Re: [Haskell-cafe] Strange behaviour with writeFile
Its about the lazyness of reading the file. The handles on the file associated (underlying readFile) is still open - hence the resource being in use. When you add that extra line the act of writing out the remainer causes the rest of the input to be fully evaluated and hence the filehandle is closed. If you wish to overwrite the existing file you have to assure that the file is not open for reading - just like with any file interface. Neil On 04/02/07, C.M.Brown [EMAIL PROTECTED] wrote: Hi, I am observing some rather strange behaviour with writeFile. Say I have the following code: answer - AbstractIO.readFile filename let (answer2, remainder) = parseAnswer answer if remainder == answer2 == then do AbstractIO.putStrLn $ completed else do AbstractIO.putStrLn answer2 AbstractIO.writeFile filename remainder With the above I get an error saying the resources to filename are locked. If I add the line AbstractIO.putStrLn $ show (answer2, remainder) before I call writeFile it suddenly magically works! Has anyone seen strange behaviour like this before? Regards, Chris. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Strange behaviour with writeFile
Hi Neil, When you add that extra line the act of writing out the remainer causes the rest of the input to be fully evaluated and hence the filehandle is closed. Ah, yes of course :) I've found that: let (answer2, remainder) = parseAnswer (force answer) where force :: Eq a = a - a force x = if x==x then x else x Seems to do the trick. Thanks! Chris. On 04/02/07, C.M.Brown [EMAIL PROTECTED] wrote: Hi, I am observing some rather strange behaviour with writeFile. Say I have the following code: answer - AbstractIO.readFile filename let (answer2, remainder) = parseAnswer answer if remainder == answer2 == then do AbstractIO.putStrLn $ completed else do AbstractIO.putStrLn answer2 AbstractIO.writeFile filename remainder With the above I get an error saying the resources to filename are locked. If I add the line AbstractIO.putStrLn $ show (answer2, remainder) before I call writeFile it suddenly magically works! Has anyone seen strange behaviour like this before? Regards, Chris. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Strange behaviour with writeFile
cmb21: fo/haskell-cafe, mailto:[EMAIL PROTECTED] Errors-To: [EMAIL PROTECTED] Status: O Content-Length: 778 Lines: 27 Hi, I am observing some rather strange behaviour with writeFile. Say I have the following code: answer - AbstractIO.readFile filename let (answer2, remainder) = parseAnswer answer if remainder == answer2 == then do AbstractIO.putStrLn $ completed else do AbstractIO.putStrLn answer2 AbstractIO.writeFile filename remainder With the above I get an error saying the resources to filename are locked. If I add the line AbstractIO.putStrLn $ show (answer2, remainder) before I call writeFile it suddenly magically works! lazy IO at play. One quick fix would be to use strict IO: import qualified Data.ByteString.Char8 as S import Data.ByteString (ByteString) main = do ans - S.readFile t -- strict file IO print (S.length ans)-- current size let (x,xs) = S.splitAt 10 ans -- parse S.writeFile t xs ans' - S.readFile t print (S.length ans')-- new size $ time ./a.out 2487212 2487202 This comes up often enough that I think we should have a strict readFile for Strings -- Don ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
