Clean unneeded stuff separating the monadic type constraint from the actual monad stack used, one more step towrds MonadFail -> MonadError

examples/getObj.hs

@@ -1,6 +1,8 @@
 {-# LANGUAGE NamedFieldPuns #-}
 {-# LANGUAGE FlexibleContexts #-}
+{-# LANGUAGE GeneralizedNewtypeDeriving #-}
 
+import Control.Monad.Fail (MonadFail(..))
 import Control.Monad.Reader (ReaderT, runReaderT)
 import Data.ByteString.Lazy.Char8 (ByteString)
 import qualified Data.ByteString.Char8 as BS (readFile)
@@ -10,15 +12,22 @@ import PDF.Box (Box(..))
 import PDF.Layer (Layer(..), unify)
 import PDF.Object (Object(..))
 import PDF.Object.Navigation (
-    Clear(..), Error(..), Raw(..), (//), objectById, origin
+    Clear(..), Raw(..), (//), objectById, origin
   )
 import PDF.Output (ObjectId(..), Output)
 import qualified PDF.Output as Output (render)
+import Prelude hiding (fail)
 import System.Environment (getArgs, getProgName)
 import System.Exit (die)
 import Text.Printf (printf)
 import Text.Read (readMaybe)
 
+newtype Error a = Error {
+    runError :: Either String a
+  } deriving (Functor, Applicative, Monad)
+instance MonadFail Error where
+  fail = Error . Left
+
 decodedStream :: Object -> Object
 decodedStream object =
   maybe object id $ r Clear object >>= flip (w Raw) object

src/PDF/Object/Navigation.hs

@@ -1,13 +1,11 @@
 {-# LANGUAGE NamedFieldPuns #-}
 {-# LANGUAGE ConstraintKinds #-}
 {-# LANGUAGE FlexibleContexts #-}
-{-# LANGUAGE GeneralizedNewtypeDeriving #-}
 {-# LANGUAGE MultiParamTypeClasses #-}
 {-# LANGUAGE FlexibleInstances #-}
 module PDF.Object.Navigation (
-      Error(..)
+      Clear(..)
     , PDFContent
-    , Clear(..)
     , Raw(..)
     , (./)
     , (//)
@@ -21,8 +19,6 @@ module PDF.Object.Navigation (
   ) where
 
 import Codec.Compression.Zlib (compress, decompress)
-import Control.Applicative (Alternative(..))
-import Control.Monad (MonadPlus(..))
 import Control.Monad.Reader (MonadReader(..))
 import Control.Monad.Fail (MonadFail(..))
 import Data.ByteString (ByteString)
@@ -39,12 +35,7 @@ import PDF.Output (ObjectId)
 import Prelude hiding (fail)
 import Text.Printf (printf)
 
-type PDFContent m = (Alternative m, MonadReader Layer m, MonadFail m)
-newtype Error a = Error {
-    runError :: Either String a
-  } deriving (Alternative, Functor, Applicative, Monad, MonadPlus)
-instance MonadFail Error where
-  fail = Error . Left
+type PDFContent m = (MonadReader Layer m, MonadFail m)
 type Component = String
 
 getDictionary :: PDFContent m => Object -> m Dictionary