April 2009 - Haskell-Cafe

Re: Is 78 characters still a good option? Was: [Haskell-cafe] breaking too long lines
by Jason Dusek 26 Apr '09

26 Apr '09

2009/04/26 Miguel <miguelimo38(a)yandex.ru>: > 2009/04/26 Jason Dusek <jason.dusek(a)gmail.com>: >> If we do not preserve the old ways, it'll be anarchy all the >> way down. > > How exactly are you going to preserve old ways? Whenever are we are presented with the a question of correct conduct, we must re-affirm our commitment to the practices handed down to us. When we revisit this question -- "Should we maintain the 80 column limit?" -- it as an opporunity to affirm this practice. Through this exercize, we perenially renew our faith in this convention, accepting the bonds of convention. This ritual -- the "line-length reminding ritual" -- is played out across all programming communities several times a year. Everyone says the same things. Then they all go away with the 80 column limit re-established in their minds. -- Jason Dusek

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installing Sqlite3 driver for windows
by Michael P Mossey 26 Apr '09

26 Apr '09

I'm working from Real World Haskell, trying to install HDBC and the Sqlite3 driver on Windows XP. It was easy enough to use Cabal to install HDBC. However, for the Sqlite3 driver things get fuzzy. I downloaded hdbc-sqlite3_2.1.0.0.zip, but don't know what I'm supposed to do with it. Also, it wasn't clear what to do with the sqlite3.dll file. On this page <http://software.complete.org/software/wiki/hdbc/FrequentlyAskedQuestions> it seems to imply you need to put it in 'gch --print-libdir'\include and %windir%\system32 but that page is really about building the driver from source. Maybe it only needs to go in the system32 directory. Thanks, Mike

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Haskell/JS -- better through typeclasses?
by Jason Dusek 26 Apr '09

26 Apr '09

I'd like to be able to translate Haskell to JavaScript. Many Haskell/JS bridges provide libraries for writing complete JavaScript programs in Haskell; some of them even include jQuery. However, my goals are more limited -- I'd like to be able to take a Haskell module and turn it into a JavaScript object. For example, I'd like to write a nice parser in Haskell and then reuse it on the client side. No need to handle all the DOM events or implement multi-threading. Of course, the place to start is by reading the commentary. A little bit of browsing suggests some questions of strategy: . Maybe a new backend is not the right thing? All the backends seem to be for real computers with real instruction sets. . Is it better to just work on transforming Core into JS directly? It seems that "External Core" is still in limbo. . Some translations strike me as baffling in principle. For example, a value like `ones`: ones = 1 : ones We'd want to avoid most native JavaScript containers, it seems; however, we are then unable to leverage the speed of native containers. It's entirely possible that translating Haskell to JavaScript may turn out not to be the best idea; maybe it is better to have a type class for types (for example, `Parser Char`) to provide their own translators? The it would be straightforward to prevent translation of programs that use concurrency libs, native ops or `IO`. -- Jason Dusek

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ANN: Bamse-0.9.4, a Windows Installer generator
by Sigbjorn Finne 26 Apr '09

26 Apr '09

Hi, a new version of Bamse has been uploaded to hackage, http://hackage.haskell.org/cgi-bin/hackage-scripts/package/bamse Bamse is a package and application for letting you quickly put together Windows Installers for your software projects/products from within the comforts of Haskell. New in this release is the support for generating MSIs from your Cabal projects, having them either be built from source or just have them be installed and registered at install-time. i.e., one-click installation of Cabal packages. See examples/Cabal.hs for a worked example of how to bundle up Cabal packages. I've found this functionality a bit useful, hope others do too. The new version also adds support for handling .NET assemblies. enjoy --sigbjorn

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Haskell/JS -- better through typeclasses?
by Dimitry Golubovsky 26 Apr '09

26 Apr '09

John wrote: > I can't speak for Jason, but for me, this is not very useful. I don't > want to write in a Haskell DSL, I want to write in Haskell. And not > the whole program, either, just the parts that really lend themselves > to functional programming (parsers, numeric computations, code > generators, various algorithms). What I presented is of course not a complete solution; this is just a tool to construct Javascript expressions in haskellized type-safe form. What I also mentioned: this monadic form may be an end-point for some other conversion, like GRIN. This answers the question how to translate a true Haskell program (like a parser) into Javascript (or a similar language). There are some experimental compilers with GRIN backends, plus I did my own experiments with GRIN that gave me some ideas. So I would just look at it as a starting point of some new family of tools which hopefully will end up opening possibility to translate Haskell things to Javascript. PS For now I am more concerned with the IDL part of it, but any suggestions on GRIN are welcome. -- Dimitry Golubovsky Anywhere on the Web

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Haskell/JS -- better through typeclasses?
by Dimitry Golubovsky 26 Apr '09

26 Apr '09

Jason and everybody interested, Please check out a package I recently (just by coincidence: I haven't seen this topic on the list until after I uploaded it) uploaded to Hackage: http://hackage.haskell.org/cgi-bin/hackage-scripts/package/jsmw-0.1 This is a basic monadic interface to Javascript code generator (based on WebBits), providing sort of a macro (like in macro-assembler) facility. HJScript was used as a (sort of) prototype, but I chose slightly different notation for EDSL. >From here, I think two directions may be taken: 1. Some techniques are described in the GRIN thesis [1] how to convert a Haskell core to monadic form. These may be explored for this case. 2. Similarly to how the Web Consortium defined interfaces to its components using IDL *, Haskell modules converted to Javascript may expose their interfaces same way, thus providing a basis for a reusable component-based approach. Any discussions and suggestions are welcome. >From my own impressions, EDSL approach is better for interactive/AJAX parts of a Javascript application, as translation of non-strict evaluation (like it was done in the Yhc/Javascript project) just causes a lot of code generated, and does not improve the user interaction performance at all. For other (internal) components, translation from Haskell may be more appropriate, just to be able to reuse the existing libraries. One of experiments with Yhc involved a user-exposed form, and a parser to validate user's input. With this hybrid approach, the user interface part might be coded using an EDSL, and the parser could be translated from Haskell core. An IDL might be generated for the parser interface, thus making the parser module a reusable component. These are of course just thoughts and ideas for now. ------------------------------------ * See the DOM package: this is an auto-generated Haskel approximation of IDL specs provided for the basic DOM components. [1] http://www.cs.chalmers.se/~boquist/phd/index.html [2] http://hackage.haskell.org/cgi-bin/hackage-scripts/package/DOM-2.0.1 -- Dimitry Golubovsky Anywhere on the Web

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Problems with Haskell Program Coverage
by Dominic Steinitz 26 Apr '09

26 Apr '09

I want to use hpc to check that the ASN.1 library tests cover all the code. When I run it with a set of tests that I *know* don't test certain things, it reports that they have been covered i.e. there are not coloured in the markup that hpc produces. I would have expected a lot of yellow. It seems to work ok on small amounts of code so I'm not clear what I'm doing wrong. I'd be happy to provide the .tix file or put the .html files somewhere if that would be helpful. Here's what I use: ghc -o NewTest NewTest.hs -fhpc --make NewTest hpc markup NewTest Dominic.

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Type constraints and classes
by Neil Brown 26 Apr '09

26 Apr '09

Hi, I have a Haskell problem that keeps cropping up and I wondered if there was any solution/work-around/dirty-hack that could help. I keep wanting to define class instances for things like Functor or Monad, but with restrictions on the inner type. I'll explain with an example, because I find explaining this in words a bit difficult. Let's say I want to create a Monad instance for Set akin to that for lists: == import Data.Set import Prelude hiding (map) instance Monad Set where return = singleton m >>= f = fold union empty (map f m) -- Error: Could not deduce (Ord a, Ord b) from the context (Monad Set) == Everything fits (I think) -- except the type-class constraints. Obviously my Monad instance won't work if you have things inside the set that aren't Ord, but I can't work out how to define a restricted instance that only exists for types that have Ord instances. I can't express the constraint on the instance because the a and b types of return and >>= aren't visible in the class header. Shifting the constraint to be present in the type doesn't seem to help either (e.g. newtype Ord a => MySet a = MySet (Set a)...). Is there any way to get such instances as the one for Set working? I cannot carry around a compare function myself in a data type that wraps Set, because return cannot create such functions without the original type-class instance. I don't actually need a Monad for Set, but it neatly demonstrates my problem of wanting constraints on the type inside a Monad (or a Functor, or an Applicative, etc). I worked around a similar problem with Functor by opting for a new Functor-like type-class with the constraints, but doing that with Monad rules out using all the monad helper functions (liftM, mapM, etc), and the do notation, which would be a step too far. All suggestions are welcome, no matter how hacky, or how many GHC extensions are required :-) (provided they don't break all the other monads, e.g. redefining the signature of Monad). Thanks, Neil.

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Re: [Haskell-cafe] ANNOUNCE: fad 1.0 -- Forward Automatic Differentiation library
by Kalman Noel 26 Apr '09

26 Apr '09

Henning Thielemann schrieb: > with advanced type classes: > http://hackage.haskell.org/packages/archive/numeric-prelude/0.0.5/doc/html/… I'll take this as another opportunity to point out that the Haddock docs of the Numeric Prelude are highly unreadable, due to all qualified class and type names appearing as just C or T. I'm wondering, too, if the Numeric Prelude could be organized more cleanly if we had a fancier module system - does someone have sufficient experience with, say, ML-style module systems to tell? Kalman

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Haskell Weekly News: Issue 115 - April 25, 2009
by Brent Yorgey 25 Apr '09

25 Apr '09

--------------------------------------------------------------------------- Haskell Weekly News http://sequence.complete.org/hwn/20090425 Issue 115 - April 25, 2009 --------------------------------------------------------------------------- Welcome to issue 115 of HWN, a newsletter covering developments in the [1]Haskell community. By all reports, the [2]5th Haskell Hackathon was a resounding success, with over 50 hackers present and many interesting Haskell projects worked on! Announcements darcs hacking sprint 2 and hac5 report. Eric Kow [3]sent out a link to a [4]report on the second darcs hacking sprint, held as part of the Haskell Hackathon. HPong-0.1.2: A simple OpenGL Pong game based on GLFW. R.A. Niemeijer [5]announced the release of [6]HPong, a simple Pong game implemented using OpenGL and GLFW. Hac5 roundup. Martijn van Steenbergen [7]reported on the 5th Haskell Hackathon. See the [8]wiki page for details, pictures, and links to blog posts. HTTP-4000.0.6. Sigbjorn Finne [9]announced a new release of the [10]HTTP package, which adds more robust handling of ill-formed cookies, and fixes a bug in normalization of certain proxy-bound requests. dataenc 0.12.1.0. Magnus Therning [11]announced version 0.12.1.0 of the [12]dataenc package. This version adds a bunch of new encodings, including xxencode, hexadecimal, quoted-printable, python escaping, and url encoding; and also fixed some bugs. list-tries-0.0 - first release. Matti Niemenmaa [13]announced the first public release of [14]list-tries, a library providing implementations of finite sets and maps for list keys using tries, both simple and of the Patricia kind. The data types are parametrized over the map type they use internally to store the child nodes: this allows extending them to support different kinds of key types or increasing efficiency. curl-1.3.5. Sigbjorn Finne [15]announced a new release of the [16]curl package, which provides Haskell bindings to libcurl. It works with ghc 6.10.2, taking into account the updated story on how to register Haskell-based finalizers. Runge-Kutta library -- solve ODEs. Uwe Hollerbach [17]announced a [18]Runge-Kutta library for numerically solving ordinary differential equations. funsat-0.6. Denis Bueno [19]announced version 0.6 of [20]funsat, a modern, DPLL-style SAT solver written in Haskell. Funsat solves formulas in conjunctive normal form and produces a total variable assignment for satisfiable problems. Version 0.6 adds a representation for logical circuits (and, or, not, onlyif, iff, if-then-else) supporting efficient conversion to CNF, and now uses the BSD3 license. control-monad-exception-0.1: Explicitly typed exceptions. Pepe Iborra [21]announced the [22]control-monad-exception package, which provides explicitly typed exceptions for Haskell. The type of a computation in the EM monad carries a list of the exceptions that the computation may throw. A exception is raised with 'throw', which in addition adds it to the type, and captured with 'catch', which correspondingly removes it from the type. Only safe computations (all exceptions handled) can escape from the monad. Haskell Implementers' Workshop 2009 (co-located with ICFP). Simon Marlow [23]issued a call for talks to be given at the ACM SIGPLAN [24]Haskell Implementers' Workshop, to be held on September 3 in Edinburgh, Scotland, in conjunction with [25]ICFP 2009. The proposal deadline in 15 June. The Haskell Implementers Workshop is a new workshop to be held alongside ICFP 2009 this year in Edinburgh, Scotland. There will be no proceedings; it is an informal gathering of people involved in the design and development of Haskell implementations, tools, libraries, and supporting infrastructure. persistent-map-0.0.0. Peter Robinson [26]announced the [27]persistent-map package, which provides a thread-safe (STM) frontend for finite map types together with a backend interface for persistent storage. A pragmatic Haskell .NET interop layer, 0.4.0. Sigbjorn Finne [28]announced a new release of [29]hs-dotnet, a Haskell .NET interop layer. It lets you access .NET functionality from Haskell and vice versa. The new version includes development done since the start of the year. Apart from rewriting the internals completely to put it all on a sounder footing, this release includes proper support for .NET generic types (classes and interfaces), mapping them naturally on to Haskell parameterized types. Utrecht Haskell Compiler (UHC) -- first release. atze [30]announced the first public release of the [31]Utrecht Haskell Compiler (UHC). UHC supports almost all Haskell98 features plus many experimental extensions. The compiler runs on MacOSX, Windows (cygwin), and various Unix flavors. Features include multiple backends, including a bytecode interpreter backend and a GRIN based, full program analysing backend; experimental language extensions, some of which have not been implemented before; implementation via attribute grammars and other high-level tools; and ease of experimentation with language variants, thanks to an aspect-oriented internal organisation. 6.10.3 plans. Ian Lynagh [32]announced plans for a 6.10.3 release of GHC, in order to fix the handling of ^C in ghci. 6.10.3 will also use haskeline instead of editline. A HERE Document syntax. Jason Dusek [33]proposed a lightweight syntax for HERE documents in Haskell. Discussion Functor and Haskell. Daryoush Mehrtash [34]asked about the link between functors in category theory and Haskell's Functor class; the resulting thread is a good introduction to the connections between Haskell and category theory for those just learning the latter. breaking too long lines. Christian Maeder [35]asked how to break long lines in Haskell source, leading to an interesting discussion of coding style. Jobs Haskell consultant wanted to develop small, Mac-based utility in Haskell or AppleScript. R J [36]announced an opportunity to develop a short program to annotate lists of words with their definitions. Blog noise [37]Haskell news from the [38]blogosphere. * Twan van Laarhoven: [39]Where do I get my non-regular types?. * Sebastian Fischer: [40]Reinventing Haskell Backtracking. * Darcs: [41]darcs hacking sprint #2 report. * Well-Typed.Com: [42]Platform progress and the Hackathon. * Roman Cheplyaka: [43]Hac5: the rest of the story (almost). * Twan van Laarhoven: [44]A non-regular data type challenge. * Magnus Therning: [45]dataenc 0.12.1.0 released. * Galois, Inc: [46]Portland Next Week: ICFP PC Functional Programming Workshop. * Christophe Poucet (vincenz): [47]Flattening Data.Map. * Roman Cheplyaka: [48]Hac5: second day. * Xmonad: [49]contribs review. * GHC / OpenSPARC Project: [50]Loose ends and register pairing. * Sean Leather: [51]Latest on the incremental fold and attributes. * >>> Matthew Podwysocki: [52]Functional Solution for the Shortest Path Problem . * Chris Smith: [53]Code for Manipulating Graphs in Haskell. * Austin Seipp: [54]A little fun with Haskabelle. Proving things about *existing* Haskell code in Isabelle. * Tupil: [55]Running Happstack applications with FastCGI. * Martijn van Steenbergen: [56]Hac5-Saturday. * beelsebob: [57]Bottoms. * Antoine Latter: [58]Using Haskeline. * Darcs: [59]darcs weekly news #26. * Martijn van Steenbergen: [60]Hacking GHC-What I've learned. * >>> Brandon Simmons: [61]Initial tests of Tries: Follow Up. * >>> Lab 49: [62]The Algebra of Data, and the Calculus of Mutation. * Martijn van Steenbergen: [63]Hac5-Friday. Pictures from the Hackathon. * >>> Matthew Podwysocki: [64]Haskell and Collective Intelligence . Quotes of the Week * Gracenotes: foldr chosen for its magical evil terminating powers * uninverted: Moving from lisp to haskell with respect to functions is like moving from c to perl with respect to strings. * Berengal: [On infinitely fast computers] The OS probably has a failsafe built in: If a program is running it's in an infinite loop and needs to be killed... * nikki93: After a bit more delving, I've come to see the power of haskell at last. You have to treat functions like crap, forget about the C idea that they're 'big things'. They're not. * Berengal: I was squashing a bug, got frustrated, and typed "fix error" in ghci... About the Haskell Weekly News New editions are posted to [65]the Haskell mailing list as well as to [66]the Haskell Sequence and [67]Planet Haskell. [68]RSS is also available, and headlines appear on [69]haskell.org. To help create new editions of this newsletter, please see the information on [70]how to contribute. Send stories to byorgey at cis dot upenn dot edu. The darcs repository is available at darcs get [71]http://code.haskell.org/~byorgey/code/hwn/ . References 1. http://haskell.org/ 2. http://www.haskell.org/haskellwiki/Hac5 3. http://article.gmane.org/gmane.comp.lang.haskell.cafe/57551 4. http://blog.darcs.net/2009/04/darcs-hacking-sprint-2-report.html 5. http://article.gmane.org/gmane.comp.lang.haskell.cafe/57493 6. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/HPong 7. http://article.gmane.org/gmane.comp.lang.haskell.cafe/57470 8. http://www.haskell.org/haskellwiki/Hac5 9. http://article.gmane.org/gmane.comp.lang.haskell.cafe/57336 10. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/HTTP 11. http://article.gmane.org/gmane.comp.lang.haskell.libraries/10945 12. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/dataenc 13. http://article.gmane.org/gmane.comp.lang.haskell.cafe/57311 14. http://iki.fi/matti.niemenmaa/list-tries/ 15. http://article.gmane.org/gmane.comp.lang.haskell.cafe/57251 16. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/curl 17. http://article.gmane.org/gmane.comp.lang.haskell.cafe/57160 18. http://www.korgwal.com/software/rk-1.0.0.tar.gz 19. http://article.gmane.org/gmane.comp.lang.haskell.cafe/57101 20. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/funsat 21. http://article.gmane.org/gmane.comp.lang.haskell.general/17120 22. http://article.gmane.org/gmane.comp.lang.haskell.general/17120 23. http://article.gmane.org/gmane.comp.lang.haskell.general/17113 24. http://haskell.org/haskellwiki/HaskellImplementorsWorkshop 25. http://www.cs.nott.ac.uk/~gmh/icfp09.html 26. http://article.gmane.org/gmane.comp.lang.haskell.general/17106 27. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/persistent-map 28. http://article.gmane.org/gmane.comp.lang.haskell.general/17105 29. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hs%2Ddotnet 30. http://article.gmane.org/gmane.comp.lang.haskell.general/17103 31. http://www.cs.uu.nl/wiki/UHC 32. http://article.gmane.org/gmane.comp.lang.haskell.glasgow.user/16792 33. http://article.gmane.org/gmane.comp.lang.haskell.prime/2787 34. http://thread.gmane.org/gmane.comp.lang.haskell.cafe/57324 35. http://thread.gmane.org/gmane.comp.lang.haskell.cafe/57207 36. http://article.gmane.org/gmane.comp.lang.haskell.cafe/57568 37. http://planet.haskell.org/ 38. http://haskell.org/haskellwiki/Blog_articles 39. http://twan.home.fmf.nl/blog/haskell/non-regular2.details 40. http://www-ps.informatik.uni-kiel.de/~sebf/pub/atps09.html 41. http://blog.darcs.net/2009/04/darcs-hacking-sprint-2-report.html 42. http://blog.well-typed.com/2009/04/platform-progress-and-the-hackathon/ 43. http://ro-che.blogspot.com/2009/04/hac5-rest-of-story-almost.html 44. http://twan.home.fmf.nl/blog/haskell/non-regular1.details 45. http://therning.org/magnus/archives/568 46. http://www.galois.com/blog/2009/04/23/portland-next-week-icfp-pc-functional… 47. http://cpoucet.wordpress.com/2009/04/18/flattening-datamap/ 48. http://ro-che.blogspot.com/2009/04/hac5-second-day.html 49. http://xmonad.wordpress.com/2009/04/22/contribs-review/ 50. http://ghcsparc.blogspot.com/2009/04/loose-ends-and-register-pairing.html 51. http://feedproxy.google.com/~r/splonderzoek/~3/KWqNCgsK1ww/latest-on-increm… 52. http://codebetter.com/blogs/matthew.podwysocki/archive/2009/04/21/functiona… 53. http://cdsmith.wordpress.com/2009/04/20/code-for-manipulating-graphs-in-has… 54. http://www.jedi-ninja.net/2009/04/20/A-little-fun.html 55. http://blog.tupil.com/running-happstack-applications-with-fastcgi/ 56. http://martijn.van.steenbergen.nl/journal/2009/04/19/hac5-saturday/ 57. http://noordering.wordpress.com/2009/04/19/bottoms/ 58. http://panicsonic.blogspot.com/2009/04/using-haskeline.html 59. http://blog.darcs.net/2009/04/darcs-weekly-news-26.html 60. http://martijn.van.steenbergen.nl/journal/2009/04/18/hacking-ghc-what-ive-l… 61. http://coder.bsimmons.name/blog/2009/04/initial-tests-of-tries-follow-up/ 62. http://blog.lab49.com/archives/3011 63. http://martijn.van.steenbergen.nl/journal/2009/04/17/hac5-friday/ 64. http://codebetter.com/blogs/matthew.podwysocki/archive/2009/04/17/haskell-a… 65. http://www.haskell.org/mailman/listinfo/haskell 66. http://sequence.complete.org/ 67. http://planet.haskell.org/ 68. http://sequence.complete.org/node/feed 69. http://haskell.org/ 70. http://haskell.org/haskellwiki/HWN 71. http://code.haskell.org/~byorgey/code/hwn/

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