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You can reach the person managing the list at beginners-ow...@haskell.org When replying, please edit your Subject line so it is more specific than "Re: Contents of Beginners digest..." Today's Topics: 1. gcd (Steve) 2. Re: parallel program in haskell in 5 steps (Sean Bartell) 3. How to wait till a process is finished before invoking the next one? (Thomas Friedrich) 4. Re: How to wait till a process is finished before invoking the next one? (Daniel Fischer) 5. Re: How to wait till a process is finished before invoking the next one? (Thomas Friedrich) 6. Real World Haskell Chapter 5 (PJ Fitzpatrick) 7. Re: How to wait till a process is finished before invoking the next one? (Daniel Fischer) 8. Re: Real World Haskell Chapter 5 (Daniel Fischer) 9. Re: How to wait till a process is finished before invoking the next one? (Brandon S. Allbery KF8NH) ---------------------------------------------------------------------- Message: 1 Date: Fri, 01 May 2009 21:30:35 +0800 From: Steve <stevech1...@yahoo.com.au> Subject: [Haskell-beginners] gcd To: beginners@haskell.org Message-ID: <1241184635.4876.18.ca...@host.localdomain> Content-Type: text/plain I had a look at the gcd definition in GHC 6.10.1 ghc-6.10.1/libraries/base/GHC/Real.lhs -- | @'gcd' x y@ is the greatest (positive) integer that divides both @x@ -- and @y@; for example @'gcd' (-3) 6@ = @3@, @'gcd' (-3) (-6)@ = @3@, -- @'gcd' 0 4@ = @4...@. @'gcd' 0 0@ raises a runtime error. gcd :: (Integral a) => a -> a -> a gcd 0 0 = error "Prelude.gcd: gcd 0 0 is undefined" gcd x y = gcd' (abs x) (abs y) where gcd' a 0 = a gcd' a b = gcd' b (a `rem` b) Why is gcd 0 0 undefined? http://en.wikipedia.org/wiki/Greatest_common_divisor says: "It is useful to define gcd(0, 0) = 0 and lcm(0, 0) = 0 because then the natural numbers become a complete distributive lattice with gcd as meet and lcm as join operation. This extension of the definition is also compatible with the generalization for commutative rings given below." An added advantage, for haskell, of defining gcd 0 0 = 0 is that gcd would change from being a partial function to a total function. Regards, Steve ------------------------------ Message: 2 Date: Wed, 6 May 2009 23:25:43 -0400 From: Sean Bartell <wingedtachik...@gmail.com> Subject: Re: [Haskell-beginners] parallel program in haskell in 5 steps To: Jack Kennedy <j...@realmode.com> Cc: beginners@haskell.org Message-ID: <dd3762960905062025j33c302q7eeb9107ffc52...@mail.gmail.com> Content-Type: text/plain; charset="utf-8" > > Does this happen for everyone, or just me? I get the same result here. Changing a to fib 100 lets me get 65-75%. The compiler's probably just being smarter than you expect and combining both instances of ack 4 10. -------------- next part -------------- An HTML attachment was scrubbed... URL: http://www.haskell.org/pipermail/beginners/attachments/20090506/7b6f0769/attachment-0001.htm ------------------------------ Message: 3 Date: Thu, 07 May 2009 12:36:08 -0400 From: Thomas Friedrich <i...@suud.de> Subject: [Haskell-beginners] How to wait till a process is finished before invoking the next one? To: beginners@haskell.org Message-ID: <4a030df8.3040...@suud.de> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Hi everyone, I have the following problem, and I hope that someone of yours might be able to help me. The Haskell program I am writing has the following setup: writeData :: [String] -> IO () writeData cs = ... runProgram:: [String] -> IO () runProgram cs = ... writeFeatures :: [String] -> IO () writeFeatures cs = ... runTestOnFeatures :: IO () runTestOnFeatures = ... main :: IO () main = do cs <- getArgs writeData cs runProgram cs writeFeatures cs runTestOnFeatures Each of the above function take a list of filenames, run certain command-line programs on them, which I invoke by runCommand, and each of them produce multiple output-files. Each function in main needs a couple of those output-files that are produced by the function directly above it. How do I get Haskell to wait, till all the data is written to the disk, before invoking the next command. The way the program is currently written, Haskell doesn't see that the input of one function depends on the output of another, and tries to run them all at the same time. Any ideas? Thanks everyone for your help. Cheers, Thomas ------------------------------ Message: 4 Date: Thu, 7 May 2009 19:10:49 +0200 From: Daniel Fischer <daniel.is.fisc...@web.de> Subject: Re: [Haskell-beginners] How to wait till a process is finished before invoking the next one? To: beginners@haskell.org Message-ID: <200905071910.50054.daniel.is.fisc...@web.de> Content-Type: text/plain; charset="iso-8859-1" Am Donnerstag 07 Mai 2009 18:36:08 schrieb Thomas Friedrich: > Hi everyone, > > Each of the above function take a list of filenames, run certain > command-line programs on them, which I invoke by runCommand, and each of > them produce multiple output-files. Each function in main needs a > couple of those output-files that are produced by the function directly > above it. How do I get Haskell to wait, till all the data is written to > the disk, before invoking the next command. System.Process.waitForProcess should do it, conveniently runCommand returns a ProcessHandle. > The way the program is > currently written, Haskell doesn't see that the input of one function > depends on the output of another, and tries to run them all at the same > time. > > Any ideas? > > Thanks everyone for your help. > > Cheers, > Thomas ------------------------------ Message: 5 Date: Thu, 07 May 2009 14:53:11 -0400 From: Thomas Friedrich <i...@suud.de> Subject: Re: [Haskell-beginners] How to wait till a process is finished before invoking the next one? To: Daniel Fischer <daniel.is.fisc...@web.de> Cc: beginners@haskell.org Message-ID: <4a032e17.4030...@suud.de> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Hi Daniel and everyone, Thanks for the reply! I thought of using waitForProcess, and in fact an earlier version of the program did. However, as the program got more complex, I don't really see how this is still possible. For example the runProgram function looks like this: runProgram :: [String] -> IO () runProgram [] = return () runProgram (c:cs) = do runCommand ("lalala " ++ c) runProgram cs It might be possible to write the function runProgram in a way, so that it returns an expression of type [IO ProcessHandle] and then try to work from there. But I have the feeling, that this will become messy very quickly, and there must be some more elegant way of doing this. The other thing is that actually not all functions are able to return ProcessHandles, e.g. writeFeatures :: [String] -> IO () writeFeatures cs = Exc.bracket (openFile training AppendMode) hClose (\h -> goo h) where goo h = go 1 cs where go :: Int -> [String] -> IO () go n [] = putStrLn "Features written." go n (c:cs) = do features <- makeFeatures n c -- makeFeatures :: Int -> String -> IO String hPutStr h features go (n+1) cs And the file that is produced here is needed in the next function. I hoped to do something with forkIO, as I would like to parallelize the whole program at the end. Especially the function runProgram would benefit hugely from this (I so don't have a clue how to do this yet;). I tried for example the following: main :: IO () main = do cs <- getArgs p1 <- forkIO $ writeData cs p2 <- forkIO $ runProgram cs p3 <- forkIO $ writeFeatures cs p4 <- forkIO $ runTestOnFeatures seq p1 (seq p2 (seq p3 (seq p4 (putStrLn "Done")))) But that of course doesn't work, because now I am not actually requesting anything. The program does in fact nothing, apart from printing out "Done". Any ideas? Cheers, Thomas Daniel Fischer wrote: > Am Donnerstag 07 Mai 2009 18:36:08 schrieb Thomas Friedrich: > >> Hi everyone, >> >> Each of the above function take a list of filenames, run certain >> command-line programs on them, which I invoke by runCommand, and each of >> them produce multiple output-files. Each function in main needs a >> couple of those output-files that are produced by the function directly >> above it. How do I get Haskell to wait, till all the data is written to >> the disk, before invoking the next command. >> > > System.Process.waitForProcess > > should do it, conveniently runCommand returns a ProcessHandle. > > >> The way the program is >> currently written, Haskell doesn't see that the input of one function >> depends on the output of another, and tries to run them all at the same >> time. >> >> Any ideas? >> >> Thanks everyone for your help. >> >> Cheers, >> Thomas >> > > > _______________________________________________ > Beginners mailing list > Beginners@haskell.org > http://www.haskell.org/mailman/listinfo/beginners > ------------------------------ Message: 6 Date: Thu, 7 May 2009 20:18:46 +0100 From: PJ Fitzpatrick <fitzpatrick...@googlemail.com> Subject: [Haskell-beginners] Real World Haskell Chapter 5 To: Beginners@haskell.org Message-ID: <32531bb40905071218k287b23b9xb1331d5af7fb0...@mail.gmail.com> Content-Type: text/plain; charset="iso-8859-1" Hi, I have compiled the SimpleJSON.hs file from chapter 5 and from another file attempted to import it. I am getting a could not find module error and the prelude tells me that the locations searched were SimpleJSON.hs and SimpleJSON.lhs. I am running Vista, GHC 6.10.2 Any ideas? tks, PJ -------------- next part -------------- An HTML attachment was scrubbed... URL: http://www.haskell.org/pipermail/beginners/attachments/20090507/6c391add/attachment-0001.htm ------------------------------ Message: 7 Date: Thu, 7 May 2009 22:04:51 +0200 From: Daniel Fischer <daniel.is.fisc...@web.de> Subject: Re: [Haskell-beginners] How to wait till a process is finished before invoking the next one? To: beginners@haskell.org Message-ID: <200905072204.51750.daniel.is.fisc...@web.de> Content-Type: text/plain; charset="iso-8859-1" Am Donnerstag 07 Mai 2009 20:53:11 schrieb Thomas Friedrich: > Hi Daniel and everyone, > > Thanks for the reply! > > I thought of using waitForProcess, and in fact an earlier version of the > program did. However, as the program got more complex, I don't really > see how this is still possible. > > For example the runProgram function looks like this: > > runProgram :: [String] -> IO () > runProgram [] = return () > runProgram (c:cs) = do > runCommand ("lalala " ++ c) > runProgram cs You could have runCommand ("lalala " ++ c) >>= waitForProcess in the penultimate line. That would ensure that the command has finished before its results are requested, but of course destroy all possibilities of parallelism :-( Another option would be runProgram [] = return [] runProgram (c:cs) = unsafeInterleaveIO $ do ph <- runCommand ("lalala " ++ c) phs <- runProgram cs return (ph:phs) and then, processHandles <- runProgram blah mapM_ waitForProcess (processHandles) next step that should work (I hope) and would allow the commands to be run in parallel while making sure all have finished before the next step is started. > > It might be possible to write the function runProgram in a way, so that > it returns an expression of type [IO ProcessHandle] and then try to work > from there. But I have the feeling, that this will become messy very > quickly, and there must be some more elegant way of doing this. The > other thing is that actually not all functions are able to return > ProcessHandles, e.g. > > writeFeatures :: [String] -> IO () > writeFeatures cs = Exc.bracket (openFile training AppendMode) hClose (\h > -> goo h) > where > goo h = go 1 cs > where > go :: Int -> [String] -> IO () > go n [] = putStrLn "Features written." > go n (c:cs) = do > features <- makeFeatures n c -- makeFeatures :: Int -> > String -> IO String > hPutStr h features > go (n+1) cs > > And the file that is produced here is needed in the next function. That can't appear in runProgram, though. I'm not sure it would work, but you coud give {-# LANGUAGE BangPatterns #-} ... !a <- writeFeatures blah more or go n (c:cs) = do features <- makeFeatures n c !a <- hPutStr h features go (n+1) cs a try. > > I hoped to do something with forkIO, as I would like to parallelize the > whole program at the end. Especially the function runProgram would > benefit hugely from this (I so don't have a clue how to do this yet;). I > tried for example the following: > > main :: IO () > main = do > cs <- getArgs > p1 <- forkIO $ writeData cs > p2 <- forkIO $ runProgram cs > p3 <- forkIO $ writeFeatures cs > p4 <- forkIO $ runTestOnFeatures > seq p1 (seq p2 (seq p3 (seq p4 (putStrLn "Done")))) > > But that of course doesn't work, because now I am not actually > requesting anything. The program does in fact nothing, apart from > printing out "Done". Huh. There doesn't seem to be a wait function for ThreadIds, so I guess you would have to communicate via MVars, QSemNs or some such means to signal that one task has been completed and the next can be started. > > Any ideas? > > Cheers, > Thomas ------------------------------ Message: 8 Date: Thu, 7 May 2009 22:10:53 +0200 From: Daniel Fischer <daniel.is.fisc...@web.de> Subject: Re: [Haskell-beginners] Real World Haskell Chapter 5 To: beginners@haskell.org Message-ID: <200905072210.53557.daniel.is.fisc...@web.de> Content-Type: text/plain; charset="iso-8859-15" Am Donnerstag 07 Mai 2009 21:18:46 schrieb PJ Fitzpatrick: > Hi, > I have compiled the SimpleJSON.hs file from chapter 5 and from another file > attempted to import it. I am getting a could not find module error and the > prelude tells me that the locations searched were SimpleJSON.hs and > SimpleJSON.lhs. > I am running Vista, GHC 6.10.2 > Any ideas? > tks, > PJ If the other file is not in the same directory, you have to tell GHC where to look for it, ghc -ipath/to/SimpleJSONDir:path/to/OtherImport --make UseSimpleJSON or build a package with SimpleJSON in it (using Cabal) and register that, then ghc --make will know where to find it. If the file is in the same directory, it may be an encoding error (or some case-muck-up), but definitely something bad. ------------------------------ Message: 9 Date: Thu, 7 May 2009 17:25:40 -0400 From: "Brandon S. Allbery KF8NH" <allb...@ece.cmu.edu> Subject: Re: [Haskell-beginners] How to wait till a process is finished before invoking the next one? To: Thomas Friedrich <i...@suud.de> Cc: beginners@haskell.org Message-ID: <3895bfdd-3c6c-46cb-adbd-6712d7d97...@ece.cmu.edu> Content-Type: text/plain; charset=US-ASCII; format=flowed; delsp=yes -----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 On May 7, 2009, at 14:53 , Thomas Friedrich wrote: > writeFeatures :: [String] -> IO () > writeFeatures cs = Exc.bracket (openFile training AppendMode) hClose > (\h -> goo h) > where > goo h = go 1 cs > where > go :: Int -> [String] -> IO () > go n [] = putStrLn "Features written." > go n (c:cs) = do > features <- makeFeatures n c -- makeFeatures :: Int -> > String -> IO String > hPutStr h features > go (n+1) cs > > And the file that is produced here is needed in the next function. You probably want to rethink how you're doing this. My own thought is that you have something like: > runThis :: FilePath -> [String] -> String -> IO (MVar String) > runThis cmd args inp = do > mvar <- newEmptyMVar > forkIO (readProcess cmd args inp >>= writeMVar mvar) > return mvar runOne launches in the background, you synchronize by doing takeMVar on the returned MVar (which will give you the output, if any). Even if there is no useful output you can still create data dependencies to insure things wait for what they need --- and that is exactly what you want to do: insure that there are data dependencies to constrain when programs are run. Otherwise, you'll have to settle for linear execution. - -- brandon s. allbery [solaris,freebsd,perl,pugs,haskell] allb...@kf8nh.com system administrator [openafs,heimdal,too many hats] allb...@ece.cmu.edu electrical and computer engineering, carnegie mellon university KF8NH -----BEGIN PGP SIGNATURE----- Version: GnuPG v2.0.10 (Darwin) iEYEARECAAYFAkoDUeAACgkQIn7hlCsL25VH/gCghNldOSJnChoHrJwjeaboseU4 Z28An39bR2DAAlP6K9g00eb+NnHhKZSU =NHpz -----END PGP SIGNATURE----- ------------------------------ _______________________________________________ Beginners mailing list Beginners@haskell.org http://www.haskell.org/mailman/listinfo/beginners End of Beginners Digest, Vol 11, Issue 7 ****************************************