- Haskell-Cafe - Haskell.org

What happened to Haskell original goals?
by Maurício 10 Jan '07

10 Jan '07

I remember reading "avoid success at all costs" somewhere. I miss the old days when I could read all messages in this list. Today, I can hardly keep up with a few of the most interesting threads. Good programming for all you guys in 2007. Thanks for your support and comments, and for helping me learning this really cool language. Maurício

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State monad strictness - how?
by Dean Herington 10 Jan '07

10 Jan '07

I can't seem to figure out how to achieve strictness in the context of the State monad. Consider: > import Control.Monad.State > try count = print final > where (_,final) = runState prog 0 > prog = sequence_ (replicate count tick) > tick :: State Int Int > tick = do n <- get > put (n+1) > return n (try 1000000) overflows the stack. It doesn't help to use: > put $! (n+1) The only way I've been able to get the necessary strictness is to add use of ($!) in the definition of (>>=): > data SState s a = SState (s -> (a,s)) > instance Monad (SState s) where > return x = SState (\s -> (x,s)) > m >>= f = SState (\s -> let SState m' = m > (x,s1) = m' s > SState f' = f x > (y,s2) = f' $! s1 > in (y,s2)) > runSState (SState m) s = m s > sget = SState (\s -> (s,s)) > sput s' = SState (\s -> ((),s')) > stry count = print final > where (_,final) = runSState prog 0 > prog = sequence_ (replicate count stick) > stick :: SState Int Int > stick = do n <- sget > sput (n+1) > return n Is there no way to get strictness using the standard State monad? Dean

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hacking ghci
by Walter Moreira 09 Jan '07

09 Jan '07

Hi Haskellers. A short while ago I asked about the possibility to have the output of ghci in color. Thanks to Donald Stewart who set up a wiki page to continue the attempt. Other people suggested HsColour and GUI's (thanks too). I'm not so interested in highlighting the snippets of code which ghci displays, but to use different colors for the different types of output: different colors for the prompt, input, warnings, exceptions, normal output, etc. Are any of these ideas viable?: 1. Hack the code of Interactive.hs in the GHC distribution and substitute the calls to 'putStr[Ln]' by some thin wrapper which can write with colors, according to a command line option (--color or --colour, for example), maybe using HsColour. This looks easy enough and I'd be willing to do it, but it's intrusive, and one has to mantain a different version of ghci in parallel with the main ghci. 2. Use GHC as library (from 6.6 on) and write a similar application as ghci, with more emphasis in the 'interactive' part of the name (in the same way as the relation between Python and the IPython extended shell). This is more work and more duplicate efforts, but it may be worthly, perhaps. 3. Write a wrapper which communicates with ghci via pipes. I read some attempts about this somewhere, and people suggested an approach as in #2. I haven't mentioned the GUI applications, since I would like to just have something in the spirit of ghci (command line oriented), but with colors or with configurable output. Which approach do you people think it is best? Sorry for the long message. Cheers, Walter

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Re: question about database interfaces
by Thomas David Baker 09 Jan '07

09 Jan '07

Eric wrote: > So I'm wondering -- in practice, what do people actually use? Is > there a more-or-less generally accepted standard database library for > Haskell? In practice I am using HDBC for a PostgreSQL database and it is very easy to use and works great. http://gopher.quux.org:70/devel/hdbc T

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question about database interfaces
by Eric Sessoms 09 Jan '07

09 Jan '07

Hi All, I've found the list of database libraries at http://www.haskell.org/haskellwiki/Libraries_and_tools/Database_interfaces but I haven't found much guidance in choosing among them. So I'm wondering -- in practice, what do people actually use? Is there a more-or-less generally accepted standard database library for Haskell? Thanks, Eric -- not about to see your light

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question about "How to Write a Haskell Program" tutorial
by Michael Vanier 09 Jan '07

09 Jan '07

First off, I apologize if this has come up before. As far as I can tell, the mailing list archives don't have a search function. I'm running ghc-6.6 and haddock-0.8, both compiled from source. I'm working my way through the "How to Write a Haskell Program" tutorial (which is a great idea, thanks guys!), and everything works fine until I get to the part about creating the haddock documentation. When I run: $ runhaskell Setup.hs haddock I get this: Preprocessing executables for haq-0.0... Running Haddock for haq-0.0... Warning: cannot use package haq-0.0: ghc-pkg failed With verbosity: $ runhaskell Setup.hs haddock -v I get this: Preprocessing executables for haq-0.0... Running Haddock for haq-0.0... /usr/local/packages/haskell-misc/bin/haddock --html --odir=dist/doc/html/haq --title=haq --use-package=haq-0.0 --use-package=base-2.0 dist/build/tmp/Haq.hs Warning: cannot use package haq-0.0: ghc-pkg failed Note that I'm installing into a non-standard location. I have no idea why haddock (called from cabal) is trying to use a package that is in the process of being created. Nevertheless, the documentation does get generated. Is this just something that should be ignored? Is it a Cabal bug? Mike

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Beta Gtk2Hs Getting Started
by Hans van Thiel 09 Jan '07

09 Jan '07

Hello All, The beta of the 'Gtk2Hs:Getting Started' short tutorial for beginners, Haskell GUI for Dummies, if you like :-) can be viewed at http://j-van-thiel.speedlinq.nl/gtk2hs/gtk2hsGetStart.html It tells what Gtk2Hs is, shows how to write and run 'Hello World', introduces the api and explains how to use it, refers to the Glade tutorials, gives an example of widget layout, and ends with some general pointers. It should take no more than 2,3 hours of the user's time. All feedback very welcome. Regards, Hans van Thiel

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Haskell Weekly News: January 09, 2007
by dons＠cse.unsw.edu.au 09 Jan '07

09 Jan '07

--------------------------------------------------------------------------- Haskell Weekly News http://sequence.complete.org/hwn/20070109 Issue 56 - January 09, 2007 --------------------------------------------------------------------------- Welcome to issue 56 of HWN, a weekly newsletter covering developments in the [1]Haskell community. More libraries and applications for the new year, and the Haskell Hackathon gets underway! 1. http://haskell.org/ Announcements Happy: LALR(1) parser generator. Simon Marlow [2]announced version 1.16 of [3]Happy, the parser generator system for Haskell. Changes from version 1.15 to 1.16 include switching to Cabal, a new %error directive, new production forms, and attribute grammar support. Happy version 1.16 is required for building GHC version 6.6 and later. 2. http://article.gmane.org/gmane.comp.lang.haskell.general/14726 3. http://www.haskell.org/happy/ Alex: lexical analyser generator. Simon Marlow [4]announced version 2.1.0 of [5]Alex. Changes in Alex 2.1.0 vs. 2.0.1 include switching to Cabal, and slight changes to the error semantics. 4. http://article.gmane.org/gmane.comp.lang.haskell.general/14728 5. http://www.haskell.org/alex/ rdtsc: reading IA-32 time register. Martin Grabmueller [6]announced version 1.0 of [7]package rdtsc has just been released. This small package contains one module called [8]'Rdtsc.Rdtsc', providing the function 'rdtsc' for accessing the 'rdtsc' machine register on modern IA-32 processors. This is a 64-bit counter which counts the number of processor cycles since the machine has been powered up. Using this instruction, you can make very precise time measurements which are independent of the actual CPU frequency. 6. http://article.gmane.org/gmane.comp.lang.haskell.cafe/18095/ 7. http://uebb.cs.tu-berlin.de/~magr/projects/rdtsc/ 8. http://uebb.cs.tu-berlin.de/~magr/darcs/rdtsc/ monadLib 3.0. Iavor Diatchki [9]announced a new version of [10]monadLib, a collection of standard monad implementations. Some of the changes compared to the previous version: the whole library is in a single module MonadLib.hs (~500 lines); simpler and more symmetric API; removed the (generic) monadic combinators; removed the search transformer; rewrote some transformers in the 'traditional' way (exceptions and output); there is an optional module that defines base monads corresponding to each transformer. 9. http://article.gmane.org/gmane.comp.lang.haskell.general/14714 10. http://www.csee.ogi.edu/~diatchki/monadLib Shellac 0.6. Robert Dockins [11]announced a simultaneously release of the following related packages: Shellac 0.6 Shellac-readline 0.3 and Shellac-vty 0.1. [12]Shellac is a framework for building read-eval-print style shells which uses configurable backend plugins. The major new feature of this release is the new Shellac-vty backend package, which uses the [13]new Vty library terminal I/O directly. It currently has basic line editing keybindings, paging, and a command history. The main package and Shellac-readline updates consist of minor API updates. 11. http://article.gmane.org/gmane.comp.lang.haskell.general/14715 12. http://www.eecs.tufts.edu/~rdocki01/shellac.html 13. http://members.cox.net/stefanor/vty/ IntelliJIDEA for Haskell. Tony Morris [14]announced syntax highlighting support for [15]Haskell in IntellijIDEA, released under a BSD licence. 14. http://article.gmane.org/gmane.comp.lang.haskell.general/14719 15. http://www.workingmouse.com/research/IntelliJIdea%2DHaskell/ Yampa + GADT for GHC 6.6. Joel Reymont [16]announced a cabalized [17]version of Yampa + GADT for GHC 6.6. Joel also sought comments on cabalisation, testing and example for this package. 16. http://article.gmane.org/gmane.comp.lang.haskell.cafe/18215 17. http://wagerlabs.com/yampa HNOP. Ashley Yakeley [18]updated the status of [19]HNOP, the Haskell library for doing nothing. It has recently been split into two Cabal packages: 'nop', a library of no-op services, and 'hnop', a program that uses nop to do nothing. Both packages can be found in darcs. The two packages are intended to be templates for Cabal projects, so I'm interested in making them as canonical and 'best practices' for packaging libraries and executables. 18. http://article.gmane.org/gmane.comp.lang.haskell.general/14720 19. http://semantic.org/hnop/ Haskell' This section covers the [20]Haskell' standardisation process. * [21]Rough draft of informal pattern-guard (qualifiers) explanations 20. http://hackage.haskell.org/trac/haskell-prime 21. http://article.gmane.org/gmane.comp.lang.haskell.prime/1982 Discussion instance Monad Set, using GADTs. Roberto Zunino [22]announced a definition of the Set datatype, with the usual operations, such that it can be made a member of the Monad class. 22. http://article.gmane.org/gmane.comp.lang.haskell.cafe/18118 GADTs are expressive. Jim Apple [23]described a data type which holds only those terms of the untyped lambda calculus that are reducible to normal form, using GADTs 23. http://thread.gmane.org/gmane.comp.lang.haskell.cafe/18210/focus=18210 Hackage interface. Ross Paterson [24]set up (temporarily) a simple first cut at an [25]interface to the Hackage package database. On a related note, there was some [26]discussion for home pages for Hackage projects, and collecting statistics. 24. http://article.gmane.org/gmane.comp.lang.haskell.libraries/6025 25. http://ross-paterson.dyndns.org/~ross/hackage/ 26. http://article.gmane.org/gmane.comp.lang.haskell.libraries/6035 Conference roundup The Haskell Hackathon. Hac 2007 [27]is being held this week, January 10-12th, in Oxford, with around 20 Haskell coders from across the world gathering to hack on libraries and practical tools for Haskell. Work is planned for at least hackage, Cabal, bytestrings, binary IO, http, GHC, YHC, Hoogle, DrHaskell, WinHugs, GHCi debugger, crypto, QuickCheck 2, Haddock and more besides. Notably, some graduates from this year's Google Summer of Code projects will be attending, with plans to integrate their work into the main project branches. Happy hacking everyone! 27. http://haskell.org/haskellwiki/Hac_2007 Blog noise [28]Haskell news from the blogosphere. * [29]Liberating Myself from the von Neumann Style * [30]First impressions of Haskell: Whoa! * [31]Comparing Gzip Code Reduction * [32]Simple demonstration of Haskell FFI * [33]Does Functional Programming Matter? * [34]2006 in review * [35]Haskell script to replace tabs * [36]Functional programming is functional * [37]The shock of the forgotten * [38]Category theory * [39]Does Haskell need macros? * [40]On darcs * [41]Learning things * [42]Folds for imperative programmers * [43]Dammit all! I've been blubbed * [44]Getting started with installing third-party Haskell packages * [45]A Nice Way to Learn FP * [46]Learning Haskell * [47]Haskell and Eclipse * [48]Haskell and Eclipse: building a server executable * [49]What makes a programming language more productive? * [50]Composability and Productivity * [51]Arithmetic coding in Haskell * [52]A quick and dirty theorem prover in Haskell * [53]Haskell is Fun! * [54]2007, the year of software reliability? * [55]Haskell, bondage-and-discipline and separation-of-concerns programming * [56]Type systems as safety belts * [57]It's Haskell! * [58]Two promising Haskell projects: Vital and Pivot * [59]Exceptions and interrupts 28. http://planet.haskell.org/ 29. http://blogs.nubgames.com/code/?p=4 30. http://blogs.nubgames.com/code/?p=15 31. http://blogs.nubgames.com/code/?p=16 32. http://blog.acolyte.co.za/articles/2007/01/01/simple-demonstration-of-haske… 33. http://denkspuren.blogspot.com/2007/01/does-functional-programming-matter.h… 34. http://koweynlg.blogspot.com/2006/12/state-of-thesis-2006-12-31.html 35. http://chill-yo.blogspot.com/2007/01/haskell-code-replace-tabs.html 36. http://gearon.blogspot.com/2006/10/functional-programming-is-functional.html 37. http://www.serpentine.com/blog/2007/01/01/the-shock-of-the-forgotten/ 38. http://comblog.net/hnbeck/archive/2007/01/05/2384.aspx 39. http://neilmitchell.blogspot.com/2007/01/does-haskell-need-macros.html 40. http://simulacra.in/2007/01/darcs/ 41. http://koweynlg.blogspot.com/2007/01/zommmmbieeee.html 42. http://blog.tmorris.net/folds-for-imperative-programmers/ 43. http://withoutane.com/rants/2007/01/damn-you-haskell 44. http://www.serpentine.com/blog/2007/01/05/getting-started-with-installing-t… 45. http://monadnation.blogspot.com/2007/01/nice-way-to-learn-fp.html 46. http://www.timeblog.net/2007/01/06/haskell/ 47. http://cohatoe.blogspot.com/2006/12/simple-example-walkthrough-ii.html 48. http://cohatoe.blogspot.com/2007/01/building-server-executable.html 49. http://kawagner.blogspot.com/2007/01/what-makes-programming-language-more.h… 50. http://cogito.blogthing.com/2007/01/07/composablility-and-productivity/ 51. http://vandreev.wordpress.com/2007/01/07/arithmetic-coding/ 52. http://vandreev.wordpress.com/2006/12/24/quick-and-dirty-theorem-prover/ 53. http://onthebalcony.wordpress.com/2007/01/08/haskell-is-fun/ 54. http://jguk.org/2007/01/2007-year-of-software-reliability.html 55. http://syntaxfree.wordpress.com/2007/01/08/haskell-bondage-and-discipline-a… 56. http://programming.reddit.com/info/xbc7/comments/cxfs0 57. http://e-scribe.com/news/322 58. http://factor-language.blogspot.com/2007/01/two-promising-haskell-projects.… 59. http://www.weaselhat.com/2007/01/08/exceptions-and-interrupts/ Quotes of the Week * Eric: The Haskell [code] contains no redundancy. In fact, in all the [Haskell] code I've written, in both production and play, each idea is expressed once and only once. It is the Zen ideal of perfect code. And thats never happened to me before. * nostrademons: Haskell is in a similar position [to Scala] - a complex language with many sustaining innovations - but it has one major disruptive innovation. Purity. Now, the question is whether that can be leveraged in a way that makes it useful in some market that existing imperative languages can't reach. My bets are on concurrency... * Excedrin: Isn't OO deprecated? * dpiponi: [monochrom] Nevermind monads. Use arrows. Come join the Dart Side! [dpiponi] Never mind arrows. Use comonads. Cojoin the other side. * nilsi: #haskell is better than Google * sigfpe: I think Haskell is a great language for short attention spans. You can get so much done in one line before you get bored. * timthelion: Oh wait, I LOVE foldr!! And I have only been learning Haskell for hours * kowey: All the things with guards are just there to siphon off the weirdos * Eric: [Haskell] astonishes me at every turn with its beauty and elegance. I've never felt such power. Haskell has brought back a joy in programming that I didnt even know I was missing. * Paul Johnson: Mutable state is actually another form of manual memory management: every time you over-write a value you are making a decision that the old value is now garbage, regardless of what other part of the program might have been using it. About the Haskell Weekly News Each week, new editions are posted to [60]the Haskell mailing list as well as to [61]the Haskell Sequence and [62]Planet Haskell. [63]RSS is also available, and headlines appear on [64]haskell.org. Headlines are available as [65]PDF. To help create new editions of this newsletter, please see the [66]contributing information. Send stories to dons at cse.unsw.edu.au. The darcs repository is available at darcs get [67]http://www.cse.unsw.edu.au/~dons/code/hwn 60. http://www.haskell.org/mailman/listinfo/haskell 61. http://sequence.complete.org/ 62. http://planet.haskell.org/ 63. http://sequence.complete.org/node/feed 64. http://haskell.org/ 65. http://www.cse.unsw.edu.au/~dons/code/hwn/archives/20070109.pdf 66. http://haskell.org/haskellwiki/HWN 67. http://www.cse.unsw.edu.au/~dons/code/hwn

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why can't you surround (+) in backticks and have it be infix?
by tpledger＠ihug.co.nz 08 Jan '07

08 Jan '07

David House wrote: : | You can fake this: | | (-!) = ($) | (!-) = flip ($) | | foo -! liftM2 (,) !- bar | | Not perfect, but it's interesting nonetheless. | | And yes, this was a product of some #haskell | brainstorming and algorithm tennis. :) :-) Was anyone in that brainstorm thinking of Chung-chieh Shan's -: and :- (http://www.haskell.org/pipermail/haskell-cafe/2002-July/003215.html) or was the similarity just a really cool coincidence? Regards, Tom

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trivial function application question
by brad clawsie 08 Jan '07

08 Jan '07

greetings to this helpful and informative list i have a small problem that will be certainly trivial for almost everyone reading this, i would appreciate a little help lets say i have a string s = "abcdefg" now i have two lists of strings, one a list of patterns to match, and a list of replacement strings: patterns = ["a","b"] replace = ["Z","Y"] from which my intent is that "a" be replaced by "Z", "b" by "Y" etc now using the replace function from MissingH.Str (which i know is now renamed), i wish to apply replace to s using (pattern[0], replace[0]), (pattern[1], replace[1])...(pattern[N], replace[N]). i am sure there is an elegant way to apply replace to s for all of these argument pairs without composing replace N times myself, but the solution escapes me. thanks in advance for any help you can provide for this trivial issue brad

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