April 2010 - Haskell-Cafe

GSoC proposal: Extend Cabal Preprocessors.
by Diego Echeverri 11 Apr '10

11 Apr '10

Hi! I finish writing my proposal (maybe a bit too late). I would be glad to read any feedback. http://socghop.appspot.com/gsoc/student_proposal/show/google/gsoc2010/diego… Best Regards, Diego Echeverri

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Dutch HUG Day: Program and Call for Participation
by Sean Leather 11 Apr '10

11 Apr '10

[Apologies for multiple copies.] ------------------------------------------- Dutch HUG Day 24 April 2010 Ordina office Niewegein, The Netherlands ------------------------------------------- *** *** Please register! *** *** Email Sean Leather <leather(a)cs.uu.nl> by 20 April! *** INTRODUCTION To celebrate our first anniversary, the Dutch Haskell Users Group (HUG) invites Haskell and functional programming enthusiasts in the Netherlands and surrounding area to an afternoon symposium. The Dutch HUG is an informal group with monthly meetings including talks on novel applications of Haskell and socializing in the neighborhood pub. The group was founded on Sunday, April 19, 2009 at the Haskell Hackathon hosted in Utrecht. After a successful year, we renew the trend with the Dutch HUG Day. INVITATION *** Please send an email to Sean Leather <leather(a)cs.uu.nl> by Tuesday, 20 April! *** Join us for a half day of fun and functional programming! We have some great "praatjes" (the Dutch word for talks) lined up. (Just in case you were confused by my "Call for Praatjes," all talks will be in English.) Along with talks, you can join us afterwards for a buffet dinner, graciously provided by our sponsor Ordina. The registration will allow Ordina to know how many people to expect and to satisfy their security concerns. They are also looking for recruiting options and will send attendees an email describing potential opportunities. PROGRAM We are happy to announce a preliminary program. Note that the particular titles or order of talks may change, but the general schedule should remain the same. 13:00 Reception 13:30 Welcome 13:45 Lightweight Program Inversion -- Janis Voigtländer (University of Bonn) 14:00 Functional Programming in the Industry? -- Stef Joosten (Ordina, Open University of the Netherlands) 14:30 BlazeHtml: Design of a Blazingly Fast HTML Combinator Library -- Jasper van der Jeugt (Ghent University) 15:00 Functional Programming at typLAB -- Erik Hesselink (typLAB) 15:30 Break 16:00 Cλash: Haskell-ish Hardware Descriptions -- Matthijs Kooijman (formerly University of Twente) 16:30 Why Haskell Does Not Matter -- Stefan Holdermans (Vector Fabrics) 17:00 Lightweight Monadic Regions -- Bas van Dijk (Radboud University Nijmegen, Sensor Sense) 17:30 Sirenial: Type-safe SQL Wrapper -- Martijn van Steenbergen (Utrecht University) 17:40 Discussion 18:00 Dinner 19:00 Depart 19:30 Drinks LOCATION The event will be held at the Ordina office in Niewegein, a town not far south of the city of Utrecht. You can get there by train to Utrecht Centraal and tram (the Utrecht "sneltram") to P+R Westraven. Details on the location can be found at the following link, and we will put more information on our website soon. * http://www.ordina.com/Vestigingen/Nieuwegein.aspx SPONSOR We are grateful to Ordina for allowing us to host this event on their premises. They are also kindly providing drinks during the breaks and dinner afterwards for all participants. You should come and hear from our host how they make use of functional programming. * http://www.ordina.com/ in English * http://www.ordina.nl/ in het Nederlands ORGANIZERS * Sean Leather * Chris Eidhof MORE INFORMATION * Dutch HUG: http://dutchhug.nl/ * Dutch HUG Day: http://dutchhug.nl/DutchHugDay/

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Re: [Haskell-cafe] haskell gsoc proposal for richer numerical type classes and supporting algorithms
by Paul McJones 10 Apr '10

10 Apr '10

Dear Carter, Although I'm not an active Haskell programmer, I'd like to add my support for you to write up your GSOC application. In the first five chapters of the book /Elements of Programming/ (Addison-Wesley, 2009), my coauthor Alex Stepanov and I undertook a somewhat similar effort, only using C++ instead of Haskell. We started with semigroups and monoids, and ended with rings and modules and a careful treatment of GCD. C++ does not have a direct analog of the Haskell type class, so we developed our own informal conventions for documenting the definitions of concepts and the corresponding type requirements in function templates and class templates. The concept definitions extracted from the book are available here: http://www.elementsofprogramming.com/eop-concepts.pdf and the source code here: http://www.elementsofprogramming.com/code.html I subsequently translated the concepts and functions from the first (functional) half of our book into Haskell. It was a useful learning exercise for me (giving me an appreciation for Edward Kmett's comments on your proposal), and has led to fruitful discussions with Henning Thielemann (see the Haskell Numerical Prelude and http://www.haskell.org/haskellwiki/Mathematical_prelude_discussion) and Jacques Carette (MathScheme, etc.). Paul McJones

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Length of lists within list of lists?
by boblettoj 10 Apr '10

10 Apr '10

Hi i want to know if there is any method i can use to count the number of items in each list in a list of lists, eg. someMethod [[a, b, c], [a], [b, d, e, f]] would return [3, 1, 4] is there anything that can do this? thanks -- View this message in context: http://old.nabble.com/Length-of-lists-within-list-of-lists--tp28203363p2820… Sent from the Haskell - Haskell-Cafe mailing list archive at Nabble.com.

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persist and retrieve of IO type?
by Daryoush Mehrtash 10 Apr '10

10 Apr '10

Is there a way to persist a [IO ()] to say a file then retrieve it later and execute it using a sequence function? Thanks, Daryoush

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unlifted types in classes
by Phyx 10 Apr '10

10 Apr '10

Hi all, I was wondering if it's possible to have a class declaration that would except both unlifted types and lifted types as instances. For instance, I'm looking for something like class Foo a b where bar :: a -> b instance Foo Int Int where bar = id instance Foo Int# Int where bar = iBox Regards, Phyx

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Pictures from Tucson
by Tom Hawkins 10 Apr '10

10 Apr '10

http://tomahawkins.org/Pictures/2010

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Hackage accounts and real names
by David House 10 Apr '10

10 Apr '10

Hi, An issue came up on #haskell recently with Hackage accounts requiring real names. The person in question (who didn't send this email as he's wishing to remain anonymous) applied for a Hackage account and was turned down, as he refused to offer his real name for the username. Those of us in the conversation thought this a bit of an odd policy, and were wondering where this came from. It also emerged that a couple of other people had been held back from getting Hackage accounts because of this reason. Seeing as it's also trivially easy to fake a name, what's the purpose of this restriction? Thanks, -David

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ANN: hledger 0.9 released
by Simon Michael 09 Apr '10

09 Apr '10

I'm pleased to announce a new hledger release, with many bugfixes and small improvements, GHC 6.12 support, and a separate library package to make building (h)ledger-compatible tools easier. Thanks to Oliver Braun and Gwern Branwen for code contributions this release. Just in time for tax filing! :) Patches, feedback, contributions welcome. Best, -Simon home: http://hledger.org Release notes: 2010/04/10 hledger 0.9 ...................... * ghc 6.12 support * split off hledger-lib package, containing core types & utils * parsing: ignore D, C, N, tag, end tag directives; we should now accept any ledger 2.6 file * parsing: allow numbers in commodities if double-quoted, like ledger * parsing: allow transactions with empty descriptions * parsing: show a better error for illegal month/day numbers in dates * parsing: don't ignore trailing junk in a smart date, eg in web add form * parsing: don't ignore unparsed text following an amount * parsing: @ was being treated as a currency symbol * add: fix precision handling in default amounts (#19) * add: elide last amount in added transactions * convert: keep original description by default, allow backreferences in replace pattern * convert: basic csv file checking, warn instead of dying when it looks wrong * convert: allow blank/comment lines at end of rules file * print: always show zero amounts as 0, hiding any commodity/ decimal places/price, like ledger * register: fix bad layout with years < 1000 * register: fix a Prelude.head error with reporting interval, -- empty, and --depth * register: fix a regression, register should not show posting comments * register: with --empty, intervals should continue to ends of the specified period * stats: better output when last transaction is in the future * stats: show commodity symbols, account tree depth, reorder slightly * web: -fweb now builds with simpleserver; to get happstack, use - fwebhappstack instead * web: pre-fill the add form with today's date * web: help links, better search form wording * web: show a proper error for a bad date in add form (#17) * web: fix for unicode search form values * web: fix stack overflow caused by regexpr, and handle requests faster (#14) * web: look for more-generic browser executables * web: more robust browser starting (#6) * error message cleanups * more tests, refactoring, docs Stats: 58 days, 2 contributors, 102 commits since last release. Now at 3983 lines of non-test code, 139 tests, 53% coverage.

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ANN: darcsum.el 1.2 released
by Simon Michael 09 Apr '10

09 Apr '10

With Christian's blessing, I have taken over maintenance of darcsum and would like to announce the 1.2 release: darcs get http://joyful.com/repos/darcsum -t 1.2 darcsum is an occasionally fragile but tremendously useful emacs ui for darcs. There is also vc-darcs.el, but I am quite productive with this one. For a long time it has been hanging with certain of my repos, due to unrecognised output from darcs; this release fixes all hangs I know about. There's plenty more in TODO so please send patches. Or, if there is a more serious emacs hacker out there willing to be maintainer for at least the next release, that would be great. Thanks to Christian and the other committers for keeping this useful tool alive. -Simon

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