diff --git a/examples/getObj.hs b/examples/getObj.hs
index a758179..778d989 100644
--- a/examples/getObj.hs
+++ b/examples/getObj.hs
@@ -4,16 +4,17 @@ import Codec.Compression.Zlib (decompress)
 import Data.ByteString.Lazy.Char8 (ByteString)
 import qualified Data.ByteString.Char8 as BS (readFile)
 import qualified Data.ByteString.Lazy.Char8 as Lazy (fromStrict, putStr, toStrict)
-import Data.Map ((!))
-import qualified Data.Map as Map (lookup)
+import Data.Map ((!?))
+import qualified Data.Map as Map (keys, lookup)
 import PDF (Document(..), parseDocument)
 import qualified PDF.EOL as EOL (Style)
 import PDF.Object (Content(..), DirectObject(..), Object(..), Name(..))
 import PDF.Output (ObjectId(..))
 import qualified PDF.Output as Output (render)
 import PDF.Update (unify)
-import System.Environment (getArgs)
-import System.IO (hPutStrLn, stderr)
+import System.Environment (getArgs, getProgName)
+import System.Exit (die)
+import Text.Printf (printf)
 
 display :: EOL.Style -> Object -> ByteString
 display eolStyle d@(Direct _) = Output.render eolStyle d
@@ -25,16 +26,28 @@ display eolStyle s@(Stream {header, streamContent}) = Output.render eolStyle $
       }
     _ -> s
 
-extractObject :: ObjectId -> Document -> ByteString
+extractObject :: ObjectId -> Document -> Either String ByteString
 extractObject objectId (Document {eolStyle, updates}) =
-  display eolStyle . (!objectId) $ objects  content
+  case objects content !? objectId of
+    Nothing -> Left $ "No object has ID " ++ show (getObjectId objectId)
+    Just o -> Right $ display eolStyle o
   where
     content = unify updates
 
+listObjectIds :: Document -> Either String [String]
+listObjectIds =
+  Right . prependTitle . toString . Map.keys . objects . unify . updates
+  where
+    toString = fmap (show . getObjectId)
+    prependTitle = ("ObjectIds defined in this PDF:":)
+
 main :: IO ()
 main = do
-  [inputFile, objectId] <- getArgs
-  result <- parseDocument <$> BS.readFile inputFile
-  case result of
-    Left parseError -> hPutStrLn stderr parseError
-    Right doc -> Lazy.putStr $ extractObject (ObjectId (read objectId)) doc
+  (inputFile, getData) <- parse =<< getArgs
+  input <- BS.readFile inputFile
+  either die id $ (parseDocument input >>= getData)
+  where
+    parse [inputFile] = return (inputFile, fmap (mapM_ putStrLn) . listObjectIds)
+    parse [inputFile, objectId] = return
+      (inputFile, fmap Lazy.putStr . extractObject (ObjectId (read objectId)))
+    parse _ = die . printf "Syntax: %s inputFile [OBJECT_ID]\n" =<< getProgName
diff --git a/src/PDF/Object.hs b/src/PDF/Object.hs
index 4510686..f4d077b 100644
--- a/src/PDF/Object.hs
+++ b/src/PDF/Object.hs
@@ -220,16 +220,18 @@ instance Output DirectObject where
     Output.string (printf "%d %d R" (getObjectId objectId) versionNumber)
 
 directObject :: MonadParser m => m DirectObject
-directObject =
-    Boolean <$> boolean
-  <|> Reference <$> reference {- defined before Number because Number is a prefix of it -}
-  <|> NumberObject <$> number
-  <|> StringObject <$> stringObject
-  <|> NameObject <$> name
-  <|> Array <$> array
-  <|> Dictionary <$> dictionary
-  <|> const Null <$> nullObject
-  <?> "direct object"
+directObject = (peek >>= dispatch) <?> "direct object"
+  where
+    dispatch 't' = Boolean <$> boolean
+    dispatch 'f' = Boolean <$> boolean
+    dispatch '(' = StringObject <$> stringObject
+    dispatch '<' = StringObject <$> stringObject <|> Dictionary <$> dictionary
+    dispatch '/' = NameObject <$> name
+    dispatch '[' = Array <$> array
+    dispatch 'n' = nullObject *> return Null
+    dispatch _ =
+        Reference <$> reference {- defined before Number because Number is a prefix of it -}
+      <|> NumberObject <$> number
 
 --
 -- Object
diff --git a/src/PDF/Parser.hs b/src/PDF/Parser.hs
index 8dc0fc0..34a0432 100644
--- a/src/PDF/Parser.hs
+++ b/src/PDF/Parser.hs
@@ -17,8 +17,8 @@ import Control.Monad.Fail (MonadFail(..))
 import Control.Monad.State (StateT(..), evalStateT)
 import Control.Monad.Trans (MonadTrans(..))
 import qualified Data.Attoparsec.ByteString.Char8 as Atto (
-      Parser, char, endOfInput, parseOnly, satisfy, string, take, takeWhile
-    , takeWhile1
+      Parser, char, endOfInput, parseOnly, peekChar', satisfy, string, take
+    , takeWhile, takeWhile1
   )
 import Data.ByteString (ByteString)
 import Data.ByteString.Char8.Util (B16Int(..))
@@ -36,6 +36,7 @@ class MonadDeps m => MonadParser m where
   endOfInput :: m ()
   hexNumber :: m B16Int
   oneOf :: String -> m Char
+  peek :: m Char
   string :: ByteString -> m ByteString
   takeAll :: (Char -> Bool) -> m ByteString
   takeAll1 :: (Char -> Bool) -> m ByteString
@@ -47,6 +48,7 @@ instance MonadParser Atto.Parser where
   decNumber = Atto.takeWhile1 (`Set.member` digits)
   hexNumber = B16Int <$> Atto.takeWhile1 (`Set.member` hexDigits)
   oneOf charSet = Atto.satisfy (`elem` charSet)
+  peek = Atto.peekChar'
   string s = Atto.string s <?> show s
   takeAll = Atto.takeWhile
   takeAll1 = Atto.takeWhile1
@@ -58,6 +60,7 @@ instance (MonadParser m, MonadTrans t, MonadDeps (t m)) => MonadParser (t m) whe
   decNumber = lift $ decNumber
   hexNumber = lift $ hexNumber
   oneOf = lift . oneOf
+  peek = lift $ peek
   string = lift . string
   takeAll = lift . takeAll
   takeAll1 = lift . takeAll1