June 2009 - Haskell-Cafe

I need a hint in list processing
by Fernan Bolando 15 Jun '09

15 Jun '09

Hi all If I have a number of list example list1 = [2,3] list2 = [1,2] list3 = [2,3,4] list4 = [1,2,3] I want to create a list from the list above with n elements, non-repeating and each elements index represents 1 of the elements from the corresponding list so for the above input I would get. a = [3,2,4,1] ofcourse there may be several set that will satisfy the problem, so a list of list that satisfies would be good. How do I do this in haskell? or is there a code snippet that seems to work similarly? thanks fernan -- http://www.fernski.com

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graphical user interface library for editing graphs?
by Claude Heiland-Allen 15 Jun '09

15 Jun '09

Greetings, I have an idea for a project. The eventual aim is rather eccentric, but the specifications I have sketched out are roughly as follows (best viewed with fixed-width font due to diagrams): 0. the graphical user interface is entirely mouse driven, mouse position/clicks/releases are shown by [ ] 1. the world consists of empty space, nodes, and links between nodes 2. nodes may either be filled ("*") or hollow ("o"); call hollow nodes "targets", targets may be "highlighted" ("O") 3a. left-click on empty creates a filled node linked to a target: [ ] * => | o 3b. left-click on a target fills it and links it to a new target: : : [o] * => | o 4a. right-click on empty creates a filled node linked to two targets: [ ] * => / \ o o 4b. right-click on a target fills it and links it to two new targets: : : [o] * => / \ o o 5a. left-click-drag on a filled node with 1 descending link highlights all targets linked under it: : : [*] [*] : => : * * / \ / \ o o O O 5b. left-click-drag as in 5a, when released on a highlighted target, creates a "weak" link (not considered as descending for purposes of 5a) from the original node to that target. that target is filled, all other targets are unhighlighted: : : * * : => :\ * * \ / \ / \| O [O] o [*] 6a. right-click-drag from a filled node at the top of a connected component highlights all targets not in that connected component: [*] * [*] * : | => : | o O 6b. right-click-drag as in 6a, when released on a highlighted target, joins the graphs together, such that the original node fills that target, and all other targets are unhighlighted: * * * : | => | [O] [*] : 7. when a connected component has no targets, double-clicking anywhere on it will launchMissiles My question: can you suggest a library that would make implementing this specification relatively painless? OpenGL-based would be preferable, as I would like to scale the graph under construction automatically to fit the display, and launchMissiles will require something with fast rendering. Thanks, Claude -- http://claudiusmaximus.goto10.org

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Haskell - string to list isusses, and more
by Gjuro Chensen 15 Jun '09

15 Jun '09

Hello everyone! Im a Haskell newbie, and Ive have few unanswered questions. For someone more experienced (at least I think so) its a very simple task, but I just cant get a grip on it and its pretty frustrating. It wouldn't be that bad if I haven't browse thru bunch of pages and tutorials and still nothing... The problem is: take a string, and if every words starts with uppercase letter then print yes, else no. Forum Text Bold -> yes Frog image File -> no Ive had my share of approaches to this, but I just cant make it work. Standard one seemed the most simple: search :: String -> String search [] = [] and then use words (splits string on space) to split the string so I could get a list and go through it recursively. But how to apply words to entered string in this form? To find the first letter I came up with: first = take 1 (head x). And compare it with elem or ASCII values to determine if its upper case. Any help, advice or suggestion is appreciated. Thanks in advance! -- View this message in context: http://www.nabble.com/Haskell---string-to-list-isusses%2C-and-more-tp240226… Sent from the Haskell - Haskell-Cafe mailing list archive at Nabble.com.

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Utrecht Attribute Grammar and Emacs
by Mads Lindstrøm 15 Jun '09

15 Jun '09

Hi Has anybody implemented an Emacs mode for the Utrecht Attribute Grammar System (UUAG), and is willing to share it ? Greetings, Mads Lindstrøm

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Re: [Haskell-cafe] [cabal] How to deal with build-depency that not under cabal's control?
by Roman Cheplyaka 15 Jun '09

15 Jun '09

I'm CC:ing Duncan, probably he can help. * Magicloud Magiclouds <magicloud.magiclouds(a)gmail.com> [2009-06-15 10:01:03+0800] > # ghc-pkg list gtk > /var/lib/ghc-6.10.3/./package.conf: > /home/shidaw/.ghc/i386-linux-6.10.3/package.conf: > gtk-0.10.1 > Well, still, I have the problem.... > > On Sun, Jun 14, 2009 at 6:52 PM, Roman Cheplyaka<roma(a)ro-che.info> wrote: > > * Magicloud Magiclouds <magicloud.magiclouds(a)gmail.com> [2009-06-14 18:48:26+0800] > >> My gtk2hs is install manually, `configure && make && make install`. So > > > > It's okay. > > > >> when I add gtk to build-dependency, it tells me > >> Setup.hs: At least the following dependencies are missing: > >> gtk -any > > > > Installation of gtk2hs registers these packages for you. > > Again, check `ghc-pkg list gtk`. If you installed gtk2hs, it must be > > there. If you, say, upgraded your ghc after you installed gtk2hs, you > > have to reinstall gtk2hs. > > > >> How to register my manual-installed gtk2hs to cabal? > >> > >> On Sun, Jun 14, 2009 at 6:25 PM, Roman Cheplyaka<roma(a)ro-che.info> wrote: > >> > * Magicloud Magiclouds <magicloud.magiclouds(a)gmail.com> [2009-06-14 17:30:33+0800] > >> >> Hi, > >> >> I use gtk2hs in linux. Well, I have no idea how to install gtk2hs by > >> >> cabal, but my program needs it, and I want my program cabalized. So > >> >> how to do this? > >> >> Thanks. > >> > > >> > gtk2hs consists of several cabal packages, e.g. gtk, glib and so on. > >> > (See `ghc-pkg list`) > >> > Specify those of them you need as dependencies in cabal file. > >> > > >> > -- > >> > Roman I. Cheplyaka :: http://ro-che.info/ > >> > "Don't let school get in the way of your education." - Mark Twain > >> > _______________________________________________ > >> > Haskell-Cafe mailing list > >> > Haskell-Cafe(a)haskell.org > >> > http://www.haskell.org/mailman/listinfo/haskell-cafe > >> > > >> > >> > >> > >> -- > >> 竹密岂妨流水过 > >> 山高哪阻野云飞 > > > > -- > > Roman I. Cheplyaka :: http://ro-che.info/ > > "Don't let school get in the way of your education." - Mark Twain > > > > > > -- > 竹密岂妨流水过 > 山高哪阻野云飞 -- Roman I. Cheplyaka :: http://ro-che.info/ "Don't let school get in the way of your education." - Mark Twain

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Fwd: [Haskell-cafe] curious about sum
by Alberto G. Corona 15 Jun '09

15 Jun '09

Once more I forgot to send my messages to the haskell cafe list. All the rest of the list which I´m suscribed to, send the mail replies to the list automatically, but this doesn´t. Please, can this be changed?. ---------- Forwarded message ---------- From: Alberto G. Corona <agocorona(a)gmail.com> Date: 2009/6/13 Subject: Re: [Haskell-cafe] curious about sum To: Deniz Dogan <deniz.a.m.dogan(a)gmail.com> first, I was completely wrong. It is foldl what is neccesary. sum is defined in terms of foldl: sum= foldl (+) 0 but Prelude> foldl (+) 0 [1..1000000] *** Exception: stack overflow that is not because + is non strict, but because foldl is: foldl f z0 xs0 = lgo z0 xs0 where lgo z [] = z lgo z (x:xs) = lgo (f z x) xs this version of foldl IS strict: foldlStrict f z0 xs0 = lgo z0 xs0 where lgo z [] = z lgo z (x:xs) =let t= f z x in t `seq` lgo t xs main= print $ foldlStrict (+) 0 [1..1000000] 500000500000 so the garbage collector do the job in freeing the consumed part of the list. 2009/6/13 Alberto G. Corona <agocorona(a)gmail.com> > > Prelude> let strictplus x y= let z=x +y in z `seq` z; sum1= foldr strictplus 0 in sum1[0..1000000] > *** Exception: stack overflow > I suppose that strictplus is strict, so the garbage collector would free the consumed part of the list. > Then, why the stack overflow? > 2009/6/13 Deniz Dogan <deniz.a.m.dogan(a)gmail.com> >> >> 2009/6/13 Jochem Berndsen <jochem(a)functor.nl>: >> > Keith Sheppard wrote: >> >> Is there any reason that sum isn't strict? I can't think of any case >> >> where that is a good thing. >> >> >> >> Prelude> sum [0 .. 1000000] >> >> *** Exception: stack overflow >> > >> > It is useful if the (+) is nonstrict; although I cannot think of any >> > useful mathematical structure where (+) would be nonstrict. >> >> I remember needing a non-strict sum at least once, but I do not >> remember the exact application. But imagine having a (very) long list >> of numbers and you want to do A if the sum exceeds a small number, >> otherwise B. >> >> if sum [0..100000] > 10 then A else B >> >> However, this idea didn't work, because of strictness. >> >> -- >> Deniz Dogan >> _______________________________________________ >> Haskell-Cafe mailing list >> Haskell-Cafe(a)haskell.org >> http://www.haskell.org/mailman/listinfo/haskell-cafe >

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a now abandoned experimental extension to Haskell?
by Vasili I. Galchin 15 Jun '09

15 Jun '09

Hello, In some code that I am cabalizing I ran into: type DataLiteral = <<< ref RDFgraph defs >>> type URIReference = <<< ref RDFgraph defs >>> type NonNegativeInteger = <<< ??? >>> What is this? Kind regards, Vasili

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Re: [Haskell-cafe] I need a hint in list processing
by Tony Morris 15 Jun '09

15 Jun '09

Just guessing. How do you know it's an accident? Richard O'Keefe wrote: > > On 15 Jun 2009, at 4:26 pm, Tony Morris wrote: > >> Prelude Data.List> nub . concat $ [[2, 3], [1, 2], [2, 3, 4], [1, 2, 3]] >> [2,3,1,4] > > In this particular case. But that's a lucky accident.\ > > -- Tony Morris http://tmorris.net/

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Haskell EDSL to generate SQL?
by Günther Schmidt 15 Jun '09

15 Jun '09

Hi, I tried to solve some large data processing solely in Haskell so I could avoid lots of eventually very long and complex SQL statements. Unfortunately, as was to be expected, that approach doesn't scale. So I do need an SQL backend. But I hope to be able to use an DSL from which I can automatically generate SQL-Strings instead of writing the SQL statements literally. Has anyone else taken a similar approach? Günther

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How to know the build dependencies?
by Magicloud Magiclouds 14 Jun '09

14 Jun '09

Hi, I am learning to use cabal for my code. Just when I start, I met a question, is there an easy way to find out what packages my code depends? Thanks.

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