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Do you need Windows USB in Haskell?
by Maurício CA 07 Dec '09

07 Dec '09

Hi, I keep this direct binding to libusb-1.0.x: http://hackage.haskell.org/package/bindings-libusb on top of which Bas maintains a nice USB library: http://hackage.haskell.org/package/usb Work has been done to support libusb-1.0.x in Windows. So, as long as my bindings-libusb works properly with that, Bas' as well as any other library based on it will work too. Problem is: I don't have a Windows machine where I could test this. So, if you need USB in windows, please keep in touch. I wouldn't ask you to write any code, but I need to know what builds and what doesn't. Best, Maurício

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Insert a laziness break into strict ST
by Henning Thielemann 07 Dec '09

07 Dec '09

I have lot of ST actions that shall be bound strictly (they write to a buffer), but somewhere between these actions I like to have a "laziness break". I thought I could do this by temporarily switching to Lazy.ST, but this does not work. It follows a simplified example Prelude> :module Control.Monad.ST.Lazy Prelude Control.Monad.ST.Lazy> runST (Monad.liftM2 (,) (return 'a') (undefined::Monad m => m Char)) ('a',*** Exception: Prelude.undefined Prelude Control.Monad.ST.Lazy> Control.Monad.ST.runST (lazyToStrictST $ Monad.liftM2 (,) (return 'a') (undefined::Monad m => m Char)) *** Exception: Prelude.undefined I hoped to get the first answer also for the second command. It seems that conversion from lazy to strict ST also removes laziness breaks. It seems that I have to stick to unsafeInterleaveIO, but I like to know, why the above method does not work.

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When are undecidables ok?
by Michael Snoyman 07 Dec '09

07 Dec '09

I know this is basically a rewording of a previous e-mail, but I realized this is the question I *really* wanted to ask. We have this language extension UndecidableInstances (not to mention OverlappingInstances), which seem to divide the Haskell camp into two factions: * Hey, GHC said to turn on this flag. Ok! * Undecidables are the devil! I get the feeling the truth lies in the middle. As I understand it (please correct me if I am wrong), the problem with undecidables is that they can create non-terminating instances. However, for certain cases the programmer should be able to prove to him/herself that the instances will terminate. My question is: how can you make such a proof? I've had to cases in particular that made me want undecidables. Both of them, IMO, could be solved by creating new extensions to GHC which would not require undecidables. Nonetheless, for now we only have undecidables at our disposal. The examples are: * Context synonyms (eg, MonadFailure = Monad + Failure). * Subclass function defaulting For an example of the second, a nifty definition of Monad would be: class Applicative m => Monad m where >>= ... return ... pure = return (<*>) = ap fmap = liftM Of course, neither of these is possible in Haskell, so we can use undecidables. How can a programmer prove that a set of instances is, in fact, safe? And if they make a mistake and right a bad set of undecidable/overlapping instances, what's the worst case scenario? Is it a compile-time or run-time error*? Michael * Yes, I mean error.

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What is the rank of a polymorphic type?
by Eugene Kirpichov 07 Dec '09

07 Dec '09

Hello. Consider the type: (forall a . a) -> String. On one hand, it is rank-2 polymorphic, because it abstracts over a rank-1 polymorphic type. On the other hand, it is monomorphic because it isn't actually quantified itself: in my intuitive view, a parametrically polymorphic type has infinitely many instantiations (for example, Int -> Int is an instantiation of forall a . a -> a, and String -> String also is), and this type doesn't have any instantiations at all. Which is correct? Is there really a contradiction? What is the definition of rank of a polymorphic type? -- Eugene Kirpichov Web IR developer, market.yandex.ru

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Haskell-Newbie and Char-Function
by MeAdAstra 07 Dec '09

07 Dec '09

Hi guys, I only started learning Haskell some days ago. Maybe one of you can give me a hint on how to implement a function that needs a character in the range (a,b,...z) and an integer number k and returns the k-next neighbor of the character? For example, fct a 5 would result in output f. Tobias -- View this message in context: http://old.nabble.com/Haskell-Newbie-and-Char-Function-tp26656676p26656676.… Sent from the Haskell - Haskell-Cafe mailing list archive at Nabble.com.

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ANN: readline-statevar-1.0.1.0
by Krzysztof Skrzętnicki 07 Dec '09

07 Dec '09

Hello I am happy to announce a release of small package called readline-statevar. It's a small wrapping library around readline, which in turn wraps libreadline. The reason I wrote it is because I wasn't happy with the API of readline. It was composed of tons of functions like setX/getX, where there could be just one StateVar instead, yielding OpenGL-kind API. This version aims to match readline-1.0.1.0. (Hence the version number chosen). I wrote it mostly manually, with a little help from my emacs-fu, so there is a chance I missed a thing or two. There is git repo available [1], along with issue tracker [2] and Hackage page [3]. Feel encouraged to: > cabal update > cabal install readline-statevar And give it a try! Best regards Krzysztof Skrzętnicki [1] http://github.com/Tener/haskell-readline-statevar/ [2] http://github.com/Tener/haskell-readline-statevar/issues [3] http://hackage.haskell.org/package/readline-statevar

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ANNOUNCE: error-message
by Gregory Crosswhite 07 Dec '09

07 Dec '09

If there is one thing that we really don't have enough of in Haskell, it is *ways to handle errors*! Thus, I am pleased to announce the release of the "error-message" package to help in filling this, erm, gap. This philosophy behind this package is that it is often better to find out all of the errors that have occured in a computation and report them simultaneously, rather than aborting as soon as the first error is encountered. Towards this end, this package supplies a type of /combinable error messages/ (ErrorMessage in the Data.ErrorMessage module) so that all of the errors from subcomputations can be gathered and presented together. The following provides an example of how these can be used: ================================================== sqrtWithError :: Float -> Either ErrorMessage Float sqrtWithError x | x < 0 = leftErrorMessageText ("Error computing the square root of " ++ (show x) ++ ":") "Square roots cannot be taken of negative numbers." | otherwise = Right (sqrt x) sumWithError :: Either ErrorMessage Float -> Either ErrorMessage Float -> Either ErrorMessage Float sumWithError (Left error1) (Left error2) = Left (error1 `mappend` error2) sumWithError (Left error) _ = Left error sumWithError _ (Left error) = Left error sumWithError (Right value1) (Right value2) = Right (value1 + value2) showSumOrErrorOf :: Float -> Float -> String showSumOrErrorOf x y = case sumWithError (sqrtWithError x) (sqrtWithError y) of Right value -> "The value is " ++ show value Left error -> show . formatErrorMessage $ error ================================================== The result of @showSumOrErrorOf (-1) (-2)@ is the string, Error computing the square root of -1: Square roots cannot be taken of negative numbers. Error computing the square root of -2: Square roots cannot be taken of negative numbers. whereas the result of @showSumOrErrorOf (-1) (-1)@ is the string, Error computing the square root of -1: Square roots cannot be taken of negative numbers. Note how the error message only appears once; this is because the process of combining the error messages automatically eliminates all identical headings under the assumption that they came from the same original computation, as was the case here. Currently, the definition of @sumWithError@ is largely boilerplate. Happily, the Haskell community has done a lot of work to identify patterns such as these and to write libraries that allow us to express them concisely. In particular, a standard trick when working with errors like this is to express the calculation as a 'Monad', such as by using the following definition: ================================================== sumWithError_2 argument1 argument2 = do value1 <- argument1 value2 <- argument2 return (value1 + value2) ================================================== Or, even more concisely: ================================================== sumWithError_3 = liftM2 (+) ================================================== Unfortunately though, neither of these definitions have the same semantics as the original @sumWithError@, as using both we get the following error message for @showSumOrErrorOf (-1) (-2)@: ================================================== Error computing the square root of -1: Square roots cannot be taken of negative numbers. ================================================== That is, we have lost the second of the two error messages. The reason for this is that 'Monad'-style error processing expresses the computation as a sequence, and gives up as soon as it sees any error. In this case of @sumWithError@, however, the evaluation of the second argument can proceed even if there was an error in the first argument. Thus, rather than using a 'Monad' pattern, we use an 'Applicative' pattern: ================================================== sumWithError_4 = liftA2 (+) ================================================== Now both error messages are displayed. Anyway, I hope that someone other than myself finds this pattern to be helpful. :-) Cheers, Greg

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help
by Ezekiel Smithburg 06 Dec '09

06 Dec '09

On Sun, Dec 6, 2009 at 4:53 AM, <haskell-cafe-request(a)haskell.org> wrote: > Send Haskell-Cafe mailing list submissions to > haskell-cafe(a)haskell.org > > To subscribe or unsubscribe via the World Wide Web, visit > http://www.haskell.org/mailman/listinfo/haskell-cafe > or, via email, send a message with subject or body 'help' to > haskell-cafe-request(a)haskell.org > > You can reach the person managing the list at > haskell-cafe-owner(a)haskell.org > > When replying, please edit your Subject line so it is more specific > than "Re: Contents of Haskell-Cafe digest..." > > Today's Topics: > > 1. Re: Low Level Audio - Writing bytes to the sound card? > (Daniel Fischer) > 2. Re: HP + Gtk2hs? (M Xyz) > 3. Re: Low Level Audio - Writing bytes to the sound card? (M Xyz) > 4. Re: Low Level Audio - Writing bytes to the sound card? > (Daniel Fischer) > 5. RE: Low Level Audio - Writing bytes to the sound card? (john lask) > 6. Re: New Hackage category: Error Handling (Henning Thielemann) > 7. Re: Low Level Audio - Writing bytes to the sound card? (M Xyz) > 8. RE: Low Level Audio - Writing bytes to the sound card? (M Xyz) > 9. PortAudio library successfully built on Windows (M Xyz) > 10. When are undecidables ok? (Michael Snoyman) > 11. Re: When are undecidables ok? (Luke Palmer) > 12. Re: When are undecidables ok? (Michael Snoyman) > 13. Re: ANNOUNCE: error-message (Ariel J. Birnbaum) > 14. Re: What is the rank of a polymorphic type? (Eugene Kirpichov) > 15. Re: universal binary version of Haskell Platform? > (Benjamin L.Russell) > 16. Re: What is the rank of a polymorphic type? (Dan Doel) > 17. Re[2]: [Haskell-cafe] Low Level Audio - Writing bytes to the > sound card? (Bulat Ziganshin) > 18. Re: universal binary version of Haskell Platform? > (Heinrich Apfelmus) > 19. Re: Low Level Audio - Writing bytes to the sound card? > (Andrew Coppin) > 20. Re: binding to C libraries on Windows was Low Level Audio - > Writing bytes to the sound card? (Andrew Coppin) > > > ---------- Forwarded message ---------- > From: Daniel Fischer <daniel.is.fischer(a)web.de> > To: haskell-cafe(a)haskell.org > Date: Sun, 6 Dec 2009 01:24:17 +0100 > Subject: Re: [Haskell-cafe] Low Level Audio - Writing bytes to the sound > card? > Am Sonntag 06 Dezember 2009 00:47:38 schrieb M Xyz: > > Daniel, Thank you for your thoughtful reply. I didn't know about those > > flags. The log is fairly long, and as I'm new to Haskell and Cabal it is > > mostly meaningless to me. I see very many incidences of "searching for > ___ > > in path. Cannot find ___ on the path" so maybe this is all as simple as > me > > not setting my environment correctly. > > If you have cpphs, hugs, jhc, greencard etc., it is probably something > about your > environment. If you don't have them, it's clear that they aren't found. > > On the other hand, that doesn't explain > > Using c2hs version 0.16.0 given by user at: C:\Program > Files\Haskell\bin\c2hs.exe > > -- so it finds c2hs, and can apparently run c2hs --version > > ("C:\\Program > Files\\Haskell\\bin\\c2hs.exe",["--include=dist\\build","--cppopts=- > D__GLASGOW_HASKELL__=610","--cppopts=-IC: > > \\A\\install\\programming\\portaudio\\portaudio\\include","--output-dir=dist\\build","-- > output=Sound\\PortAudio\\Base.hs",".\\Sound\\PortAudio\\Base.chs"]) > c2hs.exe: does not exist > C:\Program Files\Haskell\bin\c2hs.exe returned ExitFailure 1 > > -- bang > > To ascertain whether c2hs works at all, can you try to run it manually? > > (cd to an appropriate directory, > > cabal unpack portaudio > > cd portaudio (or whatever, so that Base.chs is found via > .\Sound\PortAudio\Base.chs > > md dist\build > > c2hs.exe --include=dist\build --cppopts=-D__GLASGOW_HASKELL__=610 > --cppopts=-IC: > \A\install\programming\portaudio\portaudio\include --output-dir=dist\build > -- > output=Sound\PortAudio\Base.hs .\Sound\PortAudio\Base.chs > ) > If that works, the problem is somewhere in cabal, otherwise in c2hs, either > way, we'll > know more. > > > > ---------- Forwarded message ---------- > From: M Xyz <functionallyharmonious(a)yahoo.com> > To: haskell-cafe(a)haskell.org, Andrew Coppin <andrewcoppin(a)btinternet.com> > Date: Sat, 5 Dec 2009 16:34:52 -0800 (PST) > Subject: Re: [Haskell-cafe] HP + Gtk2hs? > > > --- On *Sat, 12/5/09, Andrew Coppin <andrewcoppin(a)btinternet.com>* wrote: > > >> Hell, I even followed a C++ guide to Win32 programming and > >> managed to translate an "open a blank window" program to Haskell, and it > >> worked. Maybe somebody just needs to sit down and write a nice binding > >> for doing native GUI stuff under Win32? > > Well there's > http://haskell.org/ghc/docs/latest/html/libraries/Win32/Graphics-Win32.html… opening blank windows. ;) > > This relates to my question a couple days ago about a good cross platform > 2d library. I wonder why there isnt a Haskell library that follows in the > footsteps of Java's Swing - by that I mean, just have a very simple low > level way of opening a window, getting mouse clicks, and an abstracted > drawing layer... and make the GUIs with that. The GUIs are drawn and not OS > widgets. That's exactly why I was looking for something like Cairo. My > interest is in composable fudgets (stealing the word from fudgets). > > This way every platform can share the same GUI library and HP can ship with > the minimal tools to open a window and draw on every system. Plus OS guis > are the wrong thing for Haskell. You need to retain the power to make better > abstractions. > > > > > > ---------- Forwarded message ---------- > From: M Xyz <functionallyharmonious(a)yahoo.com> > To: haskell-cafe(a)haskell.org, Daniel Fischer <daniel.is.fischer(a)web.de> > Date: Sat, 5 Dec 2009 16:49:49 -0800 (PST) > Subject: Re: [Haskell-cafe] Low Level Audio - Writing bytes to the sound > card? > > > --- On *Sat, 12/5/09, Daniel Fischer <daniel.is.fischer(a)web.de>* wrote: > > > > If you have cpphs, hugs, jhc, greencard etc., it is probably something > about your > environment. If you don't have them, it's clear that they aren't found. > > I don't know what those things are. I have nothing but what came with HP > other than installing c2hs today. > > If that works, the problem is somewhere in cabal, otherwise in c2hs, either > way, we'll > know more. > > Alright, I followed the instructions and everything was as you said. I > still get "c2hs.exe does not exist". > > C:\A\install\programming\portaudio\haskell\portaudio-0.0.1>"C:\Program > Files\Has > kell\bin\c2hs.exe" --include=dist\build --cppopts=-D__GLASGOW_HASKELL__=610 > --cp > popts=-IC:\A\install\programming\portaudio\portaudio\include > --output-dir=dist\b > uild --output=Sound\PortAudio\Base.hs .\Sound\PortAudio\Base.chs > c2hs.exe: does not exist > > C:\A\install\programming\portaudio\haskell\portaudio-0.0.1>pause > Press any key to continue . . . > > By the way, I have posted this problem to the c2hs mailing list in case > they have some insight. > > > > > ---------- Forwarded message ---------- > From: Daniel Fischer <daniel.is.fischer(a)web.de> > To: M Xyz <functionallyharmonious(a)yahoo.com> > Date: Sun, 6 Dec 2009 02:34:17 +0100 > Subject: Re: [Haskell-cafe] Low Level Audio - Writing bytes to the sound > card? > Am Sonntag 06 Dezember 2009 01:49:49 schrieb M Xyz: > > I just had another idea. > > dafis@linux-mkk1:~> c2hs -o memyself.hs memyself.chs > c2hs: does not exist > > it's not that c2hs isn't found or something, c2hs doesn't find Base.chs! > > Try installing from the unpacked sources (cd portaudio; cabal install) or > the old- > fashioned way: > > cd portaudio-0.0.1 > > ghc --make Setup > > ./Setup configure --help > (choose your options, prefix, profiling, ...) > > ./Setup configure $OPTIONS > ./Setup build > > if all's well, > > ./Setup haddock > ./Setup install > > (dies for me with > dist/build/Sound/PortAudio/Base.chs.h:1:23: error: portaudio.h: Datei oder > Verzeichnisnicht gefunden > c2hs: Error during preprocessing custom header file > cabal: Error: some packages failed to install: > portaudio-0.0.1 failed during the building phase. The exception was: > exit: ExitFailure 1 > because I don't have portaudio installed) > > > > ---------- Forwarded message ---------- > From: john lask <jvlask(a)hotmail.com> > To: <daniel.is.fischer(a)web.de>, <functionallyharmonious(a)yahoo.com> > Date: Sun, 6 Dec 2009 02:03:32 +0000 > Subject: RE: [Haskell-cafe] Low Level Audio - Writing bytes to the sound > card? > > > I don't know whether this will help you but I just downloaded an built > the haskell portaudio package ... (I had a windows msvc build of > portaudio dll already) the process I used ... ghc 6.10.4, portaudio-19 > > make an import lib for ghc from dll: > pexports libpa19.dll > libpa19.def > dlltool --input-def libpa19.def --output-lib libpa19.a > > edit the .cabal file or use command line flags > > extra-Libraries: pa19 > extra-lib-dirs: c:\portaudio19\lib > include-dirs: c:\portaudio19\include > > runghc setup configure > > make sure you have cpp i.e. the c-preprocessor on your exe path, > otherwise you will get > 'cpp' is not recognized as an internal or external command, > operable program or batch file. > c2hs.exe: Error during preprocessing custom header file > > runghc setup build > > builds ok ...?? > > > > From: daniel.is.fischer(a)web.de > > To: functionallyharmonious(a)yahoo.com > > Subject: Re: [Haskell-cafe] Low Level Audio - Writing bytes to the sound > card? > > Date: Sun, 6 Dec 2009 02:34:17 +0100 > > CC: haskell-cafe(a)haskell.org > > > > Am Sonntag 06 Dezember 2009 01:49:49 schrieb M Xyz: > > > > I just had another idea. > > > > dafis@linux-mkk1:~> c2hs -o memyself.hs memyself.chs > > c2hs: does not exist > > > > it's not that c2hs isn't found or something, c2hs doesn't find Base.chs! > > > > Try installing from the unpacked sources (cd portaudio; cabal install) or > the old- > > fashioned way: > > > > cd portaudio-0.0.1 > > > > ghc --make Setup > > > > ./Setup configure --help > > (choose your options, prefix, profiling, ...) > > > > ./Setup configure $OPTIONS > > ./Setup build > > > > if all's well, > > > > ./Setup haddock > > ./Setup install > > > > (dies for me with > > dist/build/Sound/PortAudio/Base.chs.h:1:23: error: portaudio.h: Datei > oder > > Verzeichnisnicht gefunden > > c2hs: Error during preprocessing custom header file > > cabal: Error: some packages failed to install: > > portaudio-0.0.1 failed during the building phase. The exception was: > > exit: ExitFailure 1 > > because I don't have portaudio installed) > > _______________________________________________ > > Haskell-Cafe mailing list > > Haskell-Cafe(a)haskell.org > > http://www.haskell.org/mailman/listinfo/haskell-cafe > > ------------------------------ > Australia's #1 job site If It Exists, You'll Find it on SEEK<http://clk.atdmt.com/NMN/go/157639755/direct/01/> > > > ---------- Forwarded message ---------- > From: Henning Thielemann <lemming(a)henning-thielemann.de> > To: Michael Snoyman <michael(a)snoyman.com> > Date: Sun, 06 Dec 2009 03:05:30 +0100 (CET) > Subject: Re: [Haskell-cafe] New Hackage category: Error Handling > > On Sat, 5 Dec 2009, Henning Thielemann wrote: > > On Sun, 6 Dec 2009, Michael Snoyman wrote: >> >> I think there are plenty of examples like web servers. A text editor with >>> plugins? I >>> don't want to lose three hours worth of work just because some plugin >>> wasn't written >>> correctly. For many classes of programs, the distinction between error >>> and exception is >>> not only blurred, it's fully irrelevant. Harping on people every time >>> they use error in >>> the "wrong" sense seems unhelpful. >>> >>> Hope my commenting on this subject doesn't become my own form of >>> *pedantry*. >>> >> >> In an earlier thread I have explained that one can consider a software >> architecture as divided into levels. What is an error in one level (text >> editor plugin, web server thread, operating system process) is an exception >> in the next higher level (text editor, web server, shell respectively). This >> doesn't reduce the importance to distinguish between errors and exceptions >> within one level. All approaches so far that I have seen in Haskell just mix >> exceptions and errors in an arbitrary way. >> > > > I have just written more details on this topic: > http://www.haskell.org/haskellwiki/Error_vs._Exception > > > > ---------- Forwarded message ---------- > From: M Xyz <functionallyharmonious(a)yahoo.com> > To: Daniel Fischer <daniel.is.fischer(a)web.de> > Date: Sat, 5 Dec 2009 18:08:07 -0800 (PST) > Subject: Re: [Haskell-cafe] Low Level Audio - Writing bytes to the sound > card? > > > --- On *Sat, 12/5/09, Daniel Fischer <daniel.is.fischer(a)web.de>* wrote: > > > > cd portaudio-0.0.1 > > ghc --make Setup > > ./Setup configure --help > (choose your options, prefix, profiling, ...) > > ./Setup configure $OPTIONS > ./Setup build > > > Everything went well until "Setup build" which yielded our friend "c2hs.exe > does not exist". > > > C:\A\install\programming\portaudio\haskell\portaudio-0.0.1>ghc --make Setup > [1 of 1] Compiling Main ( Setup.hs, Setup.o ) > Linking Setup.exe ... > > C:\A\install\programming\portaudio\haskell\portaudio-0.0.1>Setup configure > --hel > p > Usage: Setup configure [FLAGS] > > Flags for configure: .......(edited out)................. > > C:\A\install\programming\portaudio\haskell\portaudio-0..0.1>Setup configure > --ext > ra-include-dirs="C:\A\install\programming\portaudio\portaudio\include" > --extra-l > > ib-dirs="C:\A\install\programming\portaudio\portaudio\build\msvc\Win32\Release" > Configuring portaudio-0.0.1... > > C:\A\install\programming\portaudio\haskell\portaudio-0.0.1>Setup build > Preprocessing library portaudio-0.0.1... > c2hs.exe: does not exist > > > > > > > ---------- Forwarded message ---------- > From: M Xyz <functionallyharmonious(a)yahoo.com> > To: daniel.is.fischer(a)web.de, john lask <jvlask(a)hotmail.com> > Date: Sat, 5 Dec 2009 18:17:29 -0800 (PST) > Subject: RE: [Haskell-cafe] Low Level Audio - Writing bytes to the sound > card? > I am going to give this a try. Thanks. > Where can I get the pexports and dlltool utilities? > > Google yields: > http://www.emmestech.com/software/pexports-0.43/download_pexports.html > http://sourceware.org/binutils/ > > Are those correct? > > --- On *Sat, 12/5/09, john lask <jvlask(a)hotmail.com>* wrote: > > > From: john lask <jvlask(a)hotmail.com> > Subject: RE: [Haskell-cafe] Low Level Audio - Writing bytes to the sound > card? > To: daniel.is.fischer(a)web.de, functionallyharmonious(a)yahoo.com > Cc: haskell-cafe(a)haskell.org > Date: Saturday, December 5, 2009, 9:03 PM > > > > I don't know whether this will help you but I just downloaded an built > the haskell portaudio package ... (I had a windows msvc build of > portaudio dll already) the process I used ... ghc 6.10.4, portaudio-19 > > make an import lib for ghc from dll: > pexports libpa19.dll > libpa19.def > dlltool --input-def libpa19.def --output-lib libpa19.a > > edit the .cabal file or use command line flags > > extra-Libraries: pa19 > extra-lib-dirs: c:\portaudio19\lib > include-dirs: c:\portaudio19\include > > runghc setup configure > > make sure you have cpp i.e. the c-preprocessor on your exe path, > otherwise you will get > 'cpp' is not recognized as an internal or external command, > operable program or batch file. > c2hs.exe: Error during preprocessing custom header file > > runghc setup build > > builds ok ...?? > > > > From: daniel.is.fischer(a)web.de > > To: functionallyharmonious(a)yahoo.com > > Subject: Re: [Haskell-cafe] Low Level Audio - Writing bytes to the sound > card? > > Date: Sun, 6 Dec 2009 02:34:17 +0100 > > CC: haskell-cafe(a)haskell.org > > > > Am Sonntag 06 Dezember 2009 01:49:49 schrieb M Xyz: > > > > I just had another idea. > > > > dafis@linux-mkk1:~> c2hs -o memyself.hs memyself.chs > > c2hs: does not exist > > > > it's not that c2hs isn't found or something, c2hs doesn't find Base.chs! > > > > Try installing from the unpacked sources (cd portaudio; cabal install) or > the old- > > fashioned way: > > > > cd portaudio-0.0.1 > > > > ghc --make Setup > > > > ./Setup configure --help > > (choose your options, prefix, profiling, ...) > > > > ./Setup configure $OPTIONS > > ./Setup build > > > > if all's well, > > > > ./Setup haddock > > ./Setup install > > > > (dies for me with > > dist/build/Sound/PortAudio/Base.chs.h:1:23: error: portaudio.h: Datei > oder > > Verzeichnisnicht gefunden > > c2hs: Error during preprocessing custom header file > > cabal: Error: some packages failed to install: > > portaudio-0.0.1 failed during the building phase. The exception was: > > exit: ExitFailure 1 > > because I don't have portaudio installed) > > _______________________________________________ > > Haskell-Cafe mailing list > > Haskell-Cafe(a)haskell.org > > http://www.haskell.org/mailman/listinfo/haskell-cafe > > ------------------------------ > Australia's #1 job site If It Exists, You'll Find it on SEEK<http://clk.atdmt.com/NMN/go/157639755/direct/01/> > > > > > ---------- Forwarded message ---------- > From: M Xyz <functionallyharmonious(a)yahoo.com> > To: john lask <jvlask(a)hotmail.com>, vanenkj(a)gmail.com > Date: Sat, 5 Dec 2009 19:47:04 -0800 (PST) > Subject: [Haskell-cafe] PortAudio library successfully built on Windows > > John Lask, > The steps you enumerated below successfully built portaudio for me! Thank > you! > > I wonder though, you said to rename the dll to libpa19.dll from > portaudio_x86.dll > and to change the .cabal entry from "extra-Libraries: portaudio" to > "extra-Libraries: pa19". > Since my .dll name and .cabal file entry were mismatched, was that what > could have been wrong all along? Was the creation of a .a file necessary? > I would delete the .a file and retry with libportaudio.dll but I won't push > my luck. > > Now if I could just get Gtk2hs working now, I could be happy *and* > productive. :) > > --- On *Sat, 12/5/09, john lask <jvlask(a)hotmail.com>* wrote: > > > From: john lask <jvlask(a)hotmail.com> > Subject: RE: [Haskell-cafe] Low Level Audio - Writing bytes to the sound > card? > To: daniel.is.fischer(a)web.de, functionallyharmonious(a)yahoo.com > Cc: haskell-cafe(a)haskell.org > Date: Saturday, December 5, 2009, 9:03 PM > > > > I don't know whether this will help you but I just downloaded an built > the haskell portaudio package ... (I had a windows msvc build of > portaudio dll already) the process I used ... ghc 6.10.4, portaudio-19 > > make an import lib for ghc from dll: > pexports libpa19.dll > libpa19.def > dlltool --input-def libpa19.def --output-lib libpa19.a > > edit the .cabal file or use command line flags > > extra-Libraries: pa19 > extra-lib-dirs: c:\portaudio19\lib > include-dirs: c:\portaudio19\include > > runghc setup configure > > make sure you have cpp i.e. the c-preprocessor on your exe path, > otherwise you will get > 'cpp' is not recognized as an internal or external command, > operable program or batch file. > c2hs.exe: Error during preprocessing custom header file > > runghc setup build > > builds ok ...?? > > > > From: daniel.is.fischer(a)web.de > > To: functionallyharmonious(a)yahoo.com > > Subject: Re: [Haskell-cafe] Low Level Audio - Writing bytes to the sound > card? > > Date: Sun, 6 Dec 2009 02:34:17 +0100 > > CC: haskell-cafe(a)haskell.org > > > > Am Sonntag 06 Dezember 2009 01:49:49 schrieb M Xyz: > > > > I just had another idea. > > > > dafis@linux-mkk1:~> c2hs -o memyself.hs memyself.chs > > c2hs: does not exist > > > > it's not that c2hs isn't found or something, c2hs doesn't find Base.chs! > > > > Try installing from the unpacked sources (cd portaudio; cabal install) or > the old- > > fashioned way: > > > > cd portaudio-0.0.1 > > > > ghc --make Setup > > > > ./Setup configure --help > > (choose your options, prefix, profiling, ...) > > > > ./Setup configure $OPTIONS > > ./Setup build > > > > if all's well, > > > > ./Setup haddock > > ./Setup install > > > > (dies for me with > > dist/build/Sound/PortAudio/Base.chs.h:1:23: error: portaudio.h: Datei > oder > > Verzeichnisnicht gefunden > > c2hs: Error during preprocessing custom header file > > cabal: Error: some packages failed to install: > > portaudio-0.0.1 failed during the building phase. The exception was: > > exit: ExitFailure 1 > > because I don't have portaudio installed) > > _______________________________________________ > > Haskell-Cafe mailing list > > Haskell-Cafe(a)haskell.org > > http://www.haskell.org/mailman/listinfo/haskell-cafe > > ------------------------------ > Australia's #1 job site If It Exists, You'll Find it on SEEK<http://clk.atdmt.com/NMN/go/157639755/direct/01/> > > > > > ---------- Forwarded message ---------- > From: Michael Snoyman <michael(a)snoyman.com> > To: Haskell Cafe <haskell-cafe(a)haskell.org> > Date: Sun, 6 Dec 2009 07:04:46 +0200 > Subject: [Haskell-cafe] When are undecidables ok? > I know this is basically a rewording of a previous e-mail, but I realized > this is the question I *really* wanted to ask. > > We have this language extension UndecidableInstances (not to mention > OverlappingInstances), which seem to divide the Haskell camp into two > factions: > > * Hey, GHC said to turn on this flag. Ok! > * Undecidables are the devil! > > I get the feeling the truth lies in the middle. As I understand it (please > correct me if I am wrong), the problem with undecidables is that they can > create non-terminating instances. However, for certain cases the programmer > should be able to prove to him/herself that the instances will terminate. My > question is: how can you make such a proof? > > I've had to cases in particular that made me want undecidables. Both of > them, IMO, could be solved by creating new extensions to GHC which would not > require undecidables. Nonetheless, for now we only have undecidables at our > disposal. The examples are: > > * Context synonyms (eg, MonadFailure = Monad + Failure). > * Subclass function defaulting > > For an example of the second, a nifty definition of Monad would be: > > class Applicative m => Monad m where > >>= ... > return ... > pure = return > (<*>) = ap > fmap = liftM > > Of course, neither of these is possible in Haskell, so we can use > undecidables. How can a programmer prove that a set of instances is, in > fact, safe? And if they make a mistake and right a bad set of > undecidable/overlapping instances, what's the worst case scenario? Is it a > compile-time or run-time error*? > > Michael > > * Yes, I mean error. > > > ---------- Forwarded message ---------- > From: Luke Palmer <lrpalmer(a)gmail.com> > To: Michael Snoyman <michael(a)snoyman.com> > Date: Sat, 5 Dec 2009 22:36:43 -0700 > Subject: Re: [Haskell-cafe] When are undecidables ok? > On Sat, Dec 5, 2009 at 10:04 PM, Michael Snoyman <michael(a)snoyman.com> > wrote: > > I know this is basically a rewording of a previous e-mail, but I realized > > this is the question I *really* wanted to ask. > > > > We have this language extension UndecidableInstances (not to mention > > OverlappingInstances), which seem to divide the Haskell camp into two > > factions: > > > > * Hey, GHC said to turn on this flag. Ok! > > * Undecidables are the devil! > > > > I get the feeling the truth lies in the middle. As I understand it > (please > > correct me if I am wrong), the problem with undecidables is that they can > > create non-terminating instances. However, for certain cases the > programmer > > should be able to prove to him/herself that the instances will terminate. > My > > question is: how can you make such a proof? > > Well, the reasoning for the "devil" camp (which I admit to being > firmly in[1]) is that such proofs must rely on the algorithm the > compiler uses to resolve instances. You might be able to prove it, > but the proof is necessarily only valid for (possibly current versions > of) GHC. The typeclass resolution algorithm is not in the report, and > there are several conceivable ways of of going about it. > > So it is fine to use them if you are okay with making your code > unportable and future-brittle. I am typically against the mere > existence of code that that is future-brittle, because it encourages > compiler authors not to innovate (and by that token, unportable too, > because it discourages compiler competition). > > Luke > > [1] > http://lukepalmer.wordpress.com/2008/04/08/stop-using-undecidable-instances/ > > > > ---------- Forwarded message ---------- > From: Michael Snoyman <michael(a)snoyman.com> > To: Luke Palmer <lrpalmer(a)gmail.com> > Date: Sun, 6 Dec 2009 08:20:09 +0200 > Subject: Re: [Haskell-cafe] When are undecidables ok? > > > On Sun, Dec 6, 2009 at 7:36 AM, Luke Palmer <lrpalmer(a)gmail.com> wrote: > >> On Sat, Dec 5, 2009 at 10:04 PM, Michael Snoyman <michael(a)snoyman.com> >> wrote: >> > I know this is basically a rewording of a previous e-mail, but I >> realized >> > this is the question I *really* wanted to ask. >> > >> > We have this language extension UndecidableInstances (not to mention >> > OverlappingInstances), which seem to divide the Haskell camp into two >> > factions: >> > >> > * Hey, GHC said to turn on this flag. Ok! >> > * Undecidables are the devil! >> > >> > I get the feeling the truth lies in the middle. As I understand it >> (please >> > correct me if I am wrong), the problem with undecidables is that they >> can >> > create non-terminating instances. However, for certain cases the >> programmer >> > should be able to prove to him/herself that the instances will >> terminate. My >> > question is: how can you make such a proof? >> >> Well, the reasoning for the "devil" camp (which I admit to being >> firmly in[1]) is that such proofs must rely on the algorithm the >> compiler uses to resolve instances. You might be able to prove it, >> but the proof is necessarily only valid for (possibly current versions >> of) GHC. The typeclass resolution algorithm is not in the report, and >> there are several conceivable ways of of going about it. >> >> So it is fine to use them if you are okay with making your code >> unportable and future-brittle. I am typically against the mere >> existence of code that that is future-brittle, because it encourages >> compiler authors not to innovate (and by that token, unportable too, >> because it discourages compiler competition). >> >> Luke >> >> [1] >> http://lukepalmer.wordpress.com/2008/04/08/stop-using-undecidable-instances/ >> > > So in that case, perhaps the compiler authors can give us some ideas as to > when it's safe to use undecidables? Seems like we should go straight to the > horse's mouth. > > Michael > > > > ---------- Forwarded message ---------- > From: "Ariel J. Birnbaum" <valgarv(a)gmx.net> > To: Gregory Crosswhite <gcross(a)phys.washington.edu> > Date: Sun, 06 Dec 2009 08:34:16 +0200 > Subject: Re: [Haskell-cafe] ANNOUNCE: error-message > > In particular, the motivation for this package was that I have written > > a build system, and I wanted to collect as many errors in the build as > > possible and show them all to the user at once. > > YMMV, but at least for me a deluge of errors is less helpful than a > short list I can fix quickly, then try again. Often by fixing one error > from the list a sizeable portion of the rest just vanish (I forget the > English term for that kind of error). > > (In before "you can use sth like quickfix to go through the first few > errors and compile again whenever you feel like it".) > > -- > Ariel J. Birnbaum > > > > > ---------- Forwarded message ---------- > From: Eugene Kirpichov <ekirpichov(a)gmail.com> > To: Stefan Holdermans <stefan(a)cs.uu.nl> > Date: Sun, 6 Dec 2009 09:42:34 +0300 > Subject: Re: [Haskell-cafe] What is the rank of a polymorphic type? > 2009/12/6 Stefan Holdermans <stefan(a)cs.uu.nl>: > > Eugene, > > > >> 1) Does there exist an authoritative source saying the same? Not that > >> I'm doubting, just supposing that the source would have other > >> interesting information, too :) > > > > You may want to have a look at the already mentioned JFP-article by > Peyton > > Jones et al. and perhaps the work of Kfoury and Wells. > > > >> 2) Is it true that rank (forall a . a, forall a . a) == 0 ? > > > > No, for pairs one takes the maximum of the constituent types. So, here > you'd > > get rank 1. > > > > Note that this is an impredicative type, which is yet another extension > of > > the standard Hindley-Milner typing discipline. > > OK, thanks. > However, isn't the type (forall a . a) -> String impredicative because > it instantiates a type variable of the type constructor (->) p q with > p = forall a . a? > > > > > Cheers, > > > > Stefan > >> > >>> > > > > > > -- > Eugene Kirpichov > Web IR developer, market.yandex.ru > > > > ---------- Forwarded message ---------- > From: Benjamin L.Russell <dekudekuplex(a)yahoo.com> > To: haskell-cafe(a)haskell.org > Date: Sun, 06 Dec 2009 16:14:06 +0900 > Subject: [Haskell-cafe] Re: universal binary version of Haskell Platform? > On Thu, 03 Dec 2009 10:52:35 +0000, Duncan Coutts > <duncan.coutts(a)googlemail.com> wrote: > > >[...] > > > >There no binary platform installer for OSX PPC. You'll have to grab > >ghc-6.10.4 for PPC from the ghc download page and then install the > >platform from the generic source tarball. > > Ah, that's too bad. That means that I won't be able to invoke GHC > outside of the Terminal application by default, and that even if I > create a Darwin shell script and alias to invoke it from Aqua, the > icon for that shell script will only be generic by default. I'd > rather click on an application icon in the Dock. > > > > >If you'd like to help us next time to make a platform binary for PPC > >then that'd be great. I don't think we have the setup to make universal > >binaries but it should be possible to make a PPC build if we have a > >volunteer. > > Sure, barring job-related time constraints, I'd be happy to volunteer. > My Mac just went out of service because of a hardware problem with the > memory, so I'm order new replacement RAM this weekend. As soon as > that arrives and I install it, the problem should be resolved. > > What should I do? > > -- Benjamin L. Russell > > > > > ---------- Forwarded message ---------- > From: Dan Doel <dan.doel(a)gmail.com> > To: haskell-cafe(a)haskell.org > Date: Sun, 6 Dec 2009 02:48:09 -0500 > Subject: Re: [Haskell-cafe] What is the rank of a polymorphic type? > On Sunday 06 December 2009 1:42:34 am Eugene Kirpichov wrote: > > OK, thanks. > > However, isn't the type (forall a . a) -> String impredicative because > > it instantiates a type variable of the type constructor (->) p q with > > p = forall a . a? > > There's probably no clear cut answer to this independent of how you think > of > (->). For instance, if we explain the Haskell type system by way of a pure > type system, (->) is a special case of a pi type, which looks like: > > pi x : k. t > > where any xs in t are bound by the pi. We then have: > > p -> q = pi _ : p. q > forall a : k. b = pi a : k. b > > pi types are given types by sets of rules, which look like triples. If > (s,t,u) > is a rule, then: > > G |- k : s G, a : k |- b : t > ------------------------------- > G |- (pi a : k. b) : u > > is the corresponding typing rule. Type systems like Haskell's are commonly > thought of in terms of the lambda cube, which has constant sorts * and [], > with * : []. The rule (*,*,*) gives you ordinary functions. (*,[],[]) gives > you dependent types, so that's out. > > ([],*,*) is an impredicative rule for polymorphism. This says that, for > instance: > > forall a. a -> a = (pi a : *. pi _ : a. a) : * > > because (pi _ : a. a) : * if a : *, by the (*,*,*) rule, and then we apply > the > impredicative rule for the universal quantification. One could also use the > predicative rule ([],*,[]), which would result in forall a. a -> a having > type > []. > > However, Haskell also has arbitrarily higher-order types. This is given by > the > rule ([],[],[]), which allows expressions like: > > (* -> *) -> * = pi _ : (pi _ : *. *). * > > This type system is called F_omega, while just the ([],*,?) rule is known > as > F_2. > > However, the F_omega rule also allows for arbitrary rank polymorphism even > with the predicative universal quantifier rule above (predicative F_2 > allows a > little, but it's very limited*). For instance, the higher rank type: > > forall a. (forall b. b) -> a > > checks thusly: > > (forall b. b) : [] via ([],*,[]) > ((forall b. b) -> a) : [] via ([],*,[]) > (forall a. (forall b. b) -> a) : [] via ([],[],[]) > > Data types, by contrast, have kinds like * -> *, so using say, > > Maybe (forall a. a -> a) > > genuinely relies on the impredicative rule. GHC's type system isn't exactly > set up in this way, but (->) is similarly special in that it somehow isn't > quite just another type constructor with kind * -> * -> * (or even whatever > special kinds GHC uses to support unboxed values and such). > > Hope that wasn't too confusing. :) > > -- Dan > > * Predicative F_2 will essentially allow one universal quantifier somewhere > in > the type. This can be: > > forall a. a -> a > > or it can be: > > (((forall a. a) -> T) -> U) -> V > > for T, U and V of kind * (the only kind in F_2), which is a rank-4 type. It > doesn't allow: > > forall a b. a -> b > > even, because the inner (forall b. a -> b) : [], so adding the forall a > requires the F_omega rule. > > Predicative F_2 and F_w also blow up with quantification on the right of an > arrow, because it looks like the rule for dependent types: > > T -> (forall a. a) > > T : *, (forall a. a) : [] > > so the rule (*,[],[]) would be invoked. > > GHC doesn't have this sort of hierarchy, and so doesn't have these sorts of > weird cases, despite being predicative of a sort. Instead it distinguishes > somehow between monotypes ([Float], String -> Int, a -> b) and polytypes > (forall a. a, ...), although it doesn't really display the difference. > Quantifiers are only supposed to range over kinds that classify monotypes > (or > monotype constructors), which keeps the predicativity (although, even this > gets fudged some: If I have forall a. a -> a, I can instantiate a to the > polytype forall a. a -> a with rank-n polymorphism, because it only seems > to > worry about the validity of the resulting type, and (->) is special; by > contrast, the same cannot be said for forall a. Maybe a, because Maybe > genuinely only accepts monotypes without -XImpredicativeTypes). > > > > ---------- Forwarded message ---------- > From: Bulat Ziganshin <bulat.ziganshin(a)gmail.com> > To: Andrew Coppin <andrewcoppin(a)btinternet.com> > Date: Sun, 6 Dec 2009 11:13:21 +0300 > Subject: Re[2]: [Haskell-cafe] Low Level Audio - Writing bytes to the sound > card? > Hello Andrew, > > Sunday, December 6, 2009, 1:09:18 AM, you wrote: > > > Maybe once I get hired by some financial modelling consultants and get > > paid shedloads of money to write Haskell all day, I'll be able to afford > > a Mac. But until then... > > with such attitude you will never be hired by financial sector. try > instead: > > mac? great! windows? i love it! unix? i've used it since 60's > > > -- > Best regards, > Bulat mailto:Bulat.Ziganshin@gmail.com > > > > > ---------- Forwarded message ---------- > From: Heinrich Apfelmus <apfelmus(a)quantentunnel.de> > To: haskell-cafe(a)haskell.org > Date: Sun, 06 Dec 2009 11:28:25 +0100 > Subject: [Haskell-cafe] Re: universal binary version of Haskell Platform? > Benjamin L.Russell wrote: > > Ah, that's too bad. That means that I won't be able to invoke GHC > > outside of the Terminal application by default, and that even if I > > create a Darwin shell script and alias to invoke it from Aqua, the > > icon for that shell script will only be generic by default. I'd > > rather click on an application icon in the Dock. > > You can write an applescript similar to > > Open Terminal Here > from http://www.entropy.ch/software/applescript/ > > and endow it with a custom icon. > > > Regards, > Heinrich Apfelmus > > -- > http://apfelmus.nfshost.com > > > > > ---------- Forwarded message ---------- > From: Andrew Coppin <andrewcoppin(a)btinternet.com> > To: haskell-cafe(a)haskell.org > Date: Sun, 06 Dec 2009 13:05:19 +0000 > Subject: Re: [Haskell-cafe] Low Level Audio - Writing bytes to the sound > card? > Bulat Ziganshin wrote: > >> Hello Andrew, >> >> Sunday, December 6, 2009, 1:09:18 AM, you wrote: >> >> >> >>> Maybe once I get hired by some financial modelling consultants and get >>> paid shedloads of money to write Haskell all day, I'll be able to afford >>> a Mac. But until then... >>> >>> >> >> with such attitude you will never be hired by financial sector. try >> instead: >> >> mac? great! windows? i love it! unix? i've used it since 60's >> >> > > That's OK. I'm reasonably sure I will never get hired by the financial > sector /anyway/. :-( > > > > > ---------- Forwarded message ---------- > From: Andrew Coppin <andrewcoppin(a)btinternet.com> > To: haskell-cafe(a)haskell.org > Date: Sun, 06 Dec 2009 13:18:59 +0000 > Subject: Re: [Haskell-cafe] binding to C libraries on Windows was Low Level > Audio - Writing bytes to the sound card? > john lask wrote: > >> I think there are some misapprehensions here:- >> >> Many haskell packages binding to c libraries will compile with ghc >> without problems on windows - without cygwin, without mingw/msys system. >> > > OK, well I haven't tried building every C binding on all of Hackage, just a > few of them. So far none of them have worked. (Including wxHaskell, SDL, one > of the database packages, etc.) It's got to the point where I've simply > given up trying. Most such packages just don't seem to work on Windows, and > nobody on the mailing lists or on IRC has any clue why. (I guess because few > people in the Haskell community use Windows and understand how it's supposed > to work.) > > Some such packages build "out of the box" on windows, like the zlib >> package which contains the c source for the c zlib library. GHC is able >> to compile and build this packages without any other c >> compiler/libraries/unix emulators etc because ghc itself contains part >> of the gcc c compiler tool chain and comes with all c standard headers, >> c++ headers and c/c++ runtime libraries. >> > > Yes, I realised long ago that GHC uses GCC and other GNU build tools. > (Presumably this makes porting to Windows far easier.) More recently I > realised that it also includes a surprisingly large set of header files, > seemingly including the entire Win32 API, which is interesting. > > There >> is only one gotch-ya - you need to have a import library for the gcc >> tool chain (thats what ghc uses) i.e. a ".a" library and not the native >> windows ".LIB" import library. >> > > They're different?? o_O > > Oh. Suddenly several things seem clearer... > > If you don't have ".a" import library >> but have the dll then the '.a' import library be built for any dll >> relativley easily. >> > > Any idea how? > > the bigest problem hamperring cleaner builds of haskell packages on >> windows is the lack of any standardised scheme for the installation of >> c-libraries and header files (and of course the availability of a >> suitable build of the library). >> > > Isn't one of Cabal's jobs to figure out where stuff is? Can't we get Cabal > on Windows to say "hey, I need to find foo.h, you know where that is?" Or > something like that? > > Another problem hampering the install of haskell packages on windows is >> the use of the unix autoconf build system (./configure) - package >> writters note! >> > > Heh. I found one Wiki page once describing how to set up a Cabal package. > When it started talking about how to integrate Automake, I hung my head is > dispair. (I believe the page in question is fixed now. But a lot of package > authors seem to assume that everybody just uses Unix of some kind...) > > > > _______________________________________________ > Haskell-Cafe mailing list > Haskell-Cafe(a)haskell.org > http://www.haskell.org/mailman/listinfo/haskell-cafe > >

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ANNOUNCE: Blueprint 0.1 -- PREVIEW
by Gregory Crosswhite 06 Dec '09

06 Dec '09

I earlier posted to this list asking for help in getting Cabal to play with a Fortran compiler. When it turned out that there was no answer to this, I of course did the obvious thing --- I wrote my own build system. :-) It already boasts the following features: * Fully self-hosting --- can both build and install itself. * Implicitly detects and tracks module dependencies. * Builds in parallel as much as possible. * Can scan through a source directory to add all files, saving the trouble of adding them manually. * Supports compiling C and Fortran sources in addition to Haskell sources, and linking everything together. * Utilizes a “tool” system to make it easy to extend its functionality, such as by adding a new language. * Flexible configuration system: tool options (e.g., path to the Fortran compiler) can be detected automatically, set in a configuration file, or specified on the command line. * Provides help messages both to list the targets and to explain the configuration command-line options. * Does not terminate at the first error, but instead tries to do as much as possible and then report all errors. (This is a general philosophy that holds both for the build, the configuration, etc.) * Easily supports multiple targets that can depend on the results from other targets. * Automatically resolves package dependencies, as read from .cabal file. Detects when a module is not in any known dependency, and reports an error that also lists all packages that export this module. What separates this system apart from others is that it uses Haskell’s built-in laziness to handle dependency ordering and parallelism. That is, one expresses the desired build result as a function of the input sources; when the result is demanded, it causes Haskell to go through and execute on-demand all of the necessary build steps. To get parallelism, just tell GHC to use multiple threads with the “+RTS -N# -RTS” option, where # is the number of threads. (All that I had to do to get this to work was put parLists in a couple of places.) This is a big win for me because it means that I get the correct behavior without having to write and test my own complicated graph data structure for tracking the dependencies between build steps. The philosophy of building up a big calculation of which only parts need be lazily demanded can be extended further to the build phases, which I call “targets”. For example, the first line of the code defining the build target is: build = configure >>= \configuration -> ... This demands the configuration target, and then uses the result in the build. So when you run “./Setup configure”, you only demand that Setup compute the value of “configure”, but when you run “./Setup build” you demand both “build” and also “configure”. All of the errors that are reported are “composable” in the sense that they can be combined into a new error message that leaves nothing out and also has no duplicates. As much as possible the system tries not to stop until it has nothing else that it can do, allowing it to uncover as many errors as possible and then compose them into a single message. I have posted Blueprint to Hackage so that people can see what I have done and possibly play with it. I hope to eventually document it and add examples, but I figured it was better to release early and get it out there sooner rather than later so that people can see what I’ve done. Thus, at this point it should be considered a PREVIEW release, not even an alpha release. Having said that, within the domain of the functionality it implements it works well enough that I use it myself as the build system for a Physics simulation code that is a mixture of C, Haskell, and Fortran. To see what Blueprint looks like in action, take a look at Setup.hs. For example, Setup can either build a library (“build” target) or it can build itself (“bootstrap” target); it is smart enough to use different flags and directories in the two cases so that there ends up being in essence two parallel builds. Setup also has a lot of targets: configure, reconfigure (delete cached configuration and then configure), build, rebuild (clean then build), clean, distclean, install, bootstrap (build itself rather than a library), haddock (documentation generation that does not work particularly well yet). Anyway, take a look if any of this sounds interesting to you, and let me know if you have any questions! - Greg PS: You're best bet for browsing through the sources is to use Leo (leo.sourceforge.net) since this makes it easier for you to see how everything is organized.

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HP + Gtk2hs?
by Andrew Coppin 06 Dec '09

06 Dec '09

So I decided to try out the Haskell Platform instead of just installing GHC directly. To be honest, I didn't really notice much difference, except for the files being installed in a different place. But then, initially HP ~= GHC; presumably the plan is for it to grow as time goes on. Anyway, I'm sure you can all see where I'm going with this: Latest Gtk2hs binary for Windows doesn't seem to like the latest HP installation. A few things: - It is unclear to be which Gtk2hs binaries require which GHC version. Can we tabulate this information somewhere? - It is also unclear to me which HP versions contain what stuff. The HP page tells you all about the *current* HP version, and contains a link to a raw directory listing for the older versions. (I especially love the way the server truncates the filenames to just before where the version number starts. Very helpful. :-D ) Can we get propper descriptions for _all_ releases of HP? A table summarising the GHC version and major packages/versions in each release would be nice. - Any idea why the HP says "beta" on it? - Apart from HP providing GHC 6.10.4 while Gtk2hs currently requires 6.10.3, it appears that the Gtk2hs installer package doesn't like GHC being installed in a path with spaces. Apparently Gtk2hs has a bug tracker. (I only just discovered this, so perhaps it needs to be more prominent?) Somebody pointed out this bug 6 months ago. Somebody else posted a potential fix a month ago. There is no visible activity from the developers. (I emphasize "visible". Maybe they've seen this and they're working on it, but there's no visible indication of activity.) Gtk2hs is currently the *only* GUI binding that actually works on Windows. It's always been slightly frustrating that every time a new version of GHC comes out, us Windows users have to beg for somebody to build a new binary. (Linux users, on the other hand, can just download the sources and compile them with any compiler they like.) Presumably going forward Gtk2hs will synchronise to the (less frequent) HP releases rather than the individual GHC releases, so many this particular frustration will be reduced. (It would be even less frustrating if Gtk2hs was *in* HP, but I gather this won't ever happen.) Of course, being able to actually build C bindings on Windows would be even better, but this is apparently infeasible... :-( That being the case, I'll settle for just a little bit more documentation.

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universal binary version of Haskell Platform?
by Benjamin L.Russell 06 Dec '09

06 Dec '09

Recently, in changing my work schedule to work mainly from home, I switched from mainly using a work Wintel machine running Windows XP Professional, Service Pack 3, to mainly using my home PowerPC G4 PowerBook Macintosh, currently upgraded to Mac OS X 10.5.8 Leopard. However, to my surprise, there does not seem to be a version of the Haskell Platform that runs natively on my current OS. Does anybody know where to find a universal binary version of the Haskell Platform, or at least of GHC 6.10.4? Otherwise, I'm stuck without a native version. -- Benjamin L. Russell -- Benjamin L. Russell / DekuDekuplex at Yahoo dot com http://dekudekuplex.wordpress.com/ Translator/Interpreter / Mobile: +011 81 80-3603-6725 "Furuike ya, kawazu tobikomu mizu no oto." -- Matsuo Basho^

4 3

Re: Optimizing Parsec 3 -- was: Wiki software?
by Howard B. Golden 05 Dec '09

05 Dec '09

On Friday December 4, 2009, John MacFarlane wrote: > I used criterion to compare pandoc compiled with parsec2 to > pandoc compiled with your version of parsec3. (The benchmark > is converting testsuite.txt from markdown to HTML.) The difference > was minor: > > parsec2: > mean: 67.66576 ms, lb 67.56722 ms, ub 67.88983 ms, ci 0.950 > std dev: 722.3878 us, lb 323.0343 us, ub 1.356013 ms, ci 0.950 > > parsec3: > mean: 68.20847 ms, lb 68.16387 ms, ub 68.26284 ms, ci 0.950 > std dev: 252.7773 us, lb 204.5512 us, ub 325.2424 us, ci 0.950 > > So, once you release the new parsec3, I am prepared to remove the > "parsec < 3" restriction from the libraries I maintain: pandoc, > highlighting-kate, filestore, gitit, and yst. I don't know what the performance of the current parsec3 is compared to parsec2. It would be helpful if you could run your benchmark for that also and include it. If the only issue is performance, I respectfully request that you remove the parsec < 3 requirement even before the new version of parsec3 is released. Thank you. Howard

2 1

Avoiding undecidables
by Michael Snoyman 05 Dec '09

05 Dec '09

Hi all, Well, I've got two problems which both want to be solved with undecidable and overlapping instances. Obviously, I'd like to try and avoid them. For the record, the problems have to do with the control-monad-failure and convertible packages. The code below *should* make clear what I'm trying to accomplish: -- failure should not be limited to just monads, so... class Failure e f where failure :: e -> f v class (Functor f, Failure e f) => FunctorFailure e f instance (Functor f, Failure e f) => FunctorFailure e f -- undecidable, overlaps class (Applicative f, Failure e f) => ApplicativeFailure e f instance (Applicative f, Failure e f) => ApplicativeFailure e f -- undecidable, overlaps class (Monad f, Failure e f) => MonadFailure e f instance (Monad f, Failure e f) => MonadFailure e f -- undecidable, overlaps And now the convertible issue. I want two type classes: Convert for anything which *might* be convertible, but might not. For example, sometimes a String can be converted to an Int (like the string "5"), but sometimes it will fail (like "five"). TotalConvert is when something *is* convertible, such as Int to String (simply the show function). Thus the following: class Convert x y where convert :: x -> Maybe y class Convert x y => TotalConvert x y where totalConvert :: x -> y instance TotalConvert x y => Convert x y where -- Boom! convert = Just . totalConvert Any ideas are most welcome. Both of these seem like cases where the compiler could do some DWIMery, but isn't. Michael

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Re: [Haskell-cafe] HP + Gtk2hs?
by Andrew Coppin 05 Dec '09

05 Dec '09

M Xyz wrote: > > > > - Apart from HP providing GHC 6.10.4 while Gtk2hs currently > requires 6.10.3, it appears that the Gtk2hs installer package > doesn't like GHC being installed in a path with spaces. Apparently > Gtk2hs has a bug tracker. (I only just discovered this, so perhaps > it needs to be more prominent?) Somebody pointed out this bug 6 > months ago. Somebody else posted a potential fix a month ago. > There is no visible activity from the developers. (I emphasize > "visible". Maybe they've seen this and they're working on it, but > there's no visible indication of activity.) > > Thank you so much for this post. I tried to install Gtk2hs yesterday > to play with > its Cairo bindings and I hit the "Setup found what appears to be a > non-working installation of GHC" brickwall. I found a closed ticket > about this problem: http://hackage.haskell.org/trac/gtk2hs/ticket/1117 > I posted this issue on the Gtk2hs-devel mailing list and got a > response today: > http://sourceforge.net/mailarchive/forum.php?thread_name=EF0EE62B-259C-4F62… > > I don't think I have the will to uninstall the Haskell Platform and > everything I've set up just to install in a path with no spaces. :) > > My information is from here: http://hackage.haskell.org/trac/gtk2hs/ticket/1165 In case it makes any difference to you. :-)

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Re: [Haskell-cafe] HP + Gtk2hs?
by M Xyz 05 Dec '09

05 Dec '09

- Apart from HP providing GHC 6.10.4 while Gtk2hs currently requires 6.10.3, it appears that the Gtk2hs installer package doesn't like GHC being installed in a path with spaces. Apparently Gtk2hs has a bug tracker. (I only just discovered this, so perhaps it needs to be more prominent?) Somebody pointed out this bug 6 months ago. Somebody else posted a potential fix a month ago. There is no visible activity from the developers. (I emphasize "visible". Maybe they've seen this and they're working on it, but there's no visible indication of activity.) Thank you so much for this post. I tried to install Gtk2hs yesterday to play with its Cairo bindings and I hit the "Setup found what appears to be a non-working installation of GHC" brickwall. I found a closed ticket about this problem: http://hackage.haskell.org/trac/gtk2hs/ticket/1117 I posted this issue on the Gtk2hs-devel mailing list and got a response today: http://sourceforge.net/mailarchive/forum.php?thread_name=EF0EE62B-259C-4F62… I don't think I have the will to uninstall the Haskell Platform and everything I've set up just to install in a path with no spaces. :)

1 0

Finding HP
by Andrew Coppin 05 Dec '09

05 Dec '09

Today I was setting up a my new, and I wanted to put Haskell on it. Rather than download GHC itself, I decided to install the Haskell Platform instead, just to see what it's like. Much to my surprise, I couldn't actually find any reference to its existence anywhere from the haskell.org home page, and I eventually had to run a search to find it. Subsequently, I realise [as somebody will no doubt point out] that the link is actually there, on the front page, right next to GHC, Hugs, et al. My suggestion is that if we really want people to grab the HP rather than download GHC directly, maybe we could make the link slightly more prominent? It also wouldn't hurt to mention it from the "Implementations" page, and maybe the GHC homepage? Just a suggestion...

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Wikipedia article
by Simon Marlow 05 Dec '09

05 Dec '09

As noted before, the Wikipedia article for Haskell is a disorganised mess. http://en.wikipedia.org/wiki/Haskell_%28programming_language%29 earlier this year, dons suggested reorganising it and posted a template on the Haskell wiki: http://haskell.org/haskellwiki/WikipediaArticleDesign I've made a start on a new version of the page: http://en.wikipedia.org/wiki/User:Simonmar/Haskell_%28programming_language%… I've kept most of the existing information, but reorganised it more or less according to Don's template, and I filled out the overview section. Also I fixed numerous things, but the page still has a long way to go Does anyone mind if I spam the existing Haskell article with this new one, or do people think we should continue editing the sandbox version until it's in better shape? Cheers, Simon

6 9

From function over expression (+, *) derive function over expression (+)
by Radek Micek 05 Dec '09

05 Dec '09

Hello. I have two types for expression: data Expr = Add Expr Expr | Mul Expr Expr | Const Int data AExpr = AAdd AExpr AExpr | AConst Int The first one supports addition and multiplication and the second only addition. I can write a function to simplify the first expression: simplify :: Expr -> Expr simplify = {- replaces: "a*1" and "1*a" by "a", "a+0" and "0+a" by a -} And I would like to use the function simplify for the second type AExpr. What can I do is to convert AExpr to Expr, simplify it and convert it back. But I don't like this solution because conversions take some time. I would prefer following: I say to the compiler that AAdd is like Add and AConst is like Const and the compiler derives function asimplify for AExpr. Is it possible to do this? In fact I want to have two distinct types where one is "extension" of the second (Expr is extension of AExpr) and I want to define a function for the extended type (Expr) and use it for the original type (AExpr). I assume that the function won't introduce Mul to the expression which had no Mul. Thanks in advance Radek Micek

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Haskell Weekly News: Issue 142 - December 05, 2009
by jfredett＠gmail.com 05 Dec '09

05 Dec '09

--------------------------------------------------------------------------- Haskell Weekly News http://sequence.complete.org/hwn/20091205 Issue 142 - December 05, 2009 --------------------------------------------------------------------------- Welcome to issue 142 of HWN, a newsletter covering developments in the [1]Haskell community. Occasionally, I have something silly or clever to say here. Usually I give a summary of the weeks news and end it with a bit of a cliche tagline, however, this is finals week, and as such, there is absolutely no brain cells left working to come up with any cleverness for here. I'll see you next week with (hopefully) more ability for humor. Until next week, the Haskell Weekly News! Announcements error-message. Gregory Crosswhite [2]announced a package for handling errors in haskell. To quote his message directly, 'If there is one thing that we really don't have enough of in Haskell, it is *ways to handle errors*!' atom-0.1.3. Tom Hawkins [3]announced a new version of the Atom DSL for designing hard realtime embedded software. Blueprint 0.1 -- PREVIEW. Gregory Crosswhite [4]announced a preview version of his 'Blueprint' configuration package. haskell-mode 2.7.0. Svein Ove Aas [5]announced another release of Haskell-mode for Emacs graphviz-2999.7.0.0. Ivan Lazar Miljenovic [6]announced a new version of his set of bindings to the graphviz tools for visualizing graphs. Haskell Job Openings (Pune, IN). Tom Hawkins [7]announced some job openings in Eaton's engineering center in Pune, India. SaC Tutorial at PPoPP 2010. Clemens Grelck [8]announced a tutorial to be held at PPoPP on SAC and it's auto-parallelizing compiler SAC2C. Call for papers: PAPP 2010, 7th International Workshop on Practical Aspects of High-level Parallel Programming. Clemens Grelck [9]announced a call for papers for the Seventh International Workshop on Practical Aspects of High-level Parallel Programming. PhD Studentships in Nottingham. Graham Hutton [10]announced some PhD openings at the University of Nottingham. Second Call for Copy: Monad.Reader Issue 15. Brent Yorgey [11]announced a second call for copy for the Monad.Reader. 3 full professor positions at DIKU. Fritz Henglein [12]announced three open professor positions at the the Department of Computer Science at the University of Copenhagen ([13]DIKU). Hubris 0.0.2, the Ruby-Haskell bridge. Mark Wotton [14]announced a new version of the Hubris package is now available on hackage. Discussion You are in a twisty maze of concurrency libraries, all different ... Patrick Caldon [15]asked about the 'right' concurrency package to use for his project. Greetings! 2D Graphics? M Xyz [16]asked (enthusiatically) about different ways to do 2-dimensional graphics in Haskell. Wikipedia article. Simon Marlow [17]rallied us all into fixing the (or at least starting to fix) wikipedia page for Haskell. Great Programs to Read? Michael Lesniak [18]asked about what programs were worth reading. Blog noise [19]Haskell news from the [20]blogosphere. Blog posts from people new to the Haskell community are marked with >>>, be sure to welcome them! * Michael Snoyman: [21]String-like. * Claude Heiland-Allen: [22]Heist: dataflow algebra. * Adam Jones: [23]Lambda Calculus Compiler: Part III: First-Order Functions. * Holumbus: [24]Hayoo! Update âŠ Again. * Mikael Vejdemo Johansson (Syzygy-): [25][MATH198] Lecture 10 (last lecture) posted. * Neil Brown: [26]Automated Wiring of Message-Passing Processes. * Computer Systems Design Laboratory at the University of Kansas: [27]ChalkBoard Release. * Bryan O'Sullivan: [28]Dense? Dense, you say?. * Ivan Lazar Miljenovic: [29]Waddaya know, testing WORKS!. * Ivan Lazar Miljenovic: [30]If wishes were tests, code would be perfect. * Ivan Lazar Miljenovic: [31]The Problems with Graphviz. Quotes of the Week * Badger: one does not simply >>= into mordor * Apocalisp: data CanHaz a = Haz a | ButIEatedIt * Apocalisp: You can't have your baby and eat it too * Dave_Benjamin: please talk to your son or daughter about parametric polymorphism * Cale: Beginners are confusing to beginners. I move that we remove them from the language altogether. * monochrom: I am 17-ary, going on 18-ary, I can take curry of you * jmillikin: [the real world is] an implementation detail of IO, pay it no mind * monochrom,ezyang: The Principle Of Idiot Savant: any sufficiently misguided opinion is indistinguishable from deep insight * Cale: I swear that most of higher-dimensional category theory must have been arrived at by some guys sitting around in a room with a blackboard and saying "What if a drew a diagram like *THIS*!?" and drawing some insane scribble up on the blackboard, and then everyone tries to figure out how to turn it into meaningful mathematics. * jbe: Here I am, happy my code compiles, and the runtime is thumbing its nose at Turing. * Ferdirand: I was TA for a C++ programming course aimed at 1st year physics once. Some girl asked for help "i wrote pseudo-code but I cannot translate it to C++". Her pseudo-code was valid haskell. I cried. * mmorrow: [regarding excessive use of categorical recursion schemes] a morphasm? * copumpkin: I'm on a rollomorphism * dons: but rumours are remarkably common when it comes to haskell * monochrom: If you read a haskell book or an FP book, by chapter 5 it's already doing data structures. It's chapter 10 in imperative books. About the Haskell Weekly News New editions are posted to [32]the Haskell mailing list as well as to [33]the Haskell Sequence and [34]Planet Haskell. [35]RSS is also available, and headlines appear on [36]haskell.org. To help create new editions of this newsletter, please see the information on [37]how to contribute. Send stories to jfredett . at . gmail . dot . com. The darcs repository is available at darcs get [38]http://patch-tag.com/r/jfredett/HWN2/pullrepo HWN2 . References 1. http://haskell.org/ 2. http://article.gmane.org/gmane.comp.lang.haskell.cafe/67149 3. http://article.gmane.org/gmane.comp.lang.haskell.cafe/67090 4. http://article.gmane.org/gmane.comp.lang.haskell.cafe/66924 5. http://article.gmane.org/gmane.comp.lang.haskell.cafe/66923 6. http://article.gmane.org/gmane.comp.lang.haskell.cafe/66920 7. http://article.gmane.org/gmane.comp.lang.haskell.cafe/66904 8. http://article.gmane.org/gmane.comp.lang.haskell.general/17661 9. http://article.gmane.org/gmane.comp.lang.haskell.general/17660 10. http://article.gmane.org/gmane.comp.lang.haskell.general/17659 11. http://article.gmane.org/gmane.comp.lang.haskell.general/17657 12. http://article.gmane.org/gmane.comp.lang.haskell.general/17656 13. http://www.diku.dk/ 14. http://article.gmane.org/gmane.comp.lang.haskell.general/17653 15. http://thread.gmane.org/gmane.comp.lang.haskell.cafe/67211 16. http://thread.gmane.org/gmane.comp.lang.haskell.cafe/67184 17. http://thread.gmane.org/gmane.comp.lang.haskell.cafe/67158 18. http://thread.gmane.org/gmane.comp.lang.haskell.cafe/66917 19. http://planet.haskell.org/ 20. http://haskell.org/haskellwiki/Blog_articles 21. http://snoyberg.wordpress.com/2009/12/04/string-like/ 22. http://claudiusmaximus.goto10.org/cm/2009-12-04_heist_dataflow_algebra.html 23. http://blog.finiteimprobability.com/2009/12/03/lambda-calculus-compiler-par… 24. http://holumbus.fh-wedel.de/blog/?p=28 25. http://blog.mikael.johanssons.org/archive/2009/12/math198-lecture-10-last-l… 26. http://chplib.wordpress.com/2009/12/02/automated-wiring-of-message-passing-… 27. http://www.ittc.ku.edu/csdlblog/?p=25 28. http://www.serpentine.com/blog/2009/12/01/dense-dense-you-say/ 29. http://ivanmiljenovic.wordpress.com/2009/11/17/waddaya-know-testing-works/ 30. http://ivanmiljenovic.wordpress.com/2009/11/26/if-wishes-were-tests-code-wo… 31. http://ivanmiljenovic.wordpress.com/2009/11/30/the-problems-with-graphviz/ 32. http://www.haskell.org/mailman/listinfo/haskell 33. http://sequence.complete.org/ 34. http://planet.haskell.org/ 35. http://sequence.complete.org/node/feed 36. http://haskell.org/ 37. http://haskell.org/haskellwiki/HWN 38. http://patch-tag.com/r/jfredett/HWN2/pullrepo%20HWN2

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Fwd: [Haskell-cafe] Haskell for Physicists
by Don Stewart 05 Dec '09

05 Dec '09

Hey all, Following up on this, I'm presenting a position paper tomorrow on the use of EDSLs to improve productivity and lower cost when developing code for new high performance architectures (like GPUs). http://www.galois.com/blog/2009/10/13/domain-specific-languages-for-domain-… It advocates for Haskell + EDSLs, much as we have been discussing in this thread. -- Don

6 6

inotify-alike for mac os x?
by Conal Elliott 05 Dec '09

05 Dec '09

I'd like to make some FRPish toys that keep files updated to have functional relationships with other files. hinotify looks like just the sort of underlying magic I could use for efficient implementation on linux. Is there any support for mac os x? Could support be either added to hinotify or maybe inotify and a mac-friendly library be abstracted into a common Haskell interface? I'm fine with an imperative interface, since I can abstract into a functional library, which I guess would be a sort of persistent simplified FRP. - Conal

7 10

GHC magic optimization ?
by Emmanuel CHANTREAU 05 Dec '09

05 Dec '09

Hello One thing is magic for me: how GHC can know what function results to remember and what results can be forgotten ? Is it just a stupid buffer algorithm or is there some mathematics truths behind this ? I'm very happy about Haskell, it's so great to put some smart ideas in a computer. thanks -- Emmanuel Chantréau

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Re: Low Level Audio - Writing bytes to the sound card?
by John Lato 05 Dec '09

05 Dec '09

> From: M Xyz <functionallyharmonious(a)yahoo.com> > >> if you get it to work > > As a spoiled Java programmer, this new role as pioneer is a bit intimidating, but I will give it a shot. :) > > I downloaded the portaudio v19 source and I'm attempting to build it. Apparently I have to register my Visual Studio Express with Microsoft. Deeper down the rabbit hole... (Interesting aside, on the registration form under "What programming language topics are you interested in?" neither F# or Haskell are listed) For doing cross-platform development, I would strongly recommend that you use MinGW (or cygwin) in preference to Visual Studio Express. This is because most Unix/Linux packages, and thus most cross-platform packages, are designed to be built with the GNU compiler toolchain (i.e. configure, make, make install), and getting them to work with Visual Studio can be a chore. I also would use PortAudio for what you describe, and have had good experience with it on OSX. Sox is a good choice as well if you don't mind piping output to another program. *shameless plug* you could also use hCsound, although it's probably higher-level than what you're looking for. Installing on Windows is tricky too, but you only need to do so once. John

2 1

Are there major inefficiencies in Haskell compared to OCaml?
by Casey Hawthorne 04 Dec '09

04 Dec '09

Are there major inefficiencies in Haskell compared to OCaml? If so, can something be done about them? -- Regards, Casey

5 4

Greetings! 2D Graphics?
by M Xyz 04 Dec '09

04 Dec '09

Greetings, my name is M. This is my first time posting to a mailing list so forgive me if I've done something wrong. I just finished "Real World Haskell" and am currently working through "School of Expression". I am new to Haskell but I already love it. My question is this... I am interested in doing graphics work in Haskell, but I am lost trying to pick a library. I've been designing engineering apps in Java for 6 years and I'll admit I've been coddled by its standard library, lol. I am looking for something very lightweight with the basic capabilities of Java's Graphics2D class (antialias, composite, clipping, transformation, simple drawing primitives, gradients). I want something simple and "lightweight" because my interest is to play with building higher level abstractions myself. I use XP and Ubuntu so I'd prefer not to use the Graphics-Win32 library used by "School of Expression" if there is a platform independent library. I've read through http://www.haskell.org/haskellwiki/Applications_and_libraries/Graphics and the pertinent libraries seem to be Haven, HGL or Cairo via Gtk2Hs right? Which is the most popular/active and appropriate for a beginner to start working with? Thank you!

4 3

seems like I'm on the wrong track
by Michael P Mossey 04 Dec '09

04 Dec '09

Perhaps someone could either (1) help me do what I'm trying to do, or (2) show me a better way. I have a problem that is very state-ful and I keep thinking of it as OO, which is driving me crazy. Haskell is several times harder to use than Python in this instance, probably because I'm doing it wrong. To give you a larger context, this problem is essentially compiling a description of music (my own) into a kind of music-machine-language (CSound). CSound is relatively untidy. In this one example, in a OO way of thinking, I have data called AssignedNumbers that assigns integers to unique strings and keeps track of the used integers and next available integer (the choice of available integer could follow a number of conventions so I wanted to hide that in an ADT.) So it has an associated function: getNumber :: String -> AssignedNumbers -> (Int,AssignedNumbers) What getNumber does is: - check if the string already has a number assigned to it. If so, return that number. - if not, pick the next available number. - in all cases, return the possibly changed state of AssignedNumbers Then in a larger data structure, it contains fields of type AssignedNumbers. Like data MusicStuff = MusicStuff { oscillatorNumbers :: AssignedNumbers , tableNumbers :: AssignedNumbers , ... } I'm using MusicStuff in a State monad, so I might write a function like doSomeMusicStuff :: String -> String -> State MusicStuff (Int,Int) doSomeMusicStuff aString1 aString2 = do ms <- get (o1,newOscNums) = getNumber aString1 (oscillatorNumbers ms) (t1,newTabNums) = getNumber aString2 (tableNumbers ms) put ms { oscillatorNumbers = newOscNums , tableNumbers = newTabNums } return (o1,t1) For what it does, this is extremely verbose and filled with distracting visual content. And this is just a very simple example---my real problem is several times more state-ful. Is there a better way? Note that in Python it would be a method def doMusicStuff( self, s1, s2 ) : return (self.oscillatorNumbers.next(s1), self.oscillatorNumbers.next(s2))

9 17

Optimization with Strings ?
by John D. Earle 04 Dec '09

04 Dec '09

Dear Emmanuel Chantréau, You may want to look into Objective CAML http://caml.inria.fr/ which is a French product as you can see from the Internet address. It is likely better suited to the task than Haskell and has a reputation for speed. For those who prefer object oriented programming it has facilities for that which may ease your transition from C++. The Microsoft F# language is based on Objective CAML. Haskell has a problem with its type system and is not rigorous. Haskell is not a suitable language for proof assistants and so I would advise you to stay clear of Haskell. Standard ML was engineered with the needs of proof assistants in mind and so you may want to look into Standard ML, but you should be very happy with Objective CAML. It has an excellent reputation. The Coq proof assistant which is another French product is based on Objective CAML. If you do decide that Haskell is the way, it will help ease your transition to Haskell. There is nothing that says you can't keep your fingers in several pies at once.

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FFI and ghci
by Patrick LeBoutillier 04 Dec '09

04 Dec '09

Hi all, I have a small FFI-based library that I like to test like this: $ ghci -I../c -L../c/.libs -lmlp t.hs GHCi, version 6.10.1: http://www.haskell.org/ghc/ :? for help Loading package ghc-prim ... linking ... done. Loading package integer ... linking ... done. Loading package base ... linking ... done. Loading object (dynamic) mlp ... done final link ... done [1 of 9] Compiling MLP ( MLP.hs, interpreted ) [2 of 9] Compiling MLP.Error ( MLP/Error.hs, interpreted ) [3 of 9] Compiling MLP.Context ( MLP/Context.hs, interpreted ) [4 of 9] Compiling MLP.Runtime ( MLP/Runtime.hs, interpreted ) [5 of 9] Compiling MLP.Object ( MLP/Object.hs, interpreted ) [6 of 9] Compiling MLP.Type ( MLP/Type.hs, interpreted ) [7 of 9] Compiling MLP.Value ( MLP/Value.hs, interpreted ) [8 of 9] Compiling MLP.Language ( MLP/Language.hs, interpreted ) [9 of 9] Compiling Main ( t.hs, interpreted ) Ok, modules loaded: MLP, MLP.Object, Main, MLP.Runtime, MLP.Context, MLP.Error, MLP.Value, MLP.Type, MLP.Language. *Main> main Note: Inside libmlp.so, another shared object is loaded using dlopen(). When running this test program I get some sporadic segmentation faults, which seem to always occur at entrypoint to the shared object that is loaded with dlopen(). But when I compile it with ghc, i.e. $ ghc --make -I../c -L../c/.libs -lmlp t.hs I can't reproduce crash. Can anyone see why this could be happening? It's quite possible that there is really a bug in the C code, but if someone knows about a bug or something in ghci that can cause this behaviour I can stop looking... Thanks a lot, Patrick -- ===================== Patrick LeBoutillier Rosemère, Québec, Canada

1 0

Re: [Haskell-cafe] Is Haskell a Fanatic?
by Brandon S. Allbery KF8NH 04 Dec '09

04 Dec '09

> 2009/12/03 Brandon S. Allbery KF8NH <allbery(a)ece.cmu.edu>: >> This "troll" was, apparently, invited by one of the Simons >> onto the Haskell' list, then asked to move his spiels here. I am informed that the "invitation" I was referring to was actually about his being invited *out*, not in, so his origin is still a mystery and "troll" is likely appropriate. (I can't say he's demonstrated much of a mathematical basis for his trollery; only a propensity for pompous declarations, and deflection when challenged on them. Put up or shut up, troll.) -- brandon s. allbery [solaris,freebsd,perl,pugs,haskell] allbery(a)kf8nh.com system administrator [openafs,heimdal,too many hats] allbery(a)ece.cmu.edu electrical and computer engineering, carnegie mellon university KF8NH

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Optimization with Strings ?
by Emmanuel CHANTREAU 04 Dec '09

04 Dec '09

Hello In my futur program, it use a lot of binary trees with strings (words) as leaf. There is just arround 1000 words and they will appear a lot of times. The program will possibly consume a lot of process and memory (it is a mathematics proover). I began this program in C++ but haskell has a prety good speed and memory footprint and is easier. But I don't know if it worth to do this optimization: having a dictionary to translate string words in Int. The answer depends on the automatic optimizations in GHC, because GHC could compare quickely two strings if it is the same object, so it depends if program generated by GHC have a dictionary (tree) of strings internaly. Someone knows this ? (Sorry for my english, I'm french) thank you -- Emmanuel Chantréau

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Re: [Haskell-cafe] Is Haskell a Fanatic?
by gladstein＠gladstein.com 04 Dec '09

04 Dec '09

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Mushrooms (edible/poisonous) and Haskell
by Hans van Thiel 04 Dec '09

04 Dec '09

Hi All, About six months ago I uploaded version 0.6 to Hackage of Emping, a prototype tool using a new algorithm for data mining/machine learning. It won't build with the newer versions of GTk2Hs because the Gtk2Hs API changed since 0.9.13, and I used older versions of GHC and Gtk2Hs. For several reasons I don't have easy access to the newer versions, so I havn't fixed it yet. It should (that famous word) take no more than 15 minutes to change a Maybe Int into an Int in the main module. Apart from that it compiles warning free and (in my own opinion) the code is pretty clean now. See the user guide for some bugs I found and haven't fixed yet. The reason for this post is that I've been testing it, and have now built an iteractive demonstration of the result of a case study. This is a well known example of a table of 8124 rows and 23 columns, and the goal is to distinguish between poisonous and edible mushrooms. Emping found 3635 rules with antecedent length of 1 to 6, and the claim is that these rules fully describe all possibilities. So, I hope people will examine this case and, hopefully, will find no examples refuting this claim. As far as I know no one has ever analized this table in such detail, but that's another thing to be found out. With regard to Haskell, imo Haskell is very suitable and practical as a language for such a tool, because it is so modular. Changing something in one place is usually pretty safe. From a practical pov, amongst all the advantages and disadvantages, maintainability is surely a strength! Anyway, for anyone who's interested in the application, see http://muitovar.com/emp/emp_get.php and related links. Yes, unfortunately the demo is not in Haskell... Regards, Hans van Thiel

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language-dot usage
by minh thu 04 Dec '09

04 Dec '09

Hi, I'm using the language-dot package to generate some .dot file. I'm wondering how to make edges. I was expecting to generate something like 1 -> {2 ; 3} but get in fact 1 -> 2 -> 3 I used the (pseudo) statements [NodeStatement $ NodeID 1, EdgeStatement [NodeId 2, NodeId 3]] What is the proper way to do that ? Thanks, Thu

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Re: [Haskell-cafe] Wikipedia article
by Sean Leather 04 Dec '09

04 Dec '09

On Fri, Dec 4, 2009 at 13:11, Max Rabkin wrote: > On Fri, Dec 4, 2009 at 1:18 PM, Sean Leather <leather(a)cs.uu.nl> wrote: > > I'm confused. When I'm logged in to Wikipedia, I see a page that is > vastly > > different from when I'm not logged in. I haven't played with Wikipedia in > a > > long time, so perhaps there is some reason for this, of which I am not > > aware. > > Wikipedia uses a caching proxy for non-logged-in users. > Ah, thanks. I talked to somebody else who had the same problem, so now we know. Regards, Sean

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I miss OO
by Michael Mossey 04 Dec '09

04 Dec '09

I'm fairly new to Haskell, and starting to write some big projects. Previously I used OO exclusively, mostly Python. I really miss the "namespace" capabilities... a class can have a lot of generic method names which may be identical for several different classes because there is no ambiguity. In my musical application, many "objects" (or in Haskell, data) have a time associated with them. In Python I would have an accessor function called "time" in every class. So if I have objects/data note1, cursor1, and staff1, Python: note1.time() cursor1.time() staff1.time() Haskell needs something like note_time note1 cursor_time cursor1 staff_time staff1 which is a lot more visually disorganized. What's worse, I have a moderate case of RSI (repetitive strain injury) so I type slowly and depend on abbreviations a lot. I use the souped-up abbreviation capabilities of Emacs. Let's say I have a field/member-variable called orientedPcSet that is used across many classes. In Python, I can create an abbreviation for that and it is useful many times. In Haskell, I might need someType_orientedPcSet someOtherType_orientedPcSet thirdType_orientedPcSet which prevents me from using abbreviations effectively (especially the dynamic-completion feature). (It would help to make the underscore not part of word syntax, but that's not ideal.) So I'm thinking of moving to a scheme in Haskell using modules, most types being defined in their own modules, and doing qualified imports. Generic names like 'time' can be defined in each module w/o clashing. Then I have Note.time note1 Cursor.time cursor1 Staff.time staff1 This is very useful because I can define abbreviations for the type name and for oft-used accessor function names and these abbrevs are more organized, easier to remember, and easier to combine. I would be interested in comments... is this a good way to do things? Am I trying too hard to impose OO on Haskell and is there a better way? Thanks, Mike

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Implicit newtype unwrapping
by Martijn van Steenbergen 04 Dec '09

04 Dec '09

So here's a totally wild idea Sjoerd and I came up with. What if newtypes were unwrapped implicitly? What advantages and disadvantages would it have? In what cases would this lead to ambiguous code? Thanks, Martijn.

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happstack homepage
by Roel van Dijk 04 Dec '09

04 Dec '09

I noticed that happstack.com and tutorial.happstack.com are both equal to patch-tag.com. Google's cache has the original pages. Is this the result of some misconfiguration or something else? I want to play with happstack and this is a slight inconvenience. On the other hand, all happstack packages build without problems so I'll build the tutorial locally and work from there. Regards, Roel

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Second Call for Copy: Monad.Reader Issue 15
by Brent Yorgey 04 Dec '09

04 Dec '09

It's not too late to write something for Issue 15 of the Monad.Reader! Whether you're an established academic or have only just started learning Haskell, if you have something to say, please consider writing an article for The Monad.Reader! The submission deadline for Issue 15 is **Friday, January 8, 2010** The Monad.Reader ~~~~~~~~~~~~~~~~ The Monad.Reader is a electronic magazine about all things Haskell. It is less formal than journal, but somehow more enduring than a wiki-page. There have been a wide variety of articles: exciting code fragments, intriguing puzzles, book reviews, tutorials, and even half-baked research ideas. Submission Details ~~~~~~~~~~~~~~~~~~ Get in touch with me if you intend to submit something -- the sooner you let me know what you're up to, the better. I am also happy to provide feedback on draft versions before the submission deadline. Please submit articles for the next issue to me by e-mail (byorgey at cis.upenn.edu) Articles should be written according to the guidelines available from http://themonadreader.wordpress.com/contributing/ Please submit your article in PDF, together with any source files you used. The sources will be released together with the magazine under a BSD license. If you would like to submit an article, but have trouble with LaTeX please let me know and we'll sort something out.

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Monomorphic local let bindings and GHCi
by Miran Lipovača 04 Dec '09

04 Dec '09

Hi! There have been proposals to abandon generalisation for local let bindings because they make specifying and implementing the type system very complicated when extensions like multi parameter type classes, type functions and GADTs are taken into consideration. I agree with what the paper says in general, I'm just interested/concerned as to how abandoning local let generealisation would affect GHCi. While we rarely rely on the polymorphism of functions defined in local let bindings, I think a lot of programmers rely on the polymorphism of functions that they define with let in GHCi. I have a feeling that GHCi would be a lot less useful if it didn't allow us to define functions that are polymorphic in it. Also, what would the behavior be anyway? If we did > let f x = x in GHCi and then inspected the type of f, what would GHCi report? Would it use defaulting and give us () -> ()? Or would it display a polymorphic type a -> a and then change that type to something monomorphic once we use f with some value? What if we defined several functions like this that called each other? So I think that if local let generalisation is abandoned, let bindings in GHCi would somehow have to be modified to remain polymorphic. Any thoughts?

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Beginner's speed problem
by Aditya M 04 Dec '09

04 Dec '09

Hi, I am trying to solve this problem: https://www.spoj.pl/problems/LASTDIG/ It is very simple. Given a and b, return the last digit of a^b. b could be large, so I used logarithmic exponentiation and wrote/submitted the code below for this problem: ---------------------------------------------------------------------- lastdigit :: Int -> Int -> Int -> Int lastdigit 0 0 _ = 1 lastdigit a b c | even b = lastdigit ( (a*a) `rem` 10 ) (b `quot` 2) c | b == 1 = (a*c) `rem` 10 | otherwise = lastdigit ( (a*a) `rem` 10 ) (b `quot` 2) (a*c) doit :: [Char] -> Int doit line = lastdigit (read $ head $ words line) (read $ last $ words line) 1 main = do n <- getLine inputs <- sequence $ take (read n) $ repeat getLine let slist = map doit inputs mapM_ (putStrLn.show) slist ------------------------------------------------------------------- As n in main is at most 30, I thought this would easily run in 1 second, but I get a time limit exceeded error on the site. Can someone tell me where my code is taking too much time? Thanks in advance! -- Aditya Manthramurthy

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Data.Binary and error handling
by Alexey Khudyakov 03 Dec '09

03 Dec '09

Hello Is there any plans to add error handling for binary? When it comes to binary parsing most awkward part is error handling I presume answer will be like "there are some vague plans but no one to implement them" so the second question how could it be done? Naive implementation of error handliing which converts Get monad into hybrid of state monad and error monad (Either like) gives about 5 times slowdown.

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Card games
by Felipe Lessa 03 Dec '09

03 Dec '09

Hi! I would like to know if anybody has already thought of or tried to code an EDSL for card games. Ideally you should be able to write the rules the games and get "for free": - Game generator: given an input deck, construct the initial state of the game. - Random game generator: besides just creating a random deck and using the item above, it should be nice to be able to randomly construct the game from the final positions. This should guarantee that all random games are solvable. - "Hints" generator: IOW list possible moves given a game state. - Playable game: probably the EDSL should include at least some information to be able to properly place the cards on the screen. - Game solver: this is somewhat harder to do efficiently, but an inneficient one should be doable. - Demo mode: related to the above, an auto-play distract-me mode. - Tutorial mode: show a screen for each of the rules written? - ...anything more? Just curious, this looks like a perfect job for an EDSL. Also, I guess anybody trying to do something like this should read PySol's code to have some ideas. -- Felipe.

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Fwd: [Haskell-cafe] Optimization with Strings ?
by Alberto G. Corona 03 Dec '09

03 Dec '09

Use makeStableName from System.Mem.StableName StableName`s are just for checking pointer equality. Instead of checking for equality of the strings, check for pointer equality of their stableNames a dirty way: pointerEq x y= unsafePerformIO $ do px <- makeStableName x py <- makeStableName y return x == y pEq x y | pointerEq x y == True = True | otherwise = x == y 2009/12/3 David Virebayre <dav.vire%2Bhaskell(a)gmail.com<dav.vire%252Bhaskell(a)gmail.com> > On Thu, Dec 3, 2009 at 1:03 PM, Emmanuel CHANTREAU > <echant%2Bhaskell(a)maretmanu.org <echant%252Bhaskell(a)maretmanu.org>> wrote: > > > In my futur program, it use a lot of binary trees with strings (words) > > as leaf. There is just arround 1000 words and they will appear a lot of > > times. The program will possibly consume a lot of process and memory > > (it is a mathematics proover). > > > I began this program in C++ but haskell has a prety good speed and > > memory footprint and is easier. But I don't know if it worth to do this > > optimization: having a dictionary to translate string words in Int. > > > The answer depends on the automatic optimizations in GHC, because GHC > > could compare quickely two strings if it is the same object, so it > > depends if program generated by GHC have a dictionary (tree) of strings > > internaly. Someone knows this ? > > It doesn't work this way : Strings are just lists of Chars. Comparison > is made recursively, Char by Char. You can have a look at the source > to make sure : > > instance (Eq a) => Eq [a] where > [] == [] = True > (x:xs) == (y:ys) = x == y && xs == ys > _xs == _ys = False > > So you will have to code your own optimisation. > > David. > > P.S. In French if you didn't understand: > > Ca ne marche pas comme ça. > Les chaines de caractères ne sont que des listes de caractères. > La comparaison sur les listes est faite récursivement, caractère par > caractère, il suffit pour s'en assurer de regarder au source : > Donc il vaut mieux que tu implémente ton propre dictionnaire. > _______________________________________________ > Haskell-Cafe mailing list > Haskell-Cafe(a)haskell.org > http://www.haskell.org/mailman/listinfo/haskell-cafe >

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Re: [Haskell-cafe] Existencial Types
by rodrigo.bonifacio 03 Dec '09

03 Dec '09

Dear Luke, thanks for your answers.... > If SelectScecario is used for other purposes, then give an explicit > cast function Sure, as I mentioned, we have different transformations and it would be worth to filter a list of transformations by a particular type or even apply the list of transformations in a particular order considering their type. > toTransformation :: SelectScenario -> Transformation > toTransformation (SelectScenario ids) = Transformation { > (<+>) = {- implementation of (<+>) just as if it were a class method -} > } I understand your idea, but I will have to implement several variations of "toTransformation", one for each kind of transformation. Moreover, I couldn't realize how is possible to define a function that could be applied to different transformations without using type classes--- I have to restrict the types of argument of such a function. Moreover, I couldn't figure out what are the benefits of your solution. Please, if possible, could you elaborate that a bit more, in order that I could understand why your design is better (I mean, more legible, reusable or concise)? Thanks in advance, Rodrigo. Em 01/12/2009 22:44, Luke Palmer < lrpalmer(a)gmail.com > escreveu: On Tue, Dec 1, 2009 at 4:21 PM, rodrigo.bonifacio wrote: > Thanks Luke. > > In fact I, will have different implementations of the Transformation type. > Something like: > > data SelectScenarios = SelectScenarios { > > scIds :: [Id] > > } What is this different type buying you? You can never "downcast" to it later. > And then I should be able to make SelectScenarios a kind of Transformation. > So I think that I really need a class. What do you think about it? > > instance Transformation SelectScenario where > > (<+>) .... So instead of making a type and an instance, just implement it directly as a Transformation: selectScenario :: [Id] -> Transformation selectScenario ids = Transformation { (<+>) = {- whatever implementation you gave for (<+>) above, using ids -} } If the only purpose of SelectScenario (your type) is to be used polymorphically as a Transformation, then this approach is isomorphic -- i.e. anything you can do with the existential type trick you can do with this approach. If SelectScecario is used for other purposes, then give an explicit cast function toTransformation :: SelectScenario -> Transformation toTransformation (SelectScenario ids) = Transformation { (<+>) = {- implementation of (<+>) just as if it were a class method -} } Existential types only buy you power when the quantified variable appears more than once on the right hand side, for example: forall a. Num a => (a,a). But even those can usually be factored out into more direct representations (I seem to recall Oleg has a proof that they always can, actually). Luke

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Re: seems like I'm on the wrong track
by John Lato 03 Dec '09

03 Dec '09

> From: Henning Thielemann <lemming(a)henning-thielemann.de> > > Michael P Mossey schrieb: >> Perhaps someone could either (1) help me do what I'm trying to do, or >> (2) show me a better way. >> >> I have a problem that is very state-ful and I keep thinking of it as OO, >> which is driving me crazy. Haskell is several times harder to use than >> Python in this instance, probably because I'm doing it wrong. >> >> To give you a larger context, this problem is essentially compiling a >> description of music (my own) into a kind of music-machine-language >> (CSound). CSound is relatively untidy. > > There are currently two public interfaces to CSound: > > http://hackage.haskell.org/packages/archive/haskore/0.1/doc/html/Haskore-In… > > http://hackage.haskell.org/package/hCsound > Incidentally, these two packages serve very different purposes. hCsound is an interface to the Csound runtime API, while the Haskore interface is an EDSL front-end to Csound's own input format. There is very little overlap in functionality between the two. The Haskore interface is much closer to what Michael wants to do, but as he's commented already, it is a bit dated. hCsound is unlikely to be of much use for compiling a secondary language to csound code. John

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Re: [Haskell-cafe] Is Haskell a Fanatic?
by John D. Earle 03 Dec '09

03 Dec '09

It will be better for all of you to figure it out for yourselves and gain more experience about what is out there. Haskell isn't the world. Haskell would be the cutting edge if it didn't have competition.

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Re: [Haskell-cafe] Implicit newtype unwrapping
by John D. Earle 03 Dec '09

03 Dec '09

There is another point that needs to be made. A type signature isn't actually a type specification. It is a type assertion and a type specification in the event that the compiler needs your help. Most of the time the compiler can care less what you think and does not require your assistance. In languages like C you get to call the shots. In languages such as Haskell you don't get that opportunity.

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[Fwd: Re: [Haskell-cafe] Implicit newtype unwrapping]
by Holger Siegel 03 Dec '09

03 Dec '09

Am Donnerstag, den 03.12.2009, 01:16 +0100 schrieb Martijn van Steenbergen: > So here's a totally wild idea Sjoerd and I came up with. > > What if newtypes were unwrapped implicitly? > > What advantages and disadvantages would it have? > In what cases would this lead to ambiguous code? 1) instance Monoid a => Monoid (Dual a) 2) instance Monoid (Endo a) instance Monoid b => Monoid (a -> b)

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Some help needed to start Haskell with Yi
by Jaco van Iterson 03 Dec '09

03 Dec '09

Hi there I'm new to Haskell and need some help to get started faster (busy busy busy). I like to adjust and extend an editor to my liking and I choose Yi. Only installation with 'cabal install yi' in a Cygwin shell under MS Windows XP ended in: Yi\Prelude.hs:182:9: Duplicate instance declarations: instance Category Accessor.T -- Defined at Yi\Prelude.hs:182:9-38 instance Category Accessor.T -- Defined in data-accessor-0.2.1:Data.Accessor.Private cabal.exe: Error: some packages failed to install: yi-0.6.1 failed during the building phase. The exception was: exit: ExitFailure 1 :( Seems easy to fix but I can't even find where on my drive I can find the source code. Where is the source? Cheers, Jaco

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Re: [Haskell-cafe] Implicit newtype unwrapping
by John D. Earle 03 Dec '09

03 Dec '09

I am uncertain if what any of you seek makes sense. The type checker is concerned with establishing a principle type and that is what is being reported, the principle type. The compiler as I pointed out in "On the Meaning of Haskell 8" by design has not a clue as to the significance your type alias has.

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