diff --git a/MNIST.hs b/MNIST.hs
index 4de5b9d..72d1e51 100644
--- a/MNIST.hs
+++ b/MNIST.hs
@@ -3,15 +3,18 @@
 import qualified Data.ByteString.Lazy as BS
 
 import Data.Int
+import Data.Binary
 import Data.List (findIndex, maximumBy)
 import Data.List.Split (chunksOf)
 import Data.Ord (comparing)
 import Debug.Trace (trace)
 
+import Codec.Compression.GZip
+import qualified Data.ByteString.Lazy as B
+
 import Control.DeepSeq
 
 import Numeric.LinearAlgebra
-import Codec.Compression.GZip
 import System.Random
 import System.Environment (getArgs)
 import System.Console.CmdArgs.Implicit
@@ -92,6 +95,23 @@ testSamples = do
     ims <- testIms
     return $! [ img --> toLabel lbl | (lbl, img) <- ims]
 
+newtype StorableSample a = StorableSample { getSample :: Sample a }
+
+instance (Element a, Binary a) => Binary (StorableSample a) where
+    put (StorableSample (vecIn, vecOut)) = do
+        put (toList vecIn)
+        put (toList vecOut)
+    get = do
+        vecIn <- get
+        vecOut <- get
+        return $ StorableSample (fromList vecIn --> fromList vecOut)
+
+loadSamples :: FilePath -> IO (Samples Double)
+loadSamples fp = fmap (map getSample . decode . decompress) (B.readFile fp)
+
+saveSamples :: FilePath -> Samples Double -> IO ()
+saveSamples fp = B.writeFile fp . compress . encode . map StorableSample
+
 classify :: Network Double -> Sample Double -> IO ()
 classify net spl = do
     putStrLn (drawImage (fst spl)
@@ -115,8 +135,8 @@ main = do
     net <- case filePath args of
             "" -> newNetwork [784, hiddenNeurons args, 10]
             fp -> loadNetwork fp :: IO (Network Double)
-    trSamples <- trainSamples
-    tstSamples <- testSamples
+    trSamples <- loadSamples "mnist-data/trainSamples.spls"
+    tstSamples <- loadSamples "mnist-data/testSamples.spls"
     let bad = tstSamples `deepseq` test net tstSamples
     putStrLn $ "Initial performance of network: recognized " ++ show bad ++ " of 10k" 
     let debug network epochs = "Left epochs: " ++ show epochs
diff --git a/Network.hs b/Network.hs
index 11f85c8..e0dc4e1 100644
--- a/Network.hs
+++ b/Network.hs
@@ -40,6 +40,7 @@ module Network (
 ) where
 
 import Data.List.Split (chunksOf)
+import Data.List (foldl')
 import Data.Binary
 import Data.Maybe (fromMaybe)
 import Text.Read (readMaybe)
@@ -146,7 +147,7 @@ output :: (Numeric a, Num (Vector a))
        -> ActivationFunction a
        -> Vector a
        -> Vector a
-output net act input = foldl f input (layers net)
+output net act input = foldl' f input (layers net)
     where f vec layer = cmap act ((weights layer #> vec) + biases layer)
 
 rawOutputs :: (Numeric a, Num (Vector a))
@@ -206,7 +207,7 @@ trainSGD :: (Numeric Double, Floating Double)
          -> Double
          -> Network Double
 trainSGD net costFunction lambda trainSamples miniBatchSize eta =
-    foldl updateMiniBatch net (chunksOf miniBatchSize trainSamples)
+    foldl' updateMiniBatch net (chunksOf miniBatchSize trainSamples)
   where updateMiniBatch = update eta costFunction lambda (length trainSamples)
 
 update :: LearningRate
@@ -220,10 +221,10 @@ update eta costFunction lambda n net spls = case newNablas of
         Nothing -> net
         Just x -> net { layers = layers' x }
     where newNablas :: Maybe [Layer Double]
-          newNablas = foldl updateNablas Nothing spls
+          newNablas = foldl' updateNablas Nothing spls
           updateNablas :: Maybe [Layer Double] -> Sample Double -> Maybe [Layer Double]
           updateNablas mayNablas sample =
-              let nablasDelta = backprop net costFunction sample
+              let !nablasDelta = backprop net costFunction sample
                   f nabla nablaDelta =
                       nabla { weights = weights nabla + weights nablaDelta,
                               biases = biases nabla + biases nablaDelta }
@@ -252,8 +253,9 @@ backprop net costFunction spl = finalNablas
           (headZ, headA) = head rawFeedforward
           -- get starting delta, based on the activation of the last layer
           startDelta = getDelta costFunction headZ headA (snd spl)
-          -- calculate weighs of last layer in advance
+          -- calculate nabla of biases
           lastNablaB = startDelta
+          -- calculate nabla of weighs of last layer in advance
           lastNablaW = startDelta `outer` previousA
             where previousA
                     | length rawFeedforward > 1 = snd $ rawFeedforward !! 1
@@ -262,7 +264,7 @@ backprop net costFunction spl = finalNablas
           -- reverse layers, analogy to the reversed (z, a) list
           layersReversed = reverse $ layers net
           -- calculate nablas, beginning at the end of the network (startDelta)
-          (finalNablas, _) = foldl calculate ([lastLayer], startDelta)
+          (finalNablas, _) = foldl' calculate ([lastLayer], startDelta)
                         [1..length layersReversed - 1]
           -- takes the index and updates nablas
           calculate (nablas, oldDelta) idx =