Hi André, The problem is that hGetContents does lazy reading of the handle. I you do: readDataFromFile "test.txt" >>= print the handle is closed by hClose (in readDataFromFile) before "print" demands the contents from the handle. Just don't close the Handle explicitly. This code works: readDataFromFile filename = do h <-openFile filename ReadMode contents <- hGetContents h return (lines contents) You do not really need to close it, because hGetContents "semi-closes" the handle. Read more: http://www.haskell.org/onlinereport/io.html (Section 21.2.2 Semi-Closed Handles) http://users.aber.ac.uk/afc/stricthaskell.html#semiclosed Cheers, Arthur On 12-aug-05, at 14:17, André Vargas Abs da Cruz wrote:
Hi everyone,
I think this is a totally newbie question as i am a complete novice to Haskell. I am trying to write down a few programs using GHC in order to get used with the language. I am having some problems with a piece of code (that is supposed to return a list of lines from a text file) which I transcribe below:
module Test where
import IO
readDataFromFile filename = do bracket (openFile filename ReadMode) hClose (\h -> do contents <- hGetContents h return (lines contents))
The question is: if i try to run this, it returns me nothing (just an empty list). Why does this happen ? When i remove the "return" and put a "print" instead, it prints everything as i expected.
Thanks in advance André _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe