Strict implementation of `tee`

Tee.hs

module Tee where

import Control.Concurrent (forkIO)
import Control.Exception (handle, throw)
import Control.Monad (forever, void)
import System.IO (Handle, hGetChar, hPutChar)
import System.IO.Error (isEOFError)

-- This implementation is actually worse than the lazy one! The lazy
-- implementation would lock up if all of the output handles became full;
-- this one locks up if *any* of the output handles become full.
tee :: Handle -> [Handle] -> IO () -> IO ()
tee inH outHs finalAct =
    void $ forkIO $ handleEOF $ forever $ do
        c <- hGetChar inH
        mapM_ (flip hPutChar c) outHs
  where
    handleEOF = handle $ \e -> if isEOFError e then finalAct else throw e