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Request for help w/ Ex. 10 in *Arrows and Computation*.
by David Banas 22 Oct '16

22 Oct '16

Hi all, I’m stuck in Ex. 10 of *Arrows and Computation*, by Ross Paterson: https://htmlpreview.github.io/?https://github.com/capn-freako/Haskell_Misc/… <https://htmlpreview.github.io/?https://github.com/capn-freako/Haskell_Misc/…> It seems to me that if, in the third step of my proof, I could convert the *left (pure fst)* into *left (first <?>)*, then I could use the **distribution** axiom to convert *pure distr >>> left (first <?>)* into *first (left <?>) >>> pure distr *. At that point, I would have (starting from the left side of my expression): *first (..) >>> first (..)*, and could apply the functor property of *first*, in order to simplify the expression. Thanks, -db

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[ANN] patat - Terminal based presentation tool built with Pandoc
by Jasper Van der Jeugt 21 Oct '16

21 Oct '16

I'm happy to announce `patat` (Presentations Atop The ANSI Terminal), a small tool that allows you to show presentations using only an ANSI terminal. The main features are: - Leverages the great Pandoc library to support many input formats including Literate Haskell. - Supports smart slide splitting. - There is a live reload mode. - Theming support. - Optionally re-wrapping text to terminal width with proper indentation. - Written in Haskell. You can find more information here: https://github.com/jaspervdj/patat/blob/master/README.md Peace, Jasper

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I cannot seem to get the second aio command to work on Create a Game with Haskell hgamer3D.org
by KC 21 Oct '16

21 Oct '16

I'm getting an error 403 permission denied aio http://www.hgamer3d.org/component/CreateProject arriccio is going to download and install the following files: -------------------------------------------------------------- (more license info can be obtained by using the "aio license" cmd) file: http://www.hgamer3d.org/downloads/lua-amd64-windows-1.0.0.tar.gz signing key: https://www.github.com/urs-of-the-backwoods.keys license: MIT License please confirm download with "yes": yes downloading: http://www.hgamer3d.org/downloads/lua-amd64-windows-1.0.0.tar.gz2016/10/20 11:23:56 cannot download urln: http://www.hgamer3d.org/downloads/lua-amd64-windows-1.0.0.tar.gz, http error: 403 -- -- Sent from an expensive device which will be obsolete in a few months! :D Casey

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PEPM 2017 Call for Poster Papers (submission deadline Tuesday 8th November)
by Jeremy Yallop 21 Oct '16

21 Oct '16

CALL FOR POSTERS Workshop on PARTIAL EVALUATION AND PROGRAM MANIPULATION (PEPM 2017) PEPM 2017 information: http://conf.researchr.org/home/PEPM-2017 Submissions: https://pepm17.hotcrp.com/ Paris, France, January 16th - 17th, 2017 (co-located with POPL 2017) PEPM is the premier forum for discussion of semantics-based program manipulation. The first ACM SIGPLAN PEPM symposium took place in 1991, and meetings have been held in affiliation with POPL every year since 2006. PEPM 2017 will be based on a broad interpretation of semantics-based program manipulation, reflecting the expanded scope of PEPM in recent years beyond the traditionally covered areas of partial evaluation and specialization. Posters ------- In order to maintain the dynamic and interactive nature of PEPM, we solicit submission of posters. Poster submissions are 2-page articles in ACM Proceedings style that present preliminary work (see "Submission guidelines" below for more details). If accepted, the work will be presented as part of an interactive poster session at PEPM. Scope ----- Topics of interest for PEPM 2017 include, but are not limited to: * Program and model manipulation techniques such as: supercompilation, partial evaluation, fusion, on-the-fly program adaptation, active libraries, program inversion, slicing, symbolic execution, refactoring, decompilation, and obfuscation. * Program analysis techniques that are used to drive program/model manipulation such as: abstract interpretation, termination checking, binding-time analysis, constraint solving, type systems, automated testing and test case generation. * Techniques that treat programs/models as data objects including metaprogramming, generative programming, embedded domain-specific languages, program synthesis by sketching and inductive programming, staged computation, and model-driven program generation and transformation. * Application of the above techniques including case studies of program manipulation in real-world (industrial, open-source) projects and software development processes, descriptions of robust tools capable of effectively handling realistic applications, benchmarking. Examples of application domains include legacy program understanding and transformation, DSL implementations, visual languages and end-user programming, scientific computing, middleware frameworks and infrastructure needed for distributed and web-based applications, embedded and resource-limited computation, and security. This list of categories is not exhaustive, and we encourage submissions describing applications of semantics-based program manipulation techniques in new domains. If you have a question as to whether a potential submission is within the scope of the workshop, please contact the programme chairs. Submission guidelines --------------------- * Posters should describe work relevant to the PEPM community, and must not exceed 2 pages in ACM Proceedings style. We invite poster submissions that present early work not yet ready for submission to a conference or journal, identify new research problems, showcase tools and technologies developed by the author(s), or describe student research projects. If accepted, the work will be presented as part of an interactive poster session at PEPM. At least one author of each accepted contribution must attend the workshop and present the work. Student participants with accepted poster papers can apply for a SIGPLAN PAC grant to help cover travel expenses and other support. 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 programme, see its web page. Publication ----------- Posters will appear along with accepted papers in formal proceedings published by ACM Press and in the ACM Digital Library. Keynote ------- Neil Jones (DIKU) will give the PEPM keynote talk, titled Compiling Untyped Lambda Calculus to Lower-level Code by Game Semantics and Partial Evaluation Submission ---------- Posters should be submitted electronically via HotCRP. https://pepm17.hotcrp.com/ Authors using LaTeX to prepare their submissions should use the new improved SIGPLAN proceedings style, and specifically the sigplanconf.cls 9pt template. Important Dates --------------- * Poster submission : Tuesday 8th November 2016 * Author notification : Friday 18th November 2016 * Camera ready : Monday 28th November 2016 * Workshop : Monday 16th - Tuesday 17th January 2017 The proceedings will be published 2 weeks pre-conference. AUTHORS TAKE NOTE: The official publication date is the date the proceedings are made available in the ACM Digital Library. This date may be up to two weeks prior to the first day of your conference. The official publication date affects the deadline for any patent filings related to published work. (For those rare conferences whose proceedings are published in the ACM Digital Library after the conference is over, the official publication date remains the first day of the conference.). PEPM'17 Programme Committee --------------------------- Elvira Albert (Complutense University of Madrid, Spain) Don Batory (University of Texas at Austin, USA) Martin Berger (University of Sussex, UK) Sebastian Erdweg (TU Delft, Netherlands) Andrew Farmer (Facebook, USA) Matthew Flatt (University of Utah, USA) John Gallagher (Roskilde University, Denmark) Robert Glück (DIKU, Denmark) Jurriaan Hage (Utrecht University, Netherlands) Zhenjiang Hu (National Institute of Informatics, Japan) Yukiyoshi Kameyama (University of Tsukuba, Japan) Ilya Klyuchnikov (Facebook, UK) Huiqing Li (EE, UK) Annie Liu (Stony Brook University, USA) Markus Püschel (ETH Zurich, Switzerland) Ryosuke SATO (University of Tokyo, Japan) Sven-Bodo Scholz (Heriot-Watt University, UK) Ulrik Schultz (co-chair) (University of Southern Denmark) Ilya Sergey (University College London, UK) Chung-chieh Shan (Indiana University, USA) Tijs van der Storm (Centrum Wiskunde & Informatica, Netherlands) Jeremy Yallop (co-chair) (University of Cambridge, UK) -- Ulrik Pagh Schultz, Associate Professor, University of Southern Denmark ups(a)mmmi.sdu.dk http://www.sdu.dk/ansat/ups +4565503570

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MTL vs Free-monads, what are your experiences
by Damian Nadales 21 Oct '16

21 Oct '16

Hi, I was looking into free monads for designing a DSL for describing scenarios of the form: scenario = do aId <- createA b0Id <- createB id b1Id <- createB id link b0 b1 In our company we use a graph database, and currently we're setting up the test data using raw queries O.O So I wanted to come up with a better abstraction, and also enable us to do property based testing (by testing on random scenarios like the one above). Anyway, I ran into this presentation: http://www.slideshare.net/jdegoes/mtl-versus-free http://degoes.net/articles/modern-fp-part-2 In which monad transformers and free monads are compared. Do you have any experience using any of these approaches. If so would you mind sharing? ;) Thanks! Damian

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Re: [Haskell-cafe] Why does [1.0, 3 ..4] contain 5?
by Bence Kodaj 20 Oct '16

20 Oct '16

Silvio, Brandon, Ben: thanks for your instructive comments. Please allow me to dwell on this issue for 5 more minutes - I'm really interested in your opinion. Do you think it would be bad if we changed the definition of numericEnumFromThenTo e1 e2 e3 in such a way that the resulting list would never contain elements that are greater than e3 (in the e1 <= e2 case)? I'm asking because you can actually be bitten by this quirk of enumerated lists of Doubles (and Floats) even if you don't use floating-point literals explicitly. Consider the following (this is how I stumbled upon this issue actually): -- "odd semi-factorial" of n osf n = product [1, 3 .. n] -- "even semi-factorial" of n esf n = product [2, 4 .. n] Load this into GHCi and then go: *Main> osf 4 3 *Main> esf 4 8 *Main> osf 4 / esf 4 1.875 This last result looks total nonsense at first glance - it took me a good 15 minutes to realize what was going on. Of course, if I provide reasonable type signatures (e.g., Integer -> Integer) for osf and esf, then the problem goes away. Still, to me this strange result is a lot more surprising and unexpected than the fact that e.g., [1.0, 1.1 .. 2.3] would not actually contain (a value close to) 2.3 if we changed the definition of numericEnumFromThenTo. After all, it's fairly common knowledge that floating-point arithmetic is inexact and you're not supposed to rely on precise equality of two floating-point values, or you shouldn't be surprised if basic mathematical identities don't hold for floating-point values (e.g., 1 + 2*0.1 /= 1 + 0.1 + 0.1). Whereas the apparent "change" in the value of osf 4 from one line to the next above is more baffling I believe. But what do you think? Regards, Bence

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Why does [1.0, 3 ..4] contain 5?
by Bence Kodaj 20 Oct '16

20 Oct '16

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tokenize parser combinators and free applicatives
by Ruben Astudillo 19 Oct '16

19 Oct '16

Hi all on [1] it is said the following "Dealing with whitespace and comments is awkward in the parser; you need to wrap everything in a token combinator. (If you decide to do that, at least use a free applicative functor to ensure that you don’t forget to consume that whitespace)." Reading on `free` the def of Ap, frankly I don't see how can the free applicative be used for this. Anybody could drop a hint? I would appreciate it. [1]: https://ro-che.info/articles/2015-01-02-lexical-analysis -- Ruben

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1TB vsize for all haskell processes?
by Michael Alan Dorman 18 Oct '16

18 Oct '16

Hey, haskell-cafe, I realize that this should not be a problem, but it is very strange to me that *every* haskell process on my system has a 1TB VSIZE. If I sort my `ps auwx` output on vsize, the top of the list looks like: mdorman 1208 0.0 0.1 1074011536 12500 ? S Oct14 0:04 /home/mdorman/.xmonad/xmonad-x86_64-linux mdorman 21900 0.0 0.2 1074111408 19712 pts/1 Sl+ 09:06 0:00 cabal run melpa2nix -- --output melpa-generated.nix --melpa /home/mdorman/src/melpa --work /home/mdorman/src/emacs2nix/.workdir mdorman 1363 0.0 0.1 1074383784 13052 ? Sl Oct14 1:14 /home/mdorman/.cache/taffybar/taffybar-linux-x86_64 +RTS -I0 -V0 --RTS --dyre-master-binary=/nix/store/6skvglp84w5xzqx8dxxydazk1zj8h2ih-taffybar-0.4.6/bin/taffybar mdorman 21981 8.6 0.5 1076223012 42308 pts/1 Sl+ 09:06 0:19 /home/mdorman/src/emacs2nix/dist/build/melpa2nix/melpa2nix --output melpa-generated.nix --melpa /home/mdorman/src/melpa --work /home/mdorman/src/emacs2nix/.workdir Each of those haskell processes has a vsize 5 orders of magnitude more than their resident set size, whether it's the two I always have running (xmonad and taffybar), or in this case, cabal itself, as well as the compiled executable it's running. I've spent a reasonable amount of time attempting to google this, to no avail. Is this perhaps a peculiarity of how GHC was built? I'm running on nixos-unstable, using ghc-8.0.1---is there some compilation that we should or shouldn't be setting? Thanks for any guidance, Mike.

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Easy cross platform CI testing of Haskell packages
by Harendra Kumar 18 Oct '16

18 Oct '16

Hi, If as a package maintainer, you want to: * test your package with cabal & stack both * test your package on Linux, Mac, Windows * test your package on travis, appveyor or local machine in the same way * make sure that the _source dist_ that you are going to upload is tested * upload coverage report to coveralls.io * customize the build your way But you do not want the drudgery and the pain of writing elaborate shell scripts inside travis or appveyor yaml config and then debug them, then this script is for you. You just have to declare some environment variables in your build matrix and finally call this script and you are done. It works consistently the same way for all build types so you don't worry about whether all platforms are testing the same way or not. * Script: https://github.com/harendra-kumar/package-test * Travis Example: https://github.com/harendra-kumar/xls/blob/master/.travis.yml * Appveyor Example: https://github.com/harendra-kumar/xls/blob/master/appveyor.yml Feedback and suggestions are welcome! -harendra

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