1.hs

data ExceptionInfo = ExceptionIf ThreadId SomeException -- constructor should be hidden

throwToEnclosed :: Exception e => ThreadId -> e -> IO () 
throwToEnclosed to ex = 
  throwTo =<< ExceptionInfo <$> myThreadId <*> pure (SomeException ex)

enclosed :: [ThreadId] -> IO a -> IO a
enclosed allowed f = mask $ \release -> do
  result <- newEmptyMVar
  internal <- forkIO $ release $ try f >>= result -- HA HA HA I'm hidden
  er <- fix $ \loop -> takeMVar result
     handles [ Handle $ (ExceptionInfo tid ex) -> do
        if tid `elem` allowed
          then throwTo internal ex >> loop
          else putStrLn "MUAHAHAHAHAHAHHA" >> loop
              , SomeException e -> putStrLn "I'm protected by GODS!" >> loop
              ]
  either throw return er