September 2014 - Haskell-Cafe

What happened to hugs?
by Thorsten Rangwich 18 Oct '14

18 Oct '14

Hi, I suppose this question is not new, but neither google nor a manual search file be file through the archives brought enlightement. www.haskell.org/hugs still exists, but none of the links there does work. Documentation and source point to cvs.haskell.org ("server does not exist") and development points to http://hackage.haskell.org/trac/hugs ("page does not exist"). Was it migrated to somewhere else or is it dead - in latter case the page would not make sense any more. "Raskell" (iPad app) provided a development environment usinh hugs, so I would at least like to install hugs on my Mac as well... Thank you very much in advance. Thorsten. Sent from my mobile phone

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Unable to build a mingw cross compiler.
by Sven Bartscher 05 Oct '14

05 Oct '14

Greetings, I'm trying to build GHC to cross compile to windows. GCC and friends are in /usr/bin/x86_64-w64-mingw32-*, libraries and headers are in /usr/x86_64-w64-mingw32/{include,lib}. I configured with: ./configure --target=x86_64-w64-mingw32 \ --with-gcc=/usr/bin/x86_64-w64-mingw32-gcc # Needed because # otherwise /usr/bin/gcc # would be used Building fails with the following error: utils/hsc2hs/dist/build/Main.o: In function `s2nI_info': (.text+0x5c5): undefined reference to `GetModuleFileNameW' collect2: error: ld returned 1 exit status (The GHC invocation line is included in the attached file) So it seems that GHC either uses the wrong linker or invokes it with the wrong search path. However, the configure script detects the right linker (/usr/bin/x86_64-w64-mingw32). Is this a bug, or a feature? System data: OS: Debian jessie Linux/GNU i386 Installed GHC (for bootstrapping): version 7.6.3 GHC I'm trying to build: version 7.8.3 Regards Sven

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context deduction in GHC
by Doug McIlroy 30 Sep '14

30 Sep '14

Why does ghci 7.6.3 not like this example, which section 4.3.2 of the language definition says is valid Haskell? class Foo a class Foo a => Bar a instance (Eq a, Show a) => Foo [a] instance Num a => Bar [a] Ghci complains, "Could not deduce (Show a) arising from the superclasses of an instance declaration from the context (Num a)". Yet Show is a superclass of Num. Hugs accepts the code. Doug McIlroy

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ANN: Nomyx 0.7 beta, the only game where you can change the rules
by Corentin Dupont 30 Sep '14

30 Sep '14

Hello everybody! I released Nomyx <http://www.nomyx.net> V0.7, the only game where You can change the rules! Here is the website: www.nomyx.net Here is a video introduction of the game: http://vimeo.com/58265498 I created a tutorial to learn how to play: http://www.corentindupont.info/blog/posts/2014-09-23-first-Nomyx-tutorial.h… Let's start a new game! I propose to call it "The Space Merchants". Dear rulers, this part of the Galaxy is yours... Please login to the game here: www.nomyx.net:8000/Nomyx. The corresponding forum thread is here: http://www.nomyx.net/forum/viewtopic.php?f=4&t=1525&p=1739 Please also register on the mailing list to follow the game: nomyx-game(a)googlegroups.com Some background: this is an implementation of a Nomic [1] game in Haskell (I believe the first complete implementation of a Nomic game on a computer). In a Nomyx game you can change the rules of the game itself while playing it. The players can submit new rules or modify existing ones, thus completely changing the behaviour of the game through time. The rules are managed and interpreted by the computer. They must be written in the Nomyx language <http://hackage.haskell.org/package/Nomyx-Language>, which is a subset of Haskell. At the beginning, the initial rules are describing: - how to add new rules and change existing ones. For example a unanimity vote is necessary to have a new rule accepted. - how to win the game. For example you win the game if you have 5 rules accepted. But of course even that can be changed! New in this beta release: - the Nomyx language is now based on functional reactive programming - the language also embeds a mechanism to separate effectful instructions from effectless ones - ability to fork an existing game into a new one - ability to type-check rules before submitting them - ability to create new games If you wanna help developing Nomyx, join us on the dev mailing-list: dev-game(a)googlegroups.com <nomyx-game(a)googlegroups.com> Cheers, Corentin [1] www.nomic.net

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Cabal Testing Pain
by Mike Craig 29 Sep '14

29 Sep '14

Hey all, I'm trying to setup an executable cabal project, the options for cabal-based testing seem poor. I poked around for discussions of this but didn't find much. My apologies if I'm beating a dead horse. The current options, as I understand them, are 1. Split code into library, executable, and test-suite. This gets you single compilation but you have to list every source file in the library's exposed/other-modules sections. 2. Split code into executable and test-suite. You don't have to list the source files, but you get double compilation and you have to declare every dependency (and version!) twice. Am I missing a third (better) option, or is this the state of things? -- Mike Craig

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the complex package is hidden
by briand＠aracnet.com 28 Sep '14

28 Sep '14

Hi, surprisingly i can't seem to google an answer to this: Could not find module `Complex' It is a member of the hidden package `haskell98-2.0.0.2'. Use -v to see a list of the files searched for. it's been quite a while since I've used ghci, and I'm just about positive I've solved this problem before, but can't seem to figure it out. Thanks for any help.

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Deploying bash completion with cabal?
by Jacob Stanley 28 Sep '14

28 Sep '14

Hi All I'm looking for a good way to deploy a bash completion script somewhere appropriate for the given operating system. Has anyone tackled this before? I was considering packaging the script in to the install using cabal data files, then having an 'install--bash-completion' option that tries to detect the right place to install it depending on the OS. Cheers Jacob

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Separate compilation
by Lars Hupel 28 Sep '14

28 Sep '14

Hi all, I'm trying to compile a couple of file separately. The main purpose for that is that we're checking student-submitted exercises, and we want to compile them with -XSafe. The test suite doesn't require -XSafe. There are basically three files: * Exercise.hs -- uploaded by the student * Exercise_Interface.hs -- imports the 'Exercise' module and creates new bindings with appropriate types * Exercise_Test.hs -- imports the interface module and contains the test code and 'main' Here's how I try to compile these files: TEMP="$(mktemp -d -p /tmp ghcXXX)" ghc -c -XSafe -outputdir "$TEMP" Exercise.hs ghc -c -outputdir "$TEMP" -i"$TEMP" Exercise_Interface.hs ghc -o "$TEMP/runner" -outputdir "$TEMP" -i"$TEMP" Exercise_Test.hs This works except for the last step: GHC complains that it can't find the module 'Exercise_Interface'. Upon closer inspection with '-v', it turns out that it's actually looking for the .hs file, which I find odd. If I add '-c' to the last invocation, it works, but I don't get an executable. What am I doing wrong? Cheers Lars

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Arrow key functionality for REPL written in Haskell
by PENG, BO YA 28 Sep '14

28 Sep '14

Hi, I'm trying to implement the arrow key functionality for a systemf REPL to recall previously entered lines. I think I should save the previous lines in a list and then traverse through the list when an arrow key is pressed, but I'm no sure how to detect an arrow key and implement this functionality. Can anyone give a brief description about the implementation or point me to some other resources? Thanks! Emma

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[ANN] lxc-0.2 and bindings-0.2 – Haskell LXC API bindings
by Nickolay Kudasov 28 Sep '14

28 Sep '14

Greetings, I am pleased to announce the Haskell LXC API bindings. Bindings are represented by 2 cabal packages: lxc and bindings-lxc. LXC is a userspace interface for the Linux kernel containment features. For more information see https://linuxcontainers.org. http://hackage.haskell.org/package/lxc High level Haskell bindings to LXC (Linux containers). Git repository: https://github.com/fizruk/lxc http://hackage.haskell.org/package/bindings-lxc Direct Haskell bindings to LXC (Linux containers) C API. Git repository: https://github.com/fizruk/bindings-lxc === Before installation make sure you have LXC installed on your system with header files and static library. Packages have been tested with Ubuntu 12.04 and 14.04. On Ubuntu 14.04 LTS (Trusty Tahr): $ sudo apt-get install lxc-dev On previous Ubuntu versions (including 12.04 LTS Precise Pangolin) standard repositories do not contain liblxc1 package. You might want to use ppa:ubuntu-lxc/stable repository instead: $ sudo apt-get install software-properties-common python-software-properties $ sudo add-apt-repository ppa:ubuntu-lxc/stable $ sudo apt-get update $ sudo apt-get install lxc-dev === To get the latest stable version of both packages: $ cabal install lxc === While Haddock documentation is absent one can either build haddock documentation locally or view it online on GitHub Pages: lxc documentation: http://fizruk.github.io/lxc/docs/ bindings-lxc documentation: http://fizruk.github.io/bindings-lxc/docs/ See also Usage section of lxc package README file: https://github.com/fizruk/lxc/blob/master/README.md#usage === Feedback of any kind is welcome! Cheers, Nickolay Kudasov

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