better error printout

src/Gidl.hs

@@ -126,7 +126,8 @@ run = do
   opts <- parseOpts args
   idl <- readFile (idlpath opts)
   case parseDecls idl of
-    Left e -> putStrLn e >> exitFailure
+    Left e -> putStrLn ("Error parsing " ++ (idlpath opts) ++ ": " ++ e)
+              >> exitFailure
     Right (te, ie) -> do
       when (debug opts) $ do
         putStrLn (ppShow te)