January 2013 - Haskell-Cafe

A Meetup Group for MN Haskellers
by Danny Gratzer 12 Jan '13

12 Jan '13

Hello, After seeing the post about Manchurian Haskellers I decided to start one for people in and around the Twin Cities. Here's the meetup page: http://www.meetup.com/HaskellMN/ If any Haskell guru's are lurking around here we'd love to have you give a talk! -- Danny Gratzer

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Seeking feedback for a tutorial paper draft about GADTs
by Anton Dergunov 12 Jan '13

12 Jan '13

Hi Haskellers, I have written a draft of an introductory-level tutorial paper about GADTs in Haskell (for submittion to proceedings of the recent LASER summer school) and I would like to seek initial feedback about its content: what information is probably missing? are there any subtle mistakes? The main idea of this article was to serve as a starting point for learning GADTs (I was missing this kind of information myself some time ago), so I have collected several examples demonstrating common use cases. Here is a link to the paper: https://docs.google.com/open?id=0B9ZIIsDR0B7Hb1VBTFZOZEUzXzA -- Best Regards, Anton Dergunov

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Is http://hackage.haskell.org/packages/hackage.html having a challenging serving up archive.tar?
by KC 11 Jan '13

11 Jan '13

:) -- -- Regards, KC

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Permanent Academic Positions (Computational Logic/Functional Programming) in Dundee Deadline 23 January
by Ekaterina Komendantskaya 11 Jan '13

11 Jan '13

****** Dundee Fellowships ****** http://www.dundee.ac.uk/dundeefellows/ University of Dundee announces several permanent positions, with a 5-year starting period of a Research Fellowship. One of the named priority areas is Computational Logic/ Functional Programming / Verification. For more details, see below or email me: Katya Komendantskaya <katya(a)computing.dundee.ac.uk> School of Computing University of Dundee Dundee Fellowship Permanent position Closing Date for applications: Wednesday 23 January 2013. University of Dundee is advertising a series of permanent academic jobs across the College of Arts & Science and Engineering, named Dundee Fellows. The aim is to bring in a series of excellent academics onto permanent contracts (subject to the completion of 3 year probation) into any research area within the College. These staff will be labelled as Dundee Fellows during their first 5 years, over which time they will receive enhanced staff development and a research focus to their duties, while automatically moving to a regular academic contract (lecturer, senior lecturer, reader or professor) at the end of these 5 years. These will be independent researchers (and not postdocs under supervision). Their teaching load will start low, and will gradually increase over the first 5 years, to phase them into teaching. As the University of Dundee moves towards its 25 year vision of becoming Scotland’s leading University, we are actively investing in the next generation of our academic community. Our Dundee Fellows scheme offers exciting opportunities to outstanding, high potential, early career researchers of any age to establish themselves at the University of Dundee and develop towards making a full and excellent contribution to research, teaching and leadership in their chosen field. Full details are available here: http://www.dundee.ac.uk/dundeefellows/ ******************************************

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Example programs with ample use of deepseq?
by Joachim Breitner 11 Jan '13

11 Jan '13

Dear Haskellers, I’m wondering if the use of deepseq to avoid unwanted lazyness might be a too large hammer in some use cases. Therefore, I’m looking for real world programs with ample use of deepseq, and ideally easy ways to test performance (so preferably no GUI applications). I’ll try to find out, by runtime observerations, which of the calls ot deepseq could be replaced by id, seq, or „shallow seqs“ that, for example, calls seq on the elements of a tuple. Thanks, Joachim -- Joachim "nomeata" Breitner mail(a)joachim-breitner.de | nomeata(a)debian.org | GPG: 0x4743206C xmpp: nomeata(a)joachim-breitner.de | http://www.joachim-breitner.de/

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[announce] second Haskell meetup in Paris
by lucas di cioccio 11 Jan '13

11 Jan '13

Hi, I am pleased to annouce that I'm bootstrapping a Haskell-enthusiastics group in Paris. We recently scheduled our second Haskell meetup in Paris. This meetup will take place next Monday (Monday, January 14, 2013). AF83 ( http://af83.com/ ) has been kind enough to offer us a room for our meeting. You don't have to, but it is recommended to, register for the meetup on http://meetup.haskell-paris.fr/ or by sending me an email. The website for our group is http://haskell-paris.fr/ (in French). You should pay it a click not only because it's written in Haskell but also to glance at our logo, propose a talk, or read the digest of past meetup(s). Regards, --Lucas DiCioccio

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Cabal bug? repeat "--reinstall"
by Niklas Hambüchen 11 Jan '13

11 Jan '13

I get the following: $ cabal install --only-dependencies --reinstall Resolving dependencies... All the requested packages are already installed: Use --reinstall if you want to reinstall anyway. Can somebody confirm that they see the same?

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Parallel cabal install ignores order
by Niklas Hambüchen 11 Jan '13

11 Jan '13

I have "jobs: 4" enabled in my cabal config to get parallel installs with cabal-install >= 1.16. When I do cabal install --reinstall --force-reinstalls world to reinstall all packages (e.g. to enable profiling or shared), it fails after some point, complaining that the required dependency package is not compiled with the needed flag (for profiling / -dyn). It looks like for reinstalls, parallel cabal-install simply ignores the necessary order. Can somebody confirm this or tell me if this is known? If not, where should it be reported? Thanks Niklas

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Re: [Haskell-cafe] Haskell-Cafe Digest, Vol 113, Issue 11
by Yuriy Solodkyy 10 Jan '13

10 Jan '13

OK. It tells me the same error message in popup, but all the projections are running after that. I'll make sure that it does not say any strange errors on empty DB in new version. Does it start projections for you as well (even if it says error)? On Tue, Jan 8, 2013 at 1:00 PM, <haskell-cafe-request(a)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. Example programs with ample use of deepseq? (Joachim Breitner) > 2. Re: Example programs with ample use of deepseq? (Edward Z. Yang) > 3. Re: Example programs with ample use of deepseq? (Joachim Breitner) > 4. Re: Example programs with ample use of deepseq? (Johan Tibell) > 5. Re: Announce: Leksah 0.13.1 (a bit experimental) (Peter Simons) > 6. Re: Announce: Leksah 0.13.1 (a bit experimental) > (Hamish Mackenzie) > > > ---------- Forwarded message ---------- > From: Joachim Breitner <mail(a)joachim-breitner.de> > To: Haskell Cafe <haskell-cafe(a)haskell.org> > Cc: > Date: Mon, 07 Jan 2013 13:06:35 +0100 > Subject: [Haskell-cafe] Example programs with ample use of deepseq? > Dear Haskellers, > > I’m wondering if the use of deepseq to avoid unwanted lazyness might be > a too large hammer in some use cases. Therefore, I’m looking for real > world programs with ample use of deepseq, and ideally easy ways to test > performance (so preferably no GUI applications). > > I’ll try to find out, by runtime observerations, which of the calls ot > deepseq could be replaced by id, seq, or „shallow seqs“ that, for > example, calls seq on the elements of a tuple. > > Thanks, > Joachim > > -- > Joachim "nomeata" Breitner > mail(a)joachim-breitner.de | nomeata(a)debian.org | GPG: 0x4743206C > xmpp: nomeata(a)joachim-breitner.de | http://www.joachim-breitner.de/ > > > > ---------- Forwarded message ---------- > From: "Edward Z. Yang" <ezyang(a)MIT.EDU> > To: Joachim Breitner <mail(a)joachim-breitner.de> > Cc: Haskell Cafe <haskell-cafe(a)haskell.org> > Date: Mon, 07 Jan 2013 04:20:43 -0800 > Subject: Re: [Haskell-cafe] Example programs with ample use of deepseq? > There are two senses in which deepseq can be overkill: > > 1. The structure was already strict, and deepseq just forces another > no-op traversal of the entire structure. This hypothetically affects > seq too, although seq is quite cheap so it's not a problem. > > 2. deepseq evaluates too much, when it was actually sufficient only to > force parts of the structure, e.g. the spine of a list. This is less > common for the common use-cases of deepseq; e.g. if I want to force pending > exceptions I am usually interested in all exceptions in a (finite) data > structure; a space leak may be due to an errant closure---if I don't > know which it is, deepseq will force all of them, ditto with work in > parallel programs. Certainly there will be cases where you will want snip > evaluation at some point, but that is somewhat difficult to encode > as a typeclass, since the criterion varies from structure to structure. > (Though, perhaps, this structure would be useful: > > data Indirection a = Indirection a > class DeepSeq Indirection > rnf _ = () > ) > > Cheers, > Edward > > Excerpts from Joachim Breitner's message of Mon Jan 07 04:06:35 -0800 2013: > > Dear Haskellers, > > > > I’m wondering if the use of deepseq to avoid unwanted lazyness might be > > a too large hammer in some use cases. Therefore, I’m looking for real > > world programs with ample use of deepseq, and ideally easy ways to test > > performance (so preferably no GUI applications). > > > > I’ll try to find out, by runtime observerations, which of the calls ot > > deepseq could be replaced by id, seq, or „shallow seqs“ that, for > > example, calls seq on the elements of a tuple. > > > > Thanks, > > Joachim > > > > > > > ---------- Forwarded message ---------- > From: Joachim Breitner <mail(a)joachim-breitner.de> > To: haskell-cafe(a)haskell.org > Cc: > Date: Mon, 07 Jan 2013 16:59:45 +0100 > Subject: Re: [Haskell-cafe] Example programs with ample use of deepseq? > Hi, > Am Montag, den 07.01.2013, 13:06 +0100 schrieb Joachim Breitner: > > I’m wondering if the use of deepseq to avoid unwanted lazyness might be > > a too large hammer in some use cases. Therefore, I’m looking for real > > world programs with ample use of deepseq, and ideally easy ways to test > > performance (so preferably no GUI applications). > > surprisingly, deepseq is not used as much as I thought. > http://packdeps.haskellers.com/reverse/deepseq lists a lot of packages, > but (after grepping through some of the code) most just define NFData > instances and/or use it in tests, but rarely in the „real“ code. For > some reason I expected it to be in more widespread use. > > But therefore I am even more interested in non-hackaged applications > that I can be allowed to stud – in return I might be able to tell you > way to speed up your application. > > Greetings, > Joachim > > -- > Joachim "nomeata" Breitner > mail(a)joachim-breitner.de | nomeata(a)debian.org | GPG: 0x4743206C > xmpp: nomeata(a)joachim-breitner.de | http://www.joachim-breitner.de/ > > > > ---------- Forwarded message ---------- > From: Johan Tibell <johan.tibell(a)gmail.com> > To: Joachim Breitner <mail(a)joachim-breitner.de> > Cc: Haskell Cafe <haskell-cafe(a)haskell.org> > Date: Mon, 7 Jan 2013 08:12:31 -0800 > Subject: Re: [Haskell-cafe] Example programs with ample use of deepseq? > On Mon, Jan 7, 2013 at 4:06 AM, Joachim Breitner > <mail(a)joachim-breitner.de> wrote: > > I’m wondering if the use of deepseq to avoid unwanted lazyness might be > > a too large hammer in some use cases. Therefore, I’m looking for real > > world programs with ample use of deepseq, and ideally easy ways to test > > performance (so preferably no GUI applications). > > I never use deepseq, except when setting up benchmark data where it's > a convenient way to make sure that the data is evaluated before the > benchmark is run. > > When removing space leaks you want to avoid creating the thunks in the > first place, not remove them after the fact. Consider a leak caused by > a list of N thunks. Even if you deepseq that list to eventually remove > those thunks, you won't lower your peak memory usage if the list was > materialized at some point. > > In addition, by not creating the thunks in the first place you avoid > some allocation costs. > > -- Johan > > > > > ---------- Forwarded message ---------- > From: Peter Simons <simons(a)cryp.to> > To: haskell-cafe(a)haskell.org > Cc: gtk2hs-devel(a)lists.sourceforge.net > Date: Mon, 07 Jan 2013 19:25:22 +0100 > Subject: Re: [Haskell-cafe] Announce: Leksah 0.13.1 (a bit experimental) > Hi Hamish, > > would it be possible to get an update for process-leksah that works with > recent versions of the 'filepath' package? I cannot build leksah-server > with GCC 7.4.2 because of this issue. > > Take care, > Peter > > > > > > ---------- Forwarded message ---------- > From: Hamish Mackenzie <hamish.k.mackenzie(a)gmail.com> > To: Peter Simons <simons(a)cryp.to> > Cc: gtk2hs-devel(a)lists.sourceforge.net, haskell-cafe(a)haskell.org > Date: Tue, 8 Jan 2013 14:05:08 +1300 > Subject: Re: [Haskell-cafe] Announce: Leksah 0.13.1 (a bit experimental) > Features in process-leksah have been merged into process. For > newer versions of GHC leksah-server just depends on process. > > If it is trying to install process-leksah then something else > has probably gone wrong. > > Check "ghc-pkg list" for old versions of leksah. Make sure > you have the latest versions of ltk, leksah and leksah-server > from github. (if you use cabal-meta they will be in > the "leksah/vendor" subdirectory). > > Here are the steps for installing from scratch... > https://github.com/leksah/leksah/blob/master/.travis.yml > > Here is what it should look like when it installs... > https://travis-ci.org/leksah/leksah > > On 8 Jan 2013, at 07:25, Peter Simons <simons(a)cryp.to> wrote: > > > Hi Hamish, > > > > would it be possible to get an update for process-leksah that works with > > recent versions of the 'filepath' package? I cannot build leksah-server > > with GCC 7.4.2 because of this issue. > > > > Take care, > > Peter > > > > > > _______________________________________________ > > Haskell-Cafe mailing list > > Haskell-Cafe(a)haskell.org > > http://www.haskell.org/mailman/listinfo/haskell-cafe > > > > > _______________________________________________ > Haskell-Cafe mailing list > Haskell-Cafe(a)haskell.org > http://www.haskell.org/mailman/listinfo/haskell-cafe > > -- Yuriy Solodkyy (y.solodkyy(a)gmail.com)

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First Los Angeles Haskell User Group Meetup
by Phil Freeman 10 Jan '13

10 Jan '13

Hello Haskell Cafe, I'd like to announce that I've created a meetup group for any Haskell users in the LA area. The first meeting will be a meet-and-greet session, held next Tuesday, 15th January 2013, at Wurstkuche in the Downtown LA Arts District. After that, the goal is to organise presentations and discussions on Haskell-related topics roughly once a month. Interested parties can register for the group and RSVP here: http://www.meetup.com/Los-Angeles-Haskell-User-Group/ Thanks, Phil Freeman.

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