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gtk2hs: adding widget during runtime
by Gary Klindt 17 Dec '11

17 Dec '11

Hello Haskellers, currently I work with the gtk2hs library to create a graphical user interface. Everything works fine, but there is one problem: How can I insert widgets into boxes during runtime? I tried something like: main = do initGUI window <- windowNew box <- vBoxNew True 0 l1 <- labelNew $ Just "label eins" bc <- buttonNewWithLabel "insert!" onClicked bc $ (\b -> do lh <- labelNew $ Just "neues label!" boxPackStart b lh PackNatural 0 widgetQueueDraw lh widgetQueueDraw b ) box boxPackStart box l1 PackNatural 0 boxPackStart box bc PackNatural 0 containerAdd window box widgetShowAll window onDestroy window mainQuit mainGUI That compiles fine, but the GUI never shows a "neues label!". What I want is a widget W, which takes a list L, and produces sub widgets for each element. There are also some Entry widgets and a button B. By clicking on that button B, I want to add an element to the list L, and add a sub widget to the widget W. Thank you for reading, Gary

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What happens if you get hit by a bus?
by Michael Litchard 17 Dec '11

17 Dec '11

I'm learning what it means to be a professional Haskell programmer, and contemplating taking on side jobs. The path of least resistance seems to be web applications, as that is what I do at work. I've been investigating what some web developers have to say about their trade. One article addresses the question above. His answer was that he uses RoR which has a large community and he is therefore easily replaceable. My question, for freelancers in general, and web developers in particular is this: How do you address this question? I imagine potential clients would need to be assuaged of their fears that hiring me would lead to a lock-in situation at best, and no one to maintain a code base at worst. Lock-in won't be part of my business model, also sooner or later we part ways with the client. When the client wonders, "What happens then?", what is a good answer?

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Dutch national FP day, January 6, Utrecht
by S D Swierstra 16 Dec '11

16 Dec '11

On http://www.cs.uu.nl/wiki/bin/view/FPDag2012/WebHome you will find the program and registration information about the next Dutch National Functional Programming day, on January 6, Utrecht University. Please forward this mail to anyone interested. Any questions can be directed to me. Hoping to meet you all, Doaitse Swierstra

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Proposal to incorporate Haskell.org
by Don Stewart 16 Dec '11

16 Dec '11

Hello everyone. The haskell.org committee[1], in the interest of the long-term stability of the open source Haskell community infrastructure, has decided to incorporate haskell.org as a legal entity. This email outlines our recommendation, and seeks input from the community on this decision. The committee's proposal is that haskell.org incorporate as an entity under the Software Freedom Conservancy umbrella organization (the same group that Darcs joined recently): http://sfconservancy.org/ If we proceed with this move, haskell.org will be a legal entity, and registered as a non-profit, allowing us to more directly accept (US tax-deductible) donations, and to invest in assets that benefit the Haskell open source community. We welcome your feedback on the proposal attached below. -- Don Stewart (on behalf of the Haskell.org committee) ------------------------------------------------------------------------ = A proposal for the incorporation of Haskell.org = In recent years, haskell.org has started to receive assets, e.g. money from Google Summer Of Code, donations for Hackathons, and a Sparc machine for use in GHC development. We have also started spending this money: in particular, on hosting haskell.org itself. There is also interest in running fundraising drives for specific things such as Hackathon sponsorship and hosting fees. However, haskell.org doesn't currently exist as a legal entity, meaning that these assets have had to be held on our behalf by other entities, such as Galois and various universities. This leads to tricky situations, with no-one being sure who should decide how the haskell.org assets can be used. To solve these problems, we propose that haskell.org applies to become a member project of the Software Freedom Conservancy (SFC) <http://conservancy.softwarefreedom.org/>. The SFC is a non-profit organization that provides free financial and administrative services to open source projects. Additionally, it has 501(c)(3) status, meaning donations from the US are tax-deductible. The SFC would hold haskell.org's money and other assets, and would be able to accept donations on behalf of haskell.org. The haskell.org committee, as described here [2], will make decisions on spending assets and other decisions related to governing the non-profit. Before proceeding, we are inviting input from the community in the form of specific objections or queries regarding the plan. We've tried to answer some of the most likely questions: Q: Does this mean that my Haskell project must now be covered by a copyleft licence such as GPL? A: No, but Haskell projects using haskell.org resource should use an Open Source licence <http://www.opensource.org/licenses/alphabetical>. Q: Will it still be possible to use community.h.o to host non-open-source material, such as academic papers? A: An overall minority of such content, as is the current situation, is not a problem. Q: Will it still be possible to have job ads on the haskell.org mailing lists and website? A: Yes. Q: Will this affect our ability to host the Haskell Symposium <http://www.haskell.org/haskell-symposium/> and Industrial Haskell Group<http://industry.haskell.org/> webpages within haskell.org? A: No. Q: What will be the relationship between haskell.org and other organizations such as the Haskell Symposium and Industrial Haskell Group? A: Those organisations will continue to exist as separate entities. Q: If an umbrella non-profit organisation "The Haskell Foundation" was created, would haskell.org be able to join it? A: Yes. It's likely that in such a scenario, the Haskell Foundation would become the owner of the haskell.org domain name, with the cost divided between the members. The entity that is part of the SFC would be renamed "community.haskell.org" in order to avoid confusion. [1]: http://www.haskell.org/haskellwiki/Haskell.org_committee [2]: http://www.haskell.org/haskellwiki/Haskell.org_committee#Operation

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DB vs read/show for persisting large data
by C K Kashyap 16 Dec '11

16 Dec '11

Hi, It has been on my todo list for some time now. I'd like to write a GTD tool that has dependency tracking support. Haskell seems like a good choice for this. I was wondering if there has been any past attempts with this? One thing that has been bothering me has been this - the persistence of data. Should I use sqlite(or someother DB) or should I use Haskell's read/show functions to read from and write to a file? I am slightly not inclined towards NOT using DB because I want to implement all the business logic in Haskell. I want to avoid having to generate SQL. It'll be great if I could get some feedback on the "read/show" approach - is this even a viable option? Regards, Kashyap

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Parallel Matrix Multiplication
by mukesh tiwari 16 Dec '11

16 Dec '11

Hello all I am trying to learn parallel Haskell and I have gone through couple of resources ( Real world Haskell and http://research.microsoft.com/en-us/um/people/simonpj/papers/parallel/AFP08… ). I understood par and pseq and I wrote matrix multiplication using these two function but it does not look. Although I did not get all these details but none of the sparks converted which is really important for parallel programming. Could some one please tell me how to improve this. Also kindly recommend me some literature for parallel programming in Haskell. Regards Mukesh Tiwari import Data.List import Control.Parallel parHelp :: ( Num a ) => [ a ] -> [ a ] -> a parHelp [] [] = 0 parHelp ( x : xs ) ( y : ys ) = ret where ret = par a ( pseq a ( a + parHelp xs ys ) ) where a = x * y helpMult :: ( Num a ) => [ a ] -> [ [ a ] ] -> [ a ] helpMult _ [] = [] helpMult x ( y : ys ) = ret where ret = par a ( pseq a ( a : helpMult x ys ) ) where a = parHelp x y mult :: ( Num a ) => [ [ a ] ] -> [ [ a ] ] -> [ [ a ] ] mult [] _ = [] mult ( x : xs ) ys = ret where ret = par a ( pseq a ( a : mult xs ys ) ) where a = helpMult x ys main = print $ mult [[1 .. 4 ] , [ 1 .. 4 ] , [ 1 .. 4 ] , [ 1 .. 4] ] ( transpose [[1 .. 4 ] , [ 1 .. 4 ] , [ 1 .. 4 ] , [ 1 .. 4] ]) [user@haskell Programming]$ ghc -O2 -threaded -rtsopts Matpar.hs [1 of 1] Compiling Main ( Matpar.hs, Matpar.o ) Linking Matpar ... [user@haskell Programming]$ ./Matpar +RTS -N2 -s ./Matpar +RTS -N2 -s [[10,20,30,40],[10,20,30,40],[10,20,30,40],[10,20,30,40]] 85,480 bytes allocated in the heap 5,216 bytes copied during GC 47,328 bytes maximum residency (1 sample(s)) 22,304 bytes maximum slop 2 MB total memory in use (0 MB lost due to fragmentation) Generation 0: 0 collections, 0 parallel, 0.00s, 0.00s elapsed Generation 1: 1 collections, 0 parallel, 0.00s, 0.00s elapsed Parallel GC work balance: -nan (0 / 0, ideal 2) MUT time (elapsed) GC time (elapsed) Task 0 (worker) : 0.00s ( 0.00s) 0.00s ( 0.00s) Task 1 (worker) : 0.00s ( 0.00s) 0.00s ( 0.00s) Task 2 (bound) : 0.00s ( 0.00s) 0.00s ( 0.00s) Task 3 (worker) : 0.00s ( 0.00s) 0.00s ( 0.00s) * SPARKS: 84 (0 converted, 0 pruned)* INIT time 0.00s ( 0.00s elapsed) MUT time 0.00s ( 0.00s elapsed) GC time 0.00s ( 0.00s elapsed) EXIT time 0.00s ( 0.00s elapsed) Total time 0.00s ( 0.00s elapsed) %GC time 33.3% (13.5% elapsed) Alloc rate 42,761,380 bytes per MUT second Productivity 33.3% of total user, 45.0% of total elapsed gc_alloc_block_sync: 0 whitehole_spin: 0 gen[0].sync_large_objects: 0 gen[1].sync_large_objects: 0 [user@haskell Programming]$

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smt solver bindings
by Dimitrios Vytiniotis 16 Dec '11

16 Dec '11

I've a quick question: Are there Haskell wrappers for the Z3 C API around? Thanks! d-

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[Alternative] some/many narrative
by Gregory Crosswhite 16 Dec '11

16 Dec '11

Okay, so how about the following as a user narrative for some and many? many v = repeatedly execute the action v and save each obtained result until v fails; at that point, *succeed* and return a list with all of the results that had been collected some v = like many v, but if v does not succeed even once then *fail* instead of return the empty list Note: If v *never* fails, then at best many/some will return infinite lists, and at worst they will repeat your action forever. Cheers, Greg P.S.: And yes, I know that many of you will complain that these definitions are not mathematically precise or what not, but it is important to be able to build up narratives at a sufficiently high level that they explain the essentials of what is going on for the benefit of users who are unfamiliar with the precise mathematical language used to precisely define their semantics.

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How to get a file path to the program invoked?
by dokondr 16 Dec '11

16 Dec '11

Hi, When my program starts it needs to know a complete path to the directory from which it was invoked. In terms of standard shell (sh) I need the Haskell function that will do equivalent to: #!/bin/sh path=$(dirname $0) How to get this path in Haskell? getProgName :: IO String defined System.Environment only returns a file name of the program without its full path. Thanks!

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indentation blues
by Martin DeMello 15 Dec '11

15 Dec '11

The vim autoindent for haskell is really bad :( Is there a better indent.hs file floating around somewhere? Alternatively, is the emacs haskell mode better enough that it's worth my time learning my way around emacs and evil? martin

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