January 2014 - Haskell-Cafe

Help with Binary Serialization
by Joey Eremondi 18 Jan '14

18 Jan '14

I was wondering if somebody could talk me through the default derived format for binary serialization used, either by binary or by cereal. I'm trying to share data between Haskell and another function language (Elm) which also supports algebraic data types, so the conversion of data should be pretty trivial. I'd like to be able to just derive encode and decode in Haskell using either binary/cereal, and then write a parser for the same format in Elm. The trick is, I don't know what that format is. Is there any documentation on it, or if not, is anybody familiar enough with it that they could explain the format to me? Thanks!

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Standard implementation of asynchronous helpers?
by Tristan Seligmann 18 Jan '14

18 Jan '14

I was wondering if a standard implementation of these helpers (or something similar) existed somewhere: startAsync :: IO a -> IO (MVar a) startAsync action = do var <- newEmptyMVar forkIO $ action >>= putMVar var return var wait :: MVar a -> IO a wait = readMVar I've found a few throwaway examples that implement something similar, and I can imagine some improvements already (I guess the MVar should be wrapped, for example, and some higher) but I was unable to find any released library that does something like this. Is it just too trivial for anyone to have bothered? -- mithrandi, i Ainil en-Balandor, a faer Ambar

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Building ghc-7.6.3 under cygwin
by Dmitry Malikov 18 Jan '14

18 Jan '14

Trying to build 7.6.3-x86_64-unknown-linux under cygwin. $ ./configure checking for path to top of build tree... ./configure: line 2121: utils/ghc-pwd/dist-install/build/tmp/ghc-pwd: cannot execute binary file configure: error: cannot determine current directory Not sure it is a libgmp issue, because linking doesn't help: $ ln -s /usr/lib/libgmp.dll.a /usr/lib/libgmp.so.3 Any ideas what is going on and how to fix this?

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Re: [Haskell-cafe] [Haskell] Just started working with Haskell. Need some help
by Henning Thielemann 18 Jan '14

18 Jan '14

moving to Haskell-Cafe ... Am 18.01.2014 18:25, schrieb Pyro Crane: > But, when I try to run a simple script, I keep getting the error : > "*Could not find module XXXXXX*".............. What precisely did you try? > And, now, I've come up against a module/package, which I am unable to > locate in Google. It's missing from my installation, and Google does > not know what it is, or where I can find it > > Is there any way to simply install ALL required packages??? I thought > I already did this, but obviously I missed something $ cabal install wantedpkg should install all dependencies of 'wantedpkg'. If it does not I am interested in how you tried to install 'wantedpkg'.

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ANNOUNCE: Diagrams 1.0
by Brent Yorgey 18 Jan '14

18 Jan '14

The diagrams team is very pleased to announce the 1.0 release of diagrams [1], a framework and embedded domain-specific language for declarative drawing in Haskell. Check out the gallery [2] for some examples of what it can do. Diagrams can be used for a wide range of purposes, from data visualization [3] to illustration [4] to art [5], and diagrams code can be seamlessly embedded in blog posts [6], LaTeX documents [7], and Haddock documentation [8], making it easy to incorporate diagrams into your documents with minimal extra work. [1] http://projects.haskell.org/diagrams [2] http://projects.haskell.org/diagrams/gallery.html [3] http://idontgetoutmuch.wordpress.com/2013/10/23/parking-in-westminster-an-a… [4] https://www.fpcomplete.com/user/edwardk/cellular-automata/part-1 [5] http://mathlesstraveled.com/2013/04/06/stars-of-the-minds-sky-with-diagrams/ [6] http://byorgey.wordpress.com/2012/08/28/creating-documents-with-embedded-di… [7] http://projects.haskell.org/diagrams/doc/latex.html [8] http://byorgey.wordpress.com/2013/03/23/introducing-diagrams-haddock/ What's new ---------- Brent recently gave a talk at the New York Haskell Users' Group [12] presenting the new release. You can find videos of the talk on vimeo: part 1 presents a basic introduction to the library [13], and part 2 talks about mathematical abstraction and DSL design [14]. The slides are also available [15]. [12] http://www.meetup.com/NY-Haskell/ [13] http://vimeo.com/84104226 [14] http://vimeo.com/84249042 [15] http://www.cis.upenn.edu/~byorgey/pub/13-11-25-nyhaskell-diagrams.pdf This release includes a number of significant new features and improvements. Highlights include: - Support for drawing arrows between given points or between diagrams, with many options for customization (tutorial [16], documentation [17], API [18]). [16] http://projects.haskell.org/diagrams/doc/arrow.html [17] http://projects.haskell.org/diagrams/doc/manual.html#arrows [18] http://projects.haskell.org/diagrams/haddock/Diagrams-TwoD-Arrow.html - A new framework for creating custom command-line-driven executables for diagram generation (tutorial [19], API [20]). [19] http://projects.haskell.org/diagrams/doc/cmdline.html [20] http://projects.haskell.org/diagrams/haddock/Diagrams-Backend-CmdLine.html - Offsets of trails and paths, i.e. compute the trail or path lying a constant distance from the given one (documentation [21], API [22]). [21] http://projects.haskell.org/diagrams/doc/manual.html#offsets-of-segments-tr… [22] http://projects.haskell.org/diagrams/haddock/Diagrams-TwoD-Offset.html - A new API, based on Metafont, for constructing cubic splines with control over things like tangents and "tension" (tutorial [23], API [24]). [23] http://projects.haskell.org/diagrams/doc/metafont.html [24] http://projects.haskell.org/diagrams/haddock/Diagrams-TwoD-Path-Metafont.ht… - Tangent and normal vectors of segments and trails (API [25]). [25] http://projects.haskell.org/diagrams/haddock/Diagrams-Tangent.html - Alignment can now be done by trace in addition to envelope (API [26]). [26] http://projects.haskell.org/diagrams/haddock/Diagrams-TwoD-Align.html - The lens [27] package is now used consistently for record fields throughout the library (documentation [28]). [27] http://hackage.haskell.org/package/lens [28] http://projects.haskell.org/diagrams/doc/manual.html#faking-optional-named-… - Across-the-board improvements in performance and size of generated files. See the release notes [29] for full details, and the migration guide [30] for help porting your diagrams 0.7 code to work with diagrams 1.0. [29] http://projects.haskell.org/diagrams/releases.html [30] http://www.haskell.org/haskellwiki/Diagrams/Dev/Migrate1.0 Try it out ---------- For the truly impatient: cabal install diagrams Diagrams is supported under GHC 7.4 and 7.6. To get started, read the quick start tutorial [31], which will introduce you to the fundamentals of the framework and provide links for further reading. For those who are less impatient and want to really dig in and use the power features, read the extensive user manual [32]. There is also a growing collection of tutorials [33] on specific topics. [31] http://projects.haskell.org/diagrams/doc/quickstart.html [32] http://projects.haskell.org/diagrams/doc/manual.html [33] http://projects.haskell.org/diagrams/documentation.html Get involved ------------ Diagrams has a friendly and growing community of users and developers. To connect with the community, subscribe to the project mailing list [34], and/or come hang out in the #diagrams IRC channel on freenode.org for help and discussion. Development continues stronger than ever, and there are a wide range of projects available for new contributors of all levels of Haskell skill. Make some diagrams. Fix some bugs [35]. Submit your cool examples for inclusion in the gallery [36] or your cool code for inclusion in the diagrams-contrib [37] package. [34] http://groups.google.com/group/diagrams-discuss [35] http://github.com/diagrams/ [36] http://projects.haskell.org/diagrams/gallery.html [37] http://hackage.haskell.org/package/diagrams%2Dcontrib Happy diagramming! Brought to you by the diagrams team: - Daniel Bergey - Jeff Rosenbluth - Ryan Yates - Brent Yorgey with contributions from: - Jan Bracker - Conal Elliott - Daniil Frumin - Sam Griffin - Niklas Haas - Peter Hall - Claude Heiland-Allen - Deepak Jois - John Lato - Felipe Lessa - Chris Mears - Ian Ross - Carlos Scheidegger - Vilhelm Sjöberg - Michael Sloan - Jim Snavely - Luite Stegeman - Kanchalai Suveepattananont - Michael Thompson - Scott Walck

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Automatic differentiation and dimension types
by Douglas McClean 18 Jan '14

18 Jan '14

Has anyone explored the intersection between automatic differentiation and dimension types (like those in the dimensional package or along the lines of any of the approaches discussed at http://www.haskell.org/haskellwiki/Physical_units)? It's tricky because for ordinary automatic differentiation the types are all the same, but when dimensions get involved that isn't the case, you have to keep dividing by the dimension of the infinitesimal. -Doug McClean

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Open researcher position at Create-Net Italy
by Corentin Dupont 17 Jan '14

17 Jan '14

Dear Haskell-cafe, CREATE-NET, a research center located in Trento, Italy, is hiring one researcher on distributed system management. The responsibility of the candidate will be to contribute to the research topic of Energy Efficiency in the Cloud with particular focus on making cloud-running applications energy-aware. The techniques used will include Constraint Programming and Functional Programming to some extent. We offer competitive compensation and a stimulating work environment in the research and innovation sector. The scenic landscape of Italian Alps doesn't hurt either. If you are interested, please submit your application to careers(a)create-net.org (with me in copy). Details on the open position and ideal profile may be found on http://www.create-net.org/it/node/3197 Don't hesitate to contact me for more details! Cheers, Corentin Dupont CREATE-NET www.create-net.org www.corentindupont.info

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Silencing 'cabal configure' warning
by Jan Stolarek 17 Jan '14

17 Jan '14

Hi all, When running 'cabal configure' I get a warning that my package database is old: [killy@xerxes : /dane/projekty/singletons] cabal configure Warning: The package list for 'hackage.haskell.org' is 25 days old. Run 'cabal update' to get the latest list of available packages. Is there a way to silence this warning other than running 'cabal update'? I don't want to update my package database and getting a warning every time I configure a package is irritating. Janek

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ANN: pooled-io
by Henning Thielemann 17 Jan '14

17 Jan '14

I uploaded the package pooled-io to Hackage: https://hackage.haskell.org/package/pooled-io It is intended to perform parallelism in the IO monad. I needed it for computations that must write intermediate data to disk. The main task of the package is to make sure that no more than a maximum number of actions is run in parallel. There are three modules: For actions without monadic results, for actions with monadic results and for actions that depend on each others results.

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Re: [Haskell-cafe] Restrict values in type
by Simon Yarde 17 Jan '14

17 Jan '14

If it's not been mentioned, this tutorial regarding Type Families and the kinds of restrictions you mention might provide a few pointers: https://www.fpcomplete.com/school/to-infinity-and-beyond/pick-of-the-week/t… In general, I've found key concepts to hold in mind are 'exclusion of bad programs' mentioned in the paper Fun With Types: http://research.microsoft.com/en-us/um/people/simonpj/papers/assoc-types/fu… I'm sorry if any of this has been mentioned previous. I asked a related question yesterday about the relative merits of creating type restrictions using using newtypes (unions), which I agree seem unwieldy, and using multi-parameter-type-classes (and/or type families) to enable exclusion-of-bad-programms via instances. I'd be interested to follow along and see what you discover. Simon Yarde

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