- Haskell-Cafe - Haskell.org

I need help getting started
by mitchell＠kaplan2.com 25 Apr '10

25 Apr '10

Hi, I'm just starting to learn, or trying to learn Haskell. I want to write a function to tell me if a number's prime. This is what I've got: f x n y = if n>=y then True else if gcd x n == 1 then f x (n+1) y else False primeQ x = f x 2 y where y = floor(sqrt(x)) The compiler is very unhappy. Apparently there's some ambiguity in this, and I'm kind of running around in circles. I'd appreciate any help that will get me started.

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Threads freezing
by Eitan Goldshtrom 25 Apr '10

25 Apr '10

Hello fellow Haskell programmers, I seem to be having problems with some threads of mine. I wrote an OpenGL program that employs some threads (forkIO) in order to separate any calculations from the OpenGL code. At first it all seemed to be working just fine. Then I added some code for keyboard input to reset the program when you press 'r'. Since then my threads have been giving me problems. Just a second after the program starts all the calculations stop. The program is still running the code to display graphics (I tested this by putting "putStrLn "still displaying" into the display function) but the threads that do all of the computation don't seem to return from their threadDelay, which is only a delay of 5000 microseconds. I tried getting rid of the code for keyboard input but the problem is still there. I tried to run the program on another computer and it ran just fine (without keyboard input). Does anyone have any idea what could be going on? Additionally, I just tried compiling it to an executable and it seems that when I run it from that it works fine, with the keyboard input too. So I'm guessing the problem is with the interpreter? I'm not really sure. Haskell is still pretty mysterious to me. -Eitan

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Re: Confusions about the Haskell Platform (for Mac)
by Gregory Collins 25 Apr '10

25 Apr '10

Yair Chuchem <yairchu(a)gmail.com> writes: > I don't have a good working solution for this, so the situation will > have to remain status quo (i.e. clicking two installers) for now. > > afaik you can make an "mpkg" installer that invokes/contains other > installers: > see http://developer.apple.com/Mac/library/documentation/DeveloperTools/Concept… If you can figure out how to take the binary package the GHC guys make and fold it into a larger .mpkg, please tell me. G. -- Gregory Collins <greg(a)gregorycollins.net>

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Cabal generating text files?
by Michał J Gajda 25 Apr '10

25 Apr '10

Hi, Does anyone know how to generate a text file in a Cabal package? E.g. I want cabal to install a text file into $share_dir/applications/ app.desktop, and fill in certain fragments of this file with paths depending of the $share_dir variable. Say: ==============Yi.desktop template================== [Desktop Entry] Name=Yi Text Editor Comment=Edit text files, and add configuration in Haskell Comment[en_CA]=Edit text files, and configure editor in Haskell Comment[en_GB]=Edit text files, and configure editor in Haskell Comment[pl]=Edytor plików tekstowych z konfiguracją w Haskellu TryExec=$yi_bindir/bin/ yi Exec=$yi_bindir/bin/yi -f %F Terminal=true Type=Application Icon=$yi_sharedir/share/art/yi +lambda.svg Categories=Utility;TextEditor; StartupNotify=false MimeType=text/plain; =============================================== Sorry I couldn't find it in Cabal documentation. -- Best regards Michal

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FGL up for adoption
by Martin Erwig 24 Apr '10

24 Apr '10

Dear FGL users and contributors, The FGL seeks a new home. I don't really have the time anymore to maintain the FGL and add new components at a level that it deserves. I am therefore looking for someone (or a group of people) who would be interested in taking over the maintenance and future development. Anybody interested? Thanks, Martin

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Second Ghent Functional Programming Group Meeting: Date and Call for Talks
by Jeroen Janssen 24 Apr '10

24 Apr '10

(apologies if you receive multiple copies) Dear all, The second Ghent Functional Programming Group (Ghent FPG) meeting takes place on Thursday, May 13 at 19:00 in the Technicum building of Ghent University (Sint-Pietersnieuwstraat 41, 9000 Gent). We have a number of 20-minute timeslots (excluding questions) available for talks, so if you are interested in giving a talk you can e-mail Jeroen Janssen (jejansse(a)gmail.com) The final program will be announced shortly. Hope to see you all then, Bart Coppens (Bart.Coppens(a)elis.ugent.be; Twitter: @BartCopp) Jasper Van der Jeugt (jaspervdj(a)gmail.com; Twitter: @jaspervdj) Jeroen Janssen (jejansse(a)gmail.com; Twitter: @jejansse) Note: if you do not want to receive any more e-mails from Ghent FPG, just send an e-mail to Jeroen Janssen (jejansse(a)gmail.com) and we will remove you from our mailinglist.

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Re: [Haskell-cafe] Using a library in a executable within same cabal package
by Arnaud Bailly 24 Apr '10

24 Apr '10

You are right, I hit "reply" without checking the destination. Thanks for your answer. Arnaud On Sat, Apr 24, 2010 at 3:24 PM, Ivan Lazar Miljenovic <ivan.miljenovic(a)gmail.com> wrote: > First of all, did you mean to reply back to -cafe as well? > > Arnaud Bailly <arnaud.oqube(a)gmail.com> writes: > >> I was not precise enough: Yes, I found the examples to have both a >> library and an executable clear enough that I managed to have >> something workable. But I found somewhat surprisingly that the modules >> used in both the library and the executable were compiled twice. I was >> expecting the executable to link to the dynamic library produced. >> I understand from your answer this is a known issue. > > Right; with Cabal 1.8 this situation is "solved", but at the expense of > not being able to build documentation (I think I was the first person to > fully try this, which is why the bug went unnoticed until recently; the > darcs people are considering using it as well but they didn't test > building haddock docs). > > So yeah, at the moment you're stuck with building the library multiple > times :s > >> >> On Sat, Apr 24, 2010 at 12:14 PM, Ivan Lazar Miljenovic >> <ivan.miljenovic(a)gmail.com> wrote: >>> Arnaud Bailly <abailly(a)oqube.com> writes: >>>> Not sure this question is totally on-topic. >>> >>> Sure is. >>> >>>> Please point me in the right direction if it is not. I would like to >>>> make a cabal package containing both an executable and several >>>> libraries, >>> >>> Each cabal package can contain only one library (which is why gtk2hs is >>> only now starting to be cabalised). >>> >>>> and link the main executable to the libraries produced in >>>> the build. It is not clear how I can achieve that from the >>>> documentation. I tried Extra-libraries option but it does not work. >>> >>> By default, you don't need to do anything extra to have executables >>> using a library in the same package (assuming they have the same source >>> directory) as GHC will find all the modules it needs. >>> >>> Cabal-1.8 has a new feature that lets executables explicitly depend upon >>> the libraries, which means the library doesn't need to get rebuilt >>> several times. However, this is causing problems with building haddock >>> documentation: http://hackage.haskell.org/trac/hackage/ticket/656 >>> >>> -- >>> Ivan Lazar Miljenovic >>> Ivan.Miljenovic(a)gmail.com >>> IvanMiljenovic.wordpress.com >>> > > -- > Ivan Lazar Miljenovic > Ivan.Miljenovic(a)gmail.com > IvanMiljenovic.wordpress.com >

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Compressing GHC tarballs with LZMA
by Leon Smith 24 Apr '10

24 Apr '10

Out of curiousity, I downloaded a binary distribution for GHC-6.12.2, and tried compressing and recompressing it with bzip2 and lzma compression, using no command line arguments (all default parameters) file: http://haskell.org/ghc/dist/6.12.2/ghc-6.12.2-x86_64-unknown-linux-n.tar.bz2 bzip2 lzma size 106M 72M compression time 2:01 9:51 decompression time 0:25 0:12 the time is reported as "minutes:seconds". At it default compression level, lzma was almost five times slower than bzip2, but it's approximately twice as fast when decompressing and produced a file nearly a third smaller. Given that many modern variants of the "tar" command support .tar.lzma files directly, and that both debian's dpkg and red hat's rpm now use lzma, maybe it's time to consider offering .tar.lzma as a download option for GHC's binary (and maybe source-code) bundles. Best, Leon

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Using a library in a executable within same cabal package
by Arnaud Bailly 24 Apr '10

24 Apr '10

Hello, Not sure this question is totally on-topic. Please point me in the right direction if it is not. I would like to make a cabal package containing both an executable and several libraries, and link the main executable to the libraries produced in the build. It is not clear how I can achieve that from the documentation. I tried Extra-libraries option but it does not work. Thanks for your help -- Arnaud Bailly

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Re: [Haskell-cafe] Proper Handling of Exceptional IEEE Floating Point Numbers
by John Lato 23 Apr '10

23 Apr '10

> From: "Barak A. Pearlmutter" <barak(a)cs.nuim.ie> > >> ... An invalid comparison evaluating to _|_ is arguably more >> correct, but I personally find the idea of introducing more bottoms >> rather distasteful. > > Too late! NaN is pretty much the _|_ of IEEE Floating Point. > > That was certainly the intent of the IEEE standard, and is why NaN is > so contagious. But they wanted to relax the usual strictness of their > languages (FORTRAN, C) when this particular _|_ is around. So NaN is > contagious through strict arithmetic (+, *, etc) like _|_. But it has > strange behaviour with respect to comparison. In the context of > Haskell, which does not have the issue of needing to relax strictness > just for NaN, I think the "right thing" would be to have compare give > _|_, and maybe also <, >, ==. After all, NaN is outside the carefully > defined total ordering of all other IEEE floating point values > including +/- Infinity. +1 John

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