- Haskell-Cafe - Haskell.org

Re: [Haskell-cafe] caml build
by Vasili I. Galchin 14 May '09

14 May '09

oops ... yes. On Wed, May 13, 2009 at 11:29 AM, Nicolas Pouillard < nicolas.pouillard(a)gmail.com> wrote: > Excerpts from Vasili I. Galchin's message of Wed May 13 18:21:55 +0200 > 2009: > > Hello, > > > > I did a "cabal build -?" and discovered -v/--version. > > So **caml** build was a typo right ? > > > > > Vasili > > > > On Wed, May 13, 2009 at 2:42 AM, Nicolas Pouillard < > > nicolas.pouillard(a)gmail.com> wrote: > > > > > Excerpts from Vasili I. Galchin's message of Tue May 12 23:23:51 +0200 > > > 2009: > > > > Hi Nicolas, > > > > > > > > I am starting a "caml build". I want line by line which module > is > > > > being built so when I get an error I have a context to reason about > to > > > fix > > > > the problem. Got it? > > > > > > Maybe you mean "cabal build" ? > > > > > > > On Tue, May 12, 2009 at 7:23 AM, Nicolas Pouillard < > > > > nicolas.pouillard(a)gmail.com> wrote: > > > > > > > > > Excerpts from Vasili I. Galchin's message of Tue May 12 00:27:26 > +0200 > > > > > 2009: > > > > > > Hello, > > > > > > > > > > > > I have forgotten whether I sent this posting out. Sorry if > I > > > did (I > > > > > > didn't see on Haskell cafe archive). > > > > > > > > > > > > I am building Swish and getting an error. I want to follow > the > > > > > > progress of "swish build" ... I don't see an additional parameter > > > like > > > > > > verbose mode that will tell which swish component is being built. > ??? > > > > > > > > > > I don't get the relation with the subject of your post, can you > > > elaborate? > > > > > > > > > > Best regards, > > > > > > > > > > -- > > > > > Nicolas Pouillard > > > > > > > > > > > -- > > > Nicolas Pouillard > > > > > -- > Nicolas Pouillard >

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Qt declarative UI
by david48 14 May '09

14 May '09

I thought that it might interest some people : http://labs.trolltech.com/page/Projects/Graphics/Kinetic/DeclarativeUI

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caml build
by Vasili I. Galchin 14 May '09

14 May '09

Hello, I have forgotten whether I sent this posting out. Sorry if I did (I didn't see on Haskell cafe archive). I am building Swish and getting an error. I want to follow the progress of "swish build" ... I don't see an additional parameter like verbose mode that will tell which swish component is being built. ??? Regards, Vasili

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Stream-fusion without the lists
by Reiner Pope 13 May '09

13 May '09

Hi everyone, With stream-fusion, we can write functions which construct and destruct lists, such as (this is the main example from the Stream Fusion paper[1]) f :: Int -> Int f n = sum [k * m | k <- [1..n], m <- [1..k]] and the rewrite rules in stream-fusion replace these operations on lists with fusible operations on the Stream (non-recursive) datatype. In this example, the domain and codomain of the function don't mention the list datatype. There seem to be many functions like this: the lists are being used internally as composable loops rather than as data-structures. The Stream datatype seems to be much better suited to representing loops than the list datatype is. So, instead of programming with the lists, why don't we just use the Stream datatype directly? For example: In Data.Stream (from the stream-fusion package) we can find most of the Prelude list functions but with Stream in all the types instead of []. For example, Data.Stream.sum :: Num a => S.Stream a -> a Using this module, we can rewrite f without mentioning lists. We first need a Monad instance for Data.Stream.Stream: > import qualified Data.List.Stream as S > > instance Monad S.Stream where > return = S.return > (>>=) = S.concatMap Now we can write > f :: Int -> Int > f n = S.sum $ do > k <- S.enumFromToInt 1 n > m <- S.enumFromToInt 1 k > return (k*m) which is essentially the same as the original f, although lacking the syntactic sugar of the list comprehension. To me, it seems that Stream is more sensible data type to use than [] when the algorithm being expressed is just a loop (rather than something which needs a [] as a cache/buffer), for the following reasons: 1. If I am programming with lists and I need some function which I can't express with Prelude functions, I have to write it myself. I will probably lose fusion in this case, because I will write it recursively in terms of lists. On the other hand, if I am programming with Streams, I will write it myself in terms of Streams, and it should be easier to maintain fusion because it won't be recursive. 2. Holding on to a [] too long can cause a space leak. This is not the case for Stream, because a Stream only ever contains one "state". More generally, the memory use of Stream is more easily predictable than that of [], since "running" a Stream only holds on to one "state" at a time, and we often know how big the "state" is. 3. Fusion doesn't rely on rewrite rules firing. I consider this point less significant than the other two. So, thoughts? Do people program with Streams directly? What have I not considered? Cheers, Reiner [1] http://www.cse.unsw.edu.au/~dons/papers/stream-fusion.pdf

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Re: [Haskell-cafe] Functional Reactive Web Application Framework?
by Claus Reinke 13 May '09

13 May '09

oops, sorry, keyboard accident > >I assume you want to write FRP in a Haskell-embedded DSL and generate >>FRP'd JavaScript. If you wish to use Flapjax as a supporting library >>I'd be glad to help. > > I'm curious: how difficult is it nowadays for in-page JavaScript to > control the evolution of its surrouding page, FRP-style? I used to > do something like that, but with VRML+JavaScript instead of HTML > +JavaScript (there's a screencast for those without VRML viewer;-): > > http://community.haskell.org/~claus/FunWorlds/VRML/ > > and I found that mapping FRP style behaviours and events wasn't > the problem (though VRML has better support for this than HTML), > the problem was gaining the same advantages one would have from > embedding FRP in a functional language. Problems included scoping, > linking dynamically created material with enclosing scope (JavaScript > being in strings with scopes separate from the enclosing VRML, > VRML to be created dynamically also via strings, also in their own > scope) This became particularly obvious for dynamic recursion of reactive behaviours, somewhat like page n = <code involving n> `until` (keypress `then` (\key-> page n)) How are such things handled in Flapjax, if it follows the embedded compiler approach? Claus

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International Summer School on Advances in Programming Languages (precedes ICFP'09)
by Matthew Fluet (ICFP Publicity Chair) 13 May '09

13 May '09

International Summer School on Advances in Programming Languages 25th-28th August, 2009 Heriot-Watt University, Edinburgh, Scotland http://www.macs.hw.ac.uk/~greg/ISS-AiPL Overview ~~~~~~~~ This four-day residential International Summer School on Advances in Programming Languages has a major theme of Concurrency, Distribution, and Multicore. Intended primarily for postgraduate research students, the School offers lectures and practical sessions on an engaging blend of cutting edge theoretical and practical techniques from international experts. The Summer School is supported by the Scottish Informatics and Computer Science Alliance (http://www.sicsa.ac.uk/) a Scottish Funding Council Research Pool. Participants from SICSA member institutions may attend at no cost. Confirmed Topics/Speakers * Static and dynamic languages, Prof Philip Wadler, University of Edinburgh * Compiler technology for data-parallel languages, Dr Sven-Bodo Scholz, University of Hertfordshire * New applications of parametricity, Dr Janis Voigtlander, Technical University of Dresden * Automatic vectorising compilation, Dr Paul Cockshott, University of Glasgow * Foundational aspects of size analysis, Prof Marko van Eekelen / Dr Olha Shakaravska, Radboud University Nijmegen * Context oriented programming, Dr Pascal Costanza, Vrije Universiteit Brussels * Multi-core programming, Dr Phil Trinder, Heriot-Watt University * Multi-core compilation, Dr Alastair Donaldson, Codeplay Software Ltd * Principles and Applications of Refinement Types, Dr Andrew D. Gordon, Microsoft Research, Cambridge * Resource aware programming in Hume, Prof Greg Michaelson, Heriot-Watt University / Prof Kevin Hammond, University of St Andrews * Haskell concurrency & parallelism, Dr Satnam Singh, Microsoft Research, Cambridge Location ~~~~~~~~ The Summer School is at Heriot-Watt University's Riccarton campus, set in pleasant parkland to the west of Edinburgh, with easy access to the airport, city and central Scotland (http://www.hw.ac.uk/welcome/directions.htm) The Summer School immediately precedes the 2009 International Conference on Functional Programming (http://www.cs.nott.ac.uk/~gmh/icfp09.html) and takes place during the Edinburgh International Festival (http://www.eif.co.uk/) , and the associated Edinburgh Festival Fringe (http://www.edfringe.com/) and Edinburgh International Book Festival (http://www.edbookfest.co.uk/) Steering Committee ~~~~~~~~~~~~~~~~~~ Prof Prof Greg Michaelson, Heriot-Watt University (Convenor), <G.Michaelson(a)hw.ac.uk> Prof Kevin Hammond, University of St Andrews Dr Patricia Johann, University of Strathclyde Prof Philip Wadler, University of Edinburgh Fee ~~~ Full rate: £400; (free for SICSA students) Includes: four nights single room, en-suite accommodation with breakfast, lunch and dinner, plus coffee breaks and session materials. Day rate: £200; (free for SICSA students) Includes: lunch, coffee breaks, session materials Registration of Interest ~~~~~~~~~~~~~~~~~~~~~~~~ If you are interested in attending the International Summer School, please complete the form available from (http://www.macs.hw.ac.uk/~greg/ISS-AiPL/ISS-AiPL%20register.doc) or below, and return it to: <ISS-AiPL-register(a)macs.hw.ac.uk> ********** International Summer School on Advances in Programming Languages 25th-28th August, 2009 Heriot-Watt University, Edinburgh, Scotland Registration of Interest Name: Address: Email: Phone: SICSA Uni: Yes / No Rate: Full / Day Accessibility requirements: Dietary requirements: Return to: ISS-AiPL-register(a)macs.hw.ac.uk **********

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2nd Call For Papers: APLAS 2009 (Korea, Dec 14-16, 2009)
by Janis Voigtlaender 13 May '09

13 May '09

=============================================================== CALL FOR PAPERS The Seventh Asian Symposium on Programming Languages and Systems (APLAS 2009) Seoul, December 14-16, 2009 http://ropas.snu.ac.kr/aplas09/ =============================================================== APLAS aims at stimulating programming language research by providing a forum for the presentation of recent results and the exchange of ideas and experience in topics concerned with programming languages and systems. APLAS is based in Asia, but is an international forum that serves the worldwide programming languages community. The APLAS series is sponsored by the Asian Association for Foundation of Software (AAFS), which has recently been founded by Asian researchers in cooperation with many researchers from Europe and the USA. The past formal APLAS symposiums were successfully held in Bangalore (2008, India), Singapore (2007), Sydney (2006, Australia), Tsukuba (2005, Japan), Taipei (2004, Taiwan) and Beijing (2003, China) after three informal workshops held in Shanghai (2002, China), Daejeon (2001, Korea) and Singapore (2000). Proceedings of the past symposiums were published in Springer-Verlag's LNCS 2895, 3302, 3780, 4279, and 5356. TOPICS: The symposium is devoted to both foundational and practical issues in programming languages and systems. Papers are solicited on, but not limited, to the following topics: * semantics, logics, foundational theory * type systems, language design * program analysis, optimization, transformation * software security, safety, verification * compiler systems, interpreters, abstract machines * domain-specific languages and systems * programming tools and environments INVITED SPEAKERS: TBA IMPORTANT DATES: Abstract Deadline: June 8 (Monday), 2009 Paper Submission Deadline: 24:00 AM (in Samoan Time), June 15 (Monday), 2009 Author Notification: August 17, 2009 Camera Ready: September 14, 2009 Conference: December 14-16, 2009 SUBMISSIONS INFORMATION: Papers should be submitted electronically online via the conference submission web page at URL <http://www.easychair.org/conferences/?conf=aplas2009>. Acceptable formats are PostScript or PDF, viewable by Ghostview or Adobe Reader. Submissions should not exceed 16 pages in LNCS format, including bibliography and figures. Submitted papers will be judged on the basis of significance, relevance, correctness, originality, and clarity. They should clearly identify what has been accomplished and why it is significant. Submitted papers must be unpublished and not submitted for publication elsewhere. The proceedings of the symposium is planned to be published as a volume in Springer-Verlag's Lecture Notes in Computer Science series. Authors of selected papers will be invited after the symposium to submit a full version for publication in a special issue of New Generation Computing. GENERAL CHAIR Kwangkeun Yi (Seoul National University, Korea) PROGRAM CHAIR Zhenjiang Hu (National Institute of Inforamtics, Japan) PROGRAM COMMITTEE Manuel M. T. Chakravarty (University of New South Wales, Australia) Wei-Ngan Chin (National University of Singapore, Singapore) Nate Foster (University of Pennsylvania, USA) Ralf Hinze (Oxford University, United Kingdom) Zhenjiang Hu (National Institute of Informatics, Japan), Chair Ik-Soon Kim (Electronics and Telecommunications Research Institute, Korea) Julia Lawall (DIKU, Denmark) Sebastian Maneth (NICTA and University of New South Wales, Australia) Sungwoo Park (Pohang University of Science and Technology, Korea) G. Ramalingam (Microsoft Research, India) Peter Thiemann (University of Freiburg, Germany) Kazushige Terui (Kyoto University, Japan) Janis Voigtländer (Technical University of Dresden, Germany) Chung-chieh Shan (Rutgers University, USA) Kazunori Ueda (Waseda University, Japan) Bow-Yaw Wang (Academia Sinica, Taiwan) Jianjun Zhao (Shanghai Jiaotong University, China) POSTER SESSION CHAIR Kiminori Matsuzaki (University of Tokyo, Japan)

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haskell & cuda?
by Dan 13 May '09

13 May '09

Hi, Does anyone know if there's a compiler from Data-Parallel Haskell to GPU code? I saw a paper on it a while back, but Google hasn't turned up any code. Cheers, - Dan

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Kind of confusing
by Anton van Straaten 13 May '09

13 May '09

GHC amused me today with this error (context omitted): Couldn't match kind `(* -> *) -> * -> *' against `?? -> ? -> *' When matching the kinds of `t :: (* -> *) -> * -> *' and `(->) :: ?? -> ? -> *' It was a silly mistake: I had used 'lift' where I intended to use 'liftM'. But I'm thinking Haskell compilers should have some sort of option which, when the ratio of punctuation to alphanumerics in an error message exceeds a certain level, just responds to the user with a more readily comprehensible message such as "WTF, dude?" Serious question: what is the significance of the question mark and double question marks in those signatures, or better yet, where can I read about it? Anton

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Main function error
by applebiz89 13 May '09

13 May '09

I have compiled each function independently and they have compiled the only problem is the main function.. I keep getting the error 'films not defined' and I am not sure why [code] type Title = String type Director = String type Year = Int type Fan = String data Film = Film Title Director Year [Fan] deriving Show -- List of films testDatabase :: [Film] testDatabase = [ (Film "Casino Royale" "Martin Campbell" 2006 ["Garry", "Dave", "Zoe"])] -- Function filmsInGivenYear :: Year -> [Film] -> [String] filmsInGivenYear year' films = [ title | (Film title director year fans) <- films, year == year'] doFilmsInGivenYear :: [Film] -> IO () doFilmsInGivenYear films = do putStrLn "which year?" text <- getLine let year' = read text :: Int let answer = filmsInGivenYear year' films print answer main :: IO () main = do doFilmsInGivenYear films main [/code] if the other functions are compiling without this error im not sure as to why the main function does not compile because of the films...any light on this? Thanks -- View this message in context: http://www.nabble.com/Main-function-error-tp23506481p23506481.html Sent from the Haskell - Haskell-Cafe mailing list archive at Nabble.com.

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Developing 3 dimensional interactive environments/functional objects
by paulfrancis＠friendbliss.com 13 May '09

13 May '09

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Problem with text and text-icu packages
by David Carter 13 May '09

13 May '09

Hi, I'm struggling with text-0.1 and text-icu-0.1, as announced at http://www.serpentine.com/blog/2009/02/27/finally-fast-unicode-support-for-… The code in http://pastebin.com/m7d8d9f91 is intended to read in a UTF-8 file a1.txt, reverse it twice, and write it out to another UTF-8 file a2.txt, which I would have thought should make a2.txt identical to a1.txt. Mostly it is, but sometimes it isn't, e.g.: % echo a > a1.txt % tryicu # <- my code % cat a2.txt ࠋ퐤 Specifically, a1.txt contains bytes 97 and 10, while a2.txt contains bytes 224 160 139 237 144 164. Have I misconstrued things, or is this a bug? I am running ghc 6.10.2 and ICU 4.0.1 on SuSE. Thanks for any help David

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Data.Map lookup signature
by Nico Rolle 13 May '09

13 May '09

Hi everyone. The docs in the web on http://www.haskell.org/ghc/docs define Data.Map.lookup as follows: http://www.haskell.org/ghc/docs lookup :: Ord k => k -> Map k a -> Maybe a but my version of ghci does i like that: Data.Map.lookup :: (Ord k, Monad m) => k -> Data.Map.Map k a -> m a but i need the 1. one. my version of ghci is 6.8.2 regards

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Re: [Haskell-cafe] Inferred typing?
by michael rice 13 May '09

13 May '09

I was looking at some code and couldn't figure out how it was returning a list since there were no list constructors present. Thanks! Michael --- On Tue, 5/12/09, Brent Yorgey <byorgey(a)seas.upenn.edu> wrote: From: Brent Yorgey <byorgey(a)seas.upenn.edu> Subject: Re: [Haskell-cafe] Inferred typing? To: haskell-cafe(a)haskell.org Date: Tuesday, May 12, 2009, 7:50 AM On Mon, May 11, 2009 at 10:59:01PM -0700, michael rice wrote: > In the code below, is the type returned by the return functions inferred from > the result type in the function type signature, i.e., just change the result > type to Maybe Int and the code will return a Maybe monad, (Just 4), instead of > a List monad? Indeed, it is. Try it! =) -Brent _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe(a)haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe

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OT: Is conference dead?
by Dušan Kolář 12 May '09

12 May '09

Hello all, I'm sorry for the OT post, is the conference dead? I've got no mail since yeasterday afternoon. And that is quite unusual. Best regards, Dusan

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Inferred typing?
by michael rice 12 May '09

12 May '09

In the code below, is the type returned by the return functions inferred from the result type in the function type signature, i.e., just change the result type to Maybe Int and the code will return a Maybe monad, (Just 4), instead of a List monad? Michael ========= import Monad fn :: [Int] -> [Int] fn l = mzero `mplus` (return (head l)) `mplus` (return (last l)) ================ *Main> :l test5 [1 of 1] Compiling Main ( test5.hs, interpreted ) Ok, modules loaded: Main. *Main> fn [4,5,6,7,8] [4,8] *Main>

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Haskell Weekly News: Issue 117 - May 12, 2009
by Brent Yorgey 12 May '09

12 May '09

--------------------------------------------------------------------------- Haskell Weekly News http://sequence.complete.org/hwn/20090512 Issue 117 - May 12, 2009 --------------------------------------------------------------------------- Welcome to issue 117 of HWN, a newsletter covering developments in the [1]Haskell community. The Haskell Platform is here! Announcements The Haskell Platform. Don Stewart [2]announced the first release of the [3]Haskell Platform: a single, standard Haskell distribution for every system. The Haskell Platform is a blessed library and tool suite for Haskell culled from Hackage, along with installers for a wide variety of systems. It saves developers work picking and choosing the best Haskell libraries and tools to use for a task. GHC version 6.10.3. Ian Lynagh [4]announced the release of [5]GHC 6.10.3. This release contains a handful of bugfixes relative to 6.10.2 and better line editing support in GHCi, so updating is recommend. See the [6]release notes for more details. Bindings for libguestfs. Richard W.M. Jones [7]announced some [8]partial bindings for [9]libguestfs. Heads up: Conflicting versions of network-2.2.1. Johan Tibell [10]announced a heads-up that the version of network-2.2.1 that shipped with GHC 6.10 differs from the one on Hackage. If you want the API additions that are present in network-2.2.1 on Hackage, be sure to use network-2.2.1.1 instead. hpc-strobe-0.1: Hpc-generated strobes for a running Haskell program. Thorkil Naur [11]announced the initial release of [12]hpc-strobe, a rudimentary library that demonstrates the possibility of using Hpc (Haskell Program Coverage) to inspect the state of a running Haskell program. hpc-strobe uses the basic machinery provided by Hpc to produce multiple tix files, also called strobes, representing the coverage at different times while the program is running. By subtracting such two tix files, again using Hpc machinery, a tix file representing the expressions used between the times of recording the subtracted tix files is produced. This may be used, for example, to get a better idea of what a long-running program is doing. It could also be used as a profiling tool, getting information about how many times individual expressions are used. BUG FIX release of regex-tdfa-1.1.2. ChrisK [13]announced version 1.1.2 of [14]regex-tdfa, a bug-fix release. Silkworm game. Duane Johnson [15]announced the release of [16]Silkworm, a game written in Haskell using [17]Hipmunk and GLFW. Discussion Platform policy question: API compatibility in minor releases. Duncan Coutts began a [18]discussion on versioning policies for major and minor releases, for packages included in the Haskell Platform. See also the [19]newly started discussion on the purpose of Haskell Platform releases. Blog noise [20]Haskell news from the [21]blogosphere. Blog posts from people new to the Haskell community are marked with >>>, be sure to welcome them! * Magnus Therning: [22]Vim haskellmode packaged for Arch. * Manuel M T Chakravarty: [23]Instant Generics: Fast and Easy.. * Bjorn Buckwalter: [24]May 2009 HCAR Submissions. * Gtk2HS: [25]Gtk2HS 0.10.1 Released. * Magnus Therning: [26]Arch and Haskell, on little snag. * Mikael Vejdemo Johansson (DrSyzygy): [27]Gröbner bases for operads - Or "What I did in my vacation". * Mads Lindstrøm: [28]WxGeneric 0.6.0. * Osfameron: [29]Is currying monadic?. * James Iry: [30]A Brief, Incomplete, and Mostly Wrong History of Programming Languages. * Duane Johnson: [31]Visualizing Typed Functions. * Well-Typed.Com: [32]Next steps for the Haskell Platform. * Don Stewart (dons): [33]The Haskell Platform. * Luke Palmer: [34]Lazy Partial Evaluation. * Christopher Lane Hinson: [35]Vec is Good. * LHC Team: [36]Constructor specialization and laziness.. * Lee Pike: [37]An Atomic Fibonacci Server: Exploring the Atom (Haskell) DSL. * John Van Enk: [38]Atom & Arduino :: First Program (pt. 2). * >>> Chris Forno: [39]Is Haskell a Good Choice for Web Applications?. * >>> Sparky: [40]Haskell and Eclipse [Part 2]. * >>> Brit Butler: [41]Playing with Haskell. * Duane Johnson: [42]Silkworm Game written in Haskell. * Matthew Podwysocki: [43]Functional Composition and Partial Application . * >>> Takashi: [44]A Prolog In Haskell. * >>> mokehehe: [45]Using DirectX from Haskell. * >>> mokehehe: [46]AO bench in Haskell. Quotes of the Week * jfredett: My haskell-spider senses were tingling, I just overshot RT and went for the Halting Problem. * NeilBrown: I heard that if you chant "I don't think this can be done in Haskell" three times in front of a text editor, Don Stewart appears and implements it in one line... * bos: The last couple of times I've wanted a book like that, I wrote the book myself. It's a very effective way to get the book you want, compared to wishing. * edwardk: {-# LANGUAGE time to pay the cutting edge typing features tax #-} * SPJ: Haha this is good news, I have slipped functional programming into your brain without you realising it is something very weird. * EvilTerran: writing machine code by hand on tape with a magnetised needle looks good compared to PHP :P * Athas: I like Lisp for its extreme expressivity, but I think it's easier to make Haskell more powerful, than to make Lisp more statically safe. * roconnor: I can't wait for the Density Comonad chapter of "learn you a haskell" About the Haskell Weekly News New editions are posted to [47]the Haskell mailing list as well as to [48]the Haskell Sequence and [49]Planet Haskell. [50]RSS is also available, and headlines appear on [51]haskell.org. To help create new editions of this newsletter, please see the information on [52]how to contribute. Send stories to byorgey at cis dot upenn dot edu. The darcs repository is available at darcs get [53]http://code.haskell.org/~byorgey/code/hwn/ . References 1. http://haskell.org/ 2. http://article.gmane.org/gmane.comp.lang.haskell.cafe/58095 3. http://hackage.haskell.org/platform/ 4. http://article.gmane.org/gmane.comp.lang.haskell.general/17178 5. http://www.haskell.org/ghc/ 6. http://haskell.org/ghc/docs/6.10.3/html/users_guide/release-6-10-3.html 7. http://article.gmane.org/gmane.comp.lang.haskell.cafe/58358 8. http://git.et.redhat.com/?p=libguestfs.git;a=blob;f=haskell/Guestfs.hs;hb=H… 9. http://et.redhat.com/~rjones/libguestfs/ 10. http://article.gmane.org/gmane.comp.lang.haskell.cafe/58349 11. http://article.gmane.org/gmane.comp.lang.haskell.cafe/58286 12. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hpc%2Dstrobe 13. http://article.gmane.org/gmane.comp.lang.haskell.cafe/58067 14. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/regex-tdfa 15. http://article.gmane.org/gmane.comp.lang.haskell.cafe/57886 16. http://blog.inquirylabs.com/2009/05/02/silkworm-game-written-in-haskell/ 17. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/Hipmunk 18. http://thread.gmane.org/gmane.comp.lang.haskell.libraries/11001 19. http://thread.gmane.org/gmane.comp.lang.haskell.libraries/11035 20. http://planet.haskell.org/ 21. http://haskell.org/haskellwiki/Blog_articles 22. http://therning.org/magnus/archives/617 23. http://justtesting.org/post/106219682 24. http://flygdynamikern.blogspot.com/2009/05/may-2009-hcar-submissions.html 25. http://haskell.org/gtk2hs/archives/2009/05/10/gtk2hs-0101-released/ 26. http://therning.org/magnus/archives/599 27. http://blog.mikael.johanssons.org/archive/2009/05/grobner-bases-for-operads… 28. http://lindstroem.wordpress.com/2009/05/08/wxgeneric-0-6-0/ 29. http://greenokapi.net/blog/2009/05/07/is-currying-monadic/ 30. http://james-iry.blogspot.com/2009/05/brief-incomplete-and-mostly-wrong.html 31. http://blog.inquirylabs.com/2009/05/07/visualizing-typed-functions/ 32. http://blog.well-typed.com/2009/05/next-steps-for-the-haskell-platform/ 33. http://donsbot.wordpress.com/2009/05/06/the-haskell-platform/ 34. http://lukepalmer.wordpress.com/2009/05/04/lazy-partial-evaluation/ 35. http://blog.downstairspeople.org/2009/05/05/vec-is-good/ 36. http://lhc-compiler.blogspot.com/2009/05/constructor-specialization-and-laz… 37. http://leepike.wordpress.com/2009/05/05/an-atomic-fibonacci-server-explorin… 38. http://blog.sw17ch.com/wordpress/?p=111 39. http://jekor.com/article/is-haskell-a-good-choice-for-web-applications 40. http://sdasrath.blogspot.com/2009/05/20090402-haskell-and-eclipse-part-2.ht… 41. http://redlinernotes.com/blog/?p=937 42. http://blog.inquirylabs.com/2009/05/02/silkworm-game-written-in-haskell/ 43. http://weblogs.asp.net/podwysocki/archive/2009/05/01/functional-composition… 44. http://propella.blogspot.com/2009/04/prolog-in-haskell.html 45. http://mokehehe.blogspot.com/ 46. http://mokehehe.blogspot.com/2009/04/ao-bench-in-haskell.html 47. http://www.haskell.org/mailman/listinfo/haskell 48. http://sequence.complete.org/ 49. http://planet.haskell.org/ 50. http://sequence.complete.org/node/feed 51. http://haskell.org/ 52. http://haskell.org/haskellwiki/HWN 53. http://code.haskell.org/~byorgey/code/hwn/

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Classes: functional dependency (type -> value)
by Belka 12 May '09

12 May '09

Hello, communion people! I seek for your advice in a matter, where it's really hard for me to determine a good programming style. Here's the problem. I'm generalizing multiple authorization procedures to one, using class definition. (if of any interest, the code is in the end.) The problem essense is folowing: ---------------- data SomeRole = Role1 | Role2 | Role3 class SomeClass a b c | a -> b, c where f1 :: ... f2 :: ... ... fn :: ... role :: SomeRole -- <-- here is the problem I want to have a fuctional dependency from a type "a" on a value of *role*, so that I could easily "inspect" the *role* from within any other class members. Is it possible? Or do I rougly violate some style traditions? Some real code using wished feature: --------------------------------------- data AuthentificationPurpose = JustValidateInput | JustGenerateForOutput | ValidateInputAndGenerateForOutput type AuthSucceded = Bool class AuthentificationStructure t_env t_realInput t_assumption t_keySet | t_realInput -> t_assumptionInput, t_keySet where authentificationPurpose :: AuthentificationPurpose makeAssumption :: t_env -> t_realInput -> IO (Either ErrorMessage t_assumption) makeFinalKeySet :: (t_realInput, t_assumption) -> t_keySet validateRealKeySet_with_Assumed :: t_realInput -> t_keySet -> Maybe ErrorMessage tryLogTheValidKey :: t_env -> (t_realInput, t_assumption) -> IO (Maybe ErrorMessage) tryLogTheAuthTry :: t_env -> (t_realInput, t_assumption, AuthSucceded) -> IO (Maybe ErrorMessage) authentificate :: AuthentificationStructure t_env t_realInput t_assumptionInput t_keySet => t_env -> t_businessInput -> IO (Either ErrorMessage (t_assumption, t_keySet)) authentificate env realInput = do err_or_assumption <- makeAssumption env realInput case err_or_assumption of Left err_msg -> return $ Left "Error! Assumption maker failed. Lower level error message: " ++ err_msg Just assumption -> do key_set <- makeFinalKeySet (realInput, assumption) err_or_keyset1 <- case authentificationPurpose of JustGenerateForOutput -> return $ Right key_set JustValidateInput -> do mb_failure <- validateRealKeySet_with_Assumed t_realInput key_set case mb_failure of Just err_msg -> return $ Left "Error! Invalid set of auth keys. Lower level error message: " ++ err_msg Nothing -> return $ Right key_set ValidateInputAndGenerateForOutput err_or_keyset2 <- case err_or_keyset1 of Left err_msg -> return err_or_keyset1 Right key_set -> do mb_failure <- tryLogTheValidKey env (realInput, assumption) case mb_failure of Just err_msg -> return $ Left "Error! Could not log valid key. Lower level error message: " ++ err_msg Nothing -> return err_or_keyset1 mb_failure <- tryLogTheAuthTry env (realInput, assumption, isRight err_or_keyset2) case mb_failure of Just err_msg1 -> case err_or_keyset2 of Left err_msg2 -> return $ Left ("1. " ++ err_msg2 ++ "\n2. " ++ err_msg1) Right _ -> return $ Left err_msg1 Nothing -> case err_or_keyset2 of Left err_msg -> return $ Left err_msg Right key_set -> return $ Right (assumption, key_set) --------------------------------- Best regards, Belka -- View this message in context: http://www.nabble.com/Classes%3A-functional-dependency-%28type--%3E-value%2… Sent from the Haskell - Haskell-Cafe mailing list archive at Nabble.com.

4 3

OT: Languages (was: Is Haskell a Good Choice for Web Applications? (ANN: Vocabulink))
by Kalman Noel 12 May '09

12 May '09

wren ng thornton schrieb: > Chris Forno (jekor) wrote: >> That being said, Esperanto, and even Japanese sentence structure perhaps >> is not as different as an agglutinative language like German. I'll need >> to study it more to find out. > > Actually, Japanese is agglutinative too (moreso than German is). I take it the above calling German agglutinative was sort of a typo, because well, it isn't, except having many compound words. Esperanto, on the other hand, is usually described as agglutinative. Kalman

5 5

ANN: AAIP Workshop on ICFP Deadline Extension
by Martin Hofmann 12 May '09

12 May '09

AAIP Workshop on ICFP Deadline Extension Please note that the submission deadline for the 3rd Workshop on Approaches and Applications of Inductive Programming has been extended to May 25. The workshop takes place for the first time at the 14th ACM SIGPLAN International Conference on Functional Programming (ICFP 2009) in Edinburgh, Scotland. If a sufficient number of high quality papers is submitted, there will be a Post-Workshop Proceedings Volume published at Springer LNCS. The workshop will present three invited speakers from the research area of functional programming who have done excellent work to make use of inductive programming techniques. The full Call for Papers and further information are available at http://www.cogsys.wiai.uni-bamberg.de/aaip09/ Submit to the workshop and help to tighten the link between the functional programming and the inductive programming community! Best regards, Ute Schmid, Rinus Plasmeijer and Emanuel Kitzelmann

1 0

Re: [Haskell-cafe] Hoogle: converting binary .hoo into text?
by Peter Verswyvelen 12 May '09

12 May '09

On Mon, May 11, 2009 at 10:25 AM, Neil Mitchell <ndmitchell(a)gmail.com>wrote: > Hi Peter, > > > I would like to use the Hoogle text format in C#. > > Out of curiosity, why? I'm just interested to know what work you're doing. Sure. We're building with a graphical representation of a Haskellish language (a tiny subset of Haskell actually). The target audience is graphical artists and designers. For testing, I would like to populate the library with primitives taken from the Haskell base libraries. I tried using the GHC API for it, but got stuck. I got the advice in #haskell to parse the Hoogle format, which indeed looks simple enough for the task. > Hoogle on Hackage comes with a bunch of binary *.hoo files. Can these be > > converted to text/xml? If not, is the binary format documented? > > The binary format is documented in the code, and there is a show command. > Try: > > hoogle +base --dump > > However the binary format is not an encoding of the text format, it > throws away lots of data, and precomputes interesting tables etc. If > you want the original, the binary is probably not that useful. > > I do have a complete set of text files though. I can upload them to > the Hoogle website, or I can distribute them with the hackage package. > I could just email them to you privately. What seems the best option > for everyone? I'm not everyone but I guess it would be useful in general. From within Haskell, ideally one would just use the GHC API (or Cabal API) to extract all information I guess, but for usage in other languages, an easy to parse format is better no? (maybe even XML, but that is bulky :-) > I know I can build hoo files using "cabal haddock --hoogle". But doing > this > > on the BASE package (which I need) from Hackage fails (I'm on Windows, > using > > MSYS): > > configure: creating ./config.status > > config.status: error: cannot find input file: include/HsBaseConfig.h.in > > Does anyone have an easy solution? Maybe I just need to switch to Linux > to > > get this working? :-) > > I have a small pile of hacks to get the base library building with > Hoogle. You are welcome to look at them (data/generate in the Hoogle > repo). Caution: these hacks may make your eyes bleed, and certainly > won't work for anything but the GHC/base version pair that I last did > it on. > > Thanks > > Neil >

2 1

ANN: Gtk2HS 0.10.1 released
by Peter Gavin 11 May '09

11 May '09

Hi everyone, I'd like to announce the release of Gtk2HS 0.10.1! This release includes mostly bug fixes and other small improvements. Most notably, GHC 6.10.1 is now supported. The source tarball may be downloaded from: http://sourceforge.net/project/showfiles.php?group_id=49207&package_id=42440 A Windows installer will be provided soon. Thanks to all the contributors!

4 6

displaying conetents of a list
by applebiz89 11 May '09

11 May '09

I want to write a function to output the entire contents of a list. not sure of how to do so...This is my list i want to output type Title = String type Director = String type Year = Int type Fan = String data Film = Film Title Director Year [Fan] deriving Show -- List of films testDatabase :: [Film] testDatabase = [(Film "Casino Royale" "Martin Campbell" 2006 ["Garry", "Dave", "Zoe"]) ] ------- I know this isnt right but this is what I have so far listFilms :: [Film] -> [Film] listFilms (film@(Film title director year fans) : films) = putStrLn . show film I know to use show and putStrLn but I just don't know how to put them into the function correctly thank you. -- View this message in context: http://www.nabble.com/displaying-conetents-of-a-list-tp23470633p23470633.ht… Sent from the Haskell - Haskell-Cafe mailing list archive at Nabble.com.

4 3

Hoogle: converting binary .hoo into text?
by Peter Verswyvelen 11 May '09

11 May '09

I would like to use the Hoogle text format in C#. Hoogle on Hackage comes with a bunch of binary *.hoo files. Can these be converted to text/xml? If not, is the binary format documented? I know I can build hoo files using "cabal haddock --hoogle". But doing this on the BASE package (which I need) from Hackage fails (I'm on Windows, using MSYS): configure: creating ./config.status config.status: error: cannot find input file: include/HsBaseConfig.h.in Does anyone have an easy solution? Maybe I just need to switch to Linux to get this working? :-)

1 0

ok, someone check me on this (type unification from the (>>=)/fmap thread)
by Brandon S. Allbery KF8NH 11 May '09

11 May '09

I can't tell where I'm making the mistake here. In the thread where (>>=) and fmap were being confused, the error cited a type (Maybe a) which was supposed to be in typeclass Num. As far as I can tell, if the typechecker gets to the point where Num and Maybe are both present and (m) is Maybe, it has to (1) be focused on the (m b) part of (a -> m b), and therefore (2) must have already unified (a) and (b). But that means (m b) must unify with (Num a => a), which is unified with (b), resulting in the attempt to unify (Num a => a) with (Maybe a); since we get the error about (Maybe a) not being a Num, it must not have gotten there. But that means it can't have related Num to (m a) with (m) bound to Maybe, which is why I assumed it had unified (m) with ((->) r) instead. Can the typechecker really get the Num to the other end of (a -> m b) without also getting the (a) there? Or is it checking for the Num constraint before it has fully evaluated the type of (m b)? I thought typeclass constraints happened later than basic type unification. -- brandon s. allbery [solaris,freebsd,perl,pugs,haskell] allbery(a)kf8nh.com system administrator [openafs,heimdal,too many hats] allbery(a)ece.cmu.edu electrical and computer engineering, carnegie mellon university KF8NH

5 4

Heads up: Conflicting versions of network-2.2.1
by Johan Tibell 11 May '09

11 May '09

Hi, The version of network-2.2.1 that shipped with GHC 6.10 differs from the one on Hackage [1]. The version that was released with GHC was never uploaded to Hackage and was never tagged in the darcs repository. When making a new release of network I forgot to check the version number on the version of network that shipped with GHC. My appologies. If you want the API additions that are present in network-2.2.1 on Hackage use network-2.2.1.1 instead to make sure that e.g. cabal-install doesn't use the version of network that comes with GHC. In the future there won't be any releases directly from the darcs repo. All releases will be made on Hackage to later be picked up by the Haskell Platform. Cheers, Johan 1. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/network-2.2.1

1 0

Just 3 >>= (1+)?
by michael rice 10 May '09

10 May '09

Why doesn't this work? Michael ================ data Maybe a = Nothing | Just a instance Monad Maybe where return = Just fail = Nothing Nothing >>= f = Nothing (Just x) >>= f = f x instance MonadPlus Maybe where mzero = Nothing Nothing `mplus` x = x x `mplus` _ = x ================ [michael@localhost ~]$ ghci GHCi, version 6.10.1: http://www.haskell.org/ghc/ :? for help Loading package ghc-prim ... linking ... done. Loading package integer ... linking ... done. Loading package base ... linking ... done. Prelude> Just 3 >>= (1+) <interactive>:1:0: No instance for (Num (Maybe b)) arising from a use of `it' at <interactive>:1:0-14 Possible fix: add an instance declaration for (Num (Maybe b)) In the first argument of `print', namely `it' In a stmt of a 'do' expression: print it Prelude>

14 19

Haskell IO problem
by applebiz89 10 May '09

10 May '09

I havent done much IO at all in haskell, only within the function itself. However I want to get the input from the interface for the function and havent done this before. // Say I have this as my data type and list of films data Film = Film String String Int [String] -- List of films testDatabase :: [Film] testDatabase = [(Film "Casino Royale" "Martin Campbell" 2006 ["Garry", "Dave", "Zoe"]) ] // with functions such as: becomeFan :: String -> String -> [Film] -> [Film] becomeFan _ _ [] = [] becomeFan filmName fanName ((Film title director year fans):xs) | filmName == title = (Film title director year fanName:fans) : xs | otherwise = (Film title director year fans) : becomeFan filmName fanName xs filmsInGivenYear :: Int -> [Film] -> [String] filmsInGivenYear filmYear films = [ title | (Film title director year fans) <- films, year == filmYear] // I want to ask the user what function they want to use, I have this so far main :: IO() do putStr "Hi there! what is your name: " fanName = getLine do putStr "1 = Insert film, 2 = Become a Fan, 3 = The number of fans of a film, 4 = Film released in a year: " input = getLine read input :: Int (if input == 1 then main x = insertFilm [] else if input == 2 then main x = becomeFan [] else if input == 3 then main x = numberOfFans []) // I thought using the if statement would work, but now I cant think how to gather the needed input for the function they have chosen? thanks apple -- View this message in context: http://www.nabble.com/Haskell-IO-problem-tp23404351p23404351.html Sent from the Haskell - Haskell-Cafe mailing list archive at Nabble.com.

3 2

Is Haskell a Good Choice for Web Applications? (ANN: Vocabulink)
by jekor＠jekor.com 10 May '09

10 May '09

I decided to find out for myself. You can find the results at http://jekor.com/article/is-haskell-a-good-choice-for-web-applications Included is the source code for the web application powering http://www.vocabulink.com/ The source is roughly 2,000 lines of Haskell, along with some SQL and JavaScript. It's written in literate style and includes a 75-page PDF. It demonstrates and explains how to: * use FastCGI to communicate with a web server (nginx in this case) * move data to and from a PostgreSQL database (HDBC) * authenticate users with cookies * interact with users via asynchronous JavaScript and JSON (AJAJ) * collect data with HTML forms (formlets) * communicate with users via email * cache with memcached * implement a custom forums system (with threaded comments) I make no claims that the code is elegant or idiomatic. It is however real code that's running "in the wild". And I hope it's useful to anyone else considering doing web development in Haskell. I welcome and encourage your feedback!

22 49

Re: [Haskell-cafe] cabal parse problems
by Vasili I. Galchin 10 May '09

10 May '09

sorrily nope, Brian ... Vasili On Wed, May 6, 2009 at 6:06 PM, <brian(a)lorf.org> wrote: > On Wednesday, 06.05.09 at 18:05, Vasili I. Galchin wrote: > > Exposed-modules: Swish.HaskellRDF.BuiltInDatatypes, > > ... > > Swish.HaskellRDF.GraphMatch, > > Think it probably doesn't like that trailing comma. >

2 4

haskell - main function
by applebiz89 10 May '09

10 May '09

Could anyone look at this segment of code; it's not compiling wondering if anyone could correct me as to why. Thanks Code: -- Film as datatype type Title = String type Director = String type Year = Int type Fan = String data Film = Film Title Director Year [Fan] -- List of films testDatabase :: [Film] testDatabase = [(Film "Casino Royale" "Martin Campbell" 2006 ["Garry", "Dave", "Zoe"]) ] becomeFan :: Title -> fanName -> [Film] -> [Film] becomeFan _ _ [] = [] becomeFan Title fanName ((Film Title Director Year fan):xs) | filmName == title = (Film Title Director Year fanName:fan) : xs | otherwise = (Film Title Director Year fan) : becomeFan Title fanName xs main :: [Film] -> IO() main db = do putStr "Hi there! what is your name: " fanName = getLine do putStr "1 = Insert film, 2 = Become a Fan, 3 = The number of fans of a film, 4 = Film released in a year, 5 = Given fan, 6 = Stop : " input = getLine x = read input :: Int if x == 1 then do putStr "Enter film title: " filmTitle <- getLine putStr "Enter director name: " filmDirector <- getLine putStr "Enter release year: " filmYear <- getLine main insertFilm [Title Director Year [Film]] else if x == 2 then do putStr "Enter film title: " filmTitle <- getLine putStr "Enter fan name: " fanName <- getLine main becomeFan [Title fanName] else if x == 3 then do putStr "Enter film title: " filmTitle <- getLine main numberOfFans [Title] else if x == 4 then do putStr "Enter film release year: " filmYear <- getLine main filmsInGivenYear [Year [Film]] else if x == 5 then do putStr "Enter the fan name: " fanName <- getLine main givenUser [fanName [Film]] else if x = 6 then return () -- View this message in context: http://www.nabble.com/haskell---main-function-tp23459841p23459841.html Sent from the Haskell - Haskell-Cafe mailing list archive at Nabble.com.

4 3

is value evaluated?
by Nikhil Patil 10 May '09

10 May '09

Hi, I am curious to know if there is a function in Haskell to find if a certain value has already been evaluated. The function I need would have the type: > (?!) :: a -> Bool And I expect it to be such that the following terminates after printing the first 101 fibonacci numbers. > fibs = 0 : 1 : zipWith (+) fibs (tail fibs) > > main = do print $ fibs !! 100 > print $ takeWhile (?!) fibs Although I guess I can imagine the following not terminating: > print $ filter (?!) fibs I would find such a function immensely useful in "printing out" my infinite lists. Thanks! nikhil

8 12

Simulation and GHC Thread Scheduling
by Thomas DuBuisson 10 May '09

10 May '09

All, I have a simple Haskell P2P library that I've been playing with in simulations of 20 to 600 nodes. To run the simulation there is a Haskell thread (forkIO) for every node in the system, one that starts up all the nodes and prints the info (so prints aren't mangled), and one that acts as the router. Before its mentioned - I understand the best way forward would be to refactor the code into IO-less 'algorithm' sections and other sections that perform the needed IO when I'm not simulating. I know this would allow me to declare what order each node runs in and would free me from the scheduler. I'd like to do that if its practical... but! None-the-less, here I am saying that there are many interesting little simulations that could be done without refactoring and the correctness isn't altered by the order of operations (not if the nodes behave properly, the slight variation is actually a good test). What I would like to know is are there any plans for GHC to incorporate user-definable scheduler? It would be useful in numerous instance beyond this poor example; I know user scheduling was briefly mentioned in Li's paper but haven't seen or heard of any interest from others since then. Thomas

3 3

runhaskell CLI parameters
by Vasili I. Galchin 09 May '09

09 May '09

Hello, I have forgotten the runhaskell CLI parameters ... sigh. In particular I want to a "local" build of a set of of package: runhaskell Setup.hs configure --user??? I just did a "runhaskell -?" which didn't tell me a lot! Kind regards, Vasili

4 3

Question concerning Haskell Foundation
by Vasili I. Galchin 09 May '09

09 May '09

Hello, With Haskell Foundation, 1) Can we still publish packages on Hackage? 2) Is Hackage going away? Regards, Vasili

4 5

Writing a compiler in Hakell
by Rouan van Dalen 09 May '09

09 May '09

Hi everyone. I am designing my own programming language. I would like to know what is the best way to go about writing my compiler in haskell. What are the tools available in haskell that can help with compiler construction? I know about Happy. Is that a good tool to use? The compiler is intended for serious use and I would like it to be very efficient, maybe competing with compilers written in C. It should also be very easy to extend as the languoge grows. Are there any good books that you can recommend on compiler construction in general and specific to haskell? On another note, how is the operator + implemented in haskell? is there a primitve (say #+) that is wrapped by the haskell operator +? Maybe something like: (+) :: a -> a -> a v1 + v2 = #+ v1 v2 Thanks in advance Rouan.

11 10

Can HLint help spot space leaks? (was: Re: [Haskell-cafe] Generating Haskell with associated types (and kind annotations))
by Jason Dagit 09 May '09

09 May '09

On Fri, May 8, 2009 at 8:49 AM, Neil Mitchell <ndmitchell(a)gmail.com> wrote: > > I've used the project extensively in HLint > (http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hlint) and > it works fantastically. Hi Neil, A bit off-topic, but your post reminded me: Does HLint currently help the user find space leaks? For example, does it recommend strict folds instead of lazy folds? I looked at the FAQ but this was not listed. I don't really know how feasible this is. Thanks, Jason

2 1

Generating Haskell with associated types (and kind annotations)
by Daniel Peebles 09 May '09

09 May '09

Hi all, I was wondering whether anyone had any suggestions on a good way to generate repetitive code with associated types and kind annotations. I'd like to use TH but as far as I understand, it doesn't support this yet (I think associated types are in HEAD but not kinds), so for now I've been using ruby with string interpolation, which feels rather ugly. It means that I have to edit the ruby script and regenerate the file in question each time I make a change, which doesn't fit in very nicely with cabal (or my patience) and so on. Ideally, I'd have something that I can write mostly like real Haskell (with "holes" to substitute values into), that can be integrated nicely into the cabal build system without using custom external preprocessors or anything like that. Any ideas? Thanks, Dan

3 4

ANNOUNCE: hpc-strobe-0.1: Hpc-generated strobes for a running Haskell program
by Thorkil Naur 09 May '09

09 May '09

I am pleased to announce the initial release of hpc-strobe: Hpc-generated strobes for a running Haskell program. hpc-strobe is a rudimentary library that demonstrates the possibility of using Hpc (Haskell Program Coverage) to inspect the state of a running Haskell program. hpc-strobe-0.1 has been uploaded to hackage: http://hackage.haskell.org/packages/archive/hpc-strobe/0.1/hpc-strobe-0.1.t… In ordinary use of Hpc, a single so-called tix file is produced at the end of a run. The tix file records how many times each expression has been used during the run. This can be used to mark up the source code, identifying expressions that have not been used. hpc-strobe uses the basic machinery provided by Hpc to produce multiple tix files, also called strobes, representing the coverage at different times while the program is running. By subtracting such two tix files, again using Hpc machinery, a tix file representing the expressions used between the times of recording the subtracted tix files is produced. This may be used, for example, to get a better idea of what a long-running program is doing. It could also be used as a profiling tool, getting information about how many times individual expressions are used. A program is included whose strobe differences produce a crude rendering of an analog clock when they are used to mark up the source code using Hpc. Please see the attached example (gunzip the file, point you browser to it, scroll down to view the canvas function). Use of the library involves a simple change of the main function and also requires the program to be enabled for hpc. At the time of writing, this means using a fairly recent version of GHC and compiling the Haskell code with the -fhpc option. For additional details, see the README included in the package. Best regards Thorkil

1 0

Re: [Haskell-cafe] Re: Is Haskell a Good Choice for Web Applications? (ANN: Vocabulink)
by Kalman Noel 09 May '09

09 May '09

Daniel Carrera schrieb: > I think it largely depends on the learner. Some people find vocabulary > easier, or more interesting, others not. I have a hard time learning a > lot of isolated facts (e.g. vocabulary), but I find it easier and more > enjoyable to learn a rule that I can apply many times. But I know people > who are the exact opposite. I wouldn't want to make an absolute rule. Or like a local physics prof likes to put it: “I guess you all have an idea of Ohm's law? Or wait, right, for the medics being with us, here are the three Ohm's laws: U = RI, R = U/I, and I= U/R.” Kalman

1 0

Poking fun at haskell and other programming languages
by Andrew Wagner 08 May '09

08 May '09

http://james-iry.blogspot.com/2009/05/brief-incomplete-and-mostly-wrong.html

1 0

monad . comonad = id
by Jan Christiansen 08 May '09

08 May '09

Hi, I have a question regarding the connection between monads and comonads. I always thought of the comonad operations as being the inverse operations of the corresponding monad functions. As I do not know the underlying theory I thought I simply ask the masters. Is there a formal verification for this intuition? That is, are there always corresponding instances for monad and comonad such that the following laws are satisfied? extract . return == id join . duplicate == id If this is the case I would like to know what the corresponding monad for the following comond could be. This comonad treats lists as pointed sets where the first element is focused. instance Comonad [] where extract = head duplicate xs = init (zipWith (++) (tails xs) (inits xs)) Obviously we can define return x = [x]. But I do not know how to define join. Cheers, Jan

3 4

Curry and Reader monad
by Daryoush Mehrtash 08 May '09

08 May '09

In the Is currying monadic?<http://greenokapi.net/blog/2009/05/07/is-currying-monadic/>post the author says: This is again a nested expression. So I wondered if you could again > "flatten" it with a monadic do block: > > let add3 = do > a <- get first parameter > b <- get second parameter > c <- get third parameter > > > return a+b+c > > OK, so I "know" that functions in Haskell (which uses currying for > functions as a general rule) are the "Reader monad". But I don't understand > it well enough to know if that means you can use Reader to implement the > above... > > (I don't understand Reader at all in fact. I must bang my head against it > again, but I find it very confusing - how the monad is represented, what the > functions are, and how they get magically applied.) > Any idea what he is talking about? Thanks Daryoush

2 1

How difficult would creating a collaborative multi-user online virtual world application be in Haskell?
by Benjamin L.Russell 08 May '09

08 May '09

One question that has been coming up at the back of my mind for the past several weeks has been how difficult would it be to create a collaborative multi-user online virtual world application in Haskell. More specifically, last August, I came across a very interesting application called Croquet (see http://www.opencroquet.org/index.php/Main_Page) which happens to be based on Squeak (see http://www.squeak.org/) a dialect of Smalltalk. Croquet, in turn, provides the basis for Cobalt (see http://www.duke.edu/~julian/Cobalt/Home.html) a "virtual workspace browser and construction toolkit for accessing, creating, and publishing hyperlinked multi-user virtual environments" (according to the home page for that project). What struck me as especially interesting was how Croquet allows multiple users to collaborate together in a multi-user online virtual world in software development and other collaborative projects. As one application, the video clip on the upper-right-hand corner of the above-mentioned Croquet home page illustrates how a user can, by writing code from inside the application, create on-the-fly additional virtual environments, which can then be entered by either the programmer or other programmers. Other applications (shown in other video clips on the "Screenshots/Videos" page (see http://www.opencroquet.org/index.php/Screenshots/Videos) show alternative applications that include text-based annotations, a 3D spreadsheet, and writing a conventional blog from within a virtual world. Unfortunately, Smalltalk is an object-oriented language. If possible, I would like to see something similar in a functional programming language such as Haskell. Does anybody know whether duplicating this project in Haskell would be feasible? -- Benjamin L. Russell -- Benjamin L. Russell / DekuDekuplex at Yahoo dot com http://dekudekuplex.wordpress.com/ Translator/Interpreter / Mobile: +011 81 80-3603-6725 "Furuike ya, kawazu tobikomu mizu no oto." -- Matsuo Basho^

4 3

Visualizing Typed Functions
by Duane Johnson 08 May '09

08 May '09

I'm not sure what the policy is on posting with graphical attachments, but I'll give this a tentative try. In case this does not come through with images, I've also posted this on my blog at http://blog.inquirylabs.com/2009/05/07/visualizing-typed-functions/ ===== As I've worked in Haskell over the past several months, I've noticed that my mind has kind of implicitly modeled functional programming as a visual/mechanical representation of concepts. I'd like to make the ideas more explicit, however, so I'm writing this post and cooking up some graphics. I wonder if others have similar "internal representations" of functions, and if perhaps others might suggest improvements over my model. The basic idea is that a function is a semi-circle with inputs on one side (left) and the output at the right. Colors represent types. Here is a function that takes one input and produces one output (of the same type): Haskell would type this as "a -> a". Next, we have a function that takes one type and returns a different type... e.g. a hashing function might take a string and return an integer: (Please ignore the vertical stripe, it's an artifact of my poor Inkscape skills). We can also create functions with more than one input, of course, so here is a binary function. It might be the '+' operator, or some other binary operator, e.g. "a -> a -> a": Haskell and many other languages also have the concept of higher-order functions, i.e. functions that take functions as inputs. Here is a binary function that takes a binary function as input, along with another input, to produce an output of the same type: I imagine polymorphic types as "banded colors" so that the bands contain another type (color). Lists are polymorphic types. Here is what the "head" function might look like ("head" returns the first element in a list): Finally, here is a composite of all of the above visualizations. The "map" function in Haskell is a function that takes a function and a list, and applies that function to each element in the list, returning a new list with the "mapped" elements: The type signature for the "map" function is "(a -> b) -> [a] -> [b]". I wonder what a Monad would look like... With these functions visualized, one could make a kind of "drag and drop" interface for Haskell programming, although that isn't really my intention. I admit this is a little convoluted even for the purpose of visualization, but at least it's a starting place. Does anyone know of another system or better representation?

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ANNOUNCE: The Haskell Platform
by Don Stewart 08 May '09

08 May '09

We're pleased to announce the first release of the Haskell Platform: a single, standard Haskell distribution for every system. Download the Haskell Platform 2009.2.0 installers and specification: http://hackage.haskell.org/platform/ The Haskell Platform is a blessed library and tool suite for Haskell culled from Hackage, along with installers for a wide variety of systems. It saves developers work picking and choosing the best Haskell libraries and tools to use for a task. What you get: http://hackage.haskell.org/platform/contents.html With regular time-based releases, we expect the platform will grow into a rich, indispensable development environment for all Haskell projects. Distro maintainers that support the Haskell Platform can be confident they're fully supporting Haskell as the developers intend it. Developers targetting the platform can be confident they have a trusted base of code to work with. *Please note that this is a beta release*. We do not expect all the installers to work perfectly, nor every developer need met, and we would appreciate feedback. You can help out by packaging the platform for your distro, or reporting bugs and feature requests, or installing Haskell onto your friends' machines. The process for adding new tools and libraries will be outlined in coming weeks. The Haskell Platform would not have been possible without the hard work of the Cabal development team, the Hackage developers and maintainers, the individual compiler, tool and library authors who contributed to the suite, and the distro maintainers who build and distribute the Haskell Platform. Thanks! -- The Platform Infrastructure Team

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beginner question: assigning local variable to a function
by Nico Rolle 08 May '09

08 May '09

hi why does this don't work? test = let a = (>) in 1 `a` 2 regards

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GLFW - Mac OS X
by Günther Schmidt 08 May '09

08 May '09

Hi, has anybody recently install the GLFW package on Mac OS X? It won't install on my machine. Günther

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Trying to contact authors of "Real World Haskell"?
by Itsme (Sophie) 08 May '09

08 May '09

I could not find any contact info for Brian O'Sullivan, Don Stewart, or John Goerzen on their book site. Any pointers to how I might locate any of them much appreciated. Thanks! Sophie

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Getting WriterT log lazily
by Magnus Therning 08 May '09

08 May '09

I've been playing around with (WriterT [Int] IO), trying to get the log out and map `print` over it... and do it lazily. However, I'm not really happy with what I have so far, since I've had to resort to `unsafePerformIO`. Any hints are welcome. What I have so far is: foo = let _tell i = do a <- return $ unsafePerformIO $ sleep 1 tell [a + 1 `seq` i] in do mapM_ _tell [1..10] main = do (_, ~res) <- runWriterT foo mapM_ print res Without the `seq` the call to sleep will simply be skipped (is there an easier way to force evaluation there?). Without `unsafePerformIO` all the sleeping is done up front, and all numbers are print at once at the end. The goal is of course to use code along the same shape to do something more useful, and then `unsafePerformIO` will really be unsafe... /M -- Magnus Therning (OpenPGP: 0xAB4DFBA4) magnus＠therning．org Jabber: magnus＠therning．org http://therning.org/magnus identi.ca|twitter: magthe

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