File: openFile007.hs

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-- !!! check that we don't truncate files if the open fails

import Control.Monad
import System.IO
import System.IO.Error

tmp = "openFile007.out"

main = do
  h <- openFile tmp WriteMode
  hPutStrLn h "hello, world"

  -- second open in write mode better fail, but better not truncate the file
  tryIOError (openFile tmp WriteMode) >>= print
  
  hClose h
  s <- readFile tmp -- make sure our "hello, world" is still there
  putStr s