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ANN: GHC-7.4.2-Eden - Parallel Haskell on multicore and cluster systems
by Eden - Functional parallel Programming (Mischa Dieterle) 17 Jun '12

17 Jun '12

We are happy to announce a new release of Eden, a parallel extension of Haskell. The release comprises: * The GHC-7.4.2-Eden compiler: GHC-7.4.2 extended with the Eden parallel runtime system. * The Eden modules: a library defining the Eden language constructs. * The Eden skeleton library: a comprehensive library with common task and data parallel patterns. * The Eden trace viewer EdenTV: an visualisation and analysis tool for eventlogs of parallel program runs. All resources are available via: http://www.mathematik.uni-marburg.de/~eden Eden extends Haskell with a small set of syntactic constructs for explicit process specification and creation. While providing enough control to implement parallel algorithms efficiently, it frees the programmer from the tedious task of managing low-level details by introducing automatic process handling, synchronisation and communication (via head-strict lazy lists). Eden is tailored for distributed systems but works equally well on multicore architectures. Processes work within disjoint address spaces and do not share any data. This simplifies Eden's implementation as there is no need for global garbage collection. A tutorial is available from http://www.mathematik.uni-marburg.de/~eden/paper/edenCEFP.pdf The compiler release includes binary packages for Linux and Windows, and a source distribution, available from http://www.mathematik.uni-marburg.de/~eden/?content=down_eden_7_4&navi=down Other features: - Extensions for GHC's event logging support. - Built-in serialisation of Haskell data structures (orthogonal to evaluation), see "Orthogonal Serialisation for Haskell", available from http://www.diku.dk/hjemmesider/ansatte/berthold/jbpubl.html - Optimised local communication. - Stand-alone version for multicore, using middleware MPI or PVM for clusters. Eden libraries and tools are available separately from hackage: - Eden modules: http://hackage.haskell.org/package/edenmodules (already included in the Eden compiler) - Eden skeleton library: http://hackage.haskell.org/package/edenskel - EdenTV: http://hackage.haskell.org/package/edentv (uses gtk2hs and glade) When built using a standard GHC, the packages will produce a threaded simulation of Eden.

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FunctionalOWL: FP Usergroup in Germany, area Bielefeld
by raichoo 16 Jun '12

16 Jun '12

Announcing FunctionalOWL in Bielefeld! Next Wednesday will be the first meetup of the FunctionalOWL at Hackerspace Bielefeld. The meetup is aimed at people who are interested in functional programming. FunctionalOWL wants to provide a wide range of interesting topics and opportunities to share and acquire knowledge. Become a part of it. When: Wed 20 June @ 19:00 Where: Sudbrackstraße 42, Bielefeld Followup meetups are planned to happen every 3rd Wednesday at the same location. We have various beamers and whiteboards. Internet and caffeinated lemonade are also available. For more information and contact, check out our website. Feel free to drop a message on our pubML or in our Chatroom. www.hackerspace-bielefeld.de Kind regards, raichoo, Hackerspace Bielefeld

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Performance with do notation, mwc-random and unboxed vector
by Dmitry Dzhus 15 Jun '12

15 Jun '12

Hello everyone. I wonder why using do notation with `<-` can ruin the performance. In essence the problem is that, for some action `f :: m Double`, running the code (in my case, `standard` from mwc-random). f for million times is fast but the code do v <- f return v is slower about a hundred times. Consider this simple source where we generate an unboxed vector with million pseudo-random numbers: ---- 8< ----- import qualified Data.Vector.Unboxed as VU import System.Random.MWC import System.Random.MWC.Distributions (standard) count = 1000000 main = do g <- create e' <- VU.replicateM count $ standard g return () ---- >8 ----- Being compiled with -O2, this runs for 0.052 s on my machine. Changing the replicateM line to use do notation brings the runtime down to 11.257 s! See below: ---- 8< ----- import qualified Data.Vector.Unboxed as VU import System.Random.MWC import System.Random.MWC.Distributions (standard) count = 1000000 main = do g <- create e' <- VU.replicateM count $ do v <- standard g return v return () ---- >8 ----- I don't quite understand why this happens. I'm using GHC 7.4.1 on Linux x86_64 system. Compiling *both* versions with profiling enabled changes runtime to 5.673 sec, which is exactly half the runtime of slow version without profiling, and this is awkward (double calculations occuring in do block?). Does anybody have an idea if this is a problem with my do, or with mwc-random, or with vector (my notation disallowing efficient unboxing?).

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Re: [Haskell-cafe] ANN: Portackage - a hackage portal
by Andrew Seniuk 15 Jun '12

15 Jun '12

Hi ___, Thank you for your suggestion to provide JSON, which seconds Derek's earlier suggestion. I have anonymised your name since you wrote to me but didn't CC the list. :) As much as I wish the web interface was up to snuff, it is really too slow. While I continue to try to resolve that, there is something like a JSON feed available now. I'm new to these things and may be doing it wrong. Any advice would be appreciated, either in accelerating the web interface or in providing the JSON. I have no idea whether it parses or not. JSON Schema: http://www.fremissant.net/portackage/packages.schema.json.txt Hopefully compressed JSON data: http://www.fremissant.net/portackage/packages.php Raw JSON data in case the compressed doesn't work: http://www.fremissant.net/portackage/packages.json The hackage data updated as of today (June 14). For now this is only the packages which expose modules (i.e. not including binary packages). No particular reason, I just ran out of time this afternoon and thought I'd post what I've got. The fields present in the JSON are those available on the HTML table version. There are several dozen other fields which come up more or less infrequently in the Hackage packages, and they could all be included. The complete list of modules is included (rather than the summary versions used in the HTML table version). A next step would be for the server to incrementally update the JSON data based on the Hackage RSS feed. Kind Regards, Andrew On Wed, Jun 13, 2012 at 7:58 AM, ___ wrote: > Hi Andrew > > Portackage is a great site for browsing packages, but it's really > really slow for filtering per column. What about offering an > additional non-javascript version of the pages -- searching with plain > text in a browser works quite well. > > On 4/30/12, Andrew Seniuk <rasfar(a)gmail.com> wrote: >> Oops, the three links in summary are: >> >> module tree: http://fremissant.net/portackage/modules.php >> library packages: http://fremissant.net/portackage/portackage.php >> other packages: http://fremissant.net/portackage/binary.php >> >> _______________________________________________ >> Haskell-Cafe mailing list >> Haskell-Cafe(a)haskell.org >> http://www.haskell.org/mailman/listinfo/haskell-cafe >> > > > -- > ___

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Installing pandoc / json with ghc 6.12.1
by Rico Moorman 15 Jun '12

15 Jun '12

Hello, I recently tried to install the latest version of pandoc on my debian stable box (with ghc 6.12.1) using virthualenv as sandboxing mechanism. But instead of a normal installation, compilation of the json package (more specifically the Text.JSON.Parsec module) hangs and causes ghc to consume around 2GB of RAM (out of 3GB) and the system to swap and hang. For reference ... I just created a plain virthualenv (for sandboxing) and after that ran (tmp) foo@bar:/tmp$ cabal install json I also tried if this has something to do with version 0.5 (the latest version) only, to no avail. Are there other users of pandoc/json or related packages who encountered/solved this issue? Am I doing something wrong here? Best regards, Rico

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class instances for kinds with finite ty constrs, does this make sense?
by ex falso 15 Jun '12

15 Jun '12

Hi, i've been using DataKinds for a while and there seems to be a recurring annoyance that could be possibly eliminated with a language extension. It goes something like this: data Tuple (l :: [*]) where Unit :: Tuple '[] Comma :: a -> Tuple as -> Tuple (a ': as) data Proxy k = Proxy class TupleLength (l :: [*]) where tupleLength :: Proxy l -> Integer instance TupleLength '[] where tupleLength _ = 0 instance (TupleLength as) => TupleLength '(a : as) where tupleLength _ = 1 + tupleLength (Proxy :: Proxy as) so far so good. but now if we want to use TupleLength: printLength :: (TupleLength l) => Tuple l -> IO () printLength t = print $ tupleLength t we always have to put the class restriction (TupleLength l) there, even though all possible type constructors of [*] have a TupleLength instance defined! If we had a way to signal that all ty constrs are catered for then the compiler could check this, and deduce that l::[*] is always an instance. Well that's the hypothesis. Of course this would only make sense for kinds with finite no. of ty constructors, namely DataKinds-lifted types. Does this make sense? ex

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Re: [Haskell-cafe] What extension do I need to write "type Job = Map k a"?
by Arlen Cuss 15 Jun '12

15 Jun '12

(resending to café, turns out I wasn't subbed from this address.) Hi Magicloud, This is correct; because you've hidden the type-variables away by universally quantifying them, there's no more level of specificity you can get back *out* of them than just "some kind of Map" (Job = M.Map k b, where k ≠ k0, b ≠ b0). If you have a Job type which can store *any* kind of Map (forall k a. Job (Map k a)), then that means you could have a Job with a Map Int Bool, and a Job with a Map String (Float -> Float), and they'd both have the same type "Job". You can't do anything with the values within, because you're being too permissive about what a Job is. You may want "data Job k a = Job (Map k a)", *or* if you do actually use one kind of Map only, then why not "data Job = Job (Map Int String)" (substituting your real types for Int and String). In this case, you could also consider using newtype ("newtype Job = Job { getJob :: Map Int String }") to provide the guarantee that you're getting a Job (and not any Map Int String) without performance loss. Let me know if I've been more confusing than helpful; Arlen On Thursday, 14 June 2012 at 1:16 PM, Magicloud Magiclouds wrote: > Hi there, > Thanks for the reply. To be clear, all I want is to "avoid having to > type type variables all over the place". What should I do? My original > code with RankNTypes and ImpredicativeTypes does not work.... > > The "type Job = forall k a. M.Map k a" works now. But function uses > it does not. Compiler complains about "Couldn't match expected type > `Job' with actual type `M.Map k0 b0'". > > On Wed, Jun 13, 2012 at 9:15 PM, Daniel Peebles <pumpkingod(a)gmail.com (mailto:pumpkingod@gmail.com)> wrote: > That doesn't require existential quantification, but it'll need Rank-2 typesif you ever do anything with Job. Unfortunately, a universally quantifiedJob like what you wrote (or what Magicloud seems to want) is only inhabitedby the empty Map. > > > An existentially quantified Job, as you might get with > > > data Job = forall k a. Job (Map k a) > > > does let you wrap up any Map containing anything in it, but unfortunatelythe only thing you can do with that map afterwards is ask for "structural"properties about it, like whether it's empty or how many elements it has init. You could ask to enumerate the elements in it, but you wouldn't be ableto touch any of them because you wouldn't know what their types were. > > > So I'm not really sure how to interpret the question. Was the goal to have aheterogeneous Map, maybe? Or just to avoid having to type type variables allover the place? Both of those are possible but require a bit moresophistication with types. > > > -Dan > > > > > On Wed, Jun 13, 2012 at 7:32 AM, Ismael Figueroa Palet<ifigueroap(a)gmail.com (mailto:ifigueroap@gmail.com)> wrote: > > > > Do you want to hide the specific types of the job? Presumably to thendefine a type JobList = [Job] ?You can do that with the ExistentialQuantification extension. > > > > type Job = forall k a. Map k atype JobList = [Job] > > > > ??Note you can't unpack the types k a once you have hidden them. But thetypechecker can use it to ensure some static property.Also you could use unsafeCoerce to do some casts, but *only if you are*sure* that things will go OK*. > > > > > > > 2012/6/13 Magicloud Magiclouds <magicloud.magiclouds(a)gmail.com (mailto:magicloud.magiclouds@gmail.com)> > > > > > Hi,I've forgotten this.This is OK:type Job k a = Map k aAnd this is OK:{-# LANGUAGE RankNTypes #-} -- or LiberalTypeSynonyms?type Job = forall a. forall k. Map k a > > > > > Then how to write it like this?type Job = Map k a--竹密岂妨流水过山高哪阻野云飞 > > > > > And for G+, please use magiclouds#gmail.com (http://gmail.com) > > > > > _______________________________________________Haskell-Cafe mailing listHaskell-Cafe(a)haskell.org (mailto:Haskell-Cafe@haskell.org) > > > > http://www.haskell.org/mailman/listinfo/haskell-cafe > > > > > > > > > > > > > > > > > > > > > > > > > --Ismael > > > > > > > _______________________________________________Haskell-Cafe mailing listHaskell-Cafe(a)haskell.org (mailto:Haskell-Cafe@haskell.org) > > > http://www.haskell.org/mailman/listinfo/haskell-cafe > > > > > > > > > > -- > 竹密岂妨流水过 > 山高哪阻野云飞 > > And for G+, please use magiclouds#gmail.com (http://gmail.com) > > _______________________________________________ > Haskell-Cafe mailing list > Haskell-Cafe(a)haskell.org (mailto:Haskell-Cafe@haskell.org) > http://www.haskell.org/mailman/listinfo/haskell-cafe

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Current uses of Haskell in industry?
by Chris Smith 14 Jun '12

14 Jun '12

It turns out I'm filling in for a cancelled speaker at a local open source user group, and doing a two-part talk, first on Haskell and then Snap. For the Haskell part, I'd like a list of current places the language is used in industry. I recall a few from Reddit stories and messages here and other sources, but I wonder if anyone is keeping a list. -- Chris

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[Announce] AusHac 2012 - The Aussie Haskell Hackathon
by Alex Mason 14 Jun '12

14 Jun '12

We know many of you have been holding your breaths for this (hopefully none of you have passed out though!) for quite a while... but we’re pleased to announce that we’re finally getting around to announcing AusHac 2012! This year, we’re moving AusHac to Sydney proper: Atlassian has kindly offered the use of their offices next to Darling Harbour, so there’s more places to stay and eat than in previous years! It’s right across the harbour from Google’s headquarters where FP-Syd is hosted, and we’re starting on the Friday after next month’s FP-Syd. When: Friday 20th - Sunday 22nd of July Where: Atlassian 173/185 Sussex Street Sydney NSW 2000, Australia (02) 9262 1443 Map: http://goo.gl/maps/JoNg If you're looking for places to stay, check out AirBnB (http://www.airbnb.com) the prices are very reasonable (around $100/night within walking distance of Atlassian if you’re lucky). This year we’d like to see a few more talks on interesting things people are working on (Yes, the stuff you are working on IS interesting, and we want to hear about it!). If you’d like to give a talk, please let us know in the sign up sheet. Speaking of which, here it is: http://tinyurl.com/AusHac2012SignUp Please let us know if you’re considering coming along, so we can organise things like adequate power etc. We’d love for you to come along for the whole time or just a few hours, we’re happy for people to drop in when they want, on any day. The more people we have come along, the more awesome it will be. We hope to see you there! Cheers, Alex Mason and Ivan Miljenovic

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What extension do I need to write "type Job = Map k a"?
by Magicloud Magiclouds 14 Jun '12

14 Jun '12

Hi, I've forgotten this. This is OK: type Job k a = Map k a And this is OK: {-# LANGUAGE RankNTypes #-} -- or LiberalTypeSynonyms? type Job = forall a. forall k. Map k a Then how to write it like this? type Job = Map k a -- 竹密岂妨流水过山高哪阻野云飞 And for G+, please use magiclouds#gmail.com.

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