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Getting a Hackage account
by Kevin Backhouse 09 Jun '13

09 Jun '13

Please could someone on this list help me to get an account on Hackage? I followed the instructions the webpage and emailed Ross Paterson, but that was two weeks ago and I have not received a response. Thank you, Kevin Backhouse

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ANNOUNCE: ig: bindings to Instagram Web Services API
by JP Moresmau 09 Jun '13

09 Jun '13

Hello all, It's my pleasure to announce the initial release of ig, a library providing bindings to the Instagram Web Services API (http://instagram.com/developer/#) I'm indebted to Felipe Lessa (and all the folks at Loyful) as I've reused a lot of ideas from his code on the Facebook library. I've tried to implement much of the API, please reports on the Github repository ( https://github.com/loyful/ig) if something is missing and of course if you find issues. At https://github.com/loyful/ig-testapp you can find a yesod test application that shows authentication, real-time subscriptions and some other calls. It's very crude but can help you started. Grab it from Hackage, of course! Thanks! -- JP Moresmau http://jpmoresmau.blogspot.com/

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Question about Newtype "op()" function arguments.
by David Banas 08 Jun '13

08 Jun '13

Hi All, Referring to the following, which is taken from the *Control.Newtype *documentation page: op :: Newtype<http://hackage.haskell.org/packages/archive/newtype/0.2/doc/html/Control-Ne…> n o => (o -> n) -> n -> oSource<http://hackage.haskell.org/packages/archive/newtype/0.2/doc/html/src/Contro…> This function serves two purposes: 1. Giving you the unpack of a newtype without you needing to remember the name. 2. Showing that the first parameter is *completely ignored* on the value level, meaning the only reason you pass in the constructor is to provide type information. Typeclasses sure are neat. As point #2, above, emphasizes, the only purpose for the first argument to the function (i.e. - the constructor "(o -> n)") is to specify the type of 'n'. However, being a *newtype*, 'n' can have only one constructor. So, why is it necessary to pass in the constructor to this function, when we're already passing in 'n'? Thanks, -db

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ANNOUNCE: Ajhc 0.8.0.5 Release
by Kiwamu Okabe 08 Jun '13

08 Jun '13

We are happy to announce Ajhc 0.8.0.5. Major change on this release is supporting haddock. You can see Ajhc's internal using web browser. Ajhc's project web site is found at http://ajhc.metasepi.org/. You can get the source code from https://github.com/ajhc/ajhc/tags. ## Changes * Support haddock. You can read haddock on http://hackage.haskell.org/package/ajhc, hopefully. * Split library from Ajhc program. * Better NAIVEGC. * Add arity "arena" to all functions compiled by Ajhc. For supporting reentrant in future. * Run SelfTest and rtstest on travis-ci. * Add jahm command to download file from Hackage DB, because sometime perl script occurs error. Enjoy. :) - - - Metasepi team

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voting sytem DSL
by Corentin Dupont 07 Jun '13

07 Jun '13

Hi haskellers! I am trying to make a DSL able to describe a voting system. That DSL should be able to describe many different voting procedures: unanimity or majority, open or secret ballot, one or two turns... It should also work for referendums (yes/no question) or elections (electing one or several people)... Are you aware of any such DSL? In Haskell I haven't see it, maybe in another language? Cheers, Corentin

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runghc dies silently when given large numbers of arguments
by Gareth Smith 07 Jun '13

07 Jun '13

Hi all, The other day, I wrote the following program in /tmp/test.hs --8<---------------cut here---------------start------------->8--- main = error "An Error message" --8<---------------cut here---------------end--------------->8--- Then I ran the following: ,---- | gds@lithium:/tmp$ runghc ./test.hs `seq 1 100000` | gds@lithium:/tmp$ ghc -o test test.hs | gds@lithium:/tmp$ ./test `seq 1 100000` | test: An Error message | gds@lithium:/tmp$ `---- Notice that when I use runghc, my main function doesn't appear to run at all. But when I run the compiled program, my main function does seem to run, and produce the error message I expected. It seems to me like runghc can't cope with that large a number of arguments or size of argument string, or similar. That seems entirely reasonable, but if so, then might it be a good idea to have an error message when we accidentally hit that limit? I'm using ghc 7.6.2 on Ubuntu 13.04. Thanks! Gareth.

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FRP memory leaks
by Łukasz Dąbek 07 Jun '13

07 Jun '13

Hello, Cafe! I've heard that one of the problems of FRP (Functional Reactive Programming) is that it's easy to create memory leaks. However I cannot find any natural examples of such leaks. Could anybody post some (pseudo)code demonstrating this phenomenon? Preferably something that arises when one is writing bigger applications in FRP style. Thanks in advance! -- Łukasz Dąbek

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PPDP'13: Last call for papers
by Tom Schrijvers 07 Jun '13

07 Jun '13

===================================================================== Last Call for Papers 15th International Symposium on Principles and Practice of Declarative Programming PPDP 2013 Special Issue of Science of Computer Programming (SCP) Madrid, Spain, September 16-18, 2013 (co-located with LOPSTR 2013) http://users.ugent.be/~tschrijv/PPDP2013/ ====================================================================== PPDP 2013 is a forum that brings together researchers from the declarative programming communities, including those working in the logic, constraint and functional programming paradigms, but also embracing a variety of other paradigms such as visual programming, executable specification languages, database languages, and knowledge representation languages. The goal is to stimulate research in the use of logical formalisms and methods for specifying, performing, and analysing computations, including mechanisms for mobility, modularity, concurrency, object-orientation, security, verification and static analysis. Papers related to the use of declarative paradigms and tools in industry and education are especially solicited. Topics of interest include, but are not limited to: * Functional programming * Logic programming * Answer-set programming * Functional-logic programming * Declarative visual languages * Constraint Handling Rules * Parallel implementation and concurrency * Monads, type classes and dependent type systems * Declarative domain-specific languages * Termination, resource analysis and the verification of declarative programs * Transformation and partial evaluation of declarative languages * Language extensions for security and tabulation * Probabilistic modelling in a declarative language and modelling reactivity * Memory management and the implementation of declarative systems * Practical experiences and industrial application This year the conference will be co-located with the 23nd International Symposium on Logic-Based Program Synthesis and Transformation (LOPSTR 2013) and held in cooperation with ACM SIGPLAN. The conference will be held in Madrid, Spain. Previous symposia were held at Leuven (Belgium), Odense (Denmark), Hagenberg (Austria), Coimbra (Portugal), Valencia (Spain), Wroclaw (Poland), Venice (Italy), Lisboa (Portugal), Verona (Italy), Uppsala (Sweden), Pittsburgh (USA), Florence (Italy), Montreal (Canada), and Paris (France). Papers must describe original work, be written and presented in English, and must not substantially overlap with papers that have been published or that are simultaneously submitted to a journal, conference, or workshop with refereed proceedings. Work that already appeared in unpublished or informally published workshop proceedings may be submitted (please contact the PC chair in case of questions). Proceedings will be published in the ACM International Conference Proceedings Series. After the symposium, a selection of the best papers will be invited to extend their submissions in the light of the feedback solicited at the symposium. The papers are expected to include at least 30% extra material over and above the PPDP version. Then, after another round of reviewing, these revised papers will be published in a special issue of SCP with a target publication date by Elsevier of 2014. Important Dates Abstract Submission: June 10, 2013 Paper submission: June 13, 2013 Notification: July 18, 2013 Camera-ready: August 4, 2013 Symposium: September 16-18, 2013 Invites for SCP: October 2, 2013 Submission of SCP: December 11, 2013 Notification from SCP: February 22, 2014 Camera-ready for SCP: March 14, 2014 Authors should submit an electronic copy of the paper (written in English) in PDF. Each submission must include on its first page the paper title; authors and their affiliations; abstract; and three to four keywords. The keywords will be used to assist us in selecting appropriate reviewers for the paper. Papers should consist of no more than 12 pages, formatted following the ACM SIG proceedings template (option 1). The 12 page limit must include references but excludes well-marked appendices not intended for publication. Referees are not required to read the appendices, and thus papers should be intelligible without them. Program Committee Sergio Antoy Portland State University, USA Manuel Carro IMDEA Software Institute, Spain Iliano Cervesato Carnegie Mellon University, Qatar Agostino Dovier Universita degli Studi di Udine, Italy Maria Garcia de la Banda Monash University, Australia Ralf Hinze University of Oxford, UK Yukiyoshi Kameyama University of Tsukuba, Japan Oleg Kiselyov USA Yanhong Annie Liu State University of New York at Stony Brook, USA Stefan Monnier Universite de Montreal, Canada Alan Mycroft University of Cambrige, UK Bruno C. d. S. Oliveira National University of Singapore, Singapore Alberto Pettorossi Universita di Roma Tor Vergata, Italy Enrico Pontelli New Mexico State University, USA Kristoffer Rose IBM Research, USA Sukyoung Ryu KAIST, South Korea Vitor Santos Costa University of Porto, Portugal Torsten Schaub University Potsdam, Germany Tom Schrijvers Ghent University, Belgium Martin Sulzmann Hochschule Karlsruhe, Germany Wouter Swierstra Universiteit Utrecht, The Netherlands Tarmo Uustalu Institute of Cybernetics, Estonia Janis Voigtlaender University of Bonn, Germany Meng Wang Chalmers University of Technology, Sweden Jan Wielemaker Universiteit van Amsterdam, The Netherlands Program Chair Tom Schrijvers Department of Applied Mathematics and Computer Science Ghent University 9000 Gent, Belgium General Chair Ricardo Pena Facultad de Informatica Universidad Complutense de Madrid 28040 Madrid, Spain -- prof. dr. ir. Tom Schrijvers Programming Languages Group Department of Applied Mathematics and Computer Science University of Ghent Krijgslaan 281 S9 9000 Gent Belgium Phone: +32 9 264 4805 http://users.ugent.be/~tschrijv/

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Typeable typeclass and type-level naturals
by TP 06 Jun '13

06 Jun '13

Hi all, I try to play with the "Typeable" typeclass, and I have some difficulties to make it work in this simple case where I use type-level naturals: --------------------- {-# LANGUAGE GADTs #-} {-# LANGUAGE DeriveDataTypeable #-} {-# LANGUAGE DataKinds #-} {-# LANGUAGE PolyKinds #-} {-# LANGUAGE StandaloneDeriving #-} import Data.Typeable data Nat = Zero | Succ Nat deriving ( Show, Eq, Ord, Typeable ) data Box where Box :: (Typeable s, Show s, Eq s) => s -> Box deriving Typeable data Proxy a = P deriving Typeable deriving instance Show Box instance Eq Box where (Box s1) == (Box s2) = Just s1 == cast s2 main = do let one = undefined :: Main.Proxy ('Succ 'Zero) let foo = Box one print foo --------------------- I obtain: --------------------- No instance for (Typeable Nat 'Zero) arising from a use of ‛Box’ In the expression: Box one In an equation for ‛foo’: foo = Box one In the expression: do { let one = ...; let foo = Box one; print foo } --------------------- Note that it is necessary to use the HEAD version of GHC to obtain this message (I use version 7.7.20130525); with GHC 7.6.2, the message is different because recent improvements in Typeable are not present (1). What is the problem? I've tried different things without success. Tell me if the "beginners" diffusion list is more suitable than Haskell- Cafe. Thanks, TP (1): http://hauptwerk.blogspot.fr/2012/11/coming-soon-in-ghc-head-poly-kinded.ht…

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Why isn't hsc2hs functionality provided by ghc?
by silly8888 06 Jun '13

06 Jun '13

I was wondering today, why hasn't hsc2hs been merged with ghc so that it would be possible to add a {-# LANGUAGE ForeignFunctionInterface #-} at the top of a source file and then load it with ghci or compile it, without the intermediate step of calling hsc2hs? This would be exactly like the CPP extension. I don't have to call cpp manually. All I have to do is to add {-# LANGUAGE CPP #-} and then ghc will take care of the rest. This would also mean that there would be no need to have a separate file extension. Surely I must not be the first person to have that thought, so there must be a good reason why this hasn't happen yet, but what is it?

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