March 2009 - Haskell-Cafe

Re: [Haskell-cafe] Ease of Haskell development on OS X?
by Cristiano Paris 20 Mar '09

20 Mar '09

2009/3/20 Mark Spezzano <mark.spezzano(a)chariot.net.au>: > Hi, > > I’ve been thinking of changing over to an iMac from my crappy old PC running > Windows Vista. > > Question: Does the iMac have good support for Haskell development? > > Question: What environment setups do people commonly use (e.g. Eclipse Xcode > etc)? > > Question: Are there any caveats I should be aware of before changing systems > (i.e. unpleasant surprises). > > I want to be able to use the machine for Haskell OpenGL programming. Take a look at this (rather long) thread on Haskell-cafè: http://www.haskell.org/pipermail/haskell-cafe/2009-February/056545.html Cristiano

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Editing Haskell wiki pages
by Colin Paul Adams 20 Mar '09

20 Mar '09

How am I supposed to edit a page on the Haskell wiki? If I click on an "Edit this page" link, then Firefox prompts me to choose a tool to open an application/x-external-editor. When i just choose the default (emacs) I get the following opened in emacs: [Process] Type=Edit text Engine=MediaWiki Script=http://www.haskell.org/haskellwiki/ Server=http://www.haskell.org Path=/haskellwiki Special namespace=Special [File] Extension=wiki URL=http://www.haskell.org/haskellwiki/?title=Applications_and_libraries/Ga… which isn't much use (and further, it's write-protected!). -- Colin Adams Preston Lancashire

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Ease of Haskell development on OS X?
by Mark Spezzano 20 Mar '09

20 Mar '09

Hi, I’ve been thinking of changing over to an iMac from my crappy old PC running Windows Vista. Question: Does the iMac have good support for Haskell development? Question: What environment setups do people commonly use (e.g. Eclipse Xcode etc)? Question: Are there any caveats I should be aware of before changing systems (i.e. unpleasant surprises). I want to be able to use the machine for Haskell OpenGL programming. Cheers, Mark Spezzano No virus found in this outgoing message. Checked by AVG. Version: 7.5.557 / Virus Database: 270.11.20/2012 - Release Date: 19/03/2009 12:26 PM

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Forcing evaluation when seq or strictness annotation are not possible [was: guess on stack-overflows - thunks build-up and tail recursion]
by Gü?nther Schmidt 20 Mar '09

20 Mar '09

Hi all, here I am again with my all time favorite unsolved problem: stack overflows. The advice I have received so far from the Haskell community (this list and #haskell) was to use strictness annotation or seq in most cases. And indeed it did help. It certainly helped when I used a data structure that I designed myself and a filling routine that I also wrote myself, thanks guys (and girls possibly, I mean I don't know). But sometimes neither of the 2 helps. Especially when you are using a brilliantly designed data structure such as IxSet, from happstack, originally HAppS. Since it's someone else code it's too late to add strictness annotation. Or the "core" insert that you have to use in your filling routine is lazy. In such cases you're just out of a luck. I have read about alternatives to the above mentioned techniques, CPS, Codensity-Monad and this http://wwwtcs.inf.tu-dresden.de/~voigt/mpc08.pdf in Blogs, Wikis and Papers, also on this mailing list a post called "stupid question #852". Well when I say alternatives I mean I *perceived* these techniques to be *meant* as alternatives, as a way to control evaluation order, or *force* evaluation. And this is my question: Am I barking up the wrong tree, is the purpose of these techniques actually not to force evaluation order? Günther

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[ANN] random-shuffle package
by Manlio Perillo 20 Mar '09

20 Mar '09

I'm pleased to announce the availability of random-shuffle package. The cabalized package is available at http://haskell.mperillo.ath.cx/random-shuffle-0.0.2.tar.gz The code is based on http://okmij.org/ftp/Haskell/perfect-shuffle.txt Thanks to Oleg Kiselyov for sharing this! I have made some changes to Oleg code: - changed coding style to what seems to be a more common Haskell coding style - Used Int, instead of Integer, for the index type - Forced some strict evaluation. It was a trial and error effort (I'm not an expert), but results are very impressive. Example program and timings/memory usage, are on: http://hpaste.org/fastcgi/hpaste.fcgi/view?id=2600 NOTE: I don't plan to upload the package to Hackage, for the near future. I'm thinking to add some other functions that operate on lists, like Python random module (random.choice, random.sample), and the partitioning function I have posted the other day (although I'm not sure this is a generic useful function). However, in this case, the package name should be changed. I'm not sure it is a good idea to release a package that implements only one function (but I may be wrong). Feedbacks (on current random-shuffle and future additions) are welcomed. Regards Manlio Perillo

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Using cabal to build an exportable library?
by Justin Bailey 20 Mar '09

20 Mar '09

I've been following this instructions at http://www.haskell.org/haskellwiki/Calling_Haskell_from_C to build a Haskell library which I can call from a C program. I'd like to use cabal to do the build in the future. Are there any examples showing how to do it?

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server directory layout for cabal-install?
by Johannes Waldmann 20 Mar '09

20 Mar '09

Hello. I wonder what is the required layout of directories and files on a server that supplies packages for cabal-install. I figure 00-index.tar.gz contains the *.cabal files. (The cabal files have to be on the server as well, unpacked?) Each $dir/$foo.cabal (in the archive) contains a "Version:$ver" line, and then $dir/$foo-$ver.tar.gz must be on the server? Are there additional constraints on the $dir part? What is the syntax of the .cabal/config file? The standard entry is repos: hackage.haskell.org:http://hackage.haskell.org/packages/archive , where the thing between "repos:" and ":http" is just a symbolic name, and I can add more lines like that? Thanks, J.W.

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Query on list comprehension
by Melanie_Green 20 Mar '09

20 Mar '09

What are the limitations of list comprehension. I want to use listcomprehension to output the pattern below. So a mixture of a's and newline characters. The part im stuck at is creating arguments in the listcomprehension to stop at some point then execute next loop. Is it even possible to create the pattern below purely from list comprehension.Thankyou in advance. a aa aaa -- View this message in context: http://www.nabble.com/Query-on-list-comprehension-tp22573574p22573574.html Sent from the Haskell - Haskell-Cafe mailing list archive at Nabble.com.

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Haskell Logo Voting has started!
by Eelco Lempsink 20 Mar '09

20 Mar '09

Hi there! I updated a couple of logo versions and ungrouped and regrouped the (former) number 31. Other than that, there was nothing standing in the way of the voting to begin imho, so I started up the competition. By now, I suppose everybody should have received their ballot. If you think you should have received it but didn't, please report it, I can resend the invitation. Also, for people not directly subscribed to the haskell-cafe mailing list, you can still send ballot requests until the end of the competition (March 24, 12:00 UTC). Make sure the message contains 'haskell logo voting ballot request' (e.g. in the subject). Depending on the winner of this voting round we can decide whether we need to continue with variations. Jared Updike already offered to donate a bit of time to help create several variations. But for now, good luck with sorting those options! :) -- Regards, Eelco Lempsink

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What unsafeInterleaveIO is unsafe
by Yusaku Hashimoto 19 Mar '09

19 Mar '09

Hello, I was studying about what unsafeInterleaveIO is.I understood unsafeInterleaveIO takes an IO action, and delays it. But I couldn't find any reason why unsafeInterleaveIO is unsafe. I have already read an example in http://www.haskell.org/pipermail/haskell-cafe/2009-March/057101.html says lazy IO may break purity, but I think real matter in this example are wrong use of seq. did I misread?

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