February 2009 - Haskell-Cafe

Gtk2HS 0.10.0 Released
by Peter Gavin 18 Feb '09

18 Feb '09

Hi everyone, Oh, dear... it seems I've forgotten how to spell "cafe", and sent this message to haskell-caft(a)haskell.org the first time around. I resent it to all the lists again (just to make sure everyone interested receives it), so I apologize for any duplicated messages you might have received. In any case... I'd like to release the announcement of Gtk2HS 0.10.0. A lot of new stuff has gone into this release, including: - Support for GHC 6.10 - Bindings to GIO and GtkSourceView-2.0 - Full switch to the new model-view implementation using a Haskell model - Support for many more model-based widgets such as IconView and an updated binding for ComboBox - Full Drag-and-Drop support - Better support for Attributes in Pango - Replaced Event for EventM monad, thereby improving efficiency and convenience - Functions for interaction between Cairo and Pixbuf drawing - Lots of bug fixes, code cleanups, and portability improvements With this release, the bindings to GnomeVFS and GtkSourceView-1.0 have been deprecated. The TreeList modules have been deprecated from the Gtk+ bindings. Source and Win32 binaries are available at: https://sourceforge.net/project/showfiles.php?group_id=49207package_id=4244… Thanks to everyone who submitted bug fixes and features this time around! Thanks, Peter Gavin Gtk2HS Release Manager

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"first class" tuples?
by Peter Verswyvelen 18 Feb '09

18 Feb '09

Tuples in Haskell always have annoyed me a bit since each tuple of different dimension is hardcoded (I guess compilers enforce a maximum dimension on tuples?) Since a tuple represents a fixed size data structure with different types at each coordinate, it feels as it should be possible to have a couple of type and data constructors to build a tuple, and to use recursion at the type level to have functions operate on tuples of any dimension. E.g. one could then have a tmap function that takes a tuple of functions and a tuple of values and applies the function at coordinate N to the value at coordinate N. Is something like this possible today in Haskell, e.g. using new features like type families, GADTs, template haskell, etc? Or do we need dependent types for it? In C++x0 I believe it is now possible to do so, since they even allow a variable number of template arguments, using recursion at compile time (see e.g. http://publib.boulder.ibm.com/infocenter/comphelp/v9v111/index.jsp?topic=/c… ) Grapefruit has something like first class records, so I guess it should be possible (and simpler) to do this for tuples?

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C-like Haskell
by drblanco 18 Feb '09

18 Feb '09

I'm trying to do a calculation for Gauss' circle problem, which counts the integer lattice points with distance to the origin <= r. It's sequence A000328 on the AT&T integer sequence database. I can't figure out a way to do it quickly in Haskell for r around 10^9. Here's my attempt, which takes about 75s for r=10^8. circ2 r = (1+4*r) + 4 * (circ2' (rs+1) r 1 0) where rs = r^2 -- circ2' :: Int64 -> Int64 -> Int64 -> Int64 -> Int64 circ2' rad x y sum | x<y = sum | rad<=rs = circ2' (rad+1+2*y) x (y+1) (sum+1+2*(x-y)) | otherwise = circ2' (rad+1-2*x) (x-1) y sum The commented out line was to try to force it to use machine-size ints, but instead it made it eat memory like mad. It overflows if everything is forced to be ints, and isn't much faster. Making rad and sum Integers fixes the overflow but still takes ~45 secs. I do already have the number I wanted, but was wondering how this could be made faster, or even why it's so slow. This is all on GHC 6.8.3 under OS X Intel, using ghc -O2. For comparison, the C code below runs in <1 second. typedef unsigned long long bigint; bigint gausscount(bigint r) { bigint sum=0; bigint x, y; bigint rs=r*r; bigint rad=rs+1; x=r; y=1; while (y<x) { while (rad>rs) { rad-=2*x; rad++; x--; } sum+=1+2*(x-y); rad+=2*y+1; y++; } sum*=4; sum++; return sum; } -- View this message in context: http://www.nabble.com/C-like-Haskell-tp21717584p21717584.html Sent from the Haskell - Haskell-Cafe mailing list archive at Nabble.com.

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Postdoctoral Research Position at Yale University
by Paul Hudak 17 Feb '09

17 Feb '09

Postdoctoral Research Position at Yale University The Nettle Project in the Computer Science Department at Yale University seeks applicants for a one-year (minimum) postdoctoral research position. The successful candidate will apply modern, high-level programming language ideas (such as embodied in Haskell) to help design and implement a language for the control of BGP-based network routers, with the goal of realizing high-level networking protocols for traffic engineering, security, and related networking concerns. The ideal candidate will have strength both in programming language concepts and implementation techniques, as well as networking fundamentals. A PhD in computer science or related field is required. Yale is an affirmative action, equal opportunity employer. Interested candidates should send their CV or resume to Professor Paul Hudak at paul.hudak(a)yale.edu.

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Polymorphism overhead
by Louis Wasserman 17 Feb '09

17 Feb '09

I have (roughly) the following code: data Foo e type MFoo e = Maybe (Foo e) instance Ord e => Monoid (Foo e) where f1 `mappend` f2 = <code invoking the mappend instance from Maybe (Foo e)> I'd expect this to optimize to the same thing as if I had implemented: meld :: Ord e => Foo e -> Foo e -> Foo e f1 `meld` f2 = -- code invoking meld' meld' :: Ord e => Maybe (Foo e) -> Maybe (Foo e) -> Maybe (Foo e) meld' (Just f1) (Just f2) = meld f1 f2 meld' m1 Nothing = m1 meld' Nothing m2 = m2 instance Ord e => Monoid (Foo e) where mappend = meld However, GHC's Core output tells me that the first piece of code reexamines the polymorphism in every recursion, so that mappend, which is used in the Monoid instance of Foo, looks up the Monoid instance of Foo *again* (for the sole purpose of looking itself up) and recurses with that. Why is this, and is there a way to fix that? Louis Wasserman wasserman.louis(a)gmail.com

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Haskell Weekly News: Issue 105 - February 17, 2009
by Brent Yorgey 17 Feb '09

17 Feb '09

--------------------------------------------------------------------------- Haskell Weekly News http://sequence.complete.org/hwn/20090217 Issue 105 - February 17, 2009 --------------------------------------------------------------------------- Welcome to issue 105 of HWN, a newsletter covering developments in the [1]Haskell community. And here's the Belated Valentine's Day HWN! Motto: "Remembering that you love someone three days after you were supposed to is better than not remembering at all." Of course, it's late because I spent the weekend working on the Typeclassopedia (although you won't find a link to it in this HWN because I've only included things through Saturday). Much Haskell love to all! Announcements Plans for GHC 6.10.2. Ian Lynagh [2]announced a quick summary of the plans for GHC 6.10.2. If there is a bug not on the [3]high-priority list that is causing you major problems, please let the developers know. A release candidate is expected to be ready by the end of the week. Bug fix to regex-tdfa, new version 0.97.3. ChrisK [4]announced a [5]new release of regex-tdfa which fixes some additional bugs. Three Cheers For QuickCheck! Google Summer of Code 2009. Malcolm Wallace [6]announced that haskell.org will once again be applying to be a Google Summer of Code mentor organization. Now is the time to begin discussing ideas for student projects. Also, if you wish to help publicize GSoC amongst students, there are [7]official posters/fliers available. A long discussion of various project ideas followed, including some analysis of the factors which contribute to project success. happs-tutorial 0.7. Creighton Hogg [8]announced the release of [9]happs-tutorial 0.7, the first release of happs-tutorial built against the new [10]Happstack project. Creighton has now taken over development of the tutorial from Thomas Hartman. first Grapefruit release. Wolfgang Jeltsch [11]announced the first official release of [12]Grapefruit, a library for Functional Reactive Programming (FRP) with a focus on user interfaces. With Grapefruit, you can implement reactive and interactive systems in a declarative style. User interfaces are described as networks of communicating widgets and windows. Communication is done via different kinds of signals which describe temporal behavior. CFP: 5th Haskell Hackathon, April 17-19, Utrecht. Sean Leather [13]issued a call for participation in the [14]5th Haskell Hackathon, which will be held in Utrecht, The Netherlands, from 17-19 April. The Haskell Hackathon is a collaborative coding festival with a simple focus: build and improve Haskell libraries, tools, and infrastructure. All are welcome! See the website for more information, or join the IRC channel (#haskell-hac5). Please register if you plan to attend! Take a break: write an essay for Onward! Essays. Simon Peyton-Jones [15]announced a call for submissions to [16]Onward! Essays. An Onward! essay is a thoughtful reflection upon software-related technology. Its goal is to help the reader to share a new insight, engage with an argument, or wrestle with a dilemma. The deadline is 20 April. Data.Stream 0.3. Wouter Swierstra [17]announced a new version of the [18]Data.Stream package, a modest library for manipulating infinite lists. Changes include support for lazy SmallCheck, an improved Show instance, stricter scans, various documentation fixes, and several new functions from Data.List. X Haskell Bindings 0.1. Antoine Latter [19]announced a new release of the [20]X Haskell Bindings (XHB) library. The goal of XHB is to provide a Haskell implementation of the X11 wire protocol, similar in spirit to the X protocol C-language Binding (XCB). Gtk2HS 0.10.0 released. Peter Gavin [21]announced a [22]new release of [23]Gtk2HS, the Haskell GTK bindings. Notable changes include support for GHC 6.10, bindings to GIO and GtkSourceView-2.0, a full switch to the new model-view implementation using a Haskell model, and many others. Discussion Haskell.org GSoC. Daniel Kraft began a [24]discussion about good topics for a Haskell GSoC project. Painting logs to get a coloured tree. Joachim Breitner asked about elegant ways to annotate trees, leading to an interesting [25]discussion. Blog noise [26]Haskell news from the [27]blogosphere. * Conor McBride: [28]FP Lunch: Djinn, monotonic. * Gregg Reynolds: [29]"Computation" considered harmful. "Value" not so hot either.. * Darcs: [30]darcs weekly news #17. * Antoine Latter: [31]Dependencies in Hackage, revisited. * GHC / OpenSPARC Project: [32]Allocate!. * Chris Done: [33]Updates: RSS and highlighting. * Chris Done: [34]Simple SMTP library with plain/login authentication. * The GHC Team: [35]Ever wondered how big a closure is?. * Luke Palmer: [36]Dana update: Core execution language, dependent combinators. * John Van Enk: [37]Distraction: Fun with diagrams!. * Magnus Therning: [38]New backend for epilicious pushed.. * Alex Mason: [39]Shootout PiDigits program kinda sucks (and possibly so does GHC). * Gtk2HS: [40]Gtk2Hs version 0.10.0 released. * Ketil Malde: [41]Notes from PADL. * Alson Kemp: [42]Kudos to Bodo. * xmonad: [43]New layout: XMonad.Layout.Cross. * Gregg Reynolds: [44]Programming Language Semiotics. * Gregg Reynolds: [45]Formal semantics for side effects. * xmonad: [46]contribs review: CycleWindows, multimedia keys, runOrCopy. * Conal Elliott: [47]From the chain rule to automatic differentiation. * Arnar Birgisson: [48]The Non-Determinism Monad. * Matthew Jones: [49]XMonad: A tiling window manager written in Haskell. * Gregg Reynolds: [50]Moggi :: CT -> Hask. * Lennart Augustsson: [51]More BASIC. Quotes of the Week * chrisdone: zipWith3 ($) (cycle [const,flip const]) "hai! haha!" "yarlysotense!" * quicksilver: I'm very unlikely to give the time of day to anything which doesn't let me continue to use emacs. * roconnor: don't let Float do your finance homework for you. * quicksilver: @go is made of STRING and FAIL. * drhodes: We're sorry Mr. Thunk, but this program is on a need to run basis, and you don't need to run. Now go away before I call the garbage collector. About the Haskell Weekly News New editions are posted to [52]the Haskell mailing list as well as to [53]the Haskell Sequence and [54]Planet Haskell. [55]RSS is also available, and headlines appear on [56]haskell.org. To help create new editions of this newsletter, please see the information on [57]how to contribute. Send stories to byorgey at cis dot upenn dot edu. The darcs repository is available at darcs get [58]http://code.haskell.org/~byorgey/code/hwn/ . References 1. http://haskell.org/ 2. http://article.gmane.org/gmane.comp.lang.haskell.glasgow.user/16304 3. http://hackage.haskell.org/trac/ghc/query?status=new&status=assigned&status… 4. http://article.gmane.org/gmane.comp.lang.haskell.general/16859 5. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/regex-tdfa 6. http://article.gmane.org/gmane.comp.lang.haskell.general/16857 7. http://code.google.com/p/google-summer-of-code/wiki/GsocFlyers 8. http://article.gmane.org/gmane.comp.lang.haskell.general/16848 9. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/happs-tutorial 10. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/happs-tutorial 11. http://article.gmane.org/gmane.comp.lang.haskell.cafe/52847 12. http://haskell.org/haskellwiki/Grapefruit 13. http://article.gmane.org/gmane.comp.lang.haskell.cafe/52689 14. http://haskell.org/haskellwiki/Hac5 15. http://article.gmane.org/gmane.comp.lang.haskell.cafe/52660 16. http://onward-conference.org/calls/foressays 17. http://article.gmane.org/gmane.comp.lang.haskell.cafe/52558 18. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/Stream/ 19. http://article.gmane.org/gmane.comp.lang.haskell.cafe/52364 20. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/xhb 21. http://www.haskell.org//pipermail/haskell-cafe/2009-February/055490.html 22. https://sourceforge.net/project/showfiles.php?group_id=49207package_id=4244… 23. http://www.haskell.org/gtk2hs/ 24. http://thread.gmane.org/gmane.comp.lang.haskell.cafe/52553 25. http://thread.gmane.org/gmane.comp.lang.haskell.cafe/52461 26. http://planet.haskell.org/ 27. http://haskell.org/haskellwiki/Blog_articles 28. http://sneezy.cs.nott.ac.uk/fplunch/weblog/?p=187 29. http://syntax.wikidot.com/blog:5 30. http://blog.darcs.net/2009/02/news-and-discussions-1_13.html 31. http://panicsonic.blogspot.com/2009/02/dependencies-in-hackage-revisited.ht… 32. http://ghcsparc.blogspot.com/2009/02/allocate.html 33. http://chrisdone.com/blog/html/2009-02-13-lang-spec-tag-rss.html 34. http://chrisdone.com/blog/html/2009-02-13-smtp.html 35. http://ghcmutterings.wordpress.com/2009/02/12/53/ 36. http://lukepalmer.wordpress.com/2009/02/12/dana-update-core-execution-langu… 37. http://blog.sw17ch.com/wordpress/?p=18 38. http://therning.org/magnus/archives/499 39. http://axman6.homeip.net/blog/2009/02/shootout-pidigits-program-kinda-sucks… 40. http://haskell.org/gtk2hs/archives/2009/02/11/gtk2hs-version-0100-released/ 41. http://blog.malde.org/index.php/2009/02/11/notes-from-padl/ 42. http://www.alsonkemp.com/haskell/kudos-to-bodo/ 43. http://xmonad.wordpress.com/2009/02/10/new-layout-xmonadlayoutcross/ 44. http://syntax.wikidot.com/blog:4 45. http://syntax.wikidot.com/blog:3 46. http://xmonad.wordpress.com/2009/02/08/contribs-review-cyclewindows-multime… 47. http://conal.net/blog/posts/from-the-chain-rule-to-automatic-differentiatio… 48. http://www.hvergi.net/2009/02/the-non-determinism-monad/ 49. http://matburt.net/?p=36 50. http://syntax.wikidot.com/blog:1 51. http://augustss.blogspot.com/2009/02/more-basic-not-that-anybody-should-car… 52. http://www.haskell.org/mailman/listinfo/haskell 53. http://sequence.complete.org/ 54. http://planet.haskell.org/ 55. http://sequence.complete.org/node/feed 56. http://haskell.org/ 57. http://haskell.org/haskellwiki/HWN 58. http://code.haskell.org/~byorgey/code/hwn/

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Re: [Haskell-cafe] Re: [Haskell] ANNOUNCE: first Grapefruit release
by Wolfgang Jeltsch 17 Feb '09

17 Feb '09

Am Montag, 16. Februar 2009 22:04 schrieben Sie: > As for how I want Hieroglyph to work interactively, I think the easiest way > is to react to the input data considered as a coherent whole. The semantic > model for visualization is that a Visualization is a function from Data to > Visual. Hmm, doesn’t this approach result in scalability problems? You always have to analyse the complete input data if a small part of it changes and you always have to update the complete picture. This is similar to the problems I see with Yampa-based UI approaches. However, you might be interested in things like incremental list signals which I’m (re-)implementing at the moment. To a large degree, the library user sees a time-varying list but internally the library takes care of not updating the whole list all the time but only the parts which actually change. > The main problem I have, which is what I want FRP for, is that to consider > the data as a coherent whole, the data have to be composable. I don’t really understand this. Could you explain this, please? Best wishes, Wolfgang

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Re: [Haskell-cafe] ANNOUNCE: first Grapefruit release
by Wolfgang Jeltsch 17 Feb '09

17 Feb '09

Am Montag, 16. Februar 2009 22:43 schrieben Sie: > * Wolfgang Jeltsch <g9ks157k(a)acme.softbase.org> [2009-02-16 14:51:18+0100] > > > Maybe there is someone interested in helping me with the graphics > > support? There is already quite some stuff implemented (thanks to > > Matthias Reisner), it’s just that this is based on the classic interface > > of Grapefruit. > > Yep, I'd like to help with graphics support. Thanks a lot. > Currently I'm still learning about all these things (FRP, arrows, Grapefruit > particularly), but if there are things which does not require deep > understanding of these concepts (or even help to gain one), please tell me. I think, you need to understand what discrete and segmented signals are. Which is not very difficult, in my opinion. You only have to know what they mean not how they are implemented. So you don’t need a deep understanding of all kinds of FRP things in order to hack on Grapfruit graphics support. Did you have a look at my e-mail conversation with Jeff Heard (in the same haskell-cafe thread)? He thinks about adapting the Hieroglyph 2D graphics library to Grapefruit. There is also the graphics implementation of classic Grapefruit which is for 3D graphics and OpenGL-based. These may be things, you want to have a look at. > Also, I'm yet not sure about Utrecht, but if Grapefruit hacking is > planned, it's worth coming for me :) This sounds very good. It’s not yet sure whether I will go to Utrecht for supervising Grapefruit hacking but it’s very likely that I will. Best wishes, Wolfgang

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StableFunPtr?
by Maurício 17 Feb '09

17 Feb '09

Hi, I've seen that if I'm going to leave a pointer to data in the hands of foreign code, I should use StablePtr so that the value it points to doesn't change. However, we also usually give FunPtr to foreign code, like when registering callbacks, but I can't found any kind of "StableFunPtr". Are all FunPtrs stable? Thanks, Maurício

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Functional GUIs again
by Fraser Wilson 17 Feb '09

17 Feb '09

Since I'm congenitally lazy, and writing a GUI by hand in the IO monad is ... not what I expect from a beautiful program, and because what I often need is a GUI that manipulates a state, and because I don't understand arrows, and having been intrigued by a recent cafe thread, I threw together a prototype GUI library with the following features: - the GUI is defined on three levels: gadgets, widgets and styles - gadgets are functions on a state - widgets are data structures which define the layout - styles are ways to modify the appearance of widgets The following quick example shows a text box and a button. Clicking on the button reverses the text in the text box. > module Main where > import Barrie > demoWidget :: Widget > demoWidget = vbox [ui "demo entry" textBox, > ui "demo command" (labelButton "click me")] > type DemoState = String > type DemoGadget = Gadget DemoState > demoGUI :: DemoGadget > demoGUI = localG "demo gui" [editorG "demo entry" id const, > commandG "demo command" reverse] > main = gtkMain demoGUI demoWidget "Hello, world" Two gadgets are used: editorG :: String -> (a -> b) -> (b -> a -> a) -> Gadget a commandG :: String -> (a -> a) -> Gadget a The editor gadget can show a value from a state, and update a state with a value. The command gadget can transform a state to a new state. gtkMain connects the gadgets to a widget, which specifies layout using the vbox, attaching the editor gadget to a text box, and the command gadget to a button. Well, that's all pretty trivial. The key thing for me was that I can easily slap a GUI onto the the front of a class of applications, which happen to be the sort of applications I've been writing lately. Also, arbitrary parts of the GUI can respond to things that happen miles away, without really having to worry about it too much. In barrie-0.1 and 0.2, which used stream-based approaches, the problem of getting state from one end of the application to the other was non-trivial. I'll sketch another quick example: > data BridgeGame = ... And a bunch of things you can do with the state: > makeBid :: Bid -> BridgeGame -> BridgeGame > playCard :: Card -> BridgeGame -> BridgeGame For bidding, each bid is represented by a gadget: > bidG :: Bid -> Gadget BridgeGame > bidG bid = enabled (bidOK bid) $ CommandG (show bid) (makeBid bid) 'enabled' switches the gadget on if its first argument returns true when applied to the current state. However, the decision about what to do with a disabled gadget is made by its corresponding widget. We get one button for each bid: > biddingG :: Gadget BridgeGame > biddingG = localG "bidding" (map bidG allBids) And they can be displayed in any old order using a widget: > biddingW :: Widget > biddingW = vbox (map suitBids [Club, Diamond, Heart, Spade] ++ [ntBids]) > where suitBids suit = hbox $ map (bidButton . flip Bid suit) [1 .. 7] > ntBids = hbox $ map (bidButton . NT) [1 .. 7] > bidButton bid = ui (show bid) $ labelButton (show bid) (You're right, double, redouble and pass are not represented. They make the lines too long). Screenshot here: http://thewhitelion.org/images/4D.png I've just bid four diamonds, so everything lower than that is automatically disabled. Currently, Barrie implements buttons, text boxes, labels, vertical/horizontal layout, single-column lists and drop lists. It current uses Gtk2hs for rendering, but it's GUI-agnostic (in fact, the first renderer was putStrLn/getLine). You can have a look by using darcs: darcs get http://thewhitelion.org/darcs/barrie Or get the tarball at http://thewhitelion.org/haskell/barrie-0.3.0-src.tar.gz One note: this is not intended to be a theoretically sound approach, merely a way of getting something done quickly. I would expect it to be most useful in putting a GUI front-end onto an existing application, in particular, an application that is driven by user actions which update a state; e.g. a calculator, a bridge game, a 4th edition D&D character creator (but that leads to a critical mass of nerdiness, so it's off the table for now) cheers, Fraser. -- http://thewhitelion.org/mysister

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