February 2014 - Haskell-Cafe

Scaling Haskell/Yesod on OpenShift
by Joey Eremondi 02 Mar '14

02 Mar '14

I was wondering, does anyone have experience with using Haskell/Yesod on the OpenShift PaaS? I've seen the Haskell and Yesod cartridges, but I'm wondering if there's any way to get Haskell playing nice with their load-balancing and automatic scaling capabilities? Would CloudHaskell be useful at all in this? I'm reasonably experienced with Haskell but very new to Cloud computing and Web stuff, so any advice, even if basic, is helpful. Thanks!

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GHC 7.6.3 and Plugins 1.5.4.0
by Fabian Bergmark 01 Mar '14

01 Mar '14

Im using the plugins library and am unable get it to work with user defined types. I.e. evaluating the string "id :: Int -> Int" works, but "id :: Test -> Test" yield the runtime-error. test: /tmp/MXXXXX27601.o: unknown symbol `testdzm0zi0zi0_DataziTestD_zdfTypeableTestD_closure' I have created a small compiling example of the bug here https://github.com/fabianbergmark/plugins-bug I have tried to move the data-type to a separate library without success. Curiously, loading the library exposing the data-type in GHCi, and running eval "id :: Test -> Test" works and yields the correct result.

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SBLP 2014 - Call for Papers
by Simon Thompson 01 Mar '14

01 Mar '14

CALL FOR PAPERS 18th Brazilian Symposium on Programming Languages (SBLP 2014) A member of CBSoft joint conference http://www.ic.ufal.br/evento/cbsoft2014/ to be held in Maceio, Brazil. SBLP happens on Thursday, Oct 2nd, and Friday, Oct 3rd. CBSoft dates are September 28, 2014 to October 3, 2014 This CFP is also available at the webpage of the event: http://www.ic.ufal.br/evento/cbsoft2014/en/call-for-papers-sblp.html IMPORTANT DATES Paper abstract submission: May 2nd, 2014 Full paper submission: May 9th, 2014 Notification of acceptance: June 13th, 2014 Final papers due: July 4th, 2014 INTRODUCTION The 18th Brazilian Symposium on Programming Languages, SBLP 2014, will be held in Maceio, a beautiful city in the Northeastern part of Brazil. The conference will happen on October 2nd, and October 3rd, 2014. SBLP provides a venue for researchers and practitioners interested in the fundamental principles and innovations in the design and implementation of programming languages and systems. SBLP 2014 invites authors to contribute with technical papers related (but not limited) to: * Program generation and transformation, including domain-specific languages and model-driven development in the context of programming languages. * Programming paradigms and styles, including functional, object-oriented, aspect-oriented, scripting languages, real-time, service-oriented, multithreaded, parallel, and distributed programming. * Formal semantics and theoretical foundations, including denotational, operational, algebraic and categorical. * Program analysis and verification, including type systems, static analysis and abstract interpretation. * Programming language design and implementation, including new programming models, programming language environments, compilation and interpretation techniques. SUBMISSIONS Contributions should be written in Portuguese or English. Papers should fall into one of two different categories: full papers, with at most 15 pages, or short papers, with at most 5 pages. Accepted papers written in English will be published in a volume of Lecture Notes in Computer Science (LNCS), by Springer. For this reason, all papers must be prepared using the LNCS template, available at http://www.springer.com/computer/lncs?SGWID=0-164-6-793341-0. We encourage the submission of short papers reporting partial results of on-going master dissertations or doctoral theses. Submissions should be done through the SBLP 2014 page at EasyChair, which is available at http://www.easychair.org/conferences/?conf=sblp2014. As in previous editions, a journal's special issue, with selected papers from accepted contributions, is anticipated. Selected papers from the 2003 to the 2008 editions of SBLP were published in special issues of the Journal of Universal Computer Science, by Springer. The post-proceedings of SBLP from 2009 to 2012, also with selected papers from the conference, have been published as special issues of Science of Computer Programming, by Elsevier. KEYNOTE SPEAKERS Louis-Noel Pouchet, University of California Los Angeles Fabrice Rastello, INRIA PROGRAMME CHAIR Fernando Magno Quintao Pereira, UFMG PROGRAMME COMMITTEE Alberto Pardo, Universidad de la República Alex Garcia, IME Alvaro Moreira, Federal University of Rio Grande do Sul Andre Rauber Du Bois, Federal University of Pelotas Carlos Camarão, Federal University of Minas Gerais Christiano Braga, Fluminense Federal University Fabio Mascarenhas, Federal University of Rio de Janeiro Fabrice Rastello, INRIA Fernando Pereira, Federal University of Minas Gerais Fernando Castor, Federal University of Pernambuco Francisco Carvalho-Junior, Federal University of Ceara Hans-Wolfgang Loidl, Heriot-Watt University Jeremy Singer University of Glasgow João Saraiva, University of Minho Joao F. Ferreira, Teesside University Louis-Noel Pouchet, University of California, Los Angeles Lucilia Figueiredo, Federal University of Ouro Preto Luis Barbosa, University of Minho Manuel A. Martins, University of Aveiro Marcello Bonsangue, Leiden University Marcelo Maia, Federal University of Uberlândia Marcelo D'Amorim, Federal University of Pernambuco Mariza Bigonha, Federal University of Minas Gerais Martin Musicante, Federal University of Rio Grande do Norte Noemi Rodriguez, PUC-Rio Peter Mosses, Swansea University Rafael Lins, Federal University of Pernambuco Renato Cerqueira, PUC-Rio Roberto Bigonha, Federal University of Minas Gerais Roberto Ierusalimschy PUC-Rio Rodrigo Geraldo, Federal University of Ouro Preto Sandro Rigo, State University of Campinas Sérgio Medeiros, Federal University of Rio Grande do Norte Simon Thompson, University of Kent Varmo Vene, University of Tartu Zongyan Qiu Peking University Simon Thompson | Professor of Logic and Computation School of Computing | University of Kent | Canterbury, CT2 7NF, UK s.j.thompson(a)kent.ac.uk | M +44 7986 085754 | W www.cs.kent.ac.uk/~sjt Simon Thompson | Professor of Logic and Computation School of Computing | University of Kent | Canterbury, CT2 7NF, UK s.j.thompson(a)kent.ac.uk | M +44 7986 085754 | W www.cs.kent.ac.uk/~sjt

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export DataKinds
by Corentin Dupont 01 Mar '14

01 Mar '14

Hi Cafe, I create kinds using the DataKinds extension: {-# LANGUAGE DataKinds #-} module MyModule where data Foo = Bar | Baz The problem is that the generated Bar and Baz type constructors are not exported! I am obliged to put the pragma DataKinds in every package that uses MyModule (a lot). Is there a way to avoid that? Thanks! Corentin

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Haskell spec vs FlexibleInstances
by Doug McIlroy 01 Mar '14

01 Mar '14

What potential evil motivates the prohibition of repeated type parameters in an instance declaration? (Restriction removed by FlexibleInstances) Doug McIlroy

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[ANN] Rasterific & FontyFruity
by Vincent Berthoux 28 Feb '14

28 Feb '14

Hello Haskellers, I'm pleased to announce two new packages, whom work hand in hand: FontyFruity, a truetype file parser, and Rasterific a vector drawing engine. This two libraries enable us to generate pictures without the need of an external C library, and saving them to a file or directly send them over the network. FontyFruity: * hackage : http://hackage.haskell.org/package/FontyFruity * Github : https://github.com/Twinside/FontyFruity Rasterific: * hackage : http://hackage.haskell.org/package/Rasterific * Github : https://github.com/Twinside/Rasterific Regards Vincent

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OutsideIn(X) question
by Alejandro Serrano Mena 27 Feb '14

27 Feb '14

Dear Haskell-café, I don't know if this is the best forum to ask questions about the OutsideIn(X) paper that lies below type inference in GHC. But given that this is the place where I know many GHC devs look at, I'll just try :) My question related about the proof of soundness and principality, specifically Lemma 7.2 (to be found in page 67). In that lemma, it's stated that QQ and \phi' Q_q ||- \phi Q_w <-> \phi' Q_w'. I'm trying to recover the proof (which is omitted in the text), but I stumble upon a wall when trying to work out what happens in the case an axiom is applied. In particular, I'm playing with an example where QQ (the set of axioms) = { forall. C a => D a } (where C and D are one-parameter type classes) Q_q = { } Q_w = { D Int } Thus, if I apply the rule DINSTW (to be found in page 65), I get a new Q_w' = { C Int } Now, if the lemma 7.2 is true, it should be the case that (1) QQ ||- C Int <-> D Int which in particular means that I have the two implications (2) { forall. C a => D a, C Int } ||- D Int (3) { forall. C a => D a, D Int } ||- C Int (2) follows easily by applying the AXIOM rule of ||- (as shown in page 54). However, I don't see how to make (3) work :( I think that understanding this example will be key for my understanding of the whole system. Anybody could point to the error in my reasoning or to places where I could find more information? Thanks in advance.

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Portfolio Analytics group at S&P CapitalIQ Hiring Summer Interns for 2014
by Gershom B 27 Feb '14

27 Feb '14

Our team is full of people with strong functional programming interests, and we even have an in-house Haskell-like DSL. To get a sense of the work we do, you can watch Edward Kmett's CUFP presentation (http://www.youtube.com/watch?v=o3m2NkusI9k) and browse his slides (http://cufp.org/sites/all/files/slides/2013/kmett.pdf) We have work that directly requires FP knowledge, and other work involving Scala, or even C# and SQL. If you are a college junior who wants to get paid to spend a summer in New York working in this environment, then apply by March 15 and see where it goes. You'll need to apply at the below web link, and _also_ email us directly so we can route your resume to our team. More than any particular experience or skills, we're interested in people who love computer science and like building new things. Application site: http://careers.mhfi.com/ShowJob/Id/131214/Software-Engineer-Summer-Intern-%… Additional contacts to email: smcfarland at spcapitaliq.com and gbazerman at spcapitaliq.com

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Berlin HUG meeting at Tuesday, March 4th
by Simon Hengel 27 Feb '14

27 Feb '14

Hi, we have regular Haskell meetings in Berlin, but I think it was never officially announced on this list. There is a meetup page [1] and the next meeting is at Tuesday, March 4th Big thanks to Adam for organizing things! One important thing, please join on meetup if you want to come! Cheers, Simon [1] http://www.meetup.com/berlinhug/

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[ANN] profiteur: a tool to visualise GHC .prof files
by Jasper Van der Jeugt 26 Feb '14

26 Feb '14

Hey all, I just released the tool profiteur [1]. You can use it to visualise GHC `.prof` files in a tree map -- I think this makes looking at huge `.prof` files a lot less unwieldy. More information can be found in this blogpost [2]. [1]: http://hackage.haskell.org/package/profiteur [2]: http://jaspervdj.be/posts/2014-02-25-profiteur-ghc-prof-visualiser.html Peace, Jasper

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