{-# OPTIONS_GHC -cpp -fglasgow-exts #-}
import System.IO
import Control.Concurrent.Locking

main = do lh <- openBinaryFile "test" ReadMode >>= addLocking
          str <- readStringAt lh 0
          print str


readStringAt lh pos =
    lock lh $ \h -> do
        saved_pos <- hTell h
        hSeek h AbsoluteSeek pos
        str <- hGetLine h
        hSeek h AbsoluteSeek saved_pos
        return str