diff --git a/pipes-key-value-csv.cabal b/pipes-key-value-csv.cabal
--- a/pipes-key-value-csv.cabal
+++ b/pipes-key-value-csv.cabal
@@ -1,5 +1,5 @@
 name:                pipes-key-value-csv
-version:             0.2.0.0
+version:             0.3.0.0
 synopsis:            Streaming processing of CSV files preceded by key-value pairs.
 description:         Nonstandard CSV files, with the table preceded by a header consisting of key-value pairs are often the output format of varius test equipment, such as digital oscilloscopes.
 homepage:            https://github.com/marcinmrotek/key-value-csv
@@ -35,7 +35,9 @@
                      , Pipes.KeyValueCsv.Internal.KeyValue
                      , Pipes.KeyValueCsv.Internal.Names
                      , Pipes.KeyValueCsv.Internal.Types
+                     , Data.Validation
   build-depends:       base               >= 4.8     && < 5
+                     , bifunctors         >= 5.3     && < 5.4
                      , containers         >= 0.5.6   && < 0.6
                      , data-default-class >= 0.0.1   && < 0.2
                      , lens               >= 4.12    && < 4.15
@@ -47,6 +49,7 @@
                      , pipes-safe         >= 2.2     && < 2.3
                      , pipes-text         >= 0.0     && < 0.1
                      , reflection         >= 1.5     && < 2.2
+                     , semigroupoids      >= 5.0.0   && < 5.1
                      , text               >= 1.2     && < 1.3
                      , vinyl              >= 0.5.2   && < 0.6
                      , vinyl-utils        >= 0.2.0.1 && < 0.4
@@ -64,7 +67,7 @@
                      , Test.Instances
                      , Test.KeyValue
                      , Test.Types
-  build-depends:       base            >= 4.8 && < 4.9
+  build-depends:       base            >= 4.8 && < 5
                      , contravariant   >= 1.2 && < 1.5
                      , pipes-key-value-csv
                      , data-default-class
@@ -75,7 +78,6 @@
                      , reflection
                      , text
                      , transformers
-                     , validation
                      , vinyl
                      , vinyl-utils
   hs-source-dirs:      test
diff --git a/src/Data/Validation.hs b/src/Data/Validation.hs
new file mode 100644
--- /dev/null
+++ b/src/Data/Validation.hs
@@ -0,0 +1,105 @@
+{-|
+Module      : Data.Validation
+Copyright   : (c) Marcin Mrotek, 2016
+License     : BSD3
+Maintainer  : marcin.jan.mrotek@gmail.com
+Stability   : experimental
+
+Accumulating Either-like type.
+-}
+
+{-# LANGUAGE 
+    DeriveDataTypeable
+  , DeriveFunctor
+  , DeriveFoldable
+  , DeriveGeneric 
+  #-}
+
+module Data.Validation (Validation(..)) where
+  
+import Control.Applicative
+import Control.Lens
+import Data.Bifunctor
+import Data.Bifoldable
+import Data.Bitraversable
+import Data.Data
+import Data.Functor.Alt
+import Data.Semigroup
+import GHC.Generics
+
+data Validation e a = Success a | Failure e
+  deriving (Show, Eq, Ord, Data, Functor, Foldable, Generic)
+
+instance Semigroup e => Semigroup (Validation e a) where
+  (<>) = app
+    where
+      app (Failure e1) (Failure e2) = Failure (e1 <> e2)
+      app v@(Success _) _ = v
+      app _ v@(Success _) = v
+      
+instance Monoid e => Monoid (Validation e a) where
+  mempty = Failure mempty
+  mappend = app
+    where
+      app (Failure e1) (Failure e2) = Failure (e1 `mappend` e2)
+      app v@(Success _) _ = v
+      app _ v@(Success _) = v
+  
+instance Semigroup e => Applicative (Validation e) where
+  pure = Success
+  (<*>) = app
+    where
+      app (Success f) (Success a) = Success (f a)
+      app (Failure e) (Success _) = Failure e
+      app (Success _) (Failure e) = Failure e
+      app (Failure e1) (Failure e2) = Failure (e1 <> e2)
+      
+altValidation :: Validation e a -> Validation e a -> Validation e a
+altValidation (Failure _) v = v
+altValidation v@(Success _) _ = v
+
+instance (Monoid e, Semigroup e) => Alternative (Validation e) where
+  empty = Failure mempty
+  (<|>) = altValidation
+      
+instance Semigroup e => Apply (Validation e) where
+  (<.>) = (<*>)
+  
+instance Alt (Validation e) where
+  (<!>) = altValidation
+
+instance Traversable (Validation e) where
+  traverse f v = 
+    case v of
+      Success a -> Success <$> f a
+      Failure e -> pure $ Failure e
+      
+instance Swapped Validation where
+  swapped = iso swap swap
+    where
+      swap (Success a) = Failure a
+      swap (Failure e) = Success e
+      
+instance Bifunctor Validation where
+  bimap f g v = 
+    case v of
+      Success a -> Success (g a)
+      Failure e -> Failure (f e)
+  first f v =
+    case v of
+      Success a -> Success a
+      Failure e -> Failure (f e)
+  second = fmap
+
+instance Bifoldable Validation where
+  bifoldMap f g v =
+    case v of
+      Success a -> g a
+      Failure e -> f e
+    
+instance Bitraversable Validation where
+  bitraverse f g v =
+    case v of
+      Success a -> Success <$> g a
+      Failure e -> Failure <$> f e
+      
diff --git a/test/Test/Csv.hs b/test/Test/Csv.hs
--- a/test/Test/Csv.hs
+++ b/test/Test/Csv.hs
@@ -36,7 +36,7 @@
 
 prop_read :: [Rec Id TestFields] -> Property
 prop_read rs = map pure rs === useDelimiter delim parsed
-    & counterexample (concat. map Text.unpack $ Pipes.toList pipe)
+    & counterexample (concatMap Text.unpack $ Pipes.toList pipe)
   where
     pipe :: Producer Text Transformers.Identity ()
     pipe = 
@@ -45,7 +45,7 @@
       . mconcat 
       . intersperse (singleton '\n')
       $ map (buildDelimited delim) rs
-    parsed :: Given Delimiter => [AccValidation [CsvError] (Rec Id TestFields)]
+    parsed :: Given Delimiter => [Validation [CsvError] (Rec Id TestFields)]
     parsed =
         map rtraverse1
       . Pipes.toList
diff --git a/test/Test/KeyValue.hs b/test/Test/KeyValue.hs
--- a/test/Test/KeyValue.hs
+++ b/test/Test/KeyValue.hs
@@ -3,6 +3,7 @@
   , FlexibleContexts
   , OverloadedStrings
   , TemplateHaskell
+  , PackageImports
   #-}
 
 module Test.KeyValue where
@@ -15,6 +16,7 @@
 import Pipes.KeyValueCsv.Common
 import Pipes.KeyValueCsv.KeyValue
 import Pipes.KeyValueCsv.Types
+import Data.Validation
 
 import Control.Lens hiding (Const)
 import qualified Data.Functor.Identity as Transformers
@@ -24,7 +26,6 @@
 import qualified Data.Text as Text
 import Data.Text.Lazy.Builder
 import Data.Reflection
-import Data.Validation
 import Data.Vinyl
 import Data.Vinyl.Functor
 import Data.Vinyl.Utils.Compose
@@ -39,7 +40,7 @@
 
 prop_read :: Rec Id TestFields -> Property
 prop_read r = pure r === useDelimiter delim parsed
-    & counterexample (concat. map Text.unpack $ Pipes.toList pipe)
+    & counterexample (concatMap Text.unpack $ Pipes.toList pipe)
   where
     names :: Rec (Const Text) TestFields
     names = Const "foo" :& Const "bar" :& Const "baz" :& RNil
@@ -52,7 +53,7 @@
       . zipWith keyValue (map fromText $ recordToList names) 
       $ build r
     keyValue k v = k <> singleton delim <> v
-    parsed :: Given Delimiter => AccValidation [KeyValueError] (Rec Id TestFields)
+    parsed :: Given Delimiter => Validation [KeyValueError] (Rec Id TestFields)
     parsed =
         rtraverse1
       . fst