- Haskell-Cafe - Haskell.org

ANNOUNCE: fgl-5.5.0.0
by Ivan Lazar Miljenovic 27 Apr '14

27 Apr '14

I'm pleased to announce a new version of the functional graph library: http://hackage.haskell.org/package/fgl-5.5.0.0 The main change in this version: proper Show, Read and Eq instances for both graph implementations. Previously, Data.Graph.Inductive.Tree had a pretty-printed Show output; now both it and PatriciaTree have Show and Read instances via the mkGraph function, and Eq via deriving (I'm not sure how well this will work because as I write this I realise it may not deal with multiple edges that well... I guess I'll be doing an updated version tomorrow after getting some sleep ;p). The previous Show behaviour of Tree is now available as a pretty-printing function for all DynGraph instances. The PatriciaTree implementation is now exported and used by default, because as far as I'm aware it will always perform better. Finally, the Data.Graph.Inductive.Graphviz module has been removed; if you want to visualise your fgl graph, please see my graphviz package on Hackage (cheap plug? moi?). -- Ivan Lazar Miljenovic Ivan.Miljenovic(a)gmail.com http://IvanMiljenovic.wordpress.com

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Packing Haskell values into a C array
by Michael Baker 27 Apr '14

27 Apr '14

I'm working on a game in Haskell and I'm at a point where I have to do some optimization so I'm looking for advice or resources from people who may have already solved my problem. Specifically, I have a grid of 10,000 circles and I need to get them rendered. This involves translating the 10,000 circles into a single C array (of CFloats in my case) so that I can ship that array off to OpenGL for rendering. This is something I can't change, that's just the way OpenGL works. What I can change is the way I create and maintain the array. Currently I'm doing the most naive thing I can, which is to convert the list of circles into a list of floats, and then convert that list into a C array every frame. This is obviously very expensive. I've thought of several things to try including: * Only allocate an array when the number of circles changes. * Convert a circles into a C struct and "poke" them directly into an existing array instead of going through the intermediate form of a list. * Do some manual memory management and index each circle into a preallocated array, only updating the values of the array that correspond to circles which have changed. I'm wondering if there are already common solutions to this sort of problem (packing a lot of Haskell values that might change each frame into an array efficiently). Any resources that are tangential to this sort of thing would also be nice. For instance, how I can use the type system to ensure that the resulting array has the shape I want.

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[ANN] codex - generate tags file from dependencies
by Alois Cochard 27 Apr '14

27 Apr '14

Hi, Just to let you know that I released a tool which allow to generate a tags[1] file for a given cabal project using the sources of all the dependencies of that project. `cabal install codex` You can simply run `codex update` in one of your cabal project directory and you'll get a 'codex.tags' file to feed in your favorite text editors. It store the source code in the hackage local cache, and it store there as well the tags file per module (so the tool just aggregate per project). I hope it will be useful to other hackers, it's a joy for me in vim when using unknown libraries. Note: This tool actually use `ctags` but that could be easily made configurable if someone need it, integrating native haskell tagger is an option too. I personally like using ctags, it's very fast. *[1]Those tags file basically contain references to functions/types definition in source code and allow "jump to definition" like functionality in text editors.* source: http://github.com/aloiscochard/codex hackage: http://hackage.haskell.org/package/codex -- *Alois Cochard* http://twitter.com/aloiscochard

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Building foreign shared libraries with Cabal
by Nikolay Amiantov 26 Apr '14

26 Apr '14

Hello, I want to use cabal to build and install shared library, which will be called from C. I've already found necessary combination of flags and options to successfully build it, but now I have two main issues: 1) The library is installed into "bin". 2) The generated "stub" C headers are not installed at all. How can I resolve this? My current options is as follows: executable libtest.so hs-source-dirs: src main-is: Test.hs default-language: Haskell2010 default-extensions: ForeignFunctionInterface build-depends: base >= 4.7 c-sources: cbits/library_init.c ghc-options: -no-hs-main -shared -dynamic cc-options: -DMODULE=Test -fPIC Thanks for any help and have a nice day, Nikolay.

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Job: Automatic Exploit Generation developer
by David Brumley 26 Apr '14

26 Apr '14

Hi, ForAllSecure is a small startup bent on checking the world's software for exploitable bugs. We have two open positions, posted at http://jobs.forallsecure.com/ 1) Performing program analysis on binary (x86) code. Our current code base is in OCaml. The product automatically finds vulnerabilities, and generate exploits to prove which ones are exploitable. 2) Automatically harden binary (x86) code against vulnerabilities. As a side project, we've ran our tools on 33,000 Debian programs, and found about 11,000 new unique crashing bugs (150 give us a shell). Please consider applying if this sounds exciting. http://jobs.forallsecure.com/ Take care, -David PS. ForAllSecure is a Carnegie Mellon University spinoff. The job is in Pittsburgh, but we will also consider highly qualified remote candidates.

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How to extract current bindings from GHCi ?
by ducis 26 Apr '14

26 Apr '14

Currently I need to manually find the last binding of a value if I want to copy-paste it into an editor. With ':show bindings' I get the result of computation. Say, if I had input 'let a = 1' and 'let b = a+2' I would only get either 'b = _' or 'b = 3' with ':show bindings', while I actually need 'b = a+2'. Are there any externel tools that can help? At 2014-04-26 20:00:04,haskell-cafe-request@haskell.org wrote: >Send Haskell-Cafe mailing list submissions to > haskell-cafe(a)haskell.org > >To subscribe or unsubscribe via the World Wide Web, visit > http://www.haskell.org/mailman/listinfo/haskell-cafe >or, via email, send a message with subject or body 'help' to > haskell-cafe-request(a)haskell.org > >You can reach the person managing the list at > haskell-cafe-owner(a)haskell.org > >When replying, please edit your Subject line so it is more specific >than "Re: Contents of Haskell-Cafe digest..." > > >Today's Topics: > > 1. Re: Unicode Haskell source -- Yippie! (Chris Warburton) > 2. Re: Unicode Haskell source -- Yippie! (Rustom Mody) > 3. Haddock CSS (Sylvain Henry) > 4. Re: [ANN] codex - generate tags file from dependencies > (Luke Taylor) > 5. Re: Haddock CSS (satvik chauhan) > 6. Re: Haddock CSS (Sylvain Henry) > 7. Re: [ANN] codex - generate tags file from dependencies > (Alois Cochard) > 8. Re: [ANN] codex - generate tags file from dependencies > (Alois Cochard) > 9. ANN: Cryptol, a DSL for cryptography (Iavor Diatchki) > > >---------------------------------------------------------------------- > >Message: 1 >Date: Fri, 25 Apr 2014 14:02:38 +0100 >From: Chris Warburton <chriswarbo(a)googlemail.com> >To: Rustom Mody <rustompmody(a)gmail.com> >Cc: Haskell Cafe <haskell-cafe(a)haskell.org> >Subject: Re: [Haskell-cafe] Unicode Haskell source -- Yippie! >Message-ID: <86wqedmuj5.fsf(a)gmail.com> >Content-Type: text/plain > >Rustom Mody <rustompmody(a)gmail.com> writes: > >> As for APL, it failed for various reasons eg >> - mixing up assembly language (straight line code with gotos) with >> functional idioms >> - the character set was a major hurdle in the 60s. Thats not an issue today >> when most OSes/editors are unicode compliant > >I know it's bikeshedding, but I think Agda and Idris are more relevant >to Haskell than APL, since their semantics are closer (and they're both >implemented in Haskell). > >Agda makes extensive (ab)use of Unicode identifiers, >eg. https://github.com/agda/agda-stdlib/blob/master/src/Algebra.agda > >Idris specifically avoids Unicode identifiers, for reasons outlined at >https://github.com/idris-lang/Idris-dev/wiki/Unofficial-FAQ > >Personally I prefer working in Idris to Agda, since the Unicode puts me >off. I usually resort to copy/pasting symbols, which is tedious compared >to typing names. > >Cheers, >Chris > > >------------------------------ > >Message: 2 >Date: Fri, 25 Apr 2014 19:00:34 +0530 >From: Rustom Mody <rustompmody(a)gmail.com> >To: Chris Warburton <chriswarbo(a)googlemail.com> >Cc: Haskell Cafe <haskell-cafe(a)haskell.org> >Subject: Re: [Haskell-cafe] Unicode Haskell source -- Yippie! >Message-ID: > <CAJ+TeocfycOCW7BOymd+=O5qCgeOx_iX2Wgz6wB5k_vGapKEuQ(a)mail.gmail.com> >Content-Type: text/plain; charset="utf-8" > >On Fri, Apr 25, 2014 at 6:32 PM, Chris Warburton ><chriswarbo(a)googlemail.com>wrote: > >> Rustom Mody <rustompmody(a)gmail.com> writes: >> >> > As for APL, it failed for various reasons eg >> > - mixing up assembly language (straight line code with gotos) with >> > functional idioms >> > - the character set was a major hurdle in the 60s. Thats not an issue >> today >> > when most OSes/editors are unicode compliant >> >> I know it's bikeshedding, but I think Agda and Idris are more relevant >> to Haskell than APL, since their semantics are closer (and they're both >> implemented in Haskell). >> >> Agda makes extensive (ab)use of Unicode identifiers, >> eg. https://github.com/agda/agda-stdlib/blob/master/src/Algebra.agda >> >> Idris specifically avoids Unicode identifiers, for reasons outlined at >> https://github.com/idris-lang/Idris-dev/wiki/Unofficial-FAQ >> >> Personally I prefer working in Idris to Agda, since the Unicode puts me >> off. I usually resort to copy/pasting symbols, which is tedious compared >> to typing names. >> >> Cheers, >> Chris >> > >Thanks Chris for that evaluation. Not bike-shedding as far as I can see. > >Yes input-ing things by some GUI-picker or copy-pasting etc would quickly >become a major pain. >I believe that there are roughly these 5 levels to this with >per-char cost decreasing and fixed cost increasing as we go down > >1. GUI-picker (IBUS etc) copy-pasting from the web etc -- ok for arm-chair >discussions; ridiculous for serious development >2. Editor based input methods eg tex input-method in emacs >3. Window-system (X/MS etc) input methods >4. OS-based input methods >5. Special purpose hardware-keyboards > >I believe 3 makes for a particularly good fixed/variable cost balance point > >eg in X-windows if you run this command >$ setxkbmap -layout "us,gr" -option "grp:switch" >then typing >abcdefg >with right-alt depressed, gives: >??????? > >For those who prefer a more moded approach (vi-users?) here is >$ setxkbmap -option "grp:switch,grp:alt_shift_toggle,grp_led:scroll" >-layout "us,gr" > >This makes the Shift-Alt chord switch in and out (ie toggle) greek keyboard >with the scroll-lock light as indicator > >All this is clearly just an analogy; what we need is not a greek keyboard >but a keyboard mapping analogous to gr(eek). Try s/gr/apl in the commands >above for apl which, while distant from haskell gives a taste for what a >*programmer* can use/make. > >regards >Rusi >

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ANN: Cryptol, a DSL for cryptography
by Iavor Diatchki 26 Apr '14

26 Apr '14

Hello, Galois is happy to announce the first open source release of Cryptol! Please visit Cryptol's website for documentation, source code, and information on how to contribute: http://www.cryptol.net/ Cryptol is a domain-specific language for specifying cryptographic algorithms. A Cryptol implementation of an algorithm resembles its mathematical specification more closely than an implementation in a general purpose language. Furthermore, Cryptol shares lots of similarities with Haskell so, hopefully, Haskell programmers should be able to start writing Cryptol programs fairly quickly. Last, but not least, we are always interested in contributors! So, if you think of a cool new feature, or discover an annoying bug, please don't be afraid to have a look at the source code. At present, we think that the easiest way to manage contributions is by using github's fork model, so just sand us a pull request. Also, if you have questions about the source code or the Cryptol language, please feel free to drop me an e-mail or a message on git-hub (I am user "yav"). Happy hacking, -Iavor and the Cryptol team

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Haddock CSS
by Sylvain Henry 25 Apr '14

25 Apr '14

Hi, I have quickly hacked a new CSS for haddock based on ocean.css (see attached file). It has a fixed maximal width and is a little bit lighter. To try it with cabal, use: > cabal haddock --css=ocean2.css [--hyperlink-source] Feel free to improve it, I am not that good at web design. -Sylvain

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Munich Haskell Meeting
by Heinrich Hördegen 25 Apr '14

25 Apr '14

Dear all, next week, our monthly Munich Haskell Meeting is scheduled for the 29th of April, 19h30 Cafe Puck. If you plan to join, please go to http://www.haskell-munich.de/dates and hit the button. Everybody is welcome! Heinrich

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Thoughts on Hakyll vs. Octopress for an experienced Haskeller but HTML newbie
by Joey Eremondi 25 Apr '14

25 Apr '14

Disclaimer: Cross-posted at http://www.reddit.com/r/haskell/comments/23xgzf/thoughts_on_hakyll_vs_octop… I'm starting a personal website/blog, just the typical thing you see a lot of programmers keeping. I'm looking at using Github Pages, but as I don't want to hand-code everything, I'll be using a static site generator. I'm choosing between Hakyll and Octopress, but I wanted to get some opinions before I put in the effort of learning and installing one. I'll start by saying that I'm comfortable with Monads, EDSLs, and Haskell in general. Conversely, I have next to no HTML/CSS skill. What I'm really wondering is, how much hand-HTML does Hakyll require you to do? In particular: 1. Does Hakyll have any support for visual "themes"? If not, are there libraries/examples of visual layouts I could choose from? 2. Does Hakyll integrate well with Github pages? 3. How hard is it to get things like a Facebook like button, twitter sidebar, comments, etc. working in Hakyll? Is there anything equivalent to Octopress's plugins <http://octopress.org/docs/blogging/plugins/>? 4. Octopress advertises itself as dealing well with code snippets. Does Hakyll deal well with code within pages? I realize that many of these things will not be built into Hakyll, so cases where it's not built in but there are lots of easy examples to take from are welcome. Reccomendations of one over the other are welcome, but I'm more looking for feedback and knowledge from people who have used Hakyll (and Octopress, though that's more tangential to this subreddit). Thanks! EDIT: Generalized to "comments" instead of just "disqus comments"

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Monad.Reader #24 call for copy
by Edward Z. Yang 25 Apr '14

25 Apr '14

Call for Copy: The Monad.Reader - Issue 24 -------------------------------------------- Whether you're an established academic or have only just started learning Haskell, if you have something to say, please consider writing an article for The Monad.Reader! The submission deadline for Issue 24 will be: **Saturday, July 5, 2014** The Monad.Reader ~~~~~~~~~~~~~~~~ The Monad.Reader is a electronic magazine about all things Haskell. It is less formal than journal, but somehow more enduring than a wiki- page. There have been a wide variety of articles: exciting code fragments, intriguing puzzles, book reviews, tutorials, and even half-baked research ideas. Submission Details ~~~~~~~~~~~~~~~~~~ NEW this issue: for my reviewing sanity, I am setting a soft page limit of fifteen pages. If you would like to write something longer, get in touch, but remember: brevity is the soul of wit. In any case, contact me if you intend to submit something -- the sooner you let me know what you're up to, the better. Please submit articles for the next issue to me by e-mail. Articles should be written according to the guidelines available from http://themonadreader.wordpress.com/contributing/ Please submit your article in PDF, together with any source files you used. The sources will be released together with the magazine under a BSD license. If you would like to submit an article, but have trouble with LaTeX please let me know and we'll work something out.

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Re: [Haskell-cafe] How to get access to Haddock HTML for newly cabal installed package?
by David Banas 24 Apr '14

24 Apr '14

Nope. I’ve had some great suggestions, but am still struggling to figure this one out. And, yes, I’m running on a MacBook using OSX Mavericks. Thanks, -db > Date: Thu, 24 Apr 2014 00:19:45 +0200 > From: Daniel D?az Casanueva <dhelta.diaz(a)gmail.com> > To: Haskell-Cafe <haskell-cafe(a)haskell.org> > Subject: Re: [Haskell-cafe] How to get access to Haddock HTML for > newly cabal installed package? > Message-ID: > <CAJFXAQjAHCfgD_vAcsGSxmzV1HmSpV_BOMyfVJZO4Ya5vJ0s+Q(a)mail.gmail.com> > Content-Type: text/plain; charset="utf-8" > > I clicked "Reply All", hoping to reach the list, and I did. And yes, you > are right about he's probably using OSX. However, I do not have access to > any OSX to look for the right path. Did you solve the problem, David? > > Best regards, > Daniel D?az.

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How to get access to Haddock HTML for newly cabal installed package?
by David Banas 24 Apr '14

24 Apr '14

Does anyone know how I get the link to the Haddock generated HTML for a newly cabal installed package to show up in: file:///Users/dbanas/Library/Haskell/doc/index.html ? I’ve got documentation=True set, in ~/.cabal/config. Thanks, -db

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Diony Rosa
by Diony Rosa 24 Apr '14

24 Apr '14

http://kagankoc.av.tr/wpjbk/fowmsjjzqavbptwpdmgezeghq.wiodhkueoruzhok

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ANN: Monad.Reader Issue 23
by Edward Z. Yang 24 Apr '14

24 Apr '14

I am pleased to announce that Issue 23 of the Monad Reader is now available. http://themonadreader.files.wordpress.com/2014/04/issue23.pdf http://themonadreader.wordpress.com/2014/04/23/issue-23/ Issue 23 consists of the following five articles: * FizzBuzz in Haskell by Embedding a Domain-Specific Language by Maciej Pírog http://themonadreader.files.wordpress.com/2014/04/fizzbuzz.pdf * Supercompilation: Ideas and Methods (+appendix) by Ilya Klyuchnikov and Dimitur Krustev http://themonadreader.files.wordpress.com/2014/04/super-final.pdf * A Haskell sound specification DSL: Ludic support and deep immersion in Nordic technology-supported LARP by Henrik Bäärnhielm, Daniel Sundström and Mikael Vejdemo-Johansson http://themonadreader.files.wordpress.com/2014/04/celestria_main.pdf * MFlow, a continuation-based web framework without continuations by Alberto Gomez Corona http://themonadreader.files.wordpress.com/2014/04/mflow.pdf * Practical Type System Benefits by Neil Brown http://themonadreader.files.wordpress.com/2014/04/nccb.pdf This time around, I have individual article files for each (and the supercompilation article has an extra appendix not included in the full issue PDF). Feel free to browse the source files. You can check out the entire repository using Git: git clone https://github.com/ezyang/tmr-issue23.git If you’d like to write something for Issue 24, please get in touch! Cheers, Edward

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Haskell Weekly News: Issue 292
by Daniel Santa Cruz 24 Apr '14

24 Apr '14

Welcome to issue 292 of the HWN, an issue covering crowd-sourced bits of information about Haskell from around the web. This issue covers from April 13 to 19, 2014 Edward Kemett wrote in to remind us of the Call For Proposals for CUFP 2014, which is going to be held in Gothenburg, Sweden between September 4-6. See more details here [1] http://goo.gl/X62cBO Quotes of the Week * pdxleif: see s.p. jones & h.p. lovecraft's paper on the subject: "generic programming with lenses, barbed wire, and the fibres of sanity" Top Reddit Stories * A time traveling debugger for Elm - pause, rewind, replay, and change history Domain: debug.elm-lang.org, Score: 87, Comments: 6 On Reddit: [2] http://goo.gl/GJahIU Original: [3] http://goo.gl/V2kcCP * OC: Haskell programming font with ligatures Domain: github.com, Score: 78, Comments: 59 On Reddit: [4] http://goo.gl/ZaFRJ4 Original: [5] http://goo.gl/m17EUj * Porting GHC: A Tale of Two Architectures Domain: chiark.greenend.org.uk, Score: 77, Comments: 12 On Reddit: [6] http://goo.gl/MJ196R Original: [7] http://goo.gl/PVVHZo * Try Idris Domain: tryidris.org, Score: 70, Comments: 22 On Reddit: [8] http://goo.gl/7hn84J Original: [9] http://goo.gl/6iPW8S * Why are examples completely absent from hackage? Am I missing something? Domain: self.haskell, Score: 67, Comments: 68 On Reddit: [10] http://goo.gl/QmZjZs Original: [11] http://goo.gl/QmZjZs * Implementing Python in Haskell - Melbourne Haskell Users Group, April 24 Domain: meetup.com, Score: 53, Comments: 6 On Reddit: [12] http://goo.gl/tYRtG9 Original: [13] http://goo.gl/oClHGb * Blog post - Haskell Gets Static Typing Right - Andres Löh Domain: skillsmatterblog.wordpress.com, Score: 51, Comments: 25 On Reddit: [14] http://goo.gl/5AQO4h Original: [15] http://goo.gl/WddMUA * Haskell for all: Scalable program architectures Domain: haskellforall.com, Score: 45, Comments: 19 On Reddit: [16] http://goo.gl/JDYSQl Original: [17] http://goo.gl/MUrRRg * GHC 7.8′s -staticlib flag makes compiling Mac libs easy Domain: maxs.io, Score: 42, Comments: 5 On Reddit: [18] http://goo.gl/SVICOm Original: [19] http://goo.gl/FwVdOv * Autocomplete command line options with GHC 7.8 Domain: self.haskell, Score: 39, Comments: 10 On Reddit: [20] http://goo.gl/bXNI20 Original: [21] http://goo.gl/bXNI20 * How to learn Haskell Domain: acm3.wustl.edu, Score: 39, Comments: 16 On Reddit: [22] http://goo.gl/oaQsAL Original: [23] http://goo.gl/TLbCEL * Calling Python from Haskell Domain: lunaryorn.com, Score: 36, Comments: 14 On Reddit: [24] http://goo.gl/9n8O4m Original: [25] http://goo.gl/j8YqgK * "latest API" link in Hackage Domain: self.haskell, Score: 30, Comments: 15 On Reddit: [26] http://goo.gl/RJnphF Original: [27] http://goo.gl/RJnphF * Functional Pearl: F for Functor Domain: cs.ox.ac.uk, Score: 27, Comments: 14 On Reddit: [28] http://goo.gl/i7TPuf Original: [29] http://goo.gl/7c33Xn Top StackOverflow Questions * Idris eager evaluation votes: 14, answers: 1 Read on SO: [30] http://goo.gl/LDpNtI * Why use such a peculiar function type in monads? votes: 11, answers: 4 Read on SO: [31] http://goo.gl/XX8KSX * How does mapA work with a Stream Function Arrow in Haskell? votes: 8, answers: 1 Read on SO: [32] http://goo.gl/vECKBa * Lenses and Monomorphism Restriction votes: 8, answers: 2 Read on SO: [33] http://goo.gl/hG44KA * Is this a GHC bug? votes: 7, answers: 1 Read on SO: [34] http://goo.gl/sqByI2 * Why do some of threepenny-gui FRP combinators operate on a MonadIO monad instead of being pure? votes: 6, answers: 2 Read on SO: [35] http://goo.gl/ySVqya * S combinator in Haskell votes: 6, answers: 2 Read on SO: [36] http://goo.gl/vnb64N * Graphing criterion benchmarks taking different orders of magnitude of time votes: 6, answers: 1 Read on SO: [37] http://goo.gl/J3jgWf * Fun with fixity votes: 6, answers: 1 Read on SO: [38] http://goo.gl/molyi9 Until next time, [39]+Daniel Santa Cruz References 1. http://cufp.org/2014cfp 2. http://debug.elm-lang.org/ 3. http://www.reddit.com/r/haskell/comments/233ff9/a_time_traveling_debugger_f… 4. https://github.com/i-tu/source-code-pro-L/ 5. http://www.reddit.com/r/haskell/comments/23g9dv/oc_haskell_programming_font… 6. http://www.chiark.greenend.org.uk/ucgi/~cjwatson/blosxom/2014-04-15-porting… 7. http://www.reddit.com/r/haskell/comments/232erb/porting_ghc_a_tale_of_two_a… 8. http://www.tryidris.org/console 9. http://www.reddit.com/r/haskell/comments/22yww7/try_idris/ 10. http://www.reddit.com/r/haskell/comments/23dxli/why_are_examples_completely… 11. http://www.reddit.com/r/haskell/comments/23dxli/why_are_examples_completely… 12. http://www.meetup.com/Melbourne-Haskell-Users-Group/events/174401572/ 13. http://www.reddit.com/r/haskell/comments/238akv/implementing_python_in_hask… 14. http://skillsmatterblog.wordpress.com/2014/04/15/guest-post-haskell-gets-st… 15. http://www.reddit.com/r/haskell/comments/233njg/blog_post_haskell_gets_stat… 16. http://www.haskellforall.com/2014/04/scalable-program-architectures.html 17. http://www.reddit.com/r/haskell/comments/2300zb/haskell_for_all_scalable_pr… 18. http://maxs.io/ghc-78-static-lib-flag/ 19. http://www.reddit.com/r/haskell/comments/23fyok/ghc_78s_staticlib_flag_make… 20. http://www.reddit.com/r/haskell/comments/236qkb/autocomplete_command_line_o… 21. http://www.reddit.com/r/haskell/comments/236qkb/autocomplete_command_line_o… 22. http://acm3.wustl.edu/functional/haskell.php 23. http://www.reddit.com/r/haskell/comments/239f2m/how_to_learn_haskell/ 24. http://www.lunaryorn.com/2014/04/15/calling-python-from-haskell.html 25. http://www.reddit.com/r/haskell/comments/2330aj/calling_python_from_haskell/ 26. http://www.reddit.com/r/haskell/comments/22xz96/latest_api_link_in_hackage/ 27. http://www.reddit.com/r/haskell/comments/22xz96/latest_api_link_in_hackage/ 28. http://www.cs.ox.ac.uk/people/daniel.james/functor/functor.pdf 29. http://www.reddit.com/r/haskell/comments/2327e7/functional_pearl_f_for_func… 30. http://stackoverflow.com/questions/23149532/idris-eager-evaluation 31. http://stackoverflow.com/questions/23051800/why-use-such-a-peculiar-functio… 32. http://stackoverflow.com/questions/23048100/how-does-mapa-work-with-a-strea… 33. http://stackoverflow.com/questions/23066099/lenses-and-monomorphism-restric… 34. http://stackoverflow.com/questions/23091080/is-this-a-ghc-bug 35. http://stackoverflow.com/questions/23044464/why-do-some-of-threepenny-gui-f… 36. http://stackoverflow.com/questions/23095224/s-combinator-in-haskell 37. http://stackoverflow.com/questions/23129649/graphing-criterion-benchmarks-t… 38. http://stackoverflow.com/questions/23142075/fun-with-fixity 39. https://plus.google.com/105107667630152149014/about

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Syntax proposal for "reverse apply"/"pipeline apply" (flip ($))
by Alexey Muranov 24 Apr '14

24 Apr '14

Hello, i am completely new to Haskell, but i am somewhat fascinated by lambda-calculus and programming. For whatever it is worth, i would like to propose for discussion a syntax for "(flip ($))" operation in Haskell. I think that a good syntax would be "|^", for example: square x = x * x y = 3 |^ square -- y == 9 Explanation: * i would have suggested just ^, but it would conflict with number exponentiation, * it is rather common in mathematics to write function application in exponential notation: x ^ f instead of f(x), especially if f is an automorphism of some structure, * (flip ($)) is exactly the exponentiation of Church numerals, * in "The calculi of lambda-conversion", Alonzo Church uses the "shorthand" notation "[N^M]" for "(MN)", where M and N are lambda-terms. * I am probably not the only person missing the ability to apply functions from the right: http://stackoverflow.com/questions/1457140/haskell-composition-vs-fs-pipe-f… Well, other notations i've thought of are "\^" and "~$". Alexey.

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Info on dependencies among libs distributed with ghc?
by Magnus Therning 23 Apr '14

23 Apr '14

I'm working on the packaging of Ghc for Arch Linux and the packaging of Ghc 7.8 was in place about a week ago. It was delivered with `Cabal` 1.18, and already now there's a 1.20 available, which is required by the latest version of `cabal-install` :( Ghc 7.8 comes with quite a few other basic libraries. Are there any dependencies between these libraries besides the obvious one on `base`? In other words, can I update Cabal without running into the diamond-dependency problem? /M -- Magnus Therning OpenPGP: 0xAB4DFBA4 email: magnus(a)therning.org jabber: magnus(a)therning.org twitter: magthe http://therning.org/magnus Most software today is very much like an Egyptian pyramid with millions of bricks piled on top of each other, with no structural integrity, but just done by brute force and thousands of slaves. -- Alan Kay

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Re: [Haskell-cafe] imports at bottom
by Doug McIlroy 23 Apr '14

23 Apr '14

> A language pragma could be used to select between top imports or bottom > imports (can't use both). > > What do you think? Warning. This one touches a personal hot button, mostly off topic. To my mind, language pragmas are blemishes. Reasonable, assuredly, to announce that code uses some nonstandard feature of a compiler, but generally unreasonable as an integral part of the language definition. As originally promulgated for ALGOL, pragmas had no effect on the meaning of a program or its conformance to the standard, though they could, for example, affect the efficiency of object code. Language pragmas stray far from this intent. As unstable features, often incompletely described (just what does FlexibleInstances permit, anyway?), language pragmas might well be banned from the Haskell Platform. Doug McIlroy

1 0

Contract opportunity
by Ian Ross 23 Apr '14

23 Apr '14

Dear all, This is kind of weird, but it might be of interest to someone and I think it's within the remit of this list, so here goes. Sorry to everyone who's not interested! I'm looking for someone to take over a contract I've been working on -- I've been offered something better and I won't have the time to carry on with this thing. I can't say too much about the details, but it's mostly GIS and geoprocessing work for a smallish business consulting firm, probably expanding to some statistical modelling soon. I've been using PostGIS with postgresql-simple to do some quite complicated geoprocessing of OpenStreetMap data for them: much of the Haskell content is really only using Haskell as a fancy scripting language to run lots of SQL, but there are a couple of more interesting bits. Anyone who was going to take this over would need to be a reasonably proficient Haskeller, know SQL well (including having some idea about query optimisation), have some familiarity with GIS work (data formats, something like QGIS or ArcGIS, ideally PostGIS and/or spatial SQL) and be persistent enough to deal with the places where the OpenStreetMap data isn't all you might hope. The client has a large number of sites in different cities that they're interested in, which means that everything has to be automated as much as possible, and that often means iterating again and again to discover geometrical or metadata problems that you need to work around. It can be quite frustrating. What's there now is pretty solid, I think, but it's quite fragile to changes in the OSM data. The rate of pay is good, there's enough work to occupy someone full-time, and the client is OK. There are the usual on-again-off-again rushes associated with this sort of business consulting. The timescale for me moving on is quite short: 2-3 weeks. I'll be organising notes and things for any potential handover, and there's another Haskell person at the client, so you would have someone to talk things over with. If you're interested, either get in touch with me if you have questions, or directly with Chad Scherrer (the Haskeller at the client: cscherrer(a)melinae.com) Cheers, Ian. -- Ian Ross Tel: +43(0)6804451378 ian(a)skybluetrades.net www.skybluetrades.net

1 0

Job offer at Create-Net, Italy
by Corentin Dupont 22 Apr '14

22 Apr '14

Hi guys, I'm surprised I didn't got any reply from the community to this job offer, that I posted some time ago: http://www.create-net.org/work-with-us/postdoctoral-researcher-cloud-comput… While it's not 100% guarantee to work in Haskell, the position is still very interesting with technologies such as Constraint Programming (I'm currently exploring SMT with the SBV library), Cloud computing and energy efficiency. Ciao, Corentin

1 0

Correctly setting up emacs + ghc-mod
by Arnaud Bailly 22 Apr '14

22 Apr '14

Hello, I am struggling to get my emacs settings right for doing significant Haskell development, eg. something more involved than a bunch of source files in a single directory. The issue I am running in currently is that when trying to load files in the interpreter, most source paths are missing which means loading inevitably fails. This is especially annoying with tests: To get things working correctly I need to explicitly add in the console > :set -iwhere/my/src/are Is there any configuration I should be aware of in my cabal files or .emacs file that would correctly set the source roots? Am I missing something? Here is my .emacs configuration. Thanks for any help. ;; haskell coding (require 'auto-complete) (require 'haskell-mode) (require 'haskell-cabal) (autoload 'ghc-init "ghc" nil t) (add-hook 'haskell-mode-hook (lambda () (ghc-init))) (eval-after-load "haskell-mode" '(progn (setq haskell-stylish-on-save t) (setq haskell-process-args-cabal-repl '("--ghc-option=-ferror-spans" "--with-ghc=ghci-ng")) (define-key haskell-mode-map (kbd "C-,") 'haskell-move-nested-left) (define-key haskell-mode-map (kbd "C-.") 'haskell-move-nested-right) (define-key haskell-mode-map (kbd "C-c v c") 'haskell-cabal-visit-file) (define-key haskell-mode-map (kbd "C-c C-c") 'haskell-compile) (define-key haskell-mode-map (kbd "C-x C-d") nil) (setq haskell-font-lock-symbols t) ;; Do this to get a variable in scope (auto-complete-mode) ;; from http://pastebin.com/tJyyEBAS (ac-define-source ghc-mod '((depends ghc) (candidates . (ghc-select-completion-symbol)) (symbol . "s") (cache))) (defun my-ac-haskell-mode () (setq ac-sources '(ac-source-words-in-same-mode-buffers ac-source-dictionary ac-source-ghc-mod))) (add-hook 'haskell-mode-hook 'my-ac-haskell-mode) (defun my-haskell-ac-init () (when (member (file-name-extension buffer-file-name) '("hs" "lhs")) (auto-complete-mode t) (setq ac-sources '(ac-source-words-in-same-mode-buffers ac-source-dictionary ac-source-ghc-mod)))) (add-hook 'find-file-hook 'my-haskell-ac-init))) (add-hook 'haskell-mode-hook 'turn-on-haskell-decl-scan) (add-hook 'haskell-mode-hook 'turn-on-haskell-indentation) (eval-after-load "which-func" '(add-to-list 'which-func-modes 'haskell-mode)) (eval-after-load "haskell-cabal" '(define-key haskell-cabal-mode-map (kbd "C-c C-c") 'haskell-compile))

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Re: [Haskell-cafe] "add ifM and whenM to Control.Monad" and other discussions like that
by Yuri de Wit 22 Apr '14

22 Apr '14

I haven't been around for long in the Haskell community, but I have seen a few of these discussions taking long email rounds in different mailing lists. I don't have a strong opinion at this point to add my vote here or there one way or the other, and I do appreciate the effort made by everyone to find a sort of consensus, as hard as that can be sometimes. However, the question I keep asking myself is why can't the compiler disambiguate between two definitions with the same name based on the actual argument types? This would allow packages to choose their own names for functions without such global-naming discussions and without much pain when using them. e.g.: > import PackageA (when) > import PackageB (when) > when (Just True) doSomething versus: > when True 1 Is there a theoretical or practical issue that makes this an undesirable feature in Haskell?

2 1

Does this typeclass have a name?
by Bardur Arantsson 22 Apr '14

22 Apr '14

Hi all, I was wondering if anyone out there knows if this type class has a name? class Foo a e where foo :: e -> a -> a bar :: a (I also have a fundep a -> e, but that's not essential.) Essentially the usage is: You have a sequence of "events" e_i and a starting value "bar" and can use the "foo" function to apply all events to that starting value foo e_n $ foo e_{n-1} $ ... $ foo e_0 $ bar and thus get the final value of the a induced by the events e_i. (I've included the "bar" starting value in the type class, but I suppose it could be supplied by a Default instance.) Regards,

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Re: [Haskell-cafe] conduit zips
by Ben Foppa 21 Apr '14

21 Apr '14

Don't know how I missed those. Thanks! On Mon, Apr 21, 2014 at 3:04 PM, Michael Snoyman <michael(a)snoyman.com>wrote: > Instead of functions, they're now newtype wrappers: ZipSource, ZipSink, > and ZipConduit (that last one never existed as a function). Some > information on each of these: > > * http://www.yesodweb.com/blog/2013/09/zipsinks-conduit-extra > * http://www.yesodweb.com/blog/2014/02/conduit-zip-source > * > http://stackoverflow.com/questions/21671688/single-stepping-a-conduit/21684… > > > On Mon, Apr 21, 2014 at 3:52 AM, Ben Foppa <benjamin.foppa(a)gmail.com>wrote: > >> Since conduit-1.1.*, the package hasn't contained conduit zipping >> functions anymore. They don't appear to have been moved to conduit-extra, >> either. Did they get lost in the ether, or are they in a separate package? >> >> _______________________________________________ >> Haskell-Cafe mailing list >> Haskell-Cafe(a)haskell.org >> http://www.haskell.org/mailman/listinfo/haskell-cafe >> >> >

1 0

ANN: v0.0.8 of treeviz package released.
by David Banas 21 Apr '14

21 Apr '14

- Split code into multiple files. - Completed Haddoc documentation. - Changed decimation style flag from Boolean to custom type, DecimationStyle, w/ constructors: DIT & DIF, as per Mark L.’s suggestion. - Introduced type alias: type Radix = Int, for readability. cabal install treeviz http://www.haskell.org/haskellwiki/Treeviz Cheers, -db

1 0

GHC-7.8.2 & Win
by Cédric Chantepie 21 Apr '14

21 Apr '14

Hi, Try to setup GHC 7.8.2 & cabal 1.8 on Windows (7/64bits), using binary distributions from haskell.org I get error when I try to install glib package using cabal : cabal: Missing dependency on a foreign library: * Missing (or bad) header file: primitive-memops.h This problem can usually be solved by installing the system package that provides this library (you may need the "-dev" version). If the library is already installed but in a non-standard location then you can use the flags --extra-include-dirs= and --extra-lib-dirs= to specify where it is. If the header file does exist, it may contain errors that are caught by the C compiler at the preprocessing stage. In this case you can re-run configure with the verbosity flag -v3 to see the error messages. Failed to install primitive-0.5.2.1 cabal: Error: some packages failed to install: Command cabal install primitive raise the same error. I have tried either within cygwin or from plain cmd. Thanks for any hint, best.

2 1

conduit zips
by Ben Foppa 21 Apr '14

21 Apr '14

Since conduit-1.1.*, the package hasn't contained conduit zipping functions anymore. They don't appear to have been moved to conduit-extra, either. Did they get lost in the ether, or are they in a separate package?

1 0

A list library without fixpoints and recursive types.
by flicky frans 21 Apr '14

21 Apr '14

Hello. I read some Oleg Kiselyov's papers and tried to write more or less efficient list library with lists represented as their right fold, as mentioned here http://okmij.org/ftp/Haskell/zip-folds.lhs : It would be interesting to see, constructively, how to build the full-fledged (FR)-list library and avoid general recursion. Let the FR-list be the only driver of iterations. Here is the code: http://ideone.com/NKNeWy I don't post it to hackage, since I'm not sure, these lists are really efficient. There are two main ideas: 1) List is represented as an accumulating right fold, and an accumulator passes from left to right. 2) For efficiency purposes elements skipping is incorporated into the cons (($:) in the code) function. So there is only one isSkipped test (d == 0 in the code) for every element, no matter, how many times drop (or tail or dropWhile) was applied. So there are no redundant (<= 0) checks, as described in the zip-folds paper: The function sdrop shows the major deficiency: we're stuck with the (<=0) test for the rest of the stream. In this case, some delimited continuation operators like `control' can help, in limited circumstances. Here are the pluses: 1) No fixpoints and recursive types. 2) These lists are totally isomorphic to ordinary haskell's, even in a strict monad. 3) No redundant (<= 0) checks. There are some not very big problems with this encoding: 1) Code becomes more complicated than with the ordinary right fold. 2) In fscanl and fsndMapAccumL functions skipped elements are traversed twice, because you need to traverse an accumulator through skipped elements too. And the same holds for the fdropWhile function with additional skipping overhead. 3) Since an accumulator passes from left to right, it's not possible to efficiently fuse fscanr and fmapAccumR functions, so they are defined in the terms of ($:) and ffoldr. And one big problem: zipWith and all other functions, that require parallel lists processing, are quadratic. And the same holds for the ftails function and all other functions, that deconstruct a list by repeatedly applying (fhead . ftail) or collect lists, obtained by repeteadly applied ftail function. However I have never seen any other representation, expressible in pure System F with higher-rank types, which allows such deconstruction in a linear time. If someone knows, give me a link, please. Any suggestions are welcome.

1 0

Re: [Haskell-cafe] Syntax proposal for "reverse apply"/"pipeline apply" (flip ($))
by Doug McIlroy 20 Apr '14

20 Apr '14

> '$$' should be strongly considered That breaks time-honored practice in hugs and ghci. Doug McIlroy

3 2

Announcing cabal 1.20
by Johan Tibell 20 Apr '14

20 Apr '14

Hi all, On behalf of all the cabal contributors, I'm proud to announce cabal 1.20. With 404 commits since the 1.18 release, this is a feature packed release. Here's a short summary of the perhaps most notable changes: * Dependency freezing * Parallel cabal build * Flag to temporary ignore upper bounds * Unnecessary re-linking avoidance * Streaming cabal test output * New cabal exec command * Haddock configuration options I did a longer write-up about the new features on my blog: http://blog.johantibell.com/2014/04/announcing-cabal-120.html ## Contributors Here are the contributors for this release, ordered by number of commits: * Mikhail Glushenkov * Johan Tibell * Duncan Coutts * Thomas Tuegel * Ian D. Bollinger * Ben Armston * Niklas Hambüchen * Daniel Trstenjak * Tuncer Ayaz * Herbert Valerio Riedel * Tillmann Rendel * Liyang HU * Dominic Steinitz * Brent Yorgey * Ricky Elrod * Geoff Nixon * Florian Hartwig * Bob Ippolito * Björn Peemöller * Wojciech Danilo * Sergei Trofimovich * Ryan Trinkle * Ryan Newton * Roman Cheplyaka * Peter Selinger * Niklas Haas * Nikita Karetnikov * Nick Smallbone * Mike Craig * Markus Pfeiffer * Luke Iannini * Luite Stegeman * John Lato * Jens Petersen * Jason Dagit * Gabor Pali * Daniel Velkov * Ben Millwood Apologies if someone was left out. Once in a while we have to make commits on behalf of an author. Those authors are not captured above. Enjoy, Johan

1 0

Minimal Haskell Platform & Syntax proposal for "reverse apply"/"pipeline apply" (flip ($))
by Mike Meyer 19 Apr '14

19 Apr '14

On Fri, Apr 18, 2014 at 5:31 AM, Johan Tibell <johan.tibell(a)gmail.com>wrote: > We use this "don't reopen issues unless circumstances have changed" policy > for HP package proposals*. I think it's a good policy, as it saves valuable > community energy to discuss new things. If things have truly changed, we > can of course have the discussion again. > Where can I find that information? I went looking through the HP pages on Haskell.org, and couldn't turn up anything on contributions, or suggestions, or similar things. I found one link to a github repository, but it didn't have a README :-(. > * We took the policy from Python's PEP proposal policy. > While I'm relatively new to the Haskell community, I've been part of the Python community since I had to explain to my clients what Python was. One of the things that's always impressed me about that community is it's devotion to maintaining the zen of the language. I've watched it grow the official (as in "import this") zen, and the PEP process, and watched various PEPS go through the process. I've even written a few myself, though I only submitted one, which was rejected. Watching the discussion of the syntax proposal reminds me of watching some of the discussions about Python language changes - though if we have a BDFL, I haven't heard of them. That's also how discussions about the Python standard library looked (they're part of the PEP process now). If we want the HP to be generally useful - not just something to make beginners lives easier or provide hard-to-use tools - it needs to be dealt with with equal care. I'd like to contribute to that process. So, questions that I couldn't find answers to: Is there a Haskell equivalent to a Python PEP? Should there be? Is there a place to discus HP issues, other than here? If I want to contribute to the development of the HP, where should I start? Thanks, Mike

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Re: [Haskell-cafe] Syntax proposal for "reverse apply"/"pipeline apply" (flip ($))
by Hans Höglund 19 Apr '14

19 Apr '14

There is also is my humble attempt to standardize the (&) formulation: http://hackage.haskell.org/package/reverse-apply As you can see, these definitions now mirror those in 'lens' exactly. I see no reason why this definition should not move to base. IMHO, the Diagrams definition is a very specific one based on the needs of that EDSL, while the lens formulation is the expected one. Mvh, Hans On 17 apr 2014, at 14:00, haskell-cafe-request(a)haskell.org wrote: > Message: 1 > Date: Wed, 16 Apr 2014 16:49:31 -0700 > From: Dan Burton <danburton.email(a)gmail.com> > To: Alexey Muranov <alexey.muranov(a)gmail.com> > Cc: haskell-cafe <haskell-cafe(a)haskell.org> > Subject: Re: [Haskell-cafe] Syntax proposal for "reverse > apply"/"pipeline apply" (flip ($)) > Message-ID: > <CALSygwf0wdBbrfQeED_raWjNfttYaX7pwDTzmBTTHaUqEkX5rg(a)mail.gmail.com> > Content-Type: text/plain; charset="utf-8" > > In the "lens" package, this is (&) at infixl 1. In the "diagrams" package, > this is (#) at infixl 8. You're certainly not the first to want this, but > nobody can ever agree what it should be called or what fixity it should > have. You can always just define it yourself. > > -- Dan Burton > > > On Wed, Apr 16, 2014 at 3:25 PM, Alexey Muranov <alexey.muranov(a)gmail.com>wrote: > >> Hello, >> >> i am completely new to Haskell, but i am somewhat fascinated by >> lambda-calculus and programming. >> >> For whatever it is worth, i would like to propose for discussion a syntax >> for "(flip ($))" operation in Haskell. >> >> I think that a good syntax would be "|^", for example: >> >> square x = x * x >> y = 3 |^ square -- y == 9 >> >> >> Explanation: >> >> * i would have suggested just ^, but it would conflict with number >> exponentiation, >> >> * it is rather common in mathematics to write function application in >> exponential notation: x ^ f instead of f(x), especially if f is an >> automorphism of some structure, >> >> * (flip ($)) is exactly the exponentiation of Church numerals, >> >> * in "The calculi of lambda-conversion", Alonzo Church uses the >> "shorthand" notation "[N^M]" for "(MN)", where M and N are lambda-terms. >> >> * I am probably not the only person missing the ability to apply functions >> from the right: >> >> http://stackoverflow.com/questions/1457140/haskell-composition-vs-fs-pipe-f… >> >> Well, other notations i've thought of are "\^" and "~$". >> >> Alexey. >> _______________________________________________ >> Haskell-Cafe mailing list >> Haskell-Cafe(a)haskell.org >> http://www.haskell.org/mailman/listinfo/haskell-cafe >> >

10 22

arbtt 0.8 released
by Joachim Breitner 19 Apr '14

19 Apr '14

Dear arbtt users, I just uploaded arbtt 0.8 to Hackage. See http://arbtt.nomeata.de/doc/users_guide/release-notes.html#release-notes-0.8 for a list of changes. This release is the result of slightly above 100 commits, closing 8 bugs and took a bit more than a year. I hope you like it! Greetings, Joachim -- Joachim “nomeata” Breitner mail(a)joachim-breitner.de • http://www.joachim-breitner.de/ Jabber: nomeata(a)joachim-breitner.de • GPG-Key: 0xF0FBF51F Debian Developer: nomeata(a)debian.org

1 0

Hackage libraries that make use of GADTs
by George Karachalias 18 Apr '14

18 Apr '14

Hello, Could you tell me some Hackage Libraries that make use (heavy or not) of GADTs? George -- things you own end up owning you

2 1

Stupid newbie question of the day: why is newMVar in the IO monad?
by Brian Hurt 17 Apr '14

17 Apr '14

So, I've hit a problem, and I'm wondering why this is. I want to write a function which returns a global monotonically incrementing int. This *should* be easy- just put a MVar in a global name, then update it as necessary: globalCounter :: MVar Integer globalCounter = undefined genId :: IO Integer genId = modifyMVar (\i -> (i+1, i)) globalCounter The problem with this is defining globalCounter- and that is because newMVar returns IO (MVar a), and not just MVar a. Now, I can go: globalCounter = unsafePerformIO $ newMVar 0 but I hate using unsafePerformIO. And I don't want to pass around the reference itself- I need to be in the IO monad with a StateT transform on top for other reasons, I don't want to complicate things. And even if I were, I would just pass the counter around instead of the reference. But it just feels like Haskell is being gratuitously difficult here. It's not just the name, it's the fact that creating the MVar is *explicitly* modifying the state of the world, which implies there is something more going on here than just allocating some memory. As an example of what I mean, newSTRef returns ST s (STRef s a). This is explicitly saying that the created STRef is only visible in the given thread. This is necessary for the implementation of the STRef, which is a mutable variable with no transactional guarantees. If it were visible from another thread, then it could be accessed from the other thread, creating a potential race condition. That I understand. But that isn't the case here- MVar's are explicitly designed to be accessed from multiple threads. So then I thought that it was something specific with MVars- maybe they need to do an OS call to set them up or something. OK, so let's try some alternatives. Like STM. Nope. newTVar has return type STM (TVar a) and newTMVar returns STM (TMVar a). Throw these into atomically, and I'm right back to where I started. newIORef returns IO (IORef a). And that's just a pointer store (I thought). It's easier for me to believe that I'm missing something here, rather than that Haskell is just being gratuitously difficult. But I honestly don't see what it is I'm missing. Help? Brian

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[ANN] 3T Software Labs MongoDB tools for Haskell programmers.
by Graham Thomson 17 Apr '14

17 Apr '14

Hello fair Haskell hackers! I’d like to announce the availability of 3T Software Labs MongoDB tools to the readers of this list. To forward-thinking Haskell adopters and MongoDB users alike, I’d like to extend a special 60-day trial of all the apps in our suite at http://3tsoftwarelabs.com/evaluation-edition using the code ‘HSKL’. My apologies for the spam if you’re not a MongoDB user. If you are, I hope you enjoy our tools and find them useful. Like many of the pioneering Haskell projects described on this list, we’ve just started our adventure, and would love to hear any feedback you have. Thanks a lot, Graham 3T Software Labs

1 0

Haskell Weekly News: Issue 291
by Daniel Santa Cruz 17 Apr '14

17 Apr '14

Welcome to issue 291 of the HWN, an issue covering crowd-sourced bits of information about Haskell from around the web. This issue covers from April 6 to 12, 2014 Quotes of the Week * geekosaur: IO, IO, it's off to (>>=) I go * edwardk: waiting for sclv to start going around door to door passing out little copies of the homotopy type theory book, and asking people if they have yet had the geometric realization that the simplicial sets are homotopically equivalent to their Lord and Savior. * carter: i'll leave you in the gentle hands of the rest of the channel Top Reddit Stories * GHC 7.8.1 Released Domain: haskell.org, Score: 226, Comments: 106 On Reddit: [1] http://goo.gl/pz4nE Original: [2] http://goo.gl/SjQ3Qv * What To Expect When You're a Platform Library Maintainer Domain: permalink.gmane.org, Score: 56, Comments: 4 On Reddit: [3] http://goo.gl/bD6VVf Original: [4] http://goo.gl/WDvy53 * Why are we relying on numeric identifiers for dependencies when we have so much richer information available? Domain: self.haskell, Score: 44, Comments: 18 On Reddit: [5] http://goo.gl/Z3gBEq Original: [6] http://goo.gl/Z3gBEq * How To Read "Pearls of Functional Algorithm Design" Domain: atamo.com, Score: 41, Comments: 8 On Reddit: [7] http://goo.gl/j4mXVz Original: [8] http://goo.gl/q41KEF * BayHac '14 Sign-Up and List of Classes Domain: self.haskell, Score: 40, Comments: 11 On Reddit: [9] http://goo.gl/xterjO Original: [10] http://goo.gl/xterjO * Is GHC the defacto standard? Domain: self.haskell, Score: 40, Comments: 39 On Reddit: [11] http://goo.gl/eiVjGM Original: [12] http://goo.gl/eiVjGM * Battleships web game written in Haskell/Yesod Domain: www-pg.iai.uni-bonn.de, Score: 34, Comments: 15 On Reddit: [13] http://goo.gl/hl2NC2 Original: [14] http://goo.gl/Wt5jqi * Heartbleed aftermath: should Haskell web frameworks allow using a pure Haskell SSL library instead of OpenSSL? Domain: self.haskell, Score: 32, Comments: 54 On Reddit: [15] http://goo.gl/ycHKNZ Original: [16] http://goo.gl/ycHKNZ * BudHac 2014 Domain: haskell.org, Score: 28, Comments: 3 On Reddit: [17] http://goo.gl/iObjrD Original: [18] http://goo.gl/KRJL2x * Hacking Haskell in nightclubs - video feature on Algorave Domain: motherboard.vice.com, Score: 27, Comments: 2 On Reddit: [19] http://goo.gl/LLG6qR Original: [20] http://goo.gl/PlzTTa * A brief introduction to ConstraintKinds extension (Wolfgang Jeltsch) Domain: jeltsch.wordpress.com, Score: 27, Comments: 4 On Reddit: [21] http://goo.gl/RadGh7 Original: [22] http://goo.gl/CZIfU8 * Generating Mazes with Inductive Graphs Domain: jelv.is, Score: 26, Comments: 11 On Reddit: [23] http://goo.gl/fufmgp Original: [24] http://goo.gl/FxAeGV Top StackOverflow Questions * Why MonadPlus and not Monad + Monoid? votes: 18, answers: 2 Read on SO: [25] http://goo.gl/J02Msv * Can a pure function have free variables? votes: 11, answers: 3 Read on SO: [26] http://goo.gl/iyJsn9 * FRP - Event streams and Signals - what is lost in using just signals? votes: 10, answers: 4 Read on SO: [27] http://goo.gl/cXwKKf * Is there a way to make GHC provide the type class constraints of typed holes? votes: 9, answers: 0 Read on SO: [28] http://goo.gl/LYxEvm * Where are the magic rules for GHC assert? votes: 8, answers: 1 Read on SO: [29] http://goo.gl/JL8OLZ * Using Haskell ranges: Why would mapping a floating point function across a range cause it to return an extra element? votes: 7, answers: 1 Read on SO: [30] http://goo.gl/mtBCBa * Why Haskell's Data.List.deleteBy takes in input a comparison function (a -> a -> Bool) and a value instead of a predicate (a -> Bool)? votes: 6, answers: 1 Read on SO: [31] http://goo.gl/Wd9evy Until next time, [32]+Daniel Santa Cruz References 1. http://www.haskell.org/pipermail/haskell/2014-April/024137.html 2. http://www.reddit.com/r/haskell/comments/22lw1b/ghc_781_released/ 3. http://permalink.gmane.org/gmane.comp.lang.haskell.libraries/21681 4. http://www.reddit.com/r/haskell/comments/22oott/what_to_expect_when_youre_a… 5. http://www.reddit.com/r/haskell/comments/22o4i1/why_are_we_relying_on_numer… 6. http://www.reddit.com/r/haskell/comments/22o4i1/why_are_we_relying_on_numer… 7. http://www.atamo.com/blog/how-to-read-pearls-by-richard-bird-1/ 8. http://www.reddit.com/r/haskell/comments/22kavg/how_to_read_pearls_of_funct… 9. http://www.reddit.com/r/haskell/comments/22d1wu/bayhac_14_signup_and_list_o… 10. http://www.reddit.com/r/haskell/comments/22d1wu/bayhac_14_signup_and_list_o… 11. http://www.reddit.com/r/haskell/comments/22r569/is_ghc_the_defacto_standard/ 12. http://www.reddit.com/r/haskell/comments/22r569/is_ghc_the_defacto_standard/ 13. http://www-pg.iai.uni-bonn.de/battleships 14. http://www.reddit.com/r/haskell/comments/22f683/battleships_web_game_writte… 15. http://www.reddit.com/r/haskell/comments/22udou/heartbleed_aftermath_should… 16. http://www.reddit.com/r/haskell/comments/22udou/heartbleed_aftermath_should… 17. http://www.haskell.org/haskellwiki/BudapestHackathon2014 18. http://www.reddit.com/r/haskell/comments/22euqt/budhac_2014/ 19. http://motherboard.vice.com/nl/read/algorave-coden-in-de-club 20. http://www.reddit.com/r/haskell/comments/22ou9y/hacking_haskell_in_nightclu… 21. http://jeltsch.wordpress.com/2013/02/14/the-constraint-kind/ 22. http://www.reddit.com/r/haskell/comments/22tfgl/a_brief_introduction_to_con… 23. http://jelv.is/blog/Generating-Mazes-with-Inductive-Graphs 24. http://www.reddit.com/r/haskell/comments/22ngz0/generating_mazes_with_induc… 25. http://stackoverflow.com/questions/23023961/why-monadplus-and-not-monad-mon… 26. http://stackoverflow.com/questions/22914878/can-a-pure-function-have-free-v… 27. http://stackoverflow.com/questions/22989253/frp-event-streams-and-signals-w… 28. http://stackoverflow.com/questions/23028124/is-there-a-way-to-make-ghc-prov… 29. http://stackoverflow.com/questions/22996814/where-are-the-magic-rules-for-g… 30. http://stackoverflow.com/questions/22901633/using-haskell-ranges-why-would-… 31. http://stackoverflow.com/questions/23000665/why-haskells-data-list-deleteby… 32. https://plus.google.com/105107667630152149014/about

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Please test: Cabal/cabal-install 1.20 RC2
by Johan Tibell 17 Apr '14

17 Apr '14

Hi all, The second, and hopefully last, release candidate for Cabal and cabal-install 1.20 is ready. If no issues are discovered, I plan to release this on Sunday, April 20th. You can help test by installing the release candidate and use it for your day-to-day work: cabal install http://johantibell.com/files/Cabal-1.20.0.0-rc2.tar.gz http://johantibell.com/files/cabal-install-1.20.0.0-rc2.tar.gz Please report any issues at https://github.com/haskell/cabal/issues -- Johan

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Re: [Haskell-cafe] Minimal Haskell Platform
by Travis Cardwell 17 Apr '14

17 Apr '14

On 2014年04月15日 14:02, Simon Hengel wrote: >> It is interesting that cabal does not (try to) install happy as a >> prerequisite for haskell-src-exts, which lists happy as a >> Build-Tools dependency [2]. It is also interesting that `cabal >> install happy` requires itself, despite indication in the >> documentation [3] that it is a valid way to install the package... >> >> Does this indicate that Cabal expects Haskell Platform? > > No, installing build tools is just a missing feature of `cabal-install` > (AFAIK). I chatted with Duncan Coutts in #haskell, and he confirmed that it is indeed just a missing feature. I found the issue here: https://github.com/haskell/cabal/issues/220 I was unable to find an issue regarding the `cabal install happy` failure, so I created one: https://github.com/haskell/cabal/issues/1777 >> Should Cabal be changed to (support minimal installations and) >> manage Build-Tools dependencies? > > Yes. In #haskell, Duncan Coutts said: > as for the global vs. minimal, yes I see it's an issue. One sometimes > wants to start a sandbox with a very minimal set. > > the issue with making a minimal sandbox is simply knowing which > packages should be in it, and we currently just base them all off of > the global one. > > but that's not the only solution, it'd also be possible to copy a > subset, if we know what subset to copy > > and I have a somewhat cunning plan along these lines (related to some > other ghc-pkg/cabal improvement work) which might make that rather > easier > > what I want is for ghc itself to come with multiple profiles, with one > being the minimum (base + rts + deps), and that could be used as a basis > for new envs With such a feature, it sounds like we can get the best of both worlds: * a feature-rich Haskell Platform to support beginners * minimal sandboxes for advanced users > I think most Haskell developers use a reasonably recent version of GHC > (that would currently still be 7.6.3 for me) and the latest version of > cabal-install. Everything else can be installed with cabal-install. In my experience, the alex and happy binaries must also be installed (for a number of packages to be installable via cabal-install). > Where would something like the HP actually make sense? For stuff that > has external dependencies that are not easily installable with > cabal-install (like curses bindings, SSL support, etc.). We have none > of this in the HP. So I think currently we just have additional costs, > but no benefits (+ we harm innovation by arbitrarily "endorsing" random > packages). I understand this point of view, but allow me to offer an opposing one. By putting packages with external dependencies into Haskell Platform, we often increase the dependencies of Haskell Platform itself. For example, Haskell Platform currently includes Graphics packages; installing Haskell Platform on a server entails installing a number of OpenGL libraries that are never used. Cheers, Travis

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Autocomplete command line options with GHC 7.8
by Jan Stolarek 16 Apr '14

16 Apr '14

Hi all, GHC 7.8 adds --show-options flag that prints all supported command line flags on standard output. This can be used to enable autocompletion of command line options for ghc in shells that support autocompletion. If you're using bash add this snippet to your ~/.bashrc file: <<<<<<<<<<<<< START # Autocomplete GHC commands _ghc() { local envs=`ghc --show-options` # get the word currently being completed local cur=${COMP_WORDS[$COMP_CWORD]} # the resulting completions should be put into this array COMPREPLY=( $( compgen -W "$envs" -- $cur ) ) } complete -F _ghc -o default ghc <<<<<<<<<<<< END Enjoy. Janek PS. I also added a wiki page: https://ghc.haskell.org/trac/ghc/wiki/AutocompleteGHCFlags Feel free to add instructions for other shells.

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Re: [Haskell-cafe] Directed rounding in haskell ?
by Barak A. Pearlmutter 16 Apr '14

16 Apr '14

One issue that arises with rounding modes in a pure lazy language like Haskell is that it's pretty hard to nail down the semantics. The "round towards negative infinity" mode is a dynamic hardware feature, available by setting a rounding mode flag in the FPU. If you execute some hunk of code with that flag having different values, you will in general get different results. So if you try to do this in Haskell, you have to decide how to expose it without violating purity. This would break things: roundWith :: RoundMode -> ( () -> a) -> a consider let x = 0.1 + 0.2 in roundWith NegInfty (\_ -> x) vs roundWith NegInfty (\_ -> 0.1 + 0.2) So you need to make different numeric types. This is what Ed Kmett's "rounding" cabal package does, albeit in a much more general way where the new floating types are parameterized by both rounding mode and precision. The bottom line is that IEEE Floating Point numbers are actually a monad. There is NaN, which makes them a Maybe, or given that there are many NaNs perhaps an Either. And there is the rounding mode, which is sort of a Reader. As an aside, changing the rounding mode flags can be surprisingly slow on modern CPUs. One trick for doing interval arithmetic efficiently is to set the flags once, say to TowardInf. Then x*y computes the product of x and y rounding towards positive infinity while -((-x)*y) computes the same product rounding towards negative infinity without fiddling with the rounding mode. So for adding intervals, instead of Interval x0 x1 + Interval y0 y1 = Interval (x0+y0) (x1+y1) Interval x0 x1 * Interval y0 y1 | x0 >= 0 && y0 >= 0 = Interval (x0*y0) (x1*y1) -- etc but with some added hair to fiddle with the rounding modes, one leaves the rounding mode fixed and writes Interval x0 x1 + Interval y0 y1 = Interval (-(-x0-y0)) (x1+y1) Interval x0 x1 * Interval y0 y1 | x0 >= 0 && y0 >= 0 = Interval (-((-x0)*y0)) (x1*y1) -- etc As a final throwaway, allowing (Interval x0 x1) where x0>x1, i.e., improper intervals, gives a very pleasant system with a surprisingly nice and rich semantics. For example, Interval 1 2 - Interval 2 1 = Interval 0 0 which makes for a group rather than just a semigroup. The system is known variously as modal intervals, Kaucher intervals, directed interval arithmetic, or generalized interval arithmetic, and can be used to automatically prove interesting arithmetic properties full of ∀s and ∃s. -- Barak A. Pearlmutter Hamilton Institute & Dept Comp Sci, NUI Maynooth, Co. Kildare, Ireland http://www.bcl.hamilton.ie/~barak/

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Current status of Mavericks CPP
by Michael Snoyman 16 Apr '14

16 Apr '14

I still seem to be getting bug reports about the CPP implementation of Mavericks. Last I'd heard, it seemed that general consensus was that packages should *not* be patched to work around the different CPP implementation, and instead Mavericks users should be installing GCC's CPP. Is this accurate? And is there a wiki page somewhere describing the situation and how to work around it? I'd like to have some authoritative URL to point people to, especially given that I have no access to a Mac system and therefore can't test this myself.

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Cabal/cabal-install 1.20 release candidates
by Johan Tibell 16 Apr '14

16 Apr '14

Hi all, I've prepared the Cabal/cabal-install 1.20 release candidates. I now need some help testing, especially on Windows as I don't have a Windows machine. There are over 300 commits since the last release and lots of interesting new features and changes. I will write them down when I make the actual release. To install the release candidates simply run: cabal install --constraint="HTTP >= 4000.2.5" http://johantibell.com/files/Cabal-1.20.0-rc.tar.gz http://johantibell.com/files/cabal-install-1.20.0-rc.tar.gz (The --constraint="HTTP >= 4000.2.5" flag is used to work around an issue I already found in the RC, it won't be needed for the real release.) Please report any issues on the bug tracker: https://github.com/haskell/cabal/issues If I haven't heard of anything release blocking bugs (or last minute important patches) in a couple of days, I will make these tarballs the official release. The commits used are tagged in the repo as Cabal-v1.20.0-rc and cabal-install-v1.20.0-rc. -- Johan

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Minimal Haskell Platform
by Travis Cardwell 16 Apr '14

16 Apr '14

Hello, I have been using Haskell Platform since it was introduced because I have always heard that it is the recommended way to use GHC. Indeed, Haskell Platform has made the installation of a Haskell environment quite straightforward. My current usage strategy is a common one: * Only install Haskell Platform in --global. * Avoid installing into ~/.cabal (when possible). * Develop exclusively in Cabal sandboxes. In a recent /r/haskell post [1], user mightybyte commented: > This. The Haskell Platform installs a bunch of packages for you in > --global. My experience is that this inevitably leads to problems if > you're doing significant Haskell development. The best thing to do is > to minimize the number of packages installed as --global. The way to do > that is to install GHC directly and avoid using the Haskell Platform or > Haskell distributions provided by your OS. Asking about it in #haskell, it seems that a number of developers recommend such a minimal installation, particularly for large projects. I am very interested in minimizing the number of packages in --global, and I would like to start testing my software against the current Haskell Platform *as well as* such a minimal installation. I my initial tests (Debian stable amd64; minimal virtual machine), I tried installing GHC 7.8.2 and cabal-install (using bootstrap.sh) only. Installation went fine, `cabal update` worked fine, and `cabal sandbox init` worked fine. I then tried `cabal install hlint` (within the sandbox), and it successfully compiles a number of packages before failing when trying to build haskell-src-exts, complaining that happy could not be found. Running `cabal install happy` failed with the "setup: The program happy is required but it could not be found" error. Building happy via the source Setup.lhs worked fine, and installing the binary into my installation bin directory results in an environment in which I am able to `cabal install hlint` (and `cabal install happy`) into a sandbox without issue. It is interesting that cabal does not (try to) install happy as a prerequisite for haskell-src-exts, which lists happy as a Build-Tools dependency [2]. It is also interesting that `cabal install happy` requires itself, despite indication in the documentation [3] that it is a valid way to install the package... Does this indicate that Cabal expects Haskell Platform? Should Cabal be changed to (support minimal installations and) manage Build-Tools dependencies? Would it be worthwhile to create a "Minimal Haskell Platform" to create a truly common platform that everybody would be happy using? Cheers, Travis [1] http://www.reddit.com/r/haskell/comments/22up8l/ghc_782_released/ [2] https://github.com/haskell-suite/haskell-src-exts/blob/9bc4daf3b51d006741c6… [3] http://www.haskell.org/happy/

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hsc2hs behaves differently under Windows?
by Dominick Samperi 16 Apr '14

16 Apr '14

It seems that hsc2hs behaves differently under Windows (when compared with Linux), causing build problems. An example foo.hsc is attached, along with the foo.hs that is generated using hsc2hs under Windows. Note the expressions my_$s in the result. It appears that under Windows the %n$s POSIX printf notation is not recognized. The correctly generated file that is produced under Linux is also attached, in foo-linux.hs. Note that proper substitution happens here. Is there a work-around for this Windows issue? Thanks, Dominick

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Re: [Haskell-cafe] [Haskell] [ANN] quantities 0.3.0
by Auke Booij 16 Apr '14

16 Apr '14

On 15 April 2014 20:29, John David Reaver <jdreaver(a)adlerhorst.com> wrote: > Hello! I am happy to publicly announce the quantities package: I think haskell-cafe is more appropriate for these kinds of libraries. Anyway, welcome. > From the description on Hackage: > > A library for creating and manipulating physical quantities, > which are a numerical value associated with a unit of > measurement. Included is an expression parser and a huge list > of predefined quantities with which to parse strings into a > Quantity datatype. Once created, a quantity can be converted > to different units or queried for its dimensionality. A user > can also operate on quantities arithmetically, and doing so > uses automatic unit conversion and simplification. > not sure if "quantities" is an appropriate name for your package: an integer, a float, complex numbers - those are quantities. doesn't this package parse units? > Just to get a taste of how this package works, here are some > examples: why can i only "unsafely" create quantities using strings? what if i know upfront what kind of a unit i want to deal with? from the looks of it, this library is only good for dealing with human-readable input - surely that's not the only use case you had in mind? > >>> fromString "min => s" > Right 60.0 second can't we find some elegant way to express this in haskell, instead of having to invent a scripting language of sorts? On a similar note, your "magnitude :: Quantity -> Double" sounds a bit like unsafeCoerce: why would you want to forget that your quantity has a unit? >From your documentation: > >>> fromString "m => 3 ft" > Left (ScalingFactorError 3.0 foot) Why isn't the outcome of this 3.28084/3=1.09361 or something along those lines? (this is just a suggestion, I'm not saying this is a bad thing.) > >>> fromString "2 ft + 6 in => ft" > Right 2.5 foot Oh, so you are trying to support arbitrary arithmetical input! Then again, there is no way to add two "Quantity"s. I have the feeling the goal of your package is a bit unclear: do you want to implement a framework to type-safely compute with units? Or do you just want to write something that parses string input to typed data? In the former case, have you considered the discussion on the haskellwiki [1]? In the latter case, why don't you write it on top of an existing units package? Well, that was a big rant, I hope you can use some of it. Auke. [1]: http://www.haskell.org/haskellwiki/Physical_units

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Re: [Haskell-cafe] quantities 0.3.0
by Henning Thielemann 16 Apr '14

16 Apr '14

Am 15.04.2014 21:29, schrieb John David Reaver: > Hello! I am happy to publicly announce the quantities package: > > Hackage: http://hackage.haskell.org/package/quantities > Github: https://github.com/jdreaver/quantities > > I feel this package is complete enough as of version > 0.3.0 (released today) to announce it to the public. I have programmed something similar years ago, first for Haskell 98 numeric classes and then for numeric-prelude. My implementation does not use an expression tree for the physical dimensions. Instead it uses a vector of base dimensions and constructs reasonable units only for string output. http://hackage.haskell.org/package/numeric-prelude-0.4.1/docs/Number-SI.html You can play around with it by unpacking the numeric-prelude package and run 'make ghci' thielema@sputnik:/tmp> cabal unpack numeric-prelude Unpacking to numeric-prelude-0.4.1/ thielema@sputnik:/tmp> cd numeric-prelude-0.4.1/ thielema@sputnik:/tmp/numeric-prelude-0.4.1> make ghci ... *Main> 25*meter/second :: SIDouble ... 25.0 m/s *Main> minute/second :: SIDouble 60.0 *Main> ampere*volt :: SIDouble 1.0 W There are many more libraries for handling of physical dimensions: http://www.haskell.org/haskellwiki/Physical_units You may add 'quantities' there.

1 0

Error in the GHC documentation for the IsList class ?
by David Virebayre 15 Apr '14

15 Apr '14

In section 7.6.5.1, the documentation describes the IsList class, then goes on writing about a FromList class ( "The FromList class and its methods are intended to be used in conjunction with the OverloadedLists extension.") Later it's written : It is perfectly fine to declare new instances of IsList, so that list notation becomes useful for completely new data types. Here are several example instances: ... instance FromList [a] where David.

2 1

ANN: clash - from haskell to hardware
by Christiaan Baaij 15 Apr '14

15 Apr '14

I'm pleased to announced to first official release of the new CλaSH compiler! Website: http://christiaanb.github.io/clash2 Hackage: http://hackage.haskell.org/package/clash-ghc Github: https://github.com/christiaanb/clash2 From the website: CλaSH (pronounced ‘clash’) is a functional hardware description language that borrows both its syntax and semantics from the functional programming language Haskell. The merits of using a functional language to describe hardware comes from the fact that combinational circuits can be directly modelled as mathematical functions and that functional languages lend themselves very well at describing and (de-)composing mathematical functions. The CλaSH compiler transforms these high-level descriptions to low-level synthesizable VHDL. There is a tutorial at: http://hackage.haskell.org/package/clash-prelude/docs/CLaSH-Tutorial.html Which also lists the (nearly-compulsory) comparison between CλaSH and Lava. -- Christiaan Baaij

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