs
@@ -87,7 +87,7 @@ computeStorePathForPath name pth recursive _pathFilter _repair = do
   recursiveContentHash :: IO (Digest SHA256)
   recursiveContentHash = hashFinalize <$> execStateT streamNarUpdate (hashInit @SHA256)
   streamNarUpdate :: StateT (Context SHA256) IO ()
-  streamNarUpdate = streamNarIO (modify . flip (hashUpdate @ByteString @SHA256)) narEffectsIO pth
+  streamNarUpdate = streamNarIO narEffectsIO pth (modify . flip (hashUpdate @ByteString @SHA256))
 
   flatContentHash :: IO (Digest SHA256)
   flatContentHash = hashlazy <$> narReadFile narEffectsIO pth