November 2012 - Haskell-Cafe

Quickcheck
by graham＠fatlazycat.com 13 Nov '12

13 Nov '12

Hi, Trying to find some good docs on QuickCheck, if anyone has one ? Been scanning what I can find, but a question. What would be the best way to generate two different/distinct integers ? Use arbitrary ( if so do you have an example ) or a conditional on the property. Though I read the later can reduce passing test count. Thanks Graham

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hackageDB haddock errors
by timothyhobbs＠seznam.cz 13 Nov '12

13 Nov '12

Hello, There are several packages without haddock documentation on hackage. The one that bugs me right now, is the latest version of gtk2hs: http://hackage. haskell.org/package/gtk I've been told that this may be due to hackage updating docs with an infrequent cron job, so that new packages don't get their docs for a long time. Whatever is causing it, the fact that hayoo http://holumbus.fh-wedel. de/hayoo/hayoo.html always uses the most frequent docs, means that I cannot currently search for anything gtk2hs related :( Can someone please look into prodding this cron job so it doesn't take days to run, or look into resolving any errors that might be causing this unfortunate behaviour? Thank you for your time, and happy hacking, Timothy

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Wrong install-name path for shared/dynamic C-library on OS X
by Christiaan Baaij 13 Nov '12

13 Nov '12

Dear List, The context of my problem is the following: - ghc-HEAD uses shared-library _only_ on OS X - A cabalized package that builds a shared/dynamic C-library (GLFW-b) And my problem is: A dynamically linked Haskell library gets the wrong install-name for a C-library: otool -L ~/.cabal/lib/GLFW-b-0.1.0.5/ghc-7.7.20121111/libHSGLFW-b-0.1.0.5-ghc7.7.20121111.dylib: /Users/baaijcpr/.cabal/lib/GLFW-b-0.1.0.5/ghc-7.7.20121111/libHSGLFW-b-0.1.0.5-ghc7.7.20121111.dylib: .... build/libglfw.dylib (compatibility version 1.0.0, current version 1.0.0) .... All the other paths reported by 'otool -L' are absolute, while the C-library (libglfw.dylib) that was part of the Cabalized package is relative. The problem presents itself when I now want to use the GLFW-b package: Loading package GLFW-b-0.1.0.5 ... can't load .so/.DLL for: /Users/baaijcpr/.cabal/lib/GLFW-b-0.1.0.5/ghc-7.7.20121111/libHSGLFW-b-0.1.0.5-ghc7.7.20121111.dylib (dlopen(/Users/baaijcpr/.cabal/lib/GLFW-b-0.1.0.5/ghc-7.7.20121111/libHSGLFW-b-0.1.0.5-ghc7.7.20121111.dylib, 9): Library not loaded: build/libglfw.dylib Referenced from: /Users/baaijcpr/.cabal/lib/GLFW-b-0.1.0.5/ghc-7.7.20121111/libHSGLFW-b-0.1.0.5-ghc7.7.20121111.dylib Reason: image not found) I can update the install-name to the correct path using: install_name_tool -change build/libglfw.dylib @loader_path/libglfw.dylib libHSGLFW-b-0.1.0.5-ghc7.7.20121111.dylib So my question are: - Where does the original install_name path (build/libglfw.dyli) come from? - What should be specified in the .cabal and/or Setup.hs file so that the haskell library is installed using the _correct_ relative path? Cheers, Christiaan

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JavaScript (SpiderMonkey, V8, etc) embedded in GHC?
by Bob Hutchison 13 Nov '12

13 Nov '12

Hi, I've looked around with no success… this surprises me actually. Has anyone embedded SpiderMonkey, V8, or any other relatively decent JavaScript interpreters in GHC (using the FFI)? I did find http://justinethier.github.com/husk-scheme/ which is a scheme R5RS implementation (I could make this work). There's also some work done embedding Lua. I also found a number of packages that compile javascript to Haskell, or the other way around, but I don't need that kind of thing. All I really need is to allow users to write some JavaScript that accepts a single JSON 'file/string' from my Haskell program and produces another JSON 'file/string' that my Haskell program will accept. Thanks, Bob

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Re: [Haskell-cafe] curl package broken in Windows
by Kevin Cantu 13 Nov '12

13 Nov '12

Heh, I was trying to build this yesterday and it was making by eyes bleed. With the curl package on Hackage, I merely need an SSL enabled version of libcurl, and every Linux distro I've tried this on has several variations of such a package. (You have a choice of OpenSSL or GNUTLS, for example.) Apparently neither OpenSSL nor cURL wants to provide such a Windows binary package, though, so I attempted to build a version of libcurl with SSL support... Sigbjorn's instructions are definitely out of date. (I couldn't use his ZIP package, either.) Using MSYS, though, I was able to compile a version of libcurl with winssl, but then every variation of cabal install command wasn't cooperating. What should I be using instead of the following, neither of which seems to tell cabal where to find libcurl? ``` $ CPPFLAGS=-Ic:/code/curl_install/include cabal install curl --ld-options=-Lc:/code/curl_install/lib $ cabal install curl --extra-lib-dirs=c:/code/curl_install/lib --extra-include-dirs=c:/code/curl_install/include ``` Detail, showing some verbose error messages: https://gist.github.com/4056331 Kevin

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ANN: fixed-vector
by Aleksey Khudyakov 12 Nov '12

12 Nov '12

Hello cafe! I want to announce library for the small vectors of fixed length fixed-vector[1]. Fixed means that vector's length is determined by its type. Generic API can work with both ATD-based vector like complex or Vec written below and array-based ones. > data Vec a = Vec a a a It's based on post by Roman Leschinsiy[2]. Library also provide array-based vectors with memory representation similar to onves from vector package. It's more compact though because there is no need to store lengh and and offset to first element. [1] http://hackage.haskell.org/package/fixed-vector [2] http://unlines.wordpress.com/2010/11/15/generics-for-small-fixed-size-vecto…

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Reminder and Forward: Wednesday 14 November 2012 NYHUG Inaugural Meetup: Ozgun Ataman on Practical Data Processing and Gershom Bazerman on Putting Cloud Haskell to Work
by Jay Sulzberger 12 Nov '12

12 Nov '12

Below is a version of the announcement sent to the haskell-cafe and the haskell mailing lists by Gershom Bazerman on 9 October 2012. oo--JS. <blockquote what="official New York Haskell Users Group announcement" rsvp="Yes, see below." more="http://en.wikipedia.org/wiki/Haskell_%28programming_language%29 [page was last modified on 11 November 2012 at 00:56] http://www.haskell.org/haskellwiki/Haskell http://www.reddit.com/r/haskell http://www.aosabook.org/en/ghc.html http://en.wikipedia.org/wiki/Type_inference [page was last modified on 15 September 2012 at 15:37] http://en.wikipedia.org/wiki/Hindley%E2%80%93Milner [page was last modified on 9 October 2012 at 17:40] http://www.users.waitrose.com/~hindley/ http://www.cs.ru.nl/~henk/ http://www.usingz.com/ http://en.wikipedia.org/wiki/Curry-Howard [page was last modified on 14 September 2012 at 22:01] http://www.paultaylor.eu/stable/prot.pdf ftp://ftp.cs.cmu.edu/usr/rwh/www/home/courses/logic/www/handouts/curry-howa… http://www.students.science.uu.nl/~3448584/TypeSystems.pdf http://www.math.ias.edu/~vladimir/Site3/Univalent_Foundations_files/2011_Go… http://math.andrej.com/2012/11/08/how-to-implement-dependent-type-theory-i/ http://math.andrej.com/2012/11/11/how-to-implement-dependent-type-theory-ii/ http://math.andrej.com/2012/10/03/am-i-a-constructive-mathematician/" exclamation-of-old-lisper-upon-first-seeing-curry-howard-theorem: "But this is clearly wrong! Look I have a function string-length which has type String->Int, but 'String->Int' is not a theorem of any usual intuitionistic propositional logic." insight-of-newbie-coming-to-haskell-from-lisp: "Lisp's now buried background would require, if a student of Lisp were to ask for an outline of this background, a book of perhaps a hundred pages. Haskell, and more generally, all the New Crazy Types programming systems, would require three hundred pages." edits="some adventitious markup and some blank space removed"> Subject: Wednesday 14 November, NY Haskell Inaugural Meetup: Practical Data Processing _and_ Putting Cloud Haskell to Work Date: Fri, 12 Oct 2012 18:05:02 -0400 From: Gershom B <gershomb(a)gmail.com> To: lisp(a)lispnyc.org ====================================================== What: New York Haskell Users Group Meeting When: Wednesday, November 14, 2012 7 PM - 9 PM Where: Pivotal Labs, 841 Broadway, 8th floor (Just south of Union Square) http://maps.google.com/maps?q=841+Broadway,+New+York RSVP: http://www.meetup.com/NY-Haskell/ ====================================================== * 7 PM - Practical Data Processing With Haskell * 8 PM - Putting Cloud Haskell to Work for Distributed Computing -------------------------------------------------------------------------------------- 7 PM - Practical Data Processing With Haskell: Ozgun Ataman will give an introductory talk on Haskell, diving right in with how you can start using Haskell for practical data manipulation tasks today. You'll be introduced to a typical setup for Haskell development and given a demonstration of how a common data format (CSV, JSON, etc.) can be parsed, processed and finally output using Haskell. The talk will include a small actual Haskell program to be modified live and some commentary around using Haskell in practical applications. 8 PM - Putting Cloud Haskell to Work for Distributed Computing: Gershom Bazerman will give an overview of the new distributed-process library that implements Cloud Haskell, providing computation across heterogeneous nodes through a message passing interface. He will discuss what this new tool provides out of the box, and what you'll have to bring to the table. The talk will include some code samples using the new library, as well as some experience about what it's like to use Haskell for distributed computing in the real world. Speaker Biographies: Ozgun Ataman is the founder of Soostone, a management consulting and analytics company built on Haskell. He is the author of many open-source Haskell libraries, and is a contributor to the Snap web framework. Gershom Bazerman is a developer at S&P Capital IQ. He is most well known in the Haskell community as the author of the JMacro library for programmatic generation of JavaScript, and for one well-received April fools joke. -------------------------------------------------------------------------------------- We're kicking off the New York Haskell Users Group with two great talks, one for people just getting started and one for those with some experience already. Both should be accessible and enjoyable no matter how much (or little) you already know. Food and refreshments will be provided, courtesy of the generosity of Pivotal Labs, and after the talks, we're planning to keep the discussion going over food and drink at a nearby establishment. </blockquote> Distributed poC TINC: Jay Sulzberger <secretary(a)lxny.org> Corresponding Secretary LXNY LXNY is New York's Free Computing Organization. http://www.lxny.org

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Hard drive thrashing with modern controllers
by timothyhobbs＠seznam.cz 12 Nov '12

12 Nov '12

Hello, I have a very general question that doesn't exactly relate to Haskell. Do I need to worry about hard drive thrashing with a modern controller? I understand, that such "thrashing" can significantly reduce the lifespan of modern SSD drives. For example, if I do: import Control.Monad foo = do forever $ writeFile "filename.foo" "Hello world!" will that destroy those sectors of my SSD after the rated 3000 write cycles? The reason I ask, is that I have a program here where I would like to save a set of files after every change/operation and I'm wondering if I should check if the files I'm saving have actually changed or if this will be handled by the OS... Thank you Timothy

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Strange behavior with listArray
by Alex Stangl 12 Nov '12

12 Nov '12

I'm stymied trying to figure out why the program below blows up with <<<loop>>> when I use "f 0" for building the array, but if I substitute g or h in place of f, they work fine. Is this a bug or am I overlooking something? I am using GHC 7.4.2. Thanks, Alex P.S. Forgive the seemingly pointless program; I distilled this test from a longer actual program that was exhibiting this behavior. -------- import Data.Array((!),Array,elems,listArray) import Data.List(intercalate) solve = let a :: Array Int Int a = listArray (0, 3) (0 : f 0) f k = if k > 0 then f (a!0) else 0 : f 1 g k = k : a!(k+1) : a!(k+1) : a!(k+2) : a!(k+3) : [] h k = a!k : h (k+1) in (intercalate " " . map show . elems) a main = putStrLn solve

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how to inject another source into conduit
by Alexander V Vershilov 12 Nov '12

12 Nov '12

Hello. I have problems with writing next code (using network-conduit) slightly simplified version: > app ad = appSource ad $$ sink > where > cMap = M.fromList [ ("upload", cmdUpload), ("download", cmdDownload) ] > sink = takeLine >>= \c -> case c of Just run -> run ; Nothing -> return () > cmdUpload = {- ... -} CB.sinkFile path > cmdDownload = do > {- code here -} > CB.sourceFile path $$ appSink ad -- this will not work because of > -- type error And I'm catching "cannot construct the infinite type". I've found an example in [1], but it's not exactly solves my problem, as all the logic is inside conduit, and it will break upload function. [1] http://www.yesodweb.com/blog/2012/06/conduit-0-5 -- Alexander Vershilov

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