June 2013 - Haskell-Cafe

Frankfurt Haskell User Group meets 19.6.13, topics: Netwire, Hackathon planning
by Peter Althainz 04 Jun '13

04 Jun '13

Dear All, all interested Haskellers are inivted to our Meetup on 19.6.13: http://www.meetup.com/Frankfurt-Haskell-User-Group/events/122879122/. Best regards Peter Althainz

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code to HTML
by Corentin Dupont 03 Jun '13

03 Jun '13

Hello everybody, I'd like to transform a .hs file into a .html file. The objective is that the .html file, when rendered, looks exactly the same that the .hs, with the exeption that every function in the code is a link to its haddock documentation. Is that possible? The result would look like that: f xs = map<http://hackage.haskell.org/packages/archive/base/latest/doc/html/Prelude.ht…> head<http://hackage.haskell.org/packages/archive/base/latest/doc/html/Prelude.ht…>xs Thanks! Corentin

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Announce: Leksah 0.13.2.2 (still a bit experimental)
by Hamish Mackenzie 03 Jun '13

03 Jun '13

Mostly just a refresh of the current development version binary installers, so people can use it with the latest Haskell Platform (which uses GHC 7.6.3). Unfortunately an official 0.14 release may still be a be a way off. I have been doing some work on getting Code Mirror working, but there are threading issues that will need to be resolved before it works (so best to leave the editor config set to GtkSourceView). I recommend you remove your ~/.leksah-0.13/prefs.lkshp file before installing as the format has changed slightly and it is not backwards compatibly. Hop on #leksah if you have any questions. OS X (Still no WebKit features) ------------------------------- Choose the version that matches your installed GHC http://leksah.org/packages/leksah-0.13.2.2-ghc-7.0.4.dmg http://leksah.org/packages/leksah-0.13.2.2-ghc-7.4.1.dmg http://leksah.org/packages/leksah-0.13.2.2-ghc-7.4.2.dmg http://leksah.org/packages/leksah-0.13.2.2-ghc-7.6.3.dmg Sorry, I am still having trouble building WebKitGTK+ on OSX. If you want a challenge... https://github.com/jralls/gtk-osx-build https://github.com/leksah/leksah/blob/master/osx/gtk.sh Alternatively we might have to build Leksah with -f-webkit to leave out the webkit stuff. Windows ------- Choose the version that matches your installed GHC http://leksah.org/packages/leksah-0.13.2.2-ghc-7.0.3.exe http://leksah.org/packages/leksah-0.13.2.2-ghc-7.0.4.exe http://leksah.org/packages/leksah-0.13.2.2-ghc-7.4.1.exe http://leksah.org/packages/leksah-0.13.2.2-ghc-7.4.2.exe http://leksah.org/packages/leksah-0.13.2.2-ghc-7.6.3.exe Linux ----- Follow the steps in the .travis.yml file... https://github.com/leksah/leksah/blob/master/.travis.yml Should go something like this... https://travis-ci.org/leksah/leksah

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APLAS 2013 second call for papers
by Chung-chieh Shan 02 Jun '13

02 Jun '13

=============================================================== APLAS 2013 11th Asian Symposium on Programming Languages and Systems 9-11 December 2013 Melbourne, Australia (colocated with CPP 2013) CALL FOR PAPERS =============================================================== ========== BACKGROUND ========== APLAS aims to stimulate programming language research by providing a forum for the presentation of latest results and the exchange of ideas in programming languages and systems. APLAS is based in Asia, but is an international forum that serves the worldwide programming language community. APLAS is sponsored by the Asian Association for Foundation of Software (AAFS) founded by Asian researchers in cooperation with many researchers from Europe and the USA. Past APLAS symposiums were successfully held in Kyoto ('12), Kenting ('11), Shanghai ('10), Seoul ('09), Bangalore ('08), Singapore ('07), Sydney ('06), Tsukuba ('05), Taipei ('04) and Beijing ('03) after three informal workshops. Proceedings of the past symposiums were published in Springer's LNCS. ====== TOPICS ====== The symposium is devoted to foundational and practical issues in programming languages and systems. Papers are solicited on topics such as * semantics, logics, foundational theory; * design of languages, type systems and foundational calculi; * domain-specific languages; * compilers, interpreters, abstract machines; * program derivation, synthesis and transformation; * program analysis, verification, model-checking; * logic, constraint, probabilistic and quantum programming; * software security; * concurrency and parallelism; * tools and environments for programming and implementation. Topics are not limited to those discussed in previous symposiums. Papers identifying future directions of programming and those addressing the rapid changes of the underlying computing platforms are especially welcome. Demonstration of systems and tools in the scope of APLAS are welcome to the System and Tool presentations category. Authors concerned about the appropriateness of a topic are welcome to consult with program chair prior to submission. ========== SUBMISSION ========== We solicit submissions in two categories: *Regular research papers* describing original scientific research results, including tool development and case studies. Regular research papers should not exceed 16 pages in the Springer LNCS format, including bibliography and figures. They should clearly identify what has been accomplished and why it is significant. Submissions will be judged on the basis of significance, relevance, correctness, originality, and clarity. In case of lack of space, proofs, experimental results, or any information supporting the technical results of the paper could be provided as an appendix or a link to a web page, but reviewers are not obliged to read them. *System and Tool presentations* describing systems or tools that support theory, program construction, reasoning, or program execution in the scope of APLAS. System and Tool presentations are expected to be centered around a demonstration. The paper and the demonstration should identify the novelties of the tools and use motivating examples. System and Tool papers should not exceed 8 pages in the Springer LNCS format, including bibliography and figures. Submissions will be judged based on both the papers and the described systems or tools. It is highly desirable that the tools are available on the web. Papers should be submitted electronically via the submission web page: https://www.easychair.org/conferences/?conf=aplas2013 Acceptable formats are PostScript or PDF. Submitted papers must be unpublished and not submitted for publication elsewhere. Papers must be written in English. The proceedings will be published as a volume in Springer's LNCS series. Accepted papers must be presented at the conference. (While the general chair and the program chair cannot submit papers, other members of the program committee can.) ===== DATES ===== Abstract due: 10 June 2013 (Monday), 23:59 UTC Submission due: 14 June 2013 (Friday), 23:59 UTC Notification: 26 August 2013 (Monday) Final paper due: 19 September 2013 (Thursday) Conference: 9-11 December 2013 (Monday-Wednesday) ========== ORGANIZERS ========== General chair: Peter Schachte (University of Melbourne) Program chair: Chung-chieh Shan (Indiana University) Program committee: Filippo Bonchi (CNRS, ENS-Lyon, France) Yu-Fang Chen (Academia Sinica, Taiwan) Shigeru Chiba (The University of Tokyo, Japan) Jacques Garrigue (Nagoya University, Japan) Robert Glück (University of Copenhagen, Denmark) R. Govindarajan (Indian Institute of Science, India) Kazuhiro Inaba (Google, Inc., Japan) Jie-Hong Roland Jiang (National Taiwan University, Taiwan) Shin-ya Katsumata (Kyoto University, Japan) Gabriele Keller (University of New South Wales, Australia) Ana Milanova (Rensselaer Polytechnic Institute, USA) Keisuke Nakano (The University of Electro-Communications, Japan) Hakjoo Oh (Seoul National University, Korea) Bruno C. d. S. Oliveira (National University of Singapore, Singapore) Kaushik Rajan (Microsoft Research, India) Max Schäfer (Nanyang Technological University, Singapore) Ulrich Schöpp (Ludwig-Maximilians-Universität München, Germany) Paula Severi (University of Leicester, UK) Gang Tan (Lehigh University, USA) Hiroshi Unno (University of Tsukuba, Japan) Meng Wang (Chalmers University of Technology, Sweden) Jingling Xue (University of New South Wales, Australia) Mingsheng Ying (University of Technology, Sydney, Australia) Kenny Q. Zhu (Shanghai Jiao Tong University, China) ======= CONTACT ======= http://aplas2013.soic.indiana.edu/ aplas2013(a)easychair.org

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Re: [Haskell-cafe] Int is broken [Was: Different answers on different machines]
by Stephen Tetley 02 Jun '13

02 Jun '13

There was a quite long discussion here: http://conal.net/blog/posts/notions-of-purity-in-haskell On 2 June 2013 22:02, Tommy Thorn <tt1729(a)yahoo.com> wrote: ... > I wish this fatal flaw would be reconsidered for the next major revision. >

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Two GHC-related GSoC Proposals
by Patrick Palka 02 Jun '13

02 Jun '13

Hi, I'm interested in participating in the GSoC by improving GHC with one of these two features: 1) Implement native support for compiling modules in parallel (see #910<http://hackage.haskell.org/trac/ghc/ticket/910>). This will involve making the compilation pipeline thread-safe, implementing the logic for building modules in parallel (with an emphasis on keeping compiler output deterministic), and lots of testing and benchmarking. Being able to seamlessly build modules in parallel will shorten the time it takes to recompile a project and will therefore improve the life of every GHC user. 2) Improve existing constant folding, strength reduction and peephole optimizations on arithmetic and logical expressions, and optionally implement a core-to-core pass for optimizing nested comparisons (relevant tickets include #2132 <http://hackage.haskell.org/trac/ghc/ticket/2132>, #5615 <http://hackage.haskell.org/trac/ghc/ticket/5615>,#4101<http://hackage.haskell.org/trac/ghc/ticket/4101>). GHC currently performs some of these simplifications (via its BuiltinRule framework), but there is a lot of room for improvement. For instance, the core for this snippet is essentially identical to the Haskell source: foo :: Int -> Int -> Int -> Int foo a b c = 10*((b+7+a+12+b+9)+4) + 5*(a+7+b+12+a+9) + 7 + b + c Yet the RHS is actually equivalent to 20*a + 26*b + c + 467 And: bar :: Int -> Int -> Int bar a b = a + b - a - b -- the RHS is should be optimized away to 0 Other optimizations include: multiplication and division by powers of two should be converted to shifts; multiple plusAddr calls with constant operands should be coalesced into a single plusAddr call; floating point functions should be constant folded, etc.. GHC should be able to perform all these algebraic simplifications. Of course, emphasis should be placed on the correctness of such transformations. A flag for performing unsafe optimizations like assuming floating point arithmetic is associative and distributive should be added. This proposal will benefit anybody writing or using numerically intensive code. I'm wondering what the community thinks of these projects. Which project is a better fit for GSoC, or are both a good fit? Is a mentor willing to supervise one of these projects? Thanks for your time. Patrick (A little about myself: I'm a Mathematics student in the US, and I've been programming in Haskell for about 3.5 years. Having a keen interest in Haskell and compilers, I began studying the GHC source about 1 year ago and I've since gotten a good understanding of its internals, contributing a few patches along the way.)

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question about "singletons"
by TP 02 Jun '13

02 Jun '13

Hi all, Following a discussion on Haskell Cafe some time ago (1), Roman C. wrote: """ On the other hand, the type 'Succ 'Zero has kind 'Nat and doesn't have any inhabitants — only types of kind * do. """ Indeed, this is what seems to occur in the following example: ----------------------- {-# LANGUAGE DataKinds #-} data Nat = Zero | Succ Nat deriving ( Show, Eq, Ord ) main = do let one = undefined :: 'Succ 'Zero print one ----------------------- We obtain an error (ghc 7.6.2): ----------------------- Kind mis-match Expected kind `OpenKind', but `Succ Zero' has kind `Nat' In an expression type signature: Succ Zero In the expression: undefined :: Succ Zero In an equation for `one': one = undefined :: Succ Zero ----------------------- (note that the error is slightly different in the HEAD version of GHC (2)). Is it related to the sentence "As bottom is an inhabitant of every type (though with some caveats concerning types of unboxed kind), bottoms can be used wherever a value of that type would be. " found at address (3)? Here we have a non-* kind, such that bottom would not be an inhabitant of ('Succ 'Zero). Why is this so? This seems to be an assumed choice (4), but I would like to understand the reason for this design, which makes necessary to use singletons, as explained at (4). Now, if I use a singleton to make my example work, I obtain an error when trying to make the type (Sing a) an instance of Show: ----------------------- {-# LANGUAGE DataKinds #-} {-# LANGUAGE PolyKinds #-} {-# LANGUAGE StandaloneDeriving #-} data Nat = Zero | Succ Nat deriving ( Show, Eq, Ord ) data Sing :: a -> * deriving instance Show (Sing a) main = do let one = undefined :: Sing ('Succ 'Zero) print one ----------------------- The error is simply: ----------------------- test_noinhabitant_corrected.hs: Void showsPrec ----------------------- Why? Thanks, TP References: ---------- (1): https://groups.google.com/forum/?fromgroups#!topic/haskell-cafe/AltmX5iCFi8 (2): ----------------------- Expected a type, but ‛Succ Zero’ has kind ‛Nat’ In an expression type signature: Succ Zero In the expression: undefined :: Succ Zero In an equation for ‛one’: one = undefined :: Succ Zero ----------------------- (3): http://www.haskell.org/haskellwiki/Bottom (4): http://hackage.haskell.org/trac/ghc/wiki/TypeNats/Basics """ Both numeric and symbol literal types are empty---they have no inhabitants. However, they may be used as parameters to other type constructors, which makes them useful. """ """ A singleton type is simply a type that has only one interesting inhabitant. """

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Re: [Haskell-cafe] question about "singletons"
by wren ng thornton 01 Jun '13

01 Jun '13

On 6/1/13 3:18 PM, TP wrote: > In other words, bottom can be an inhabitant of a concrete type, not a type > constructor, which I can understand. But a type of kind Nat is a concrete > type, so why bottom cannot be an inhabitant of this type? The technical term is "proper type". That is, types are used as a way of characterizing collections of values; but, all sorts of things can exist at the type level. For lack of a better name, we call everything at the type level a "type", in order to distinguish them from things at the value level or kind level, etc. But in order to be a *proper* type, a type-level expression must serve to characterize a collection of values. Types of kind * are proper types, because they serve to characterize collections of values. Types of other kinds are not proper, since they do not characterize collections of values. Thus, we can't say: undefined :: (->) nor: undefined :: Maybe because (->) and Maybe are not proper types. It doesn't make sense to say that some value (like undefined) belongs to the collection of values characterized by them, since there is no such collection to belong to! The same sort of thing holds for datakinds. Types of kind 'Nat are not proper, in exactly the same way that types of kind *->* or *->*->* are not proper. -- Live well, ~wren

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ANN: hledger 0.21
by Simon Michael 01 Jun '13

01 Jun '13

I'm pleased to announce hledger and hledger-web 0.21! hledger is a command-line tool and haskell library for tracking financial transactions, which are stored in a human-readable plain text format. In addition to reporting, it can also help you record new transactions, or convert CSV data from your bank. Add-on packages include hledger-web (providing a web interface), hledger-irr and hledger-interest. hledger is inspired by and compatible with John Wiegley's Ledger. For more, see http://hledger.org . Install it: cabal update; cabal install hledger [hledger-web] For more installation help, see http://hledger.org/MANUAL.html#installing . Or, sponsor a ready-to-run binary for your platform: http://hledger.org/DOWNLOAD.html . Release notes (http://hledger.org/NEWS.html#hledger-0.21) **Bugs fixed:** - parsing: don't fail when a csv amount has trailing whitespace (fixes #113) - web: don't show prices in the accounts sidebar (fixes #114) - web: show one line per commodity in charts. Needs more polish, but fixes #109. - web: bump yesod-platform dependency to avoid a cabal install failure **Journal reading:** - balance assertions are now checked after reading a journal **web command:** - web: support/require yesod 1.2 - web: show zero-balance accounts in the sidebar (fixes #106) - web: use nicer select2 autocomplete widgets in the add form **Documentation and infrastructure:** - add basic cabal test suites for hledger-lib and hledger Release contributors: - Xinruo Sun enhanced the hledger-web add form - Clint Adams added cabal test suites - Jeff Richards did hledger-web cleanup - Peter Simons provided the build bot

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Simplest way to learn FRP through use
by Christopher Howard 01 Jun '13

01 Jun '13

I want to learn FRP but am having trouble wading through all the theory about how FRP is implemented and how it /could/ be used for various applications. What is the simplest, easiest-to-learn module or system allowing you to quickly make something interesting (if not very impressive) in an FRP style? Say, a simple simulation of some physical phenomena outputting its state to the terminal; or an object moving on the screen; or some other toy application that I could create and play with. -- frigidcode.com

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