diff --git a/aeson-value-parser.cabal b/aeson-value-parser.cabal
--- a/aeson-value-parser.cabal
+++ b/aeson-value-parser.cabal
@@ -1,5 +1,5 @@
 name: aeson-value-parser
-version: 0.18.1
+version: 0.19
 synopsis: API for parsing "aeson" JSON tree into Haskell types
 description:
   A flexible parser DSL of JSON AST produced by the \"aeson\" library
@@ -27,17 +27,18 @@
   default-extensions: Arrows, BangPatterns, ConstraintKinds, DataKinds, DefaultSignatures, DeriveDataTypeable, DeriveFoldable, DeriveFunctor, DeriveGeneric, DeriveTraversable, EmptyDataDecls, FlexibleContexts, FlexibleInstances, FunctionalDependencies, GADTs, GeneralizedNewtypeDeriving, LambdaCase, LiberalTypeSynonyms, MagicHash, MultiParamTypeClasses, MultiWayIf, NoImplicitPrelude, NoMonomorphismRestriction, OverloadedStrings, PatternGuards, PatternSynonyms, ParallelListComp, QuasiQuotes, RankNTypes, RecordWildCards, ScopedTypeVariables, StandaloneDeriving, TemplateHaskell, TupleSections, TypeFamilies, TypeOperators, UnboxedTuples
   default-language: Haskell2010
   exposed-modules:
-    Aeson.ValueParser
+    AesonValueParser
   other-modules:
-    Aeson.ValueParser.Error
-    Aeson.ValueParser.Prelude
-    Aeson.ValueParser.Vector
+    AesonValueParser.Error
+    AesonValueParser.Prelude
+    AesonValueParser.Vector
   build-depends:
     aeson ==1.*,
     attoparsec >=0.13 && <0.14,
     base >=4.9 && <5,
     bytestring >=0.10 && <0.12,
     hashable >=1.3 && <2,
+    megaparsec >=8 && <9,
     mtl >=2.2 && <3,
     scientific ==0.3.*,
     text ==1.*,
diff --git a/library/Aeson/ValueParser.hs b/library/Aeson/ValueParser.hs
deleted file mode 100644
--- a/library/Aeson/ValueParser.hs
+++ /dev/null
@@ -1,311 +0,0 @@
-{-
-Parser DSL for the \"aeson\" model of JSON tree.
-
-The general model of this DSL is about switching between contexts.
--}
-module Aeson.ValueParser
-(
-  Value,
-  run,
-  runWithTextError,
-  Error.Error(..),
-  -- * Value parsers
-  object,
-  array,
-  null,
-  nullable,
-  nullableMonoid,
-  string,
-  number,
-  bool,
-  fromJSON,
-  -- * String parsers
-  String,
-  text,
-  matchedText,
-  parsedText,
-  -- * Number parsers
-  Number,
-  scientific,
-  integer,
-  floating,
-  matchedScientific,
-  matchedInteger,
-  matchedFloating,
-  -- * Object parsers
-  Object,
-  field,
-  oneOfFields,
-  fieldMap,
-  foldlFields,
-  -- * Array parsers
-  Array,
-  element,
-  elementVector,
-  foldlElements,
-  foldrElements,
-)
-where
-
-import Aeson.ValueParser.Prelude hiding (bool, null, String)
-import qualified Aeson.ValueParser.Error as Error
-import qualified Data.Aeson as Aeson
-import qualified Data.Attoparsec.Text as Attoparsec
-import qualified Data.HashMap.Strict as HashMap
-import qualified Data.HashSet as HashSet
-import qualified Data.Scientific as Scientific
-import qualified Data.Text.Encoding as Text
-import qualified Data.Vector as Vector
-import qualified Aeson.ValueParser.Vector as Vector
-
-
--- * Value
--------------------------
-
-{-|
-JSON `Aeson.Value` AST parser.
-
-Its `Alternative` instance implements the logic of choosing between the possible types of JSON values.
--}
-newtype Value a =
-  Value (ReaderT Aeson.Value (MaybeT (Either Error.Error)) a)
-  deriving (Functor, Applicative)
-
-{-|
-Implements the logic of choosing between the possible types of JSON values.
-
-If you have multiple parsers of the same type of JSON value composed,
-only the leftmost will be affective.
-The errors from deeper parsers do not trigger the alternation,
-instead they get propagated to the top.
--}
-instance Alternative Value where
-  empty = Value $ ReaderT $ const $ MaybeT $ return Nothing
-  (<|>) (Value leftParser) (Value rightParser) = Value (leftParser <|> rightParser)
-
-{-# INLINE run #-}
-run :: Value a -> Aeson.Value -> Either Error.Error a
-run = \ (Value parser) value -> (=<<) (maybe (Left (typeError value)) Right) $ runMaybeT $ runReaderT parser value where
-  typeError = \ case
-    Aeson.Array _ -> "Unexpected type: array"
-    Aeson.Object _ -> "Unexpected type: object"
-    Aeson.String _ -> "Unexpected type: string"
-    Aeson.Number _ -> "Unexpected type: number"
-    Aeson.Bool _ -> "Unexpected type: bool"
-    Aeson.Null -> "Unexpected type: null"
-
-{-# INLINE runWithTextError #-}
-runWithTextError :: Value a -> Aeson.Value -> Either Text a
-runWithTextError parser = left Error.toText . run parser
-
-runString :: String a -> Text -> Either (Maybe Text) a
-runString (String a) b = runExcept (runReaderT a b)
-
--- ** Definitions
--------------------------
-
-{-# INLINE array #-}
-array :: Array a -> Value a
-array (Array parser) = Value $ ReaderT $ \ case
-  Aeson.Array x -> lift $ join $ runExcept $ runExceptT $ runReaderT parser x
-  _ -> empty
-
-{-# INLINE object #-}
-object :: Object a -> Value a
-object (Object parser) = Value $ ReaderT $ \ case
-  Aeson.Object x -> lift $ join $ runExcept $ runExceptT $ runReaderT parser x
-  _ -> empty
-
-{-# INLINE null #-}
-null :: Value ()
-null = Value $ ReaderT $ \ case
-  Aeson.Null -> pure ()
-  _ -> empty
-
-{-# INLINE nullable #-}
-nullable :: Value a -> Value (Maybe a)
-nullable (Value parser) = Value $ ReaderT $ \ case
-  Aeson.Null -> pure Nothing
-  x -> fmap Just (runReaderT parser x)
-
-{-# INLINE nullableMonoid #-}
-nullableMonoid :: Monoid a => Value a -> Value a
-nullableMonoid (Value parser) = Value $ ReaderT $ \ case
-  Aeson.Null -> pure mempty
-  x -> runReaderT parser x
-
-{-# INLINE string #-}
-string :: String a -> Value a
-string (String parser) = Value $ ReaderT $ \ case
-  Aeson.String x -> lift $ left (Error.message . fromMaybe "No details") $ runExcept $ runReaderT parser x
-  _ -> empty
-
-{-# INLINE number #-}
-number :: Number a -> Value a
-number (Number parser) = Value $ ReaderT $ \ case
-  Aeson.Number x -> lift $ left (Error.message . fromMaybe "No details") $ runExcept $ runReaderT parser x
-  _ -> empty
-
-{-# INLINE bool #-}
-bool :: Value Bool
-bool = Value $ ReaderT $ \ case
-  Aeson.Bool x -> return x
-  _ -> empty
-
-{-# INLINE fromJSON #-}
-fromJSON :: Aeson.FromJSON a => Value a
-fromJSON = Value $ ReaderT $ Aeson.fromJSON >>> \ case
-  Aeson.Success r -> return r
-  Aeson.Error m -> lift $ Left $ fromString m
-
-
--- * String parsers
--------------------------
-
-newtype String a =
-  String (ReaderT Text (Except (Maybe Text)) a)
-  deriving (Functor, Applicative, Alternative)
-
-{-# INLINE text #-}
-text :: String Text
-text = String ask
-
-{-# INLINE matchedText #-}
-matchedText :: (Text -> Either Text a) -> String a
-matchedText parser = String $ ReaderT $ except . left Just . parser
-
-{-# INLINE parsedText #-}
-parsedText :: Attoparsec.Parser a -> String a
-parsedText parser = matchedText $ left fromString . Attoparsec.parseOnly parser
-
-
--- * Number parsers
--------------------------
-
-newtype Number a =
-  Number (ReaderT Scientific (Except (Maybe Text)) a)
-  deriving (Functor, Applicative, Alternative)
-
-{-# INLINE scientific #-}
-scientific :: Number Scientific
-scientific = Number ask
-
-{-# INLINE integer #-}
-integer :: (Integral a, Bounded a) => Number a
-integer = Number $ ReaderT $ \ x -> if Scientific.isInteger x
-  then case Scientific.toBoundedInteger x of
-    Just int -> return int
-    Nothing -> throwError (Just (fromString ("Number " <> show x <> " is out of integer range")))
-  else throwError (Just (fromString ("Number " <> show x <> " is not integer")))
-
-{-# INLINE floating #-}
-floating :: RealFloat a => Number a
-floating = Number $ ReaderT $ \ a -> case Scientific.toBoundedRealFloat a of
-  Right b -> return b
-  Left c -> if c == 0
-    then throwError (Just (fromString ("Number " <> show a <> " is too small")))
-    else throwError (Just (fromString ("Number " <> show a <> " is too large")))
-
-{-# INLINE matchedScientific #-}
-matchedScientific :: (Scientific -> Either Text a) -> Number a
-matchedScientific matcher = Number $ ReaderT $ except . left Just . matcher
-
-{-# INLINE matchedInteger #-}
-matchedInteger :: (Integral integer, Bounded integer) => (integer -> Either Text a) -> Number a
-matchedInteger matcher = Number $ case integer of
-  Number parser -> parser >>= either (throwError . Just) return . matcher
-
-{-# INLINE matchedFloating #-}
-matchedFloating :: RealFloat floating => (floating -> Either Text a) -> Number a
-matchedFloating matcher = Number $ case floating of
-  Number parser -> parser >>= either (throwError . Just) return . matcher
-
-
--- * Object parsers
--------------------------
-
-{-|
-JSON `Aeson.Object` parser.
--}
-newtype Object a =
-  Object (ReaderT (HashMap Text Aeson.Value) (ExceptT Error.Error (Except Error.Error)) a)
-  deriving (Functor, Applicative, Alternative, Monad, MonadPlus, MonadError Error.Error)
-
-instance MonadFail Object where
-  fail = throwError . fromString
-
-{-# INLINE field #-}
-field :: Text -> Value a -> Object a
-field name fieldParser = Object $ ReaderT $ \ object -> case HashMap.lookup name object of
-  Just value -> case run fieldParser value of
-    Right parsedValue -> return parsedValue
-    Left error -> lift $ throwE $ Error.named name error
-  Nothing -> throwE (Error.Error (pure name) "Object contains no field with this name")
-
-{-# INLINE oneOfFields #-}
-oneOfFields :: [Text] -> Value a -> Object a
-oneOfFields keys valueParser = asum (fmap (flip field valueParser) keys)
-
-{-# INLINE fieldMap #-}
-fieldMap :: (Eq a, Hashable a) => String a -> Value b -> Object (HashMap a b)
-fieldMap keyParser fieldParser = Object $ ReaderT $ fmap HashMap.fromList . traverse mapping . HashMap.toList where
-  mapping (keyText, ast) = 
-    case runString keyParser keyText of
-      Right parsedKey -> case run fieldParser ast of
-        Right parsedField -> return (parsedKey, parsedField)
-        Left error -> lift (throwE (Error.named keyText error))
-      Left error -> lift (throwE (maybe mempty Error.message error))
-
-{-# INLINE foldlFields #-}
-foldlFields :: (state -> key -> field -> state) -> state -> String key -> Value field -> Object state
-foldlFields step state keyParser fieldParser = Object $ ReaderT $ \ object -> HashMap.foldlWithKey' newStep (pure state) object where
-  newStep stateE key fieldAst = 
-    case runString keyParser key of
-      Right !parsedKey -> case run fieldParser fieldAst of
-        Right !parsedField -> do
-          !state <- stateE
-          return $ step state parsedKey parsedField
-        Left error -> lift (throwE (Error.named key error))
-      Left error -> lift (throwE (maybe mempty Error.message error))
-
-
--- * Array parsers
--------------------------
-
-{-|
-JSON `Aeson.Array` parser.
--}
-newtype Array a =
-  Array (ReaderT (Vector Aeson.Value) (ExceptT Error.Error (Except Error.Error)) a)
-  deriving (Functor, Applicative, Alternative, Monad, MonadPlus, MonadError Error.Error)
-
-instance MonadFail Array where
-  fail = throwError . fromString
-
-{-# INLINE element #-}
-element :: Int -> Value a -> Array a
-element index elementParser = Array $ ReaderT $ \ array -> case array Vector.!? index of
-  Just element -> case run elementParser element of
-    Right result -> return result
-    Left error -> lift $ throwE $ Error.indexed index error
-  Nothing -> throwE $ Error.Error (pure (fromString (show index))) "Array contains no element by this index"
-
-{-# INLINE elementVector #-}
-elementVector :: Value a -> Array (Vector a)
-elementVector elementParser = Array $ ReaderT $ \ arrayAst -> flip Vector.imapM arrayAst $ \ index ast -> case run elementParser ast of
-  Right element -> return element
-  Left error -> lift $ throwE $ Error.indexed index error
-
-{-# INLINE foldlElements #-}
-foldlElements :: (state -> Int -> element -> state) -> state -> Value element -> Array state
-foldlElements step state elementParser = Array $ ReaderT $ Vector.ifoldM' newStep state where
-  newStep state index ast = case run elementParser ast of
-    Right element -> return $ step state index element
-    Left error -> lift $ throwE $ Error.indexed index error
-
-{-# INLINE foldrElements #-}
-foldrElements :: (Int -> element -> state -> state) -> state -> Value element -> Array state
-foldrElements step state elementParser = Array $ ReaderT $ Vector.ifoldrM newStep state where
-  newStep index ast nextState = case run elementParser ast of
-    Right element -> return $ step index element nextState
-    Left error -> lift $ throwE $ Error.indexed index error
diff --git a/library/Aeson/ValueParser/Error.hs b/library/Aeson/ValueParser/Error.hs
deleted file mode 100644
--- a/library/Aeson/ValueParser/Error.hs
+++ /dev/null
@@ -1,43 +0,0 @@
-module Aeson.ValueParser.Error
-where
-
-import Aeson.ValueParser.Prelude
-import qualified Data.Text as Text
-import qualified Text.Builder as TextBuilder
-
-
-data Error = Error [Text] {-^ Path -} Text {-^ Message -}
-
-instance Semigroup Error where
-  (<>) _ b = b
-
-instance Monoid Error where
-  mempty = Error [] ""
-  mappend = (<>)
-
-instance IsString Error where
-  fromString = message . fromString
-
-instance Show Error where
-  show = Text.unpack . toText
-
-{-# INLINE indexed #-}
-indexed :: Int -> Error -> Error
-indexed = named . fromString . show
-
-{-# INLINE named #-}
-named :: Text -> Error -> Error
-named name (Error path message) = Error (name : path) message
-
-{-# INLINE message #-}
-message :: Text -> Error
-message = Error []
-
-toText :: Error -> Text
-toText = TextBuilder.run . toTextBuilder
-
-toTextBuilder :: Error -> TextBuilder.Builder
-toTextBuilder (Error path message) =
-  "AST parsing error at path " <>
-  foldMap (\ x -> "/" <> TextBuilder.text x) path <> ": " <>
-  TextBuilder.text message
diff --git a/library/Aeson/ValueParser/Prelude.hs b/library/Aeson/ValueParser/Prelude.hs
deleted file mode 100644
--- a/library/Aeson/ValueParser/Prelude.hs
+++ /dev/null
@@ -1,114 +0,0 @@
-module Aeson.ValueParser.Prelude
-(
-  module Exports,
-  showText,
-)
-where
-
-
--- base
--------------------------
-import Control.Applicative as Exports
-import Control.Arrow as Exports
-import Control.Category as Exports
-import Control.Concurrent as Exports
-import Control.Exception as Exports
-import Control.Monad as Exports hiding (fail, mapM_, sequence_, forM_, msum, mapM, sequence, forM)
-import Control.Monad.IO.Class as Exports
-import Control.Monad.Fail as Exports
-import Control.Monad.Fix as Exports hiding (fix)
-import Control.Monad.ST as Exports
-import Data.Bits as Exports
-import Data.Bool as Exports
-import Data.Char as Exports
-import Data.Coerce as Exports
-import Data.Complex as Exports
-import Data.Data as Exports
-import Data.Dynamic as Exports
-import Data.Either as Exports
-import Data.Fixed as Exports
-import Data.Foldable as Exports hiding (toList)
-import Data.Function as Exports hiding (id, (.))
-import Data.Functor as Exports
-import Data.Functor.Identity as Exports
-import Data.Int as Exports
-import Data.IORef as Exports
-import Data.Ix as Exports
-import Data.List as Exports hiding (sortOn, isSubsequenceOf, uncons, concat, foldr, foldl1, maximum, minimum, product, sum, all, and, any, concatMap, elem, foldl, foldr1, notElem, or, find, maximumBy, minimumBy, mapAccumL, mapAccumR, foldl')
-import Data.List.NonEmpty as Exports (NonEmpty(..))
-import Data.Maybe as Exports
-import Data.Monoid as Exports hiding (Last(..), First(..), (<>))
-import Data.Ord as Exports
-import Data.Proxy as Exports
-import Data.Ratio as Exports
-import Data.Semigroup as Exports
-import Data.STRef as Exports
-import Data.String as Exports
-import Data.Traversable as Exports
-import Data.Tuple as Exports
-import Data.Unique as Exports
-import Data.Version as Exports
-import Data.Word as Exports
-import Debug.Trace as Exports
-import Foreign.ForeignPtr as Exports
-import Foreign.Ptr as Exports
-import Foreign.StablePtr as Exports
-import Foreign.Storable as Exports hiding (sizeOf, alignment)
-import GHC.Conc as Exports hiding (withMVar, threadWaitWriteSTM, threadWaitWrite, threadWaitReadSTM, threadWaitRead)
-import GHC.Exts as Exports (lazy, inline, sortWith, groupWith, IsList(..))
-import GHC.Generics as Exports (Generic)
-import GHC.IO.Exception as Exports
-import Numeric as Exports
-import Prelude as Exports hiding (fail, concat, foldr, mapM_, sequence_, foldl1, maximum, minimum, product, sum, all, and, any, concatMap, elem, foldl, foldr1, notElem, or, mapM, sequence, id, (.))
-import System.Environment as Exports
-import System.Exit as Exports
-import System.IO as Exports
-import System.IO.Error as Exports
-import System.IO.Unsafe as Exports
-import System.Mem as Exports
-import System.Mem.StableName as Exports
-import System.Timeout as Exports
-import Text.ParserCombinators.ReadP as Exports (ReadP, ReadS, readP_to_S, readS_to_P)
-import Text.ParserCombinators.ReadPrec as Exports (ReadPrec, readPrec_to_P, readP_to_Prec, readPrec_to_S, readS_to_Prec)
-import Text.Printf as Exports (printf, hPrintf)
-import Text.Read as Exports (Read(..), readMaybe, readEither)
-import Unsafe.Coerce as Exports
-
--- transformers
--------------------------
-import Control.Monad.Trans.Class as Exports
-import Control.Monad.Trans.Except as Exports hiding (liftCatch, liftCallCC)
-import Control.Monad.Trans.Maybe as Exports hiding (liftCatch, liftCallCC, liftListen, liftPass)
-import Control.Monad.Trans.Reader as Exports hiding (liftCatch, liftCallCC)
-
--- mtl
--------------------------
-import Control.Monad.Error.Class as Exports hiding (Error)
-
--- bytestring
--------------------------
-import Data.ByteString as Exports (ByteString)
-
--- text
--------------------------
-import Data.Text as Exports (Text)
-
--- unordered-containers
--------------------------
-import Data.HashMap.Strict as Exports (HashMap)
-
--- vector
--------------------------
-import Data.Vector as Exports (Vector)
-
--- scientific
--------------------------
-import Data.Scientific as Exports (Scientific)
-
--- hashable
--------------------------
-import Data.Hashable as Exports (Hashable)
-
-
-showText :: Show a => a -> Text
-showText = fromString . show
diff --git a/library/Aeson/ValueParser/Vector.hs b/library/Aeson/ValueParser/Vector.hs
deleted file mode 100644
--- a/library/Aeson/ValueParser/Vector.hs
+++ /dev/null
@@ -1,11 +0,0 @@
-module Aeson.ValueParser.Vector
-where
-
-import Aeson.ValueParser.Prelude hiding (Vector)
-import Data.Vector.Generic
-import qualified Data.Vector.Fusion.Bundle.Monadic as BundleM
-
-
-{-# INLINE ifoldrM #-}
-ifoldrM :: (Vector v a, Monad m) => (Int -> a -> b -> m b) -> b -> v a -> m b
-ifoldrM f z = BundleM.foldrM (uncurry f) z . BundleM.indexed . BundleM.fromVector
diff --git a/library/AesonValueParser.hs b/library/AesonValueParser.hs
new file mode 100644
--- /dev/null
+++ b/library/AesonValueParser.hs
@@ -0,0 +1,319 @@
+{-
+Parser DSL for the \"aeson\" model of JSON tree.
+
+The general model of this DSL is about switching between contexts.
+-}
+module AesonValueParser
+(
+  Value,
+  run,
+  runWithTextError,
+  Error.Error(..),
+  -- * Value parsers
+  object,
+  array,
+  null,
+  nullable,
+  nullableMonoid,
+  string,
+  number,
+  bool,
+  fromJSON,
+  -- * String parsers
+  String,
+  text,
+  matchedText,
+  attoparsedText,
+  megaparsedText,
+  -- * Number parsers
+  Number,
+  scientific,
+  integer,
+  floating,
+  matchedScientific,
+  matchedInteger,
+  matchedFloating,
+  -- * Object parsers
+  Object,
+  field,
+  oneOfFields,
+  fieldMap,
+  foldlFields,
+  -- * Array parsers
+  Array,
+  element,
+  elementVector,
+  foldlElements,
+  foldrElements,
+)
+where
+
+import AesonValueParser.Prelude hiding (bool, null, String)
+import qualified AesonValueParser.Error as Error
+import qualified Data.Aeson as Aeson
+import qualified Data.Attoparsec.Text as Attoparsec
+import qualified Text.Megaparsec as Megaparsec
+import qualified Data.HashMap.Strict as HashMap
+import qualified Data.HashSet as HashSet
+import qualified Data.Scientific as Scientific
+import qualified Data.Text.Encoding as Text
+import qualified Data.Vector as Vector
+import qualified AesonValueParser.Vector as Vector
+
+
+-- * Value
+-------------------------
+
+{-|
+JSON `Aeson.Value` AST parser.
+
+Its `Alternative` instance implements the logic of choosing between the possible types of JSON values.
+-}
+newtype Value a =
+  Value (ReaderT Aeson.Value (MaybeT (Either Error.Error)) a)
+  deriving (Functor, Applicative)
+
+{-|
+Implements the logic of choosing between the possible types of JSON values.
+
+If you have multiple parsers of the same type of JSON value composed,
+only the leftmost will be affective.
+The errors from deeper parsers do not trigger the alternation,
+instead they get propagated to the top.
+-}
+instance Alternative Value where
+  empty = Value $ ReaderT $ const $ MaybeT $ return Nothing
+  (<|>) (Value leftParser) (Value rightParser) = Value (leftParser <|> rightParser)
+
+{-# INLINE run #-}
+run :: Value a -> Aeson.Value -> Either Error.Error a
+run = \ (Value parser) value -> (=<<) (maybe (Left (typeError value)) Right) $ runMaybeT $ runReaderT parser value where
+  typeError = \ case
+    Aeson.Array _ -> "Unexpected type: array"
+    Aeson.Object _ -> "Unexpected type: object"
+    Aeson.String _ -> "Unexpected type: string"
+    Aeson.Number _ -> "Unexpected type: number"
+    Aeson.Bool _ -> "Unexpected type: bool"
+    Aeson.Null -> "Unexpected type: null"
+
+{-# INLINE runWithTextError #-}
+runWithTextError :: Value a -> Aeson.Value -> Either Text a
+runWithTextError parser = left Error.toText . run parser
+
+runString :: String a -> Text -> Either (Maybe Text) a
+runString (String a) b = runExcept (runReaderT a b)
+
+-- ** Definitions
+-------------------------
+
+{-# INLINE array #-}
+array :: Array a -> Value a
+array (Array parser) = Value $ ReaderT $ \ case
+  Aeson.Array x -> lift $ join $ runExcept $ runExceptT $ runReaderT parser x
+  _ -> empty
+
+{-# INLINE object #-}
+object :: Object a -> Value a
+object (Object parser) = Value $ ReaderT $ \ case
+  Aeson.Object x -> lift $ join $ runExcept $ runExceptT $ runReaderT parser x
+  _ -> empty
+
+{-# INLINE null #-}
+null :: Value ()
+null = Value $ ReaderT $ \ case
+  Aeson.Null -> pure ()
+  _ -> empty
+
+{-# INLINE nullable #-}
+nullable :: Value a -> Value (Maybe a)
+nullable (Value parser) = Value $ ReaderT $ \ case
+  Aeson.Null -> pure Nothing
+  x -> fmap Just (runReaderT parser x)
+
+{-# INLINE nullableMonoid #-}
+nullableMonoid :: Monoid a => Value a -> Value a
+nullableMonoid (Value parser) = Value $ ReaderT $ \ case
+  Aeson.Null -> pure mempty
+  x -> runReaderT parser x
+
+{-# INLINE string #-}
+string :: String a -> Value a
+string (String parser) = Value $ ReaderT $ \ case
+  Aeson.String x -> lift $ left (Error.message . fromMaybe "No details") $ runExcept $ runReaderT parser x
+  _ -> empty
+
+{-# INLINE number #-}
+number :: Number a -> Value a
+number (Number parser) = Value $ ReaderT $ \ case
+  Aeson.Number x -> lift $ left (Error.message . fromMaybe "No details") $ runExcept $ runReaderT parser x
+  _ -> empty
+
+{-# INLINE bool #-}
+bool :: Value Bool
+bool = Value $ ReaderT $ \ case
+  Aeson.Bool x -> return x
+  _ -> empty
+
+{-# INLINE fromJSON #-}
+fromJSON :: Aeson.FromJSON a => Value a
+fromJSON = Value $ ReaderT $ Aeson.fromJSON >>> \ case
+  Aeson.Success r -> return r
+  Aeson.Error m -> lift $ Left $ fromString m
+
+
+-- * String parsers
+-------------------------
+
+newtype String a =
+  String (ReaderT Text (Except (Maybe Text)) a)
+  deriving (Functor, Applicative, Alternative)
+
+{-# INLINE text #-}
+text :: String Text
+text = String ask
+
+{-# INLINE matchedText #-}
+matchedText :: (Text -> Either Text a) -> String a
+matchedText parser = String $ ReaderT $ except . left Just . parser
+
+{-# INLINE attoparsedText #-}
+attoparsedText :: Attoparsec.Parser a -> String a
+attoparsedText parser = matchedText $ left fromString . Attoparsec.parseOnly parser
+
+{-# INLINE megaparsedText #-}
+megaparsedText :: Megaparsec.Parsec Void Text a -> String a
+megaparsedText = matchedText . matcher where
+  matcher :: Megaparsec.Parsec Void Text a -> Text -> Either Text a
+  matcher p = left (fromString . Megaparsec.errorBundlePretty) . Megaparsec.runParser (p <* Megaparsec.eof) ""
+
+
+-- * Number parsers
+-------------------------
+
+newtype Number a =
+  Number (ReaderT Scientific (Except (Maybe Text)) a)
+  deriving (Functor, Applicative, Alternative)
+
+{-# INLINE scientific #-}
+scientific :: Number Scientific
+scientific = Number ask
+
+{-# INLINE integer #-}
+integer :: (Integral a, Bounded a) => Number a
+integer = Number $ ReaderT $ \ x -> if Scientific.isInteger x
+  then case Scientific.toBoundedInteger x of
+    Just int -> return int
+    Nothing -> throwError (Just (fromString ("Number " <> show x <> " is out of integer range")))
+  else throwError (Just (fromString ("Number " <> show x <> " is not integer")))
+
+{-# INLINE floating #-}
+floating :: RealFloat a => Number a
+floating = Number $ ReaderT $ \ a -> case Scientific.toBoundedRealFloat a of
+  Right b -> return b
+  Left c -> if c == 0
+    then throwError (Just (fromString ("Number " <> show a <> " is too small")))
+    else throwError (Just (fromString ("Number " <> show a <> " is too large")))
+
+{-# INLINE matchedScientific #-}
+matchedScientific :: (Scientific -> Either Text a) -> Number a
+matchedScientific matcher = Number $ ReaderT $ except . left Just . matcher
+
+{-# INLINE matchedInteger #-}
+matchedInteger :: (Integral integer, Bounded integer) => (integer -> Either Text a) -> Number a
+matchedInteger matcher = Number $ case integer of
+  Number parser -> parser >>= either (throwError . Just) return . matcher
+
+{-# INLINE matchedFloating #-}
+matchedFloating :: RealFloat floating => (floating -> Either Text a) -> Number a
+matchedFloating matcher = Number $ case floating of
+  Number parser -> parser >>= either (throwError . Just) return . matcher
+
+
+-- * Object parsers
+-------------------------
+
+{-|
+JSON `Aeson.Object` parser.
+-}
+newtype Object a =
+  Object (ReaderT (HashMap Text Aeson.Value) (ExceptT Error.Error (Except Error.Error)) a)
+  deriving (Functor, Applicative, Alternative, Monad, MonadPlus, MonadError Error.Error)
+
+instance MonadFail Object where
+  fail = throwError . fromString
+
+{-# INLINE field #-}
+field :: Text -> Value a -> Object a
+field name fieldParser = Object $ ReaderT $ \ object -> case HashMap.lookup name object of
+  Just value -> case run fieldParser value of
+    Right parsedValue -> return parsedValue
+    Left error -> lift $ throwE $ Error.named name error
+  Nothing -> throwE (Error.Error (pure name) "Object contains no field with this name")
+
+{-# INLINE oneOfFields #-}
+oneOfFields :: [Text] -> Value a -> Object a
+oneOfFields keys valueParser = asum (fmap (flip field valueParser) keys)
+
+{-# INLINE fieldMap #-}
+fieldMap :: (Eq a, Hashable a) => String a -> Value b -> Object (HashMap a b)
+fieldMap keyParser fieldParser = Object $ ReaderT $ fmap HashMap.fromList . traverse mapping . HashMap.toList where
+  mapping (keyText, ast) = 
+    case runString keyParser keyText of
+      Right parsedKey -> case run fieldParser ast of
+        Right parsedField -> return (parsedKey, parsedField)
+        Left error -> lift (throwE (Error.named keyText error))
+      Left error -> lift (throwE (maybe mempty Error.message error))
+
+{-# INLINE foldlFields #-}
+foldlFields :: (state -> key -> field -> state) -> state -> String key -> Value field -> Object state
+foldlFields step state keyParser fieldParser = Object $ ReaderT $ \ object -> HashMap.foldlWithKey' newStep (pure state) object where
+  newStep stateE key fieldAst = 
+    case runString keyParser key of
+      Right !parsedKey -> case run fieldParser fieldAst of
+        Right !parsedField -> do
+          !state <- stateE
+          return $ step state parsedKey parsedField
+        Left error -> lift (throwE (Error.named key error))
+      Left error -> lift (throwE (maybe mempty Error.message error))
+
+
+-- * Array parsers
+-------------------------
+
+{-|
+JSON `Aeson.Array` parser.
+-}
+newtype Array a =
+  Array (ReaderT (Vector Aeson.Value) (ExceptT Error.Error (Except Error.Error)) a)
+  deriving (Functor, Applicative, Alternative, Monad, MonadPlus, MonadError Error.Error)
+
+instance MonadFail Array where
+  fail = throwError . fromString
+
+{-# INLINE element #-}
+element :: Int -> Value a -> Array a
+element index elementParser = Array $ ReaderT $ \ array -> case array Vector.!? index of
+  Just element -> case run elementParser element of
+    Right result -> return result
+    Left error -> lift $ throwE $ Error.indexed index error
+  Nothing -> throwE $ Error.Error (pure (fromString (show index))) "Array contains no element by this index"
+
+{-# INLINE elementVector #-}
+elementVector :: Value a -> Array (Vector a)
+elementVector elementParser = Array $ ReaderT $ \ arrayAst -> flip Vector.imapM arrayAst $ \ index ast -> case run elementParser ast of
+  Right element -> return element
+  Left error -> lift $ throwE $ Error.indexed index error
+
+{-# INLINE foldlElements #-}
+foldlElements :: (state -> Int -> element -> state) -> state -> Value element -> Array state
+foldlElements step state elementParser = Array $ ReaderT $ Vector.ifoldM' newStep state where
+  newStep state index ast = case run elementParser ast of
+    Right element -> return $ step state index element
+    Left error -> lift $ throwE $ Error.indexed index error
+
+{-# INLINE foldrElements #-}
+foldrElements :: (Int -> element -> state -> state) -> state -> Value element -> Array state
+foldrElements step state elementParser = Array $ ReaderT $ Vector.ifoldrM newStep state where
+  newStep index ast nextState = case run elementParser ast of
+    Right element -> return $ step index element nextState
+    Left error -> lift $ throwE $ Error.indexed index error
diff --git a/library/AesonValueParser/Error.hs b/library/AesonValueParser/Error.hs
new file mode 100644
--- /dev/null
+++ b/library/AesonValueParser/Error.hs
@@ -0,0 +1,43 @@
+module AesonValueParser.Error
+where
+
+import AesonValueParser.Prelude
+import qualified Data.Text as Text
+import qualified Text.Builder as TextBuilder
+
+
+data Error = Error [Text] {-^ Path -} Text {-^ Message -}
+
+instance Semigroup Error where
+  (<>) _ b = b
+
+instance Monoid Error where
+  mempty = Error [] ""
+  mappend = (<>)
+
+instance IsString Error where
+  fromString = message . fromString
+
+instance Show Error where
+  show = Text.unpack . toText
+
+{-# INLINE indexed #-}
+indexed :: Int -> Error -> Error
+indexed = named . fromString . show
+
+{-# INLINE named #-}
+named :: Text -> Error -> Error
+named name (Error path message) = Error (name : path) message
+
+{-# INLINE message #-}
+message :: Text -> Error
+message = Error []
+
+toText :: Error -> Text
+toText = TextBuilder.run . toTextBuilder
+
+toTextBuilder :: Error -> TextBuilder.Builder
+toTextBuilder (Error path message) =
+  "AST parsing error at path " <>
+  foldMap (\ x -> "/" <> TextBuilder.text x) path <> ": " <>
+  TextBuilder.text message
diff --git a/library/AesonValueParser/Prelude.hs b/library/AesonValueParser/Prelude.hs
new file mode 100644
--- /dev/null
+++ b/library/AesonValueParser/Prelude.hs
@@ -0,0 +1,115 @@
+module AesonValueParser.Prelude
+(
+  module Exports,
+  showText,
+)
+where
+
+
+-- base
+-------------------------
+import Control.Applicative as Exports
+import Control.Arrow as Exports
+import Control.Category as Exports
+import Control.Concurrent as Exports
+import Control.Exception as Exports
+import Control.Monad as Exports hiding (fail, mapM_, sequence_, forM_, msum, mapM, sequence, forM)
+import Control.Monad.IO.Class as Exports
+import Control.Monad.Fail as Exports
+import Control.Monad.Fix as Exports hiding (fix)
+import Control.Monad.ST as Exports
+import Data.Bits as Exports
+import Data.Bool as Exports
+import Data.Char as Exports
+import Data.Coerce as Exports
+import Data.Complex as Exports
+import Data.Data as Exports
+import Data.Dynamic as Exports
+import Data.Either as Exports
+import Data.Fixed as Exports
+import Data.Foldable as Exports hiding (toList)
+import Data.Function as Exports hiding (id, (.))
+import Data.Functor as Exports
+import Data.Functor.Identity as Exports
+import Data.Int as Exports
+import Data.IORef as Exports
+import Data.Ix as Exports
+import Data.List as Exports hiding (sortOn, isSubsequenceOf, uncons, concat, foldr, foldl1, maximum, minimum, product, sum, all, and, any, concatMap, elem, foldl, foldr1, notElem, or, find, maximumBy, minimumBy, mapAccumL, mapAccumR, foldl')
+import Data.List.NonEmpty as Exports (NonEmpty(..))
+import Data.Maybe as Exports
+import Data.Monoid as Exports hiding (Last(..), First(..), (<>))
+import Data.Ord as Exports
+import Data.Proxy as Exports
+import Data.Ratio as Exports
+import Data.Semigroup as Exports
+import Data.STRef as Exports
+import Data.String as Exports
+import Data.Traversable as Exports
+import Data.Tuple as Exports
+import Data.Unique as Exports
+import Data.Version as Exports
+import Data.Void as Exports
+import Data.Word as Exports
+import Debug.Trace as Exports
+import Foreign.ForeignPtr as Exports
+import Foreign.Ptr as Exports
+import Foreign.StablePtr as Exports
+import Foreign.Storable as Exports hiding (sizeOf, alignment)
+import GHC.Conc as Exports hiding (withMVar, threadWaitWriteSTM, threadWaitWrite, threadWaitReadSTM, threadWaitRead)
+import GHC.Exts as Exports (lazy, inline, sortWith, groupWith, IsList(..))
+import GHC.Generics as Exports (Generic)
+import GHC.IO.Exception as Exports
+import Numeric as Exports
+import Prelude as Exports hiding (fail, concat, foldr, mapM_, sequence_, foldl1, maximum, minimum, product, sum, all, and, any, concatMap, elem, foldl, foldr1, notElem, or, mapM, sequence, id, (.))
+import System.Environment as Exports
+import System.Exit as Exports
+import System.IO as Exports
+import System.IO.Error as Exports
+import System.IO.Unsafe as Exports
+import System.Mem as Exports
+import System.Mem.StableName as Exports
+import System.Timeout as Exports
+import Text.ParserCombinators.ReadP as Exports (ReadP, ReadS, readP_to_S, readS_to_P)
+import Text.ParserCombinators.ReadPrec as Exports (ReadPrec, readPrec_to_P, readP_to_Prec, readPrec_to_S, readS_to_Prec)
+import Text.Printf as Exports (printf, hPrintf)
+import Text.Read as Exports (Read(..), readMaybe, readEither)
+import Unsafe.Coerce as Exports
+
+-- transformers
+-------------------------
+import Control.Monad.Trans.Class as Exports
+import Control.Monad.Trans.Except as Exports hiding (liftCatch, liftCallCC)
+import Control.Monad.Trans.Maybe as Exports hiding (liftCatch, liftCallCC, liftListen, liftPass)
+import Control.Monad.Trans.Reader as Exports hiding (liftCatch, liftCallCC)
+
+-- mtl
+-------------------------
+import Control.Monad.Error.Class as Exports hiding (Error)
+
+-- bytestring
+-------------------------
+import Data.ByteString as Exports (ByteString)
+
+-- text
+-------------------------
+import Data.Text as Exports (Text)
+
+-- unordered-containers
+-------------------------
+import Data.HashMap.Strict as Exports (HashMap)
+
+-- vector
+-------------------------
+import Data.Vector as Exports (Vector)
+
+-- scientific
+-------------------------
+import Data.Scientific as Exports (Scientific)
+
+-- hashable
+-------------------------
+import Data.Hashable as Exports (Hashable)
+
+
+showText :: Show a => a -> Text
+showText = fromString . show
diff --git a/library/AesonValueParser/Vector.hs b/library/AesonValueParser/Vector.hs
new file mode 100644
--- /dev/null
+++ b/library/AesonValueParser/Vector.hs
@@ -0,0 +1,11 @@
+module AesonValueParser.Vector
+where
+
+import AesonValueParser.Prelude hiding (Vector)
+import Data.Vector.Generic
+import qualified Data.Vector.Fusion.Bundle.Monadic as BundleM
+
+
+{-# INLINE ifoldrM #-}
+ifoldrM :: (Vector v a, Monad m) => (Int -> a -> b -> m b) -> b -> v a -> m b
+ifoldrM f z = BundleM.foldrM (uncurry f) z . BundleM.indexed . BundleM.fromVector