- Haskell-Cafe - Haskell.org

SoC Proposals?
by Jeff Wheeler 17 Mar '10

17 Mar '10

Is there any way to propose a SoC idea right now? My account doesn't seem to have been created correctly, so I can't login to the Trac. I think it'd be interesting for a student to abstract the layout model in xmonad, separating it into an independent library. Other applications could then use this library, like Yi, for other types of tiling. I'd love to see other ideas related to Yi, too. It's a great project but on the verge of death (although the maintainer, JPB, is interested in mentoring). -- Jeff Wheeler Undergraduate, Electrical Engineering University of Illinois at Urbana-Champaign

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Extending Cabal's Preprocessors for GSoC?
by Diego Echeverri 17 Mar '10

17 Mar '10

Hi guys! Thomas Schilling suggested me to cross-post this here. Basically I'm thinking about the possibility of extending Cabal's Preprocessor mechanism for the GSoC. I've been working to provide uuagc with a Custom build mechanism for Cabal and in this process I have stumbled upon some difficulties (Dependency resolution and configurability). I believe is possible to extend the current preprocessing mechanism to provide the following: * Independence from physical representation (Currently the module is assumed to be built from a single file with the same name that the module) * Dependency checks (precompile when one of the files on which it depends changed. I had to trick cabal and duplicate functionality to do this for uuagc. There should be a better way!) * Composability (Add the ability to chain existing preprocessors) * Configurabily (Make easier to add configuration sections to the cabal file. I've been using "x-" sections but I guess is possible to make it look like the already-supported preprocessors). Any feedback about this? Suggestions are greatly appreciated. Diego Echeverri On Mon, Mar 15, 2010 at 10:33 AM, Thomas Schilling <nominolo(a)googlemail.com> wrote: > Yes, you sent it to the right list. In fact for discussing summer of > code it might not be a bad idea to cross-post to haskell-cafe to get > some feedback from Cabal users. > > In my experience, it is most important for Summer of Code to have a > clearly defined set of "deliverables", i.e., have a good idea of what > features you want to have working at the end of the 10 weeks. (It's > actually 12 weeks, but the last 2 weeks are expected to be used for > documenting stuff.) > > Your problem description sounds plausable, but for a GSoC project it's > good to also have an idea how to solve the problem. E.g., do you plan > to build a custom framework or just extend Cabal to support more kinds > of preprocessors? > > Duncan and others have been working on a true dependency tracking > system similar to Make, but I think there are too many open questions > to turn that into a GSoC project just yet. It does raise the > question, however, how much overlap there would be with your idea. > Maybe you can find a well-defined subset? > > In any case, try to ask haskell-cafe for feedback and apply for both > ideas. I think you can apply for up to 10 projects, so it's no > problem to apply for more than one. But keep in mind that the quality > of the proposals matters. > > On 14 March 2010 01:40, Diego Echeverri <diegoeche(a)gmail.com> wrote: >> Hi guys! >> >> I was wondering about the possibility to work on Cabal for the >> summer of code. I've been helping one of my teachers to >> provide (improve) a "plugin" for the uuagc (I haven't spent too >> much time on it, but here's the fork I'm working on >> http://github.com/diegoeche/uuagc) I have found how flexible the >> cabal libraries are but also some things haven't been >> straightforward to do (I've been using Cabal 1.6.0.3). >> >> Basically there's seems to be an assumption of a one-to-one >> relation of modules and the sources of the files which is not >> followed by the uuagc pre-processor. I can use List.ag and inside >> of it use an include declaration to List-Data.ag. If I modify >> List-Data.ag cabal won't precompile it again because it will only >> check dates against List.ag (cabal doesn't know that the >> file that generates List.hs depends not only in List.ag). I had >> to override the build hook, duplicate the check (this time >> getting all the dependencies) and delete the generated file to >> trick cabal to precompile again... and well... that's seems quite >> a nasty hack to me. >> >> This assumption also affect the possibility to make the output of >> the pre-processor not necessarily an .hs file (and not necessarily >> carrying the same name). Checking the code for the >> pre-processors (Distribution.Simple.PreProcess) I noticed it would >> be good to have the possibility to chain pre-processors. I believe >> both issues are pretty much connected. >> >> I also found the following proposal here: >> http://hackage.haskell.org/trac/summer-of-code/ticket/1581 which >> sound also interesting to me. (and there's already a mentor >> available!) >> >> Do you think this could be a good project for the summer of code? >> Maybe any other ideas I should explore? Did I write to the right >> list? (please excuse me if I didn't) >> >> Thanks! >> Diego Echeverri >> >> _______________________________________________ >> cabal-devel mailing list >> cabal-devel(a)haskell.org >> http://www.haskell.org/mailman/listinfo/cabal-devel >>

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Re: [Haskell-cafe] How to define instance for type synonym with parameter.
by Vasyl Pasternak 17 Mar '10

17 Mar '10

> > Aren't ErrorT and ReaderT instances of Applicative already? (At least in > 'transformers' package?) > > what difference between 'mtl' and 'transformers' packages ? 'mtl' goes with Haskell Platform as standard package, so what is the benefit of 'transformers' library ? Thanks, Vasyl

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new Quake 3 BSP loader and viewer
by Csaba Hruska 16 Mar '10

16 Mar '10

Hi! I did a little experiment in last week with haskell. According this ( http://graphics.cs.brown.edu/games/quake/quake3.html) tutorial, I wrote a quake 3 bsp map loader and viewer from scratch. (It is independent from frag) The code is quiet small (~900 lines with comments) and it is based on binary and vector libraries. You can find the cabalized code here: http://code.google.com/p/lambdacube/source/browse/#svn/trunk/bsploader This was my first meet with vector library, so the code is probably not the most efficient one. Any improvement suggestions are welcome! :) Cheers Csaba PS: read the README file. navigation: arrows + mouse (holding right shift increase cam speed)

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HGL concurrency problems
by Carsten Schultz 16 Mar '10

16 Mar '10

[Cc to the HGL maintainer, I hope that is ok.] Hallo, I am trying to use HGL. My configuration is Mac OS X 10.6.2 (using X11) ghc 6.12.1 HGL 3.2.0.2 (via cabal-install) My program opens a window, draws points and lines, with a considerable amount of calculation between the lines, and then waits for a key stroke before exiting. What happens depends on whether I compile with -threaded or without. With -threaded: The programs runs ok, but after a short time stops updating the window, so that I never see when it has finished. Moving the mouse over the window can trigger updates. Without -threaded: Similar as in the other, but the program nor only stops updating the window, it also stops the calculation and sits idle. Playing with the mouse can again make it run for a short time. I attach the program in case that this might help. I did not try to extract a minimal example, but the program is short. Thanks for any help. I would also like to know if it works on other platforms/versions. Carsten module Main where {- Calculates the convex hull of a set of points in an inefficient way. O(n^3) For each `o' on stdout a red line segment should be drawn -} import qualified Graphics.HGL as HGL import System.Random import System.IO nrOfPoints = 10000 -- CONFIGURE HERE data Point = Point {xc, yc :: Float} randomPoints :: Int -> IO [Point] randomPoints n = sequence $ replicate n randomPoint where randomPoint = do phi <- randomRIO (0, 2*pi) r0 <- randomRIO (0,0.48 ** 2) let r = sqrt r0 return $ Point (r * cos phi + 0.5) (r * sin phi + 0.5) boundarySegments :: [Point] -> [(Point, Point)] boundarySegments ps = filter isBoundary (pairs' ps) where pairs' l = concat [[(a,b), (b,a)] | (a,b) <- pairs l] isBoundary s = all (`leftOf` s) ps leftOf :: Point -> (Point, Point) -> Bool q `leftOf` (p1,p2) = (xc p2-xc p1)*(yc q-yc p1) - (yc p2-yc p1)*(xc q-xc p1) >= 0 pairs :: [a] -> [(a,a)] pairs [] = [] pairs [x] = [] pairs (x:xs) = [(x,x') | x' <- xs] ++ pairs xs main :: IO () main = do HGL.runGraphics $ do points <- randomPoints nrOfPoints redPen <- HGL.createPen HGL.Solid 1 (HGL.RGB 255 0 0) w <- HGL.openWindowEx "hull" Nothing (ww,wh) HGL.Unbuffered Nothing drawInWindow w $ sequence_ $ map pt points drawInWindow w $ (HGL.selectPen redPen >> return ()) sequence_ $ map ((drawInWindow w) . seg) $ boundarySegments points drawInWindow w $ HGL.text (0,0) "done" putStr "\ndone\n" HGL.getKey w HGL.closeWindow w where drawInWindow w a = do putStr "o" >> hFlush stdout HGL.drawInWindow w a ww, wh :: Int ww = 400 * 2 wh = 300 * 2 wwf = fromIntegral ww whf = fromIntegral wh xf, yf :: Point -> Float xf p = xc p * wwf yf p = yc p * whf x, y :: Point -> Int x = round . xf y = round . yf pt :: Point -> HGL.Graphic pt (Point x y) = HGL.ellipse (round (x*wwf-2),(round(y*whf-2))) (round (x*wwf+2),(round(y*whf+2))) seg :: (Point, Point) -> HGL.Graphic seg (u,v) = HGL.line (x u, y u) (x v, y v)

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Second Call for Copy: Monad.Reader Issue 16
by Brent Yorgey 16 Mar '10

16 Mar '10

I already have one or two submissions, but a few more would be great. If you've been thinking about submitting something but weren't sure or haven't gotten around to it yet, now's the time! -------------- 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 16 will be: **Friday, April 16, 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. 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 work something out.

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More strange errors when compiling code
by Giuseppe Maggiore 16 Mar '10

16 Mar '10

Hi! I am getting more problems with compilation. The two files where the problem occurs (a bit more of a general case of the sample of a few hours ago) are: ------------------------------------------------- --------------------Methods.hs------------------- ------------------------------------------------- {-# LANGUAGE MultiParamTypeClasses, FunctionalDependencies, FlexibleInstances, UndecidableInstances, FlexibleContexts, EmptyDataDecls, ScopedTypeVariables, TypeOperators, TypeSynonymInstances #-} module Methods where import Records import References class Converter a rec_a where convert :: a -> rec_a data Method s a b = Method (s -> a -> (b,s)) (<<-) :: forall rec_a s a b c n . (CNum n, HasField n (b->(c,a)) (rec_a), Converter a rec_a) => (Reference s (rec_a)) -> n -> Method s b c (<<-) r n = Method(\s -> \(x :: b) -> let (v,s') = getter r s :: (rec_a,s) m = v .! n :: (b -> (c,a)) (y,v') = m x :: (c, a) v'' = convert v' :: rec_a ((),s'') = setter r s' v'' in (y,s'')) (.!!) :: Method s a b -> a -> Reference s b (Method m) .!! x = from_constant (Constant (\s -> m s x)) ------------------------------------------------- ---------------------Main.hs--------------------- ------------------------------------------------- {-# LANGUAGE MultiParamTypeClasses, FunctionalDependencies, FlexibleInstances, UndecidableInstances, FlexibleContexts, EmptyDataDecls, ScopedTypeVariables, TypeOperators, TypeSynonymInstances #-} --module Main where import Records import References import ReferenceMonad import Methods val = firstLabel incr = nextLabel val instance Converter RecCounter (Counter RecCounter) where convert (RecCounter r) = r type Counter k = (Integer :* (() -> ((),k)) :* EmptyRecord) data RecCounter = RecCounter (Counter RecCounter) mk_test :: Integer -> RecCounter mk_test i = RecCounter( val .= i .* incr .= (\() -> ((), mk_test (i+1))) .* EmptyRecord) RecCounter test' = mk_test 0 res2 :: Reference (Counter RecCounter) Integer res2 = do (this <<- incr :: Method (Counter RecCounter) () ()) .!! () v <- (this <-- val) return v count = fst (getter res2 test') Whenever I try to compile I get the following error: *Methods> :load Main.hs [1 of 5] Compiling Records ( Records.hs, interpreted ) [2 of 5] Compiling References ( References.hs, interpreted ) [3 of 5] Compiling ReferenceMonad ( ReferenceMonad.hs, interpreted ) [4 of 5] Compiling Methods ( Methods.hs, interpreted ) [5 of 5] Compiling Main ( Main.hs, interpreted ) Main.hs:55:11: No instances for (HasField Z (() -> ((), a)) (AddField (() -> ((), RecCounter)) Emp tyRecord), Converter a (Counter RecCounter)) arising from a use of `<<-' at Main.hs:55:11-23 Possible fix: add an instance declaration for (HasField Z (() -> ((), a)) (AddField (() -> ((), RecCounter)) EmptyRecord), Converter a (Counter RecCounter)) In the first argument of `(.!!)', namely `(this <<- incr :: Method (Counter RecCounter) () ())' In a stmt of a 'do' expression: (this <<- incr :: Method (Counter RecCounter) () ()) .!! () In the expression: do (this <<- incr :: Method (Counter RecCounter) () ()) .!! () v <- (this <-- val) return v Failed, modules loaded: Methods, References, Records, ReferenceMonad. *Methods> Any hints? PS: just to give some perspective on the code: I am putting together a system for expressing mutable objects through monads. I could provide the rest of my code in case of need :) -- Giuseppe Maggiore Ph.D. Student (Languages and Games) Microsoft Student Partner Mobile: +393319040031 Office: +390412348444

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Re: [Haskell-cafe] ANNOUNCE: tupleinstances-0.0.1
by Diego Echeverri 16 Mar '10

16 Mar '10

On Tue, Mar 16, 2010 at 11:15 AM, Henning Thielemann <thunderbird(a)henning-thielemann.de> wrote: > > newtype T3 a = T3 (a,a,a) > > which could well be > > data T3 a = T3 a a a > I chose that specific representation just because at the end I want to use normal tuples. I thought this way was easier for "boxing" an "unboxing" > Are these types used for vector computations or what application do you have > in mind? I didn't have any specific application for the library. One day I just wanted to do an fmap with a tuple and somebody in #haskell suggested join (***) Of course this only works for binary tuples. I thought this would be a good excuse to play with template-haskell and give instances to some of the type classes I learnt about in the Typeclassopedia. I found it useful for vector computations. But aggregating with the Foldable instance is also handy. > Then again, is tuple-instance still an appropriate name? "There are only two hard things in Computer Science: cache invalidation and naming things" - Phil Karlton I'm open to suggestions :-) Diego Echeverri

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calling hledger zurihackers
by Simon Michael 16 Mar '10

16 Mar '10

Roman C. has cleverly added hledger to the list of topics for this weekend's ZuriHac. I will be working remotely at least on sunday (PDT), and available to support where possible. You are invited to join us! Some ideas - - add Chart or google charts to the web ui - smarter add/convert commands - separate library package - plugins - a how-to for tracking project finances; a tutorial; screencasts - portability, packaging, installability - code review/design review/planning Even one commit helps! Discussions too. Hope to see you "there". -Simon (sm) #ledger, #zurihac http://hledger.org http://www.haskell.org/haskellwiki/ZuriHac

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ANNOUNCE: direct-plugins-1.0
by Dan Knapp 16 Mar '10

16 Mar '10

For some time I have relied on Dons's Plugins package, which was perhaps something of a mistake as it's kind of messy inside and I don't think it's maintained. With the upgrade to GHC 6.12, it broke for me, and I wasn't able to get it fixed. But I was able to write my own subset of its functionality. I don't do most of the things that Plugins does - in fact I export only a single function, "load" - but I think it might be useful to somebody, so I've decided to release it. direct-plugins: Lightweight replacement for Plugins, specific to GHC http://hackage.haskell.org/package/direct-plugins This is my first post to this list; I hope it's appropriate. Please let me know if not. -- Dan Knapp "An infallible method of conciliating a tiger is to allow oneself to be devoured." (Konrad Adenauer)

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