April 2007 - Haskell-Cafe

Re: [Haskell] Re: Newbie: what are the advantages of Haskell?
by Neil Mitchell 28 Apr '07

28 Apr '07

Moving to haskell-cafe@ ... > Hi Neil, a good debugger ? What is in Google Summer of Code about it ? Updating Hat, www.haskell.org/hat - see http://code.google.com/soc/haskell/about.html > I was studing about debuging techs for haskell to build a nice > debugging enviorment in HIDE or some other IDE. It's my bacharelor > final work. > > I and my teacher are thoughting about trying "observes" in a transparent way. > The user click and point to in a source local... but the observes dont > appear in the code. We will try integrate another technique from HAT > in this imaginary (still)debugging interface. You probably want to check out the GHCi debugger (in GHC head), and GuiHat [http://www-users.cs.york.ac.uk/~ndm/hat/] Thanks Neil

1 0

IDE support
by Philipp Volgger 28 Apr '07

28 Apr '07

What IDE support is available for Haskell (Visuall Haskell, EclipseFP), anything else?

12 18

run-time type testing in haskell?
by Eric 28 Apr '07

28 Apr '07

In imperative languages one can test the type of a variable and downcast if necessary. Here's an example in Pseudojava: T v := ... ; if (v instanceof T') T' v' := (T')v Is it possible to do something like this in Haskell? Eric.

6 6

Parsec beginners problem
by Jim Burton 28 Apr '07

28 Apr '07

I have a couple of questions about my first use of Parsec, which is trying to read morse code symbols from a string. I have a map of symbols: import qualified Data.Map as M morsemap = M.fromList [('A', ".-") ... , ('Z', "--..")] a string to parse, like test = "...---..-....-" and a Parser to read a single morse letter: morse1 :: GenParser Char st String morseletter = try $ M.fold ((<|>) . string) (string "") morsemap which I am hoping would be equivalent to try (string ".-") <|> (string "-.") ...etc <|> string "" but I don't know what the base of the fold should be (string "" is wrong I suppose) - what is the unit of <|>? Is there a readymade combinator for this? It fails anyway: *Main> run morse1 test parse error at (line 1, column 1): unexpected "." expecting ".-" I suppose this is because the strings I'm looking for overlap but I thought the use of try..<|> would avoid this error...? Thanks, -- View this message in context: http://www.nabble.com/Parsec-beginners-problem-tf3657821.html#a10219707 Sent from the Haskell - Haskell-Cafe mailing list archive at Nabble.com.

5 7

I need help on AVL trees
by iliali16 28 Apr '07

28 Apr '07

Can someone advise me how can I build an AVL tree becouse I have difficulties with the rotations. Since if I add a node I want to be abel to check whether the tree is balanced or not if balanced ok but if not I need to do one of the 4 rotations which is a problem for me and I want to be able to give the nodes from the keyboard. What I mean is that it is possible to build the tree from scratch. Thanks to all! -- View this message in context: http://www.nabble.com/I-need-help-on-AVL-trees-tf3657386.html#a10218190 Sent from the Haskell - Haskell-Cafe mailing list archive at Nabble.com.

3 2

tiff reader or libtiff bindings
by Andreas Voellmy 27 Apr '07

27 Apr '07

Hi, Does anyone know of a haskell library to read (and write) tiff files? Or has someone written a binding to libtiff? Thanks, Andreas

2 1

New HaskODell user groups
by dons＠cse.unsw.edu.au 27 Apr '07

27 Apr '07

I've created a new wiki page documenting all the new user groups for Haskell that are springing up! http://haskell.org/haskellwiki/User_groups If you're starting a new group, please add it here, and publicise. -- Don P.S. Some obvious user group candidates, in my opinion, would be a Portland group, a Bay Area group and something at Chalmers... ;-)

3 2

Question: template-haskell and profiling
by ET 27 Apr '07

27 Apr '07

Hi, folks Trying to profile the modules, those contain a template-haskell splices, I have ran into problem - GHC6.4 (win2K) returns an error message and then stops. Without the "-prof" option all works fine. Is there a way to bypass this inconsistency? Example below illustrates the problem: ============================ {-# OPTIONS_GHC -fth #-} module Main where import MainTH main :: IO () main = putStrLn . show . fact $ 100 fact :: Integer -> Integer fact n = $(thFact "n") ============================ module MainTH where import Language.Haskell.TH thFact :: String -> ExpQ thFact s = appE (dyn "product") (arithSeqE (fromToR (litE . integerL $ 1) (dyn s))) preview :: IO () preview = runQ (thFact "x") >>= putStrLn . pprint ============================ >ghc --make -prof Main.hs Chasing modules from: Main.hs Compiling MainTH ( ./MainTH.hs, ./MainTH.o ) Compiling Main ( Main.hs, Main.o ) Loading package base-1.0 ... linking ... done. Loading package haskell98-1.0 ... linking ... done. Loading package template-haskell-1.0 ... linking ... done. ghc: ./MainTH.o: unknown symbol `_era' With function "MainTH.preview" excluded from export list, final phrase were ghc: ./MainTH.o: unknown symbol `_entering_PAP'

3 2

Multi Line String literals
by Bas van Dijk 27 Apr '07

27 Apr '07

Hello, Just for fun I'm trying to define multi line string literals. I have the following code and I'm wondering if it can be improved (understandability, elegance, performance): http://hpaste.org/1582 (look at the second annotation) regards, Bas van Dijk

6 8

Haskell Weekly News: April 27, 2007
by dons＠cse.unsw.edu.au 27 Apr '07

27 Apr '07

--------------------------------------------------------------------------- Haskell Weekly News http://sequence.complete.org/hwn/20070427 Issue 61 - April 27, 2007 --------------------------------------------------------------------------- Welcome to issue 61 of HWN, a weekly newsletter covering developments in the [1]Haskell community. The last week was a very exciting week for the Haskell community, with a new GHC release, the first release of Xmonad, a window manager written in Haskell, and DisTract, a new distributed bug tracker, written in Haskell. A number of new Haskell jobs were announced, and several new user groups were formed! 1. http://haskell.org/ Announcements GHC 6.6.1. Ian Lynagh [2]announced a new patchlevel release of GHC. This release contains a significant number of bugfixes relative to 6.6, so we recommend upgrading. Release notes are [3]here. GHC is a state-of-the-art programming suite for Haskell. Included is an optimising compiler generating good code for a variety of platforms, together with an interactive system for convenient, quick development. The distribution includes space and time profiling facilities, a large collection of libraries, and support for various language extensions, including concurrency, exceptions, and foreign language interfaces. 2. http://article.gmane.org/gmane.comp.lang.haskell.glasgow.user/12075 3. http://haskell.org/ghc/docs/6.6.1/html/users_guide/release-6-6-1.html Xmonad 0.1. Spencer Janssen [4]announced the inaugural release of [5]Xmonad. Xmonad is a minimalist tiling window manager for X, written in Haskell. Windows are managed using automatic layout algorithms, which can be dynamically reconfigured. At any time windows are arranged so as to maximise the use of screen real estate. All features of the window manager are accessible purely from the keyboard: a mouse is entirely optional. Xmonad is configured in Haskell, and custom layout algorithms may be implemented by the user in config files. 4. http://article.gmane.org/gmane.comp.lang.haskell.general/15131 5. http://xmonad.org/ DisTract: Distributed Bug Tracker implemented in Haskell. Matthew Sackman [6]announced DisTract, a [7]Distributed Bug Tracker. We're all now familiar with working with distributed software control systems, such as Monotone, Git, Darcs, Mercurial and others, but bug trackers still seem to be fully stuck in the centralised model: Bugzilla and Trac both have single centralised servers. This is clearly wrong, as if you're able to work on the Train, off the network and still perform local commits of code then surely you should also be able to locally close bugs too. DisTract allows you to manage bugs in a distributed manner through your web-browser. The distribution is achieved by making use of a distributed software control system, Monotone. Thus Monotone is used to move files across the network, perform merging operations and track the development of every bug. Finally, the glue in the middle that generates the HTML summaries and modifies the bugs is written in Haskell. 6. http://article.gmane.org/gmane.comp.lang.haskell.cafe/21857 7. http://www.distract.wellquite.org/ IOSpec 0.1. Wouter Swierstra [8]announced the first release of the [9]Test.IOSpec library, that provides a pure specification of some functions in the IO monad. This may be of interest to anyone who wants to debug, reason about, analyse, or test impure code. Essentially, by importing libraries from IOSpec you can the same code you would normally write in the IO monad. Once you're satisfied that your functions are reasonably well-behaved, you can remove the Test.IOSpec import and replace it with the 'real' functions instead. 8. http://article.gmane.org/gmane.comp.lang.haskell.general/15134 9. http://www.cs.nott.ac.uk/~wss/repos/IOSpec wl-pprint-1.0: Wadler/Leijen pretty printer. Stefan O'Rear [10]announced wl-pprint-1.0, the classic Wadler / Leijen pretty printing combinators, now in 100% easier to use [11]Cabalised form! PPrint is an implementation of the pretty printing combinators described by Philip Wadler (1997). In their bare essence, the combinators of Wadler are not expressive enough to describe some commonly occurring layouts. The PPrint library adds new primitives to describe these layouts and works well in practice. 10. http://thread.gmane.org/gmane.comp.lang.haskell.general/15112 11. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/wl-pprint-1.0 London Haskell User Group. Neil Bartlett [12]announced the first meeting of the [13]London Haskell User Group on Wednesday 23rd May from 6:30PM. The meeting will be held at City University's main campus in central London, and Simon Peyton Jones will be coming to give a talk. 12. http://article.gmane.org/gmane.comp.lang.haskell.cafe/21955 13. http://www.londonhug.net/2007/04/26/announcement-first-meeting-of-the-londo… New York Functional Programmers Network. Howard Mansell [14]announced a New York area-based network for Haskell (and functional) programmers. The idea is to have a regular meeting through which functional programmers can meet to discuss experiences, get and give information, find jobs. 14. http://article.gmane.org/gmane.comp.lang.haskell.cafe/21856 Data.Proposition 0.1. Neil Mitchell [15]announced the release of [16]Data.Proposition, a library that handles propositions, logical formulae consisting of literals without quantification. It automatically simplifies a proposition as it is constructed using simple rules provided by the programmer. Implementations of propositions in terms of an abstract syntax tree and as a Binary Decision Diagram (BDD) are provided. A standard interface is provided for all propositions. 15. http://article.gmane.org/gmane.comp.lang.haskell.general/15117 16. http://www-users.cs.york.ac.uk/~ndm/proposition/ Book reviews for the Journal of Functional Programming. Simon Thompson [17]sought interested contributors for book reivews for the Journal of Functional Programming. There is a list of books [18]currently available for review. 17. http://article.gmane.org/gmane.comp.lang.haskell.general/15136 18. http://www.cs.kent.ac.uk/people/staff/sjt/JFP/available.html Reminder: HCAR May 2007. Andres Loeh [19]reminded us that the deadline for the May 2007 edition of the Haskell Communities and Activities Report is only a few days away -- but this is still enough time to make sure that the report contains a section on your project, on the interesting stuff that you've been doing; using or affecting Haskell in some way. 19. http://article.gmane.org/gmane.comp.lang.haskell.general/15161 Template 0.1: Simple string substitution. Johan Tibell [20]announced a simple [21]string substitution library that supports substitution ala Perl or Python. 20. http://article.gmane.org/gmane.comp.lang.haskell.general/15135 21. http://darcs.johantibell.com/template hpaste for emacs. David House [22]announced hpaste.el, an Emacs Lisp library that integrates [23]hpaste, the Haskell pastebin, into Emacs. It provides two functions, hpaste-paste-region and hpaste-paste-buffer, which send the region or buffer to the hpaste server as required. 22. http://thread.gmane.org/gmane.comp.lang.haskell.glasgow.user/12046 23. http://hpaste.org/ Haskell' This section covers the [24]Haskell' standardisation process. * [25]General pattern bindings * [26]Relax the restriction on Bounded derivation * [27]data syntax * [28]Mathematical preludes * [29]Literate Haskell specification 24. http://hackage.haskell.org/trac/haskell-prime 25. http://thread.gmane.org/gmane.comp.lang.haskell.prime/2178 26. http://thread.gmane.org/gmane.comp.lang.haskell.prime/2183 27. http://thread.gmane.org/gmane.comp.lang.haskell.prime/2184 28. http://thread.gmane.org/gmane.comp.lang.haskell.prime/2189 29. http://thread.gmane.org/gmane.comp.lang.haskell.prime/2190 Libraries This week's proposals and extensions to the [30]standard libraries. * [31]Add a MonadState instance for the Parsec monad * [32]Use 'Wide' API if System has it 30. http://haskell.org/haskellwiki/Library_submissions 31. http://thread.gmane.org/gmane.comp.lang.haskell.libraries/6778 32. http://thread.gmane.org/gmane.comp.lang.haskell.libraries/6848 Hackage This week's new libraries in [33]the Hackage library database. * [34]X11-extras-0.1 * [35]hinstaller-2007.4.24 * [36]IOSpec-0.1.1 * [37]gd-3000.0.1 * [38]xmonad-0.1 * [39]YamlReference-0.3 * [40]parsedate-2006.11.10 * [41]chunks-2007.4.18 * [42]wl-pprint-1.0 * [43]Emping-0.1 * [44]hsns-0.5.1 * [45]htar-0.1 * [46]cabal-upload-0.3 * [47]unix-compat-0.1 * [48]tar-0.1 33. http://hackage.haskell.org/ 34. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/X11-extras-0.1 35. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hinstaller-2007.… 36. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/IOSpec-0.1.1 37. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/gd-3000.0.1 38. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/xmonad-0.1 39. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/YamlReference-0.3 40. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/parsedate-2006.1… 41. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/chunks-2007.4.18 42. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/wl-pprint-1.0 43. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/Emping-0.1 44. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hsns-0.5.1 45. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/htar-0.1 46. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/cabal-upload-0.3 47. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/unix-compat-0.1 48. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/tar-0.1 Discussion GHC Release Plans. Simon Marlow [49]initiated a discussion on possibe release timelines for upcoming GHC versions. 49. http://thread.gmane.org/gmane.comp.lang.haskell.glasgow.user/12014 More inlining. Duncan Coutts [50]asked about more fine grained control over inlining in GHC, to ease term rewriting with RULES 50. http://thread.gmane.org/gmane.comp.lang.haskell.glasgow.user/12046 Haskell version of Norvig's Python Spelling Corrector. Pete Kazmier [51]spawned a long thread covering various implementations of spelling correctors in Haskell 51. http://thread.gmane.org/gmane.comp.lang.haskell.cafe/21780 Jobs Quantitative Functional Programmer. Credit Suisse. [52]The Global Modelling and Analytics Group (GMAG) is responsible for producing state-of-the-art pricing, trading and hedging models for Credit Suisse. These models are used across a range of businesses in the Fixed Income and Equity Divisions. The groups mandate covers all major asset classes including Credit Derivatives, Commodities, Emerging Markets, Equity Derivatives and Convertibles, Exotics, Foreign Exchange, Fund Linked Products, Interest Rate Products and Mortgage Derivatives. GMAG operates globally with 85 members located in New York, London, Hong Kong and Tokyo. We are currently building a Domain Specific Language (embedded in Haskell) that will be used within GMAG. We require intelligent, motivated people to develop and extend this language. These individuals will also work with modellers to aid them in effectively applying these new tools. 52. http://tinyurl.com/2lqoq9 Haskell programmer positions. HAppS. HAppS LLC has [53]part-time and full-time positions open for Haskell programmers to: improve the open source Haskell codebase at HAppS.org; implement infrastructure to make it work well in Amazon S3/EC2 environments; make http://pass.net reliable enough to be used by live apps; build the mass market apps we want to run on top of the HAppS/Pass.net platform. We are looking for people who: have substantial experience programming Haskell; have experience building Internet apps (not necessarily in Haskell but would be good), and live in any of these places: the Internet, New York, San Francisco Los Angeles. 53. http://article.gmane.org/gmane.comp.lang.haskell.cafe/21951 Vacancy for a PhD student. Johan Jeuring [54]announced a vacancy for a PhD student in the Strategy Feedback project. Knowledge of Haskell is a big plus; implementation of most of the tools will be done in Haskell. Length: 1+3 years, Open University the Netherlands, Location: Heerlen. 54. http://article.gmane.org/gmane.comp.lang.haskell.cafe/21740 Blog noise [55]Haskell news from the blogosphere. * [56]Overloading Haskell numbers, part 1, symbolic expressions * [57]Overloading Haskell numbers, part 2, Forward Automatic Differentiation * [58]Overloading Haskell numbers, part 3, Fixed Precision * [59]More Haskell parallelism * [60]Haskell status: impressed * [61]On haskell: writing a packet sniffer * [62]Must-see Haskell talks at OSCON 07 * [63]Zen and the Art of Functional Programming * [64]Playing with sections in Haskell * [65]More playing with sections (and flip) * [66]Thinking in objects * [67]Robot localization using a particle system monad * [68]21 open problems in typed lambda calculus * [69]Arrows and security in Haskell * [70]Haskell GUI Programing * [71]Splitting a string in Haskell * [72]Introduction to Haskell: I like it a lot * [73]Haskell (ish) code, Java gui * [74]Haskell wikibook blurb * [75]Functional and Object-Oriented Programming * [76]Xmonad: a lightweight window manager * [77]Xmonad: a tiling window manager written in Haskell * [78]Xmonad: Haskell window management has arrived * [79]Xmonad: a minimal window manager in Haskell * [80]Xmonad: in the footsteps of wmii * [81]Xmonad: a new window manager * [82]Haskell code * [83]IO in Haskell * [84]Haskell records considered grungy 55. http://planet.haskell.org/ 56. http://augustss.blogspot.com/2007/04/overloading-haskell-numbers-part-1.html 57. http://augustss.blogspot.com/2007/04/overloading-haskell-numbers-part-2.html 58. http://augustss.blogspot.com/2007/04/overloading-haskell-numbers-part-3.html 59. http://mikeburrell.wordpress.com/2007/04/16/more-haskell-parallelism/ 60. http://austin.youareinferior.net/?q=node/21 61. http://austin.youareinferior.net/?q=node/24 62. http://www.serpentine.com/blog/2007/04/16/must-see-haskell-talks-at-oscon-0… 63. http://azaidi.blogspot.com/2007/04/zen-and-art-of-functional-programming.ht… 64. http://gimbo.org.uk/blog/2007/04/13/playing-with-sections-in-haskell/ 65. http://gimbo.org.uk/blog/2007/04/19/more-playing-with-sections-and-flip-in-… 66. http://braindump.dk/tech/2007/04/16/thinking-in-objects/ 67. http://www.randomhacks.net/articles/2007/04/19/robot-localization-particle-… 68. http://tlca.di.unito.it/opltlca/ 69. http://abstractabsurd.blogspot.com/2007/04/arrows-security.html 70. http://araujoluis.blogspot.com/2007/04/haskell-gui-programing.html 71. http://gimbo.org.uk/blog/2007/04/20/splitting-a-string-in-haskell/ 72. http://www.noulakaz.net/weblog/2007/04/20/i-like-haskell-a-lot/ 73. http://jpmoresmau.blogspot.com/2007/04/haskell-code-java-ui.html 74. http://koweycode.blogspot.com/2007/04/haskell-wikibook-blurb.html 75. http://weblog.raganwald.com/2007/04/we-dont-need-no-stinkin-scientific.html 76. http://lennartkolmodin.blogspot.com/2007/04/xmonad.html 77. http://www.osnews.com/story.php/17744/Xmonad-a-Tiling-Window-Manager-Writte… 78. http://existentialtype.net/?p=113 79. http://gimbo.org.uk/blog/2007/04/22/xmonad-a-minimal-window-manager-in-hask… 80. http://ephemient.livejournal.com/38438.html 81. http://jpatrao-online.blogspot.com/2007/04/xmonad-new-windowmanager.html 82. http://www.wardtek.ca/2007/04/haskell-code-number-one/ 83. http://www.friendofthepigeon.co.uk/wordpress/?p=54 84. http://bloggablea.wordpress.com/2007/04/24/haskell-records-considered-grung… Quotes of the Week * apfelmus: Programming in Haskell is like dual-wielding two light sabers whereas programming in imperative languages is like being equipped with a blunt kitchen knife. * mwc: C++ is multiparadigm in the same way a dog with 4 table legs nailed onto it is an octopus * ptolomy: Sometimes Haskell feels like a personal trainer for proper program construction. You half-ass something, and the compiler doesn't let you get away with it and won't let you move on until you do it right. * dons: I wish you success and may your lambdas always beta reduce * quicksilver: May your years be long and your type inference algorithms sound. * inverselimit: So I tried as my first project in Haskell to write something that decomposes modules of polynomials using Schur-Weyl duality. This turned out to be a little tricky without being comfortable with the syntax * jcreigh: Could not find instance Ord for type ProgrammingLanguage Code Watch Apr 19 07:23:58 PDT 2007. Simon Marlow. [85]More debugger improvements. :list shows the code around the current breakpoint. Also it highlights the current expression in bold (the bold/unbold codes are hardwired to the ANSI codes right now, I'll provide a way to change them later). :set stop cmd' causes cmd to be run each time we stop at a breakpoint. In particular, :set stop :list is particularly useful. 85. http://article.gmane.org/gmane.comp.lang.haskell.cvs.ghc/20269 Wed Apr 25 03:18:32 PDT 2007. simonpj. [86]Add -fwarn-monomorphism-restriction (on by default) to warn when the MR is used. Users often trip up on the Dreaded Monomorphism Restriction. This warning flag tells you when the MR springs into action. Currently it's on by default, but we could change that. 86. http://article.gmane.org/gmane.comp.lang.haskell.cvs.ghc/20359 Thu Apr 26 02:37:19 PDT 2007. Pepe Iborra. New section on [87]debugging lambdas in the ghci user guide 87. http://article.gmane.org/gmane.comp.lang.haskell.cvs.ghc/20404 About the Haskell Weekly News Each week, new editions are posted to [88]the Haskell mailing list as well as to [89]the Haskell Sequence and [90]Planet Haskell. [91]RSS is also available, and headlines appear on [92]haskell.org. Headlines are available as [93]PDF. To help create new editions of this newsletter, please see the [94]contributing information. Send stories to dons at cse.unsw.edu.au. The darcs repository is available at darcs get [95]http://www.cse.unsw.edu.au/~dons/code/hwn 88. http://www.haskell.org/mailman/listinfo/haskell 89. http://sequence.complete.org/ 90. http://planet.haskell.org/ 91. http://sequence.complete.org/node/feed 92. http://haskell.org/ 93. http://www.cse.unsw.edu.au/~dons/code/hwn/archives/20070427.pdf 94. http://haskell.org/haskellwiki/HWN 95. http://www.cse.unsw.edu.au/~dons/code/hwn

1 0