- Haskell-Cafe - Haskell.org

Multiple versions of a cabal package Or what's the right way to update?
by david fries 11 Apr '10

11 Apr '10

Dear Caféistas I desperately need your collective knowledge I have been working on porting the haskell-platform to the FreeBSD operating system for a while now and some versioning issues have come up. FreeBSD is still running on GHC-6.10.4 (6.12 is in the works). The ghc package contains a couple of libraries that ghc is built against and requires to run. For instance, network-2.2.1.2 is one of them. The problem is that the Haskell Platform requires version 2.2.1.4. Under normal circumstances we would port network-2.2.1.4 to FreeBSD and then specify it as a dependency of the Platform port. But then we end up with two (exposed) versions of network installed on the system. For example, let's assume that I have the following Haskell source (Networking.hs): module Networking where import Data.ByteString.Lazy import Data.Maybe import Network.HTTP import Network.Stream import Network.URI getBinary :: String -> IO ByteString getBinary url = do uri <- return $ fromJust $ parseURI url rsp <- simpleHTTP $ request uri getResponseBody rsp where request uri = Request { rqURI = uri , rqMethod = GET , rqHeaders = [] , rqBody = empty } When I try to compile it (`ghc --make Networking.hs`) I get the following: Networking.hs:12:30: Couldn't match expected type `network-2.2.1.2:Network.URI.URI' against inferred type `URI' In the first argument of `request', namely `uri' In the second argument of `($)', namely `request uri' In a stmt of a 'do' expression: rsp <- simpleHTTP $ request uri However, the following thing could help: $ ghc --make Networking.hs -package network-2.2.1.2 The workaround ain't acceptable to the FreeBSD committers, so I have to come up with something better... In a perfect world, I'd be able to install the required HP dependencies without tripping ghc up. Then we could switch over to the platform as a foundation of GHC-6.12. I have lots of questions. Is it smart to have multiple installed versions of the same library? Up until now, we could avoid such situations. What would be the correct approach to updating network? I guess it would involve rebuilding all installed packages that had previously been compiled with ghc? Though I hope not - our package management system could pull that off if necessary. If it is perhaps a bad idea to update certain "core" libraries, is there a way to declare them as such in the cabal file? regards and TIA, dave

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Cabal-install
by Andrew Coppin 11 Apr '10

11 Apr '10

OK, so apparently my Google skills are lacking. I can't find anything but the most terse documentation of the cabal-install tool online. Somewhere there surely must be something which explains how to control this thing. Anyway, can anybody tell me how I can change the default settings so that I get profiling libraries built by default, and Haddock documentation built by default? (I'm on Windows, in case that makes a difference...)

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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 11 Apr '10

11 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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