- Haskell-Cafe - Haskell.org

Wiki spam
by Stefan Holdermans 12 Jun '13

12 Jun '13

Hi all, The last days, some spam was added to the GHC developer wiki (http://hackage.haskell.org/trac/ghc) . I have removed some of it, but I could not get rid of the bits that were added through attachments; see for example the bottom of http://hackage.haskell.org/trac/ghc/wiki/Building. Can someone with wiki admin rights have a go at it? Thanks, Stefan

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[ANN] Haskell-Paris meetup
by lucas di cioccio 11 Jun '13

11 Jun '13

Dear all, I'm happy to announce that the Haskell-Paris group will meet on June 25th in Paris. Please register (free) at http://www.meetup.com/haskell-paris/events/122515522/ . Program is not decided yet (contributions are welcome). We'll update once we know the lineup. I don't like to send spammy emails but I would like to take advantage of this announcement to invite any non-Parisian Haskellers to get in touch with us (email, twitter, or meetup page) if you are in town. We may an event scheduled close in time and we can anyway propose a get-together in a restaurant so that visitors can taste our great food&drink and everyone can chat about her favorite programming language. I did this type of semi-planned dinners a few times with some Ruby folks and it's a good way to build ties :). Regards, --Lucas DiCioccio

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(no subject)
by Zed Becker 11 Jun '13

11 Jun '13

Hi all, Haskell, is arguably the best example of a design-by-committee language. The syntax is clean and most importantly, consistent. The essence of a purely functional programming is maintained, without disturbing its real world capacity. To all the people who revise the Haskell standard, and implement the language, 1. Promise to me, and the rest of the community, that you will keep up the good effort :) 2. Promise to me, and the rest of the community, that Haskell will always spiritually remain the same clean, consistent programming language as it is now! Regards, Zed Becker

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writing a function to make a correspondance between type-level integers and value-level integers
by TP 11 Jun '13

11 Jun '13

Hi all, Following a discussion on Haskell-Cafe, Richard E. made the following proposition of a "Singleton" to make a correspondance between type-level integers and value-level integers: """ > data SNat :: Nat -> * where > SZero :: SNat 'Zero > SSucc :: SNat n -> SNat ('Succ n) """ (found at [1], and an example of application can be found at [2], also proposed by Richard E.) Now I asked myself if there is some means to write a function that would take any value of type e.g. `Succ (Succ Zero)`, and would return the value `SSucc (SSucc SZero)`. I have tried hard, but did not succeed (see below). I am constantly refrained by the fact a function or data constructor cannot take a value of type having a kind different from `*` (if I am right). Is there any solution to this problem? Below is my attempt, which yields a compilation error test_typeinteger_valueinteger_conversion.hs:18:14: Expected a type, but ‛n’ has kind ‛Nat’ In the type ‛(n :: Nat)’ In the definition of data constructor ‛P’ In the data declaration for ‛Proxy’ ---------------------- {-# LANGUAGE GADTs #-} {-# LANGUAGE DataKinds #-} {-# LANGUAGE KindSignatures #-} {-# LANGUAGE StandaloneDeriving #-} -- type level integers data Nat = Zero | Succ Nat deriving ( Show, Eq, Ord ) -- Singleton allowing a correspondance between type-level and value-level -- integers. data SNat :: Nat -> * where SZero :: SNat Zero SSucc :: SNat n -> SNat (Succ n) deriving instance Show (SNat n) data Proxy :: Nat -> * where P :: (n::Nat) -> Proxy n class MkSNat (n::Nat) where mkSNat :: Proxy n -> SNat n instance MkSNat Zero where mkSNat _ = SZero instance MkSNat (Succ n) where mkSNat (P (Succ n)) = SSucc (mkSNat (P n)) main = do let one = undefined :: Proxy ('Succ 'Zero) print one print $ mkSNat (P one) ---------------------- Thanks, TP References: ----------- [1]: https://groups.google.com/forum/?fromgroups#!topic/haskell-cafe/mGDhPqHZAz8 [2]: https://groups.google.com/d/msg/haskell-cafe/Rh65kdPkX70/T2zZpV6ZpjoJ

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Re: [Haskell-cafe] [Hackathon] ANN: ZuriHac 2013 & FP Afternoon with keynote by Simon Marlow
by Bas van Dijk 11 Jun '13

11 Jun '13

On 10 June 2013 19:38, Roman Cheplyaka <roma(a)ro-che.info> wrote: > Hi Bas, > >> When: Thursday 30 August - Friday 1 September >> Where: Erudify offices, Zurich, Switzerland > > Is this a mistake? 30 August is Friday, 1 September is Sunday. Oops! You're right, that's embarrassing :-) Thanks, Bas

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Workshop on Generic Programming, Second CFP
by Jacques Carette 11 Jun '13

11 Jun '13

====================================================================== CALL FOR PAPERS WGP 2013 9th ACM SIGPLAN Workshop on Generic Programming Boston, Massachusetts, USA Saturday, September 29th, 2013 http://www.wgp-sigplan.org/2013 Co-located with the International Conference on Functional Programming (ICFP 2013) ====================================================================== Goals of the workshop --------------------- Generic programming is about making programs more adaptable by making them more general. Generic programs often embody non-traditional kinds of polymorphism; ordinary programs are obtained from them by suitably instantiating their parameters. In contrast with normal programs, the parameters of a generic program are often quite rich in structure; for example they may be other programs, types or type constructors, class hierarchies, or even programming paradigms. Generic programming techniques have always been of interest, both to practitioners and to theoreticians, and, for at least 20 years, generic programming techniques have been a specific focus of research in the functional and object-oriented programming communities. Generic programming has gradually spread to more and more mainstream languages, and today is widely used in industry. This workshop brings together leading researchers and practitioners in generic programming from around the world, and features papers capturing the state of the art in this important area. We welcome contributions on all aspects, theoretical as well as practical, of * generic programming, * programming with (C++) concepts, * meta-programming, * programming with type classes, * programming with modules, * programming with dependent types, * type systems for generic programming, * polytypic programming, * adaptive object-oriented programming, * component-based programming, * strategic programming, * aspect-oriented programming, * family polymorphism, * object-oriented generic programming, * implementation of generic programming languages, * static and dynamic analyses of generic programs, * and so on. Program Committee ----------------- Jeremiah Willcock (co-chair), Indiana University Jacques Carette (co-chair), McMaster University Florian Rabe, Jacobs University Bremen Emilie Balland, INRIA Bordeaux Jeremy Siek, University of Colorado, Boulder Gabriel Dos Reis, Texas A&M University Christophe Raffalli, Savoie University Anya Helene Bagge, Universitetet i Bergen Tiark Rompf, Ecole Polytechnique Federale de Lausanne Andreas Abel, Ludwig-Maximilians-Universitat Munchen Edward Kmett, S&P Capital IQ William Cook, University of Texas, Austin Proceedings and Copyright ------------------------- We plan to have formal proceedings, published by the ACM. Authors must transfer copyright to ACM upon acceptance (for government work, to the extent transferable), but retain various rights (http://www.acm.org/publications/policies/copyright_policy) Authors are encouraged to publish auxiliary material with their paper (source code, test data, etc.); they retain copyright of auxiliary material. Submission details ------------------ Deadline for submission: Friday 2013-06-14 Notification of acceptance: Wednesday 2013-07-11 Final submission due: Tuesday 2013-07-25 Workshop: Sunday 2013-09-28 Papers should be submitted via EasyChair at https://www.easychair.org/conferences/?conf=wgp2013 Submitted papers should be in portable document format (PDF), formatted using the ACM SIGPLAN style guidelines (two-column, 9pt). The length is restricted to 12 pages. Travel Support -------------- Student attendees with accepted papers can apply for a SIGPLAN PAC grant to help cover travel expenses. PAC also offers other support, such as for child-care expenses during the meeting or for travel costs for companions of SIGPLAN members with physical disabilities, as well as for travel from locations outside of North America and Europe. For details on the PAC program, see its web page (http://www.sigplan.org/PAC.htm) History of the Workshop on Generic Programming ---------------------------------------------- Earlier Workshops on Generic Programming have been held in * Copenhagen, Denmark 2012 (affiliated with ICFP12), * Tokyo, Japan 2011 (affiliated with ICFP11), * Baltimore, Maryland, US 2010 (affiliated with ICFP10), * Edinburgh, UK 2009 (affiliated with ICFP09), * Victoria, BC, Canada 2008 (affiliated with ICFP), * Portland 2006 (affiliated with ICFP), * Ponte de Lima 2000 (affiliated with MPC), * Marstrand 1998 (affiliated with MPC). Furthermore, there were a few informal workshops * Utrecht 2005 (informal workshop), * Dagstuhl 2002 (IFIP WG2.1 Working Conference), * Nottingham 2001 (informal workshop). There were also (closely related) DGP workshops in Oxford (June 3-4 2004), and a Spring School on DGP in Nottingham (April 24-27 2006, which had a half-day workshop attached). WGP Steering Committee ---------------------- Marcin Zalewski (chair) Bruno Oliveira Jaako Järvi Shin-Cheng Mu Andres Löh Ronald Garcia Magne Haveraaen Tim Sheard Stephanie Weirich

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ANN: ZuriHac 2013 & FP Afternoon with keynote by Simon Marlow
by Bas van Dijk 11 Jun '13

11 Jun '13

Dear Haskellers, we are delighted to announce ZuriHac 2013 and a Zurich FP Afternoon. Zurich FP Afternoon 2013 ------------------------ When: Thursday 29 August Where: ETH, Zurich, Switzerland Half a day of talks by FP practitioners, with Simon Marlow giving the keynote speech. ZuriHac 2013 ------------ When: Thursday 30 August - Friday 1 September Where: Erudify offices, Zurich, Switzerland An international, grassroots, collaborative coding festival with a simple focus, to build and improve Haskell libraries, tools, and infrastructure. This is a great opportunity to meet your fellow Haskellers in real life, find new contributors for your project, improve existing libraries and tools, or even start new ones! Registration ------------ If you wish to attend one or both events, please register by filling in this form: http://bit.ly/ZuriHac2013Reg Please note that we have a limited number of places for the Hackathon -- first come, first served. Arrangements ------------ Full details, including accommodation arrangements, can be found on the wiki page: http://www.haskell.org/haskellwiki/ZuriHac2013 We look forward to seeing you there! -- The organisers of ZuriHac 2013 ZuriHac 2013 is sponsored by Erudify and ETH

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Non-deterministic behaviour of aeson's parser
by Roman Cheplyaka 10 Jun '13

10 Jun '13

I am observing a non-deterministic behaviour of aeson's parser. I'm writing here in addition to filing a bug report [1] to draw attention to this (pretty scary) problem. To try to reproduce this problem, do this: git clone https://gist.github.com/5604887.git aeson cd aeson ghc aeson.hs ./aeson | sort | uniq -c This is my result: 32 Left "key \"module\" not present" 55 Left "When parsing the record SymValue of type Main.SymValueInfo the key fixity was not present." 1913 Right () Can others reproduce this in their environments? Does anyone have ideas about where the bug may lie? Many aeson's dependencies do unsafe IO stuff that could lead to such consequences. Roman [1]: https://github.com/bos/aeson/issues/125

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[ANNOUNCE] rainbow - print colored text on UNIX-like systems
by Omari Norman 10 Jun '13

10 Jun '13

Hi all, rainbow is a simple package to help you print colored text on UNIX-like systems. It's different from packages like terminfo (upon which it is based) and ansi-terminal in two ways. First, rainbow assumes you print text one "chunk" at a time. The properties of the terminal are reset with every chunk. That way you do not need to remember what the terminal's properties were before you print a new chunk. One chunk does not affect the next chunk. It's a state-free model that fits in well with functional programming. Second, rainbow makes it easy to use both 8- and 256-color terminals. Some sample things you can do in ghci: :set -XOverloadedStrings :m +System.Console.Rainbow putChunkLn $ "Hello bold green world!" <> f_green <> bold putChunkLn $ "Red on 8-color, pink on 256-color" <> f_red <> c256_f_201 mapM_ putChunk ["green on blue" <> f_green <> b_blue, " ", "blue on green" <> f_blue <> b_green, "\n"] So, add some color to things: http://hackage.haskell.org/package/rainbow

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ANNOUNCE: standalone-haddock-1.0
by Roman Cheplyaka 09 Jun '13

09 Jun '13

I am happy to announce the first release of standalone-haddock. http://feuerbach.github.io/standalone-haddock/ standalone-haddock generates standalone haddock Haskell documentation. When you simply run `cabal haddock`, the resulting HTML documentation contains hyperlinks to other packages on your system. As a result, you cannot publish it on the internet (well, you can, but the links will be broken). standalone-haddock takes several packages for which you want to publish documentation. It generates documentation for them with proper links: * links to identifiers inside this package set are relative * links to identifiers from external packages lead to hackage Thus the resulting directory with HTML is relocatable and publishable. **TL;DR**: it just works. See the [haskell-suite][] documentation for an example output. [haskell-suite]: http://haskell-suite.github.io/docs Usage ----- Usage: standalone-haddock [--package-db DB-PATH] -o OUTPUT-PATH [PACKAGE-PATH] Available options: -h,--help Show this help text --package-db DB-PATH Additional package database -o OUTPUT-PATH Directory where html files will be placed `PACKAGE-PATH` is the path to the (unpacked) package — i.e. a directory with a `.cabal` file. For example: standalone-haddock -o doc haskell-names haskell-packages haskell-src-exts hse-cpp cabal/Cabal **NOTE**: dependencies of every package need to be already installed in the system with documentation (even those dependencies that themselves belong to the current package set). If they are installed in a non-standard package database (e.g. if you use sandboxes), use the `--package-db` option. Cabal dependency ---------------- The program only builds with (unreleased) Cabal 1.17 which you can get from [github](https://github.com/haskell/cabal). I spent some time trying to make it compatible with Cabal 1.16 (see [Cabal-1.16][] branch), but the API seems to have changed too much. If you seriously care about this, feel free to send a patch, but it's really easier just to install Cabal HEAD. [Cabal-1.16]: https://github.com/feuerbach/standalone-haddock/tree/Cabal-1.16 Roman

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