- Haskell-Cafe - Haskell.org

cabal-install to produce a dependency tree
by Ozgur Akgun 14 Sep '11

14 Sep '11

Dear Cafe, What would be the easiest way of generating the following output, given a package name optionally with additional constraints? $- foo "X > 3" "X > 3" depends on A-2.2, B-1.0, C-1.2 A-2.2 depends on D-1.2.3 ... I assume cabal-install internally does this anyway while creating the installation plan, so is there an easy way to get this info out of cabal install? Thanks, Ozgur

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Undefined symbol error coming from shared, dynamic library.
by David Banas 14 Sep '11

14 Sep '11

Hi all, I'm trying to build a shared, dynamic library for use with a C program. I'm getting an `undefined symbol' error, when I try to run that C program, and was hoping that the last line in the output, below, might mean something to someone. I include the entire output of a `make rebuild' command, below, hoping that, maybe, I just have my command line options a little wrong. Thanks! -db dbanas@dbanas-eeepc:~/prj/haskell/AMIParse/trunk$ make rebuild make clean make[1]: Entering directory `/home/dbanas/prj/haskell/AMIParse/trunk' rm -f *.hi *.o *.out ami_test *.so make[1]: Leaving directory `/home/dbanas/prj/haskell/AMIParse/trunk' make all make[1]: Entering directory `/home/dbanas/prj/haskell/AMIParse/trunk' gcc -I/usr/lib/ghc-6.12.3/include/ -g -fPIC -c -o ami_test.o ami_test.c gcc -rdynamic -o ami_test ami_test.o -ldl ghc -c ApplicativeParsec.hs -cpp -package parsec-3.1.1 -package dsp -dynamic -fPIC ghc -c AMIParse.hs -cpp -package parsec-3.1.1 -package dsp -dynamic -fPIC ghc -c ExmplUsrModel.hs -cpp -package parsec-3.1.1 -package dsp -dynamic -fPIC ghc -c AMIModel.hs -cpp -package parsec-3.1.1 -package dsp -dynamic -fPIC gcc -I/usr/lib/ghc-6.12.3/include/ -g -fPIC -c -o ami_model.o ami_model.c rm -f libami.so ghc -o libami.so -shared -dynamic -package parsec-3.1.1 -package dsp AMIParse.o AMIModel.o ami_model.o AMIModel_stub.o ApplicativeParsec.o ExmplUsrModel.o make[1]: Leaving directory `/home/dbanas/prj/haskell/AMIParse/trunk' dbanas@dbanas-eeepc:~/prj/haskell/AMIParse/trunk$ ./ami_test test.ami /usr/lib/ghc-6.12.3/ghc-prim-0.2.0.0/libHSghc-prim-0.2.0.0-ghc6.12.3.so: undefined symbol: stg_newByteArrayzh

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Final CFP: PEPM12 - Workshop on Partial Evaluation and Program Manipulation
by oleg＠okmij.org 14 Sep '11

14 Sep '11

Final Call For Papers Paper submission deadline: Mon, October 10, 2011, 23:59, GMT ACM SIGPLAN 2012 Workshop on Partial Evaluation and Program Manipulation January 23-24, 2012. Philadelphia, Pennsylvania, USA (co-located with POPL'12) http://www.program-transformation.org/PEPM12 The PEPM Symposium/Workshop series aims to bring together researchers and practitioners working in the broad area of program transformation, which spans from refactoring, partial evaluation, supercompilation, fusion and other metaprogramming to model-driven development, program analyses including termination, inductive programming, program generation and applications of machine learning and probabilistic search. PEPM focuses on techniques, supporting theory, tools, and applications of the analysis and manipulation of programs. Each technique or tool of program manipulation should have a clear, although perhaps informal, statement of desired properties, along with an argument how these properties could be achieved. Topics of interest for PEPM'12 include, but are not limited to: - Program and model manipulation techniques such as: supercompilation, partial evaluation, fusion, on-the-fly program adaptation, active libraries, program inversion, slicing, symbolic execution, refactoring, decompilation, and obfuscation. - Program analysis techniques that are used to drive program/model manipulation such as: abstract interpretation, termination checking, binding-time analysis, constraint solving, type systems, automated testing and test case generation. - Techniques that treat programs/models as data objects including metaprogramming, generative programming, embedded domain-specific languages, program synthesis by sketching and inductive programming, staged computation, and model-driven program generation and transformation. - Application of the above techniques including case studies of program manipulation in real-world (industrial, open-source) projects and software development processes, descriptions of robust tools capable of effectively handling realistic applications, benchmarking. Examples of application domains include legacy program understanding and transformation, DSL implementations, visual languages and end-user programming, scientific computing, middleware frameworks and infrastructure needed for distributed and web-based applications, resource-limited computation, and security. To maintain the dynamic and interactive nature of PEPM, we will continue the category of `short papers' for tool demonstrations and for presentations of exciting if not fully polished research, and of interesting academic, industrial and open-source applications that are new or unfamiliar. Student attendants with accepted papers can apply for a SIGPLAN PAC grant to help cover travel expenses and other support. All accepted papers, short papers included, will appear in formal proceedings published by ACM Press and will be included in the ACM Digital Library. Selected papers may later on be invited for a journal special issue dedicated to PEPM'12. Submission Categories and Guidelines Authors are strongly encouraged to consult the advice for authoring research papers and tool papers before submitting. The PC Chairs welcome any inquiries about the authoring advice. Regular research papers must not exceed 10 pages in ACM Proceedings style. Short papers are up to 4 pages in ACM Proceedings style. Authors of tool demonstration proposals are expected to present a live demonstration of the described tool at the workshop (tool papers should include an additional appendix of up to 6 extra pages giving the outline, screenshots, examples, etc. to indicate the content of the proposed live demo at the workshop). Important Dates - Paper submission: Mon, October 10, 2011, 23:59, GMT - Author notification: Tue, November 8, 2011 - Workshop: Mon-Tue, January 23-24, 2012 Invited Speakers - Markus Pueschel (ETH Zurich, Switzerland) - Martin Berger (University of Sussex, UK) Program Chairs - Oleg Kiselyov (Monterey, CA, USA) - Simon Thompson (University of Kent, UK) Program Committee Members - Emilie Balland (INRIA, France) - Ewen Denney (NASA Ames Research Center, USA) - Martin Erwig (Oregon State University, USA) - Sebastian Fischer (National Institute of Informatics, Japan) - Lidia Fuentes (Universidad de Malaga, Spain) - John Gallagher (Roskilde University, Denmark and IMDEA Software, Spain) - Dave Herman (Mozilla Research, USA) - Stefan Holdermans (Vector Fabrics, the Netherlands) - Christian Kaestner (University of Marburg, Germany) - Emanuel Kitzelmann (International Computer Science Institute, USA) - Andrei Klimov (Keldysh Institute of Applied Mathematics, Russian Academy of Sciences) - Shin-Cheng Mu (Academia Sinica, Taiwan) - Alberto Pardo (Universidad de la Repu'blica, Uruguay) - Kostis Sagonas (Uppsala University, Sweden and National Technical University of Athens, Greece) - Anthony M. Sloane (Macquarie University, Australia) - Armando Solar-Lezama (MIT, USA) - Aaron Stump (The University of Iowa, USA) - Kohei Suenaga (University of Kyoto, Japan) - Eric Van Wyk (University of Minnesota, USA) - Kwangkeun Yi (Seoul National University, Korea)

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Haskell 101 on classes .... duh ..... :^)
by Vasili I. Galchin 14 Sep '11

14 Sep '11

Hello, I am trying to model multigraphs ....but getting errors with ghci and can't figure out why.... I have a serious blind spot .... {-# LANGUAGE MultiParamTypeClasses, FunctionalDependencies #-} module Bonzo where class Graph arrow node where source :: arrow -> node target :: arrow -> node data Arrow = Arrow (Int, Int) instance Graph Arrow Int where source Arrow = fst Arrow target Arrow = snd Arrow ~ ~ {-# LANGUAGE MultiParamTypeClasses, FunctionalDependencies #-} module Bonzo where class Graph arrow node where source :: arrow -> node target :: arrow -> node data Arrow = Arrow (Int, Int) instance Graph Arrow Int where source Arrow = fst Arrow target Arrow = snd Arrow ~ ~ ghci> :load junk1.hs [1 of 1] Compiling Bonzo ( junk1.hs, interpreted ) junk1.hs:19:12: Constructor `Arrow' should have 1 argument, but has been given 0 In the pattern: Arrow In the definition of `source': source Arrow = fst Arrow In the instance declaration for `Graph Arrow Int' junk1.hs:21:12: Constructor `Arrow' should have 1 argument, but has been given 0 In the pattern: Arrow In the definition of `target': target Arrow = snd Arrow In the instance declaration for `Graph Arrow Int' Regards, Vasili

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Question about type families
by Grigory Sarnitskiy 13 Sep '11

13 Sep '11

Is there a way to make the following code working? {-# LANGUAGE TypeFamilies #-} data family Foo a data instance (Num a) => Foo a = A a deriving Show data instance (Fractional a) => Foo a = B a deriving Show I want to have different constructors for 'Foo a' depending on a class of 'a'. Note also, that in the example above I also meant constructor A to be available for (Fractional a) => Foo, since in that case 'a' has Num too. How can I achieve it, maybe not with TypeFamilies? Current error is Conflicting family instance declarations: data instance Foo a -- Defined at 1.hs:7:33-35 data instance Foo a -- Defined at 1.hs:5:33-35

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Can't resolve class dependences (making Boolean class)
by Grigory Sarnitskiy 13 Sep '11

13 Sep '11

Hello! I'm trying to have a class for booleans called Boolean (the methods are not complete): class MyEq a where (===) :: (Boolean b) => a -> a -> b class (MyEq a) => Boolean a where (/\) :: a -> a -> a instance MyEq Bool where x === y = x==y instance Boolean Bool where (/\) = (&&) However, to make Bool an instance of Boolean I need to make it an instance of MyEq first, which I can't, because to define === I need Bool to be in Boolean. Indeed the code above give the error: Could not deduce (b ~ Bool) from the context (Boolean b) bound by the type signature for === :: Boolean b => Bool -> Bool -> b at 1.hs:8:5-18 `b' is a rigid type variable bound by the type signature for === :: Boolean b => Bool -> Bool -> b at 1.hs:8:5 In the expression: x == y In an equation for `===': x === y = x == y In the instance declaration for `MyEq Bool' Failed, modules loaded: none. How can I overcome the issue?

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extending and reusing cmdargs option specs ?
by Simon Michael 13 Sep '11

13 Sep '11

Hi Neil, I just spent a day converting hledger from getopt to cmdargs. cmdargs feels more high level and featureful and nicer. And yet... I haven't reduced the line count that much - nothing like your HLint 3:1 ratio. And, I may have made things worse for myself in the reuse/avoiding boilerplate department: I'm not sure how to reuse a cmdargs options data structure, extending it with a few more options. Using getopt I was able to do this without repeating myself (as long as I defined the full set of Opt constructors in one place.) I've looked at the more advanced cmdargs api, but don't see a way yet - would you have any ideas ? I want this because I have multiple executables (hledger, hledger-vty, hledger-web etc.) which should share most (but not all) options. Also, I'd like to move a generic subset of report options, without the ui- specific ones, into hledger-lib for use by all apps. Also, the hledger executable has multiple commands, so I'd like to define a mode for each, but not have to redeclare all the same options for each mode - I didn't see how to do that. As always, thanks a lot for cmdargs! -Simon

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Can't link OpenCL on Windows
by Jason Dagit 13 Sep '11

13 Sep '11

Hello, I'm trying to get the OpenCLRaw bindings to a point where I can use them on windows. I've forked the the OpenCLRaw repo on github so I can make modifications as needed. My branch is here: https://github.com/dagit/OpenCLRaw I've been mostly working out of my "FunPtr" branch. The issue I'm having is this: I installed AMD's OpenCL SDK, converted their Visual Studio specific .lib file to a file that gcc can handle (.a file), but ghc can't seem to link with it. I get undefined symbols for everything I use in the OpenCL API. I was able to build a "trivial" C program and link it using the .a file that I generated and gcc from mingw (not from the Haskell install). I'm using the latest windows release of the Haskell platform. These are the steps I used for generating the .a file: http://forums.amd.com/forum/messageview.cfm?catid=390&threadid=138890 I used the commands in the example script (e.g., gendef and dlltool). I've tried to use 32bit everything as much as possible, as I know that GHC will want everything to be 32bit, so I don't think it's a 32bit vs. 64bit issue. Does anyone know if there is something different about invoking gcc under ghc instead of the gcc that I get from mingw? I've also played with the ghc command line (I used cabal-dev --verbose=3 to inspect the command line) and I'm still unable to massage it into a working state. Any help would be appreciated! Thanks, Jason

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Haskell Platform Older Releases for Linux
by Luis Cabellos 12 Sep '11

12 Sep '11

Hi, I search the Haskell Platform webpage for older releases, I found it but maybe it's worth to put a table of older releases as tar.gz file with their ghc dependency, like (versions totally make up): HP 2011.2.0.0 source, March 2011. -> ghc 13.1 HP 2010.2.0.0 source, July 2010. -> ghc 3.14 HP 2010.1.0.0 source, March 2010. -> ghc 616 HP 2009.2.0.2 source, July 2009. -> ghc 1 HP 2009.2.0.1 source, June 2009. -> ghc 0 HP 2009.2.0 source, May 2009. -> ghc -1 Thanks, Luis

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Package descriptions on hackage
by Joachim Breitner 12 Sep '11

12 Sep '11

Dear hackage package authors, this is a short message from your distribution package creators: Please, if possible, write good, not too short descriptions, and also keep them up to date. Of course, users browsing hackage will benefit as well. Keep in mind that the users do not know what other packages this relates to. So if the package is part of a larger set of corresponding packages, include a general blob and then explain this particular packages. This is especially true for packages that contain the base types for a suite of packages. Also think about all the possible keywords that someone might enter in a search engine when looking for something like your package, and ideally explain how your library relates to these keywords so that the user can estimate whether it useful for him even before reading the API. Here a few negative examples, not to expose particular authors, but selected because they were the most resent that the Debian Haskell Team had packaged. ========= The http-enumerator package This package uses attoparsec for parsing the actual contents of the HTTP connection. The only gotcha is the withHttpEnumerator function, otherwise should do exactly what you expect. (A list of supported features would be great, maybe a short note what enumerator means. Also, the second sentence is incomprehensible to me and the latest version does not contain a withHttpEnumerator function any more) ========= The representable-functors package Representable functors (Clearly not helpful. Here is what Iulian came up for for the Debian package, from the individual module documentation, but I still think the author could do better This package provides a generalized Store comonad, parameterized by a Representable functor (the representation of that functor serves as the index of the store) and a generalized State monad, parameterized by a Representable functor (the representation of that functor serves as the state). Representable functors on Hask all monads, being isomorphic to a reader monad. Representable contravariant endofunctors over the category of Haskell types are isomorphic to (_ -> r) and resemble mappings to a fixed range. Representable endofunctors over the category of Haskell types are isomorphic to the reader monad and so inherit a very large number of properties for free.) ========= The data-lens package Haskell 98 Lenses (Also not helpful. And probably a very useful package! Iulian wrote „A lense is a composable notion of a purely functional field accessor.“ which is still quite short, but explains the use of the package much better) ========= The algebra package Constructive abstract algebra (Seems to be the “main” package of a series of packages. Yet another reason for having a good description. Here a suggestion, again by Iulian: “This package provides algebraic structures, such as groups, fields, rings, modules. It also provides bands, also known as idempotent semigroups (band is a semigroup where every element is equal to its own square), coalgebras, semirings (rigs), idempotent semirings, also known as dioids.“) ========= I know that most people have better things to do than to write API documentation, so it is not unexpected that, after having written the API documentation after all, they don’t spend too much time on the description. But think about it: It is the first thing possible users are going to see from your package. So if you want to attract users, do take your time to write a comprehensive and comprehensible description. 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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TypeOperators and Unicode
by Grigory Sarnitskiy 12 Sep '11

12 Sep '11

I want to have Unicode symbols for type operator: {-# LANGUAGE TypeOperators #-} data a ── b = Foo a b But it doesn't work. Any suggestions?

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matrix vector product
by kolli kolli 12 Sep '11

12 Sep '11

Hi, can anyone help me with the matrix vector product ....

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Parsec: non-greedy 'between'
by Scott Lawrence 11 Sep '11

11 Sep '11

Hey all, Trying to match C-style comments, I have: between (string "/*") (string "*/") $ many anyChar Which doesn't work, because it is equivalent (ignoring returned values) to do {string "/*"; many anyChar; string "*/"} If the termination criterion was a single character, then I could use noneOf or (satisfy . not), but that doesn't help here. So... what am I missing? Thanks in advance. -- Scott Lawrence

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Functional Programming eXchange 2012: Call for abstracts
by Robert Pickering 11 Sep '11

11 Sep '11

Hello all, I’m sending this email to several mailing lists so my apologies if you see this twice. Functional Programming eXchange is a developer conference that focuses on functional programming. The 2012 edition will take place on Friday March 16th March 2012, at the Skills Matter eXchange, in London. Typically talks are explore concepts that often crop up in functional programming such as parallelism or domain specific languages, look at frameworks built in functional languages or are cases studies of using functional programming in industry. Previous speakers have included: Simon Peyton Jones, Miles Sabin, David Pollak, Adam Granicz, Antonio Cisternino, Tomas Petricek, Jonas Boner, and Viktor Klang. Videos of the talks at the previous events can be found here: http://skillsmatter.com/event/scala/functionalpx-2011 http://skillsmatter.com/event/cloud-grid/functional-programming-exchange-20… If you are interested at speaking at this conference please send a talk abstract to talks_functionalpx(a)skillsmatter.com. I’m aiming to make the decision about which talks have been chosen around 14th October so if you submit an abstract expect to hear from me around this time. Kind regards, Robert

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ANN: Netwire 1.2.4
by Ertugrul Soeylemez 11 Sep '11

11 Sep '11

Hello there, version 1.2.4 of netwire is out. Major changes: * Changed the semantics of time. Previously if a wire was not run (because of an earlier inhibiting wire), then its local time was suspended. Example: proc _ -> do t1 <- time -< () fps1 <- avgFps 1000 -< () require_ <<< wackelkontakt -< () t2 <- time -< () fps2 <- avgFps 1000 -< () identity -< printf "Time: %8.2f %8.2f\nFPS : %8.2f %8.2f" t1 t2 fps1 fps2 In the previous version t2 would be about half of t1, because the {require_ <<< wackelkontakt} wire inhibits for about half of all instances. Further fps1 and fps2 would be about equal. In other words, time was local, while FPS were global. This is not very useful in practical applications. With the new semantics t1 and t2 will be equal. Instead the framerate will drop after the inhibiting wire, such that fps2 will be about half of fps1. So now time is global and FPS are local. This is useful e.g. in a stateless network application (like a web app) to ban users, who are trying logins too fast. The following wire allows one login trial per second in average over the last 10 trials (the faster you try the longer you have to wait): login :: Wire MyApp IpAddress User login = context $ proc ipAddr -> do fps <- avgFps 10 -< () require_ -< fps < 1 {- login procedure -} Used with ArrowPlus this easily lets you fetch the currently logged in user from the session, and if there is none, request a login: getUser :: Wire MyApp IpAddress User getUser = getCurrentUser <+> login * Context-sensitive wires. There is now a new wire transformer called 'context', which is essentially a context switcher establishing multiple wire threads of control: context :: (Ord a, Monad m) => Wire m a b -> Wire m a b It takes a base wire and evolves it individually for each possible input value. This is a very convenient alternative to parallel routing switches. The 'context' wire transformer never forgets a context. For many applications (like sessions in a web application) this is not desirable. For them there is an alternative transformer 'contextLimited', which allows you to garbage-collect. Minor changes: * More responsive calculus wires. Reflect changes immediately without the one-instant delay. If you need the delay for feedback, use 'delay' explicitly. * New analysis wires 'collect' and 'lastSeen'. * New inhibition wires 'forbid_', 'inhibit_' and 'require_'. * Separate session starting/cleaning functions in FRP.NetWire.Session. However, the exception-safe withWire function is the preferred way. * Optimized internal representation. There are now only two constructors WGen and WArr for the Wire type instead of four. I dropped WConst and WId, because they are representable as special cases of WArr without noticable performance loss. This improves overall performance, because now there are only two constructors to pattern-match against. Right now I'm working intensively on netwire, so if you have any feature requests, just mail me. There is a good chance to find your desired feature implemented quickly. Note: I have been too quick with version numbers. Major version 2 will be the one with the stabilized API, so for now with increasing minor version numbers (but not patch levels!) you have to be prepared for API changes, although I don't expect big changes anymore. Enjoy and keep the feedback coming! Greets, Ertugrul -- nightmare = unsafePerformIO (getWrongWife >>= sex) http://ertes.de/

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ANN: cabal-ghci 0.1
by Etienne Laurin 11 Sep '11

11 Sep '11

Hello fellow hackers. Here is a helpful package I wrote to ease the development of projects using cabal. It includes a :cabalset ghci command to set ghci options for your project, and a cabal-ghci executable to launch ghci with those options. Do you get errors when loading your project into ghci? Prelude> a ← return 1 <interactive>:1:3: Not in scope: `←' Prelude> :load Main Could not find module `Main': it is not a module in the current program, or in any known package. cabalset fixes these problems for you. Prelude> :cabalset :set "-i/home/atnnn/up1/src/dist/build/autogen" :set "-i/home/atnnn/up1/src/web" :set "-XUnicodeSyntax" :set "-Wall" Prelude> a ← return 1 <interactive>:1:12: Warning: Defaulting the following constraint(s) to type `Integer' (Num t0) arising from the literal `1' Prelude> :load Main Ok, modules loaded: Main, Application, Handlers. This works from any sub-directory of your project and accepts the following arguments: -fflag enable flag -f-flag disable flag exec load options for the exec executable To install: $ cabal update $ cabal install cabal-ghci $ cat >> ~/.ghci :m + Distribution.Dev.Interactive :def cabalset cabalSet :cabalset :m - Distribution.Dev.Interactive ^D Etienne Laurin

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hledger subcommand detection, RFC
by Simon Michael 11 Sep '11

11 Sep '11

When I split up the hledger package, I always intended to make the hledger program act as a single front end for hledger-* executables. I finally got around to trying that, just pushed to darcs [1]. So hledger now searches your PATH at startup and offer any hledger-* executables as subcommands. To make this fully modular, so that options can be reused and third-party add-ons don't need to be baked in to hledger in any way, there has also been a rather extensive options overhaul, using cmdargs. Below is an example [2] of the new help output with all hledger-* packages plus a local hledger-report.hs script installed. I'm not sure if this is fully safe, cross-platform, robust, quick enough to be unnoticeable, etc. I have about 20 dirs and 4k files in my PATH. I haven't noticed a slowdown on macbook or vps, but have not measured. More testing of this on diverse platforms and machines, or code review, would be very welcome. -Simon [1] http://joyful.com/darcsden/simon/hledger/browse/hledger/Hledger/Cli/Options… [2] $ hledger hledger [COMMAND] ... [OPTIONS] run the specified hledger command. hledger COMMAND --help for more detail. In general, COMMAND should precede OPTIONS. Misc commands: add prompt for new transactions and append them to the journal convert show the specified CSV file as hledger journal entries test run self-tests, or just the ones matching REGEXPS Report commands: accounts (or balance) show matched accounts and their balances entries (or print) show matched journal entries postings (or register) show matched postings and running total activity show a barchart of transactions per interval stats show quick statistics for a journal (or part of it) Add-on commands found: chart [-- OPTIONS] run the hledger-chart program interest [-- OPTIONS] run the hledger-interest program report [-- OPTIONS] run the hledger-report program vty [-- OPTIONS] run the hledger-vty program web [-- OPTIONS] run the hledger-web program -? --help Display help message --debug Show extra debug output -V --version Print version information

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Improvements to Vim Haskell Syntax file - Is anyone the maintainer?
by David Terei 10 Sep '11

10 Sep '11

Hi All, I have made some improvements to the syntax highlighting file for Haskell included with Vim. I'd like to push them upstream. The haskell.vim syntax file included with Vim lists this mailing list as the maintainer. I take that to mean no one. Is this right or does someone actually have responsibility for the Vim Haskell syntax file? here are some screenshots of the changes I've made: http://www.scs.stanford.edu/~davidt/vim-syntax.html Cheers, David

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compiler "pragma"'s
by Vasili I. Galchin 10 Sep '11

10 Sep '11

Hello, Is there a list of compiler pragmas? Specifically I am looking at how to specify more than one type variable in a class definition. Also I have forgotten the "meta syntax" for specifying a pragma ... some kind of Haskell comment? Thanks, Vasili

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matrix manipulations and calculations
by Thomas Friedrich 09 Sep '11

09 Sep '11

Hi everyone, I need to do a lot of matrix manipulation and it needs to be fast. There seems to be a whole bunch of packages dealing with matrix calculations on HackageDB. I am wondering, what is the current state-of-the-art? I started of using hmatrix [1] now. However, I eventually would like to use some functions from the statisics-package [2]. They both use different types for their vector representations. In hmatrix a vector is of type Data.Packed.Vector. In the statistics package, vectors are based on [3]. I found this: http://www.haskell.org/haskellwiki/Linear_algebra but the last post is from 2005. That is 6 years ago. What is the state now? What would you recommend me to use? I don't want to code and then realise in a few month, I made the wrong decision. So, help is greatly appreciated. Thanks, Thomas -- [1] http://hackage.haskell.org/package/hmatrix-0.12.0.0 [2] http://hackage.haskell.org/package/statistics-0.9.0.0 [3] http://hackage.haskell.org/package/vector-0.9

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First CfP: International Conference on Test and Proofs (TAP 2012), Next Deadline: 2011-12-14
by Achim D. Brucker 09 Sep '11

09 Sep '11

(Apologies for duplicates) CALL FOR PAPERS Full and short Research Paper, Industrial Expierence Papers, Tool Papers Abstract submission: Dec 14, 2011, Paper submission Dec 21, 2012 6th INTERNATIONAL CONFERENCE ON TEST AND PROOFS (TAP 2012) http://lifc.univ-fcomte.fr/tap2012/ May 31 - June 1, 2012, Prague, Czech Republic Part of the TOOLS Federated Conferences 2012 http://tools2012.fit.cvut.cz/ The TAP conference is devoted to the convergence of proofs and tests, to the application of techniques from both sides and their combination for the advancement of software quality. Test and Proof seem to be contradictory techniques: if you have proved your program to be correct, it is fruitless to comb it for bugs; and if you are testing it, that is surely a sign that you have given up on any hope to prove its correctness. Accordingly, proofs and tests have, since the onset of software engineering research, been pursued by distinct communities. However, the development of both approaches lead to the discovery of common issues and to the realization that each may need the other. The emergence of model checking has been one of the first signs that contradiction may yield to complementarity. Further evidence give test data generation techniques from models or programs which boil down to constraint resolution techniques for relatively large formula; the advent of powerful SMT solvers have therefore powered new testing techniques. Finally, since formal, proof-based verification is costly, testing invariants and background theories can be helpful to detect errors early and to improve cost effectivity. Summing up, in the past few years an increasing number of research efforts have encountered the need for combining proofs and tests, dropping earlier dogmatic views of incompatibility and taking instead the best of what each of these software engineering domains has to offer. The TAP conference aims to bring together researchers and practitioners working in the converging fields of testing and proving, and will offer a generous allocation of papers, panels and informal discussions. Topics of interest cover theory definitions, tool constructions and experimentations and include (other topics related to TAP are welcome): - Transfer of concepts from testing to proving (e.g., coverage criteria) and from proving to testing - Program proving with the aid of testing techniques - New problematics in automated reasoning emerging from specificities of test generation - Verification and testing techniques combining proofs and tests - Generation of test data, oracles, or preambles by deductive techniques such as: theorem proving, model checking, symbolic execution, constraint logic programming - Model-based testing and verification - Generation of specifications by deduction - Automatic bug finding - Debugging of programs combining static and dynamic analysis - Formal frameworks - Tool descriptions and experience reports - Case studies combining tests and proofs - Applying combination of test and proof techniques to new application domains such as validating security procotols or vulnerability detection of programs Important Dates: ================ Abstract submission: December 14, 2011 Paper submission: December 21, 2011 Notification: March 2, 2012 Camera ready version: March 19, 2012 TAP conference: May 31 - June 1, 2012 (to be confirmed) TOOLS conferences (TOOLS, ICMT, SC, TAP): May 29 - June 01, 2012 Conference Chairs: Bertrand Meyer Program Chairs: Achim D. Brucker and Jacques Julliand Program Committee (to be extended): =================================== Nazareno Aguirre, Bernhard K. Aichernig, Paul Ammann, Dirk Beyer, Nikolaj Bjorner, Robert Clarisó, Marco Comini, Catherine Dubois, Gordon Fraser, Angelo Gargantini, Patrice Godefroid, Martin Gogolla, Arnaud Gotlieb, Reiner Hähnle, Bart Jacobs, Thierry Jéron, Gregory Kapfhammer, Nikolai Kosmatov, Victor Kuliamin, Karl Meinke, Holger Schlingloff, T.H. Tse, Margus Veanes, Luca Viganò, Burkhart Wolff, Fatiha Zaidi Submission: =========== Please submit your papers via http://lifc.univ-fcomte.fr/tap2012/. TAP 2012 will accept two types of papers: - Research papers: full papers with at most 16 pages in LNCS format (pdf), which have to be original, unpublished and not submitted elsewhere. - Short contributions: work in progress, (industrial) experience reports or tool demonstrations, position statements; an extended abstract with at most 6 pages in LNCS format (pdf) is expected. Accepted papers will be published in the Springer LNCS series and will be available at the conference. The contents of previous TAP proceedings is available at: http://www.informatik.uni-trier.de/~ley/db/conf/tap/ -- Dr. Achim D. Brucker, SAP Research, Vincenz-Priessnitz-Str. 1, D-76131 Karlsruhe Phone: +49 6227 7-52595, Fax: +49-6227 78-50502, http://www.brucker.ch

1 0

Leipzig (Germany) Haskell Workshop 7 October - Program and Registration
by Johannes Waldmann 09 Sep '11

09 Sep '11

Dear all, the 6th Haskell in Leipzig workshop, on October 7, will present an absolutely thrilling mixture of tutorials and talks, with special emphasis on parallel programming. for details and registration, http://portal.imn.htwk-leipzig.de/events/hal6-haskell-workshop See you - Johannes Waldmann.

1 0

Converting wiki pages into pdf
by mukesh tiwari 09 Sep '11

09 Sep '11

Hello all I am trying to write a Haskell program which download html pages from wikipedia including images and convert them into pdf . I wrote a small script import Network.HTTP import Data.Maybe import Data.List main = do x <- getLine htmlpage <- getResponseBody =<< simpleHTTP ( getRequest x ) -- open url --print.words $ htmlpage let ind_1 = fromJust . ( \n -> findIndex ( n `isPrefixOf`) . tails $ htmlpage ) $ "" ind_2 = fromJust . ( \n -> findIndex ( n `isPrefixOf`) . tails $ htmlpage ) $ "" tmphtml = drop ind_1 $ take ind_2 htmlpage writeFile "down.html" tmphtml and its working fine except some symbols are not rendering as it should be. Could some one please suggest me how to accomplish this task. Thank you Mukesh Tiwari

7 10

mapM is supralinear?
by Travis Erdman 09 Sep '11

09 Sep '11

The performance of mapM appears to be supralinear in the length of the list it is mapping on. Does it need to be this way? As a comparison, both mapM_ and map are linear in the length of the list. To wit: travis@PW:~/Documents/insurer$ ghci GHCi, version 7.0.3: http://www.haskell.org/ghc/ :? for help Loading package ghc-prim ... linking ... done. Loading package integer-gmp ... linking ... done. Loading package base ... linking ... done. Loading package ffi-1.0 ... linking ... done. Prelude> :set +s Prelude> :set +t Prelude> :m Data.List Data.Maybe Prelude Data.List Data.Maybe> foldl' (+) 0 $ fromJust $ mapM (\x -> Just x) [1..500000] 125000250000 it :: Integer (2.23 secs, 112875864 bytes) Prelude Data.List Data.Maybe> foldl' (+) 0 $ fromJust $ mapM (\x -> Just x) [1..1000000] 500000500000 it :: Integer (6.86 secs, 214002204 bytes) Prelude Data.List Data.Maybe> foldl' (+) 0 $ fromJust $ mapM (\x -> Just x) [1..2000000] 2000001000000 it :: Integer (24.39 secs, 429299748 bytes) Prelude Data.List Data.Maybe> foldl' (+) 0 $ map (\x -> x - 1) [1..1000000] 499999500000 it :: Integer (0.77 secs, 171213436 bytes) Prelude Data.List Data.Maybe> foldl' (+) 0 $ map (\x -> x - 1) [1..10000000] 49999995000000 it :: Integer (7.42 secs, 1723399472 bytes) Prelude Data.List Data.Maybe> foldl' (+) 0 $ map (\x -> x - 1) [1..40000000] 799999980000000 it :: Integer (30.46 secs, 6894835952 bytes) Prelude Data.List Data.Maybe> mapM_ (\x -> Just x) [1..1000000] Just () it :: Maybe () (0.42 secs, 82761248 bytes) Prelude Data.List Data.Maybe> mapM_ (\x -> Just x) [1..10000000] Just () it :: Maybe () (3.87 secs, 808012660 bytes) Prelude Data.List Data.Maybe> mapM_ (\x -> Just x) [1..100000000] Just () it :: Maybe () (38.40 secs, 8054769564 bytes) Prelude Data.List Data.Maybe>

5 6

Next European Hackathon
by Christopher Done 08 Sep '11

08 Sep '11

‘Ello! Any plans for the next European hackathon location that will presumably be in 6~ months? I need time to reap potential participants. Wonder if we could arrange an Italian hackathon? Verohac? Hm. :-) Maybe Utrecht? Hac6? Ciao!

2 1

Solving the configuration problem with parametrized modules
by Joachim Breitner 08 Sep '11

08 Sep '11

Hi Cafe, this is an idea that has been floating in my head for a while, and I’m wondering about its feasibility and, if feasible, complexity (in the range from „trivial“ over “blog post” over “paper” to “thesis”). Application authors in Haskell often face the problem of run-time constants, e.g. values that are expected to be determined once during program start and then stay fixed for the remainder of the run. Good examples are user configuration values (--verbose, certain paths, debugging level, etc.). Usually in Haskell, you’d determine them in the main function and then pass them in an argument to all functions needing them, or you wrap that in a monad. This works and has the advantage of being explicit. One can locally change the value when passing it to another function – this can be a good thing (more powerful) or a bad thing (if the programmer had runtime-constant behavior in mind, an invariant not enforced by the type system or the compiler). The big downside is the verbosity of the approach: A lot of parameters need to be passed, and if one such value is suddenly required in a function where it was not before, this function’s signature and all functions using it have to be modified. Also, I expect that the explicit passing causes a small performance penalty. A less idiomatic approach would be something like this: ====== module M confRef = unsafePerformIO $ newIORef (error "not set yet") conf = unsafePerformIO $ readIORef confRef f = ... conf ... ====== import M main = do ... writeIORef confRef theValue ... f ... ====== This has the nice effect that the programmer can use "conf" as if it is a proper constant value. It could also be quicker, as nothing needs to be passed on the stack. But besides the subtle issues about inlining, this has the big issue of glaring unsafeness: There is no guarantee that confRef is actually set before conf is evaluated, and any code can easily change the confRef anywhere during the runtime. I’d like to propose (on the theoretical level for now, don’t worry) an extension to the language to support _parametrized modules_, which work internally similar to the example above, but with the compiler statically ensuring correctness, where correctness means * The parameter is not evaluated before it is set. * It is set at most once. Rouch syntax sketch: ====== module M parameters (conf1, conf2) f = ... conf ... ====== import M main = do ... M.setParameters someVal1 someVal2 ... f ... ====== where setParameters is a symbol generated by the compiler. The tricky part is, of course, ensuring the correctness. For example while > main = do > M.setParameters 1 2 > ...f... should be easy to check, how about > main = do > id $ M.setParameters 1 2 > ...f... or even > main = do > bool <- someIOAction > guard bool $ M.setParameters 1 2 > ...f... ? I envision a ghc extensions that would allow to one to hook into the type checker and attach bits of information (here: „uses conf“ and „initizalizes M“) to the types, and also check certain conditions (e.g. a >>= b is invalid if a and b both have „initializes M“ attached). If this extension was loaded when id was compiled, it should probably accept the second case, but when no such information is available, or in the third case, reject the code. A framework for such attached bits would surely enable more extensions that statically check some condition that is hard or unwieldy to express in the type system. I have more ideas in that direction, but before I start brabbling, maybe I should first wait for your reactions. Do you think this could be useful (from a user point of view)? Has this idea maybe already been proposed? 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/

8 12

Haskell Weekly News: Issue 198
by Daniel Santa Cruz 08 Sep '11

08 Sep '11

Welcome to issue 198 the HWN, a newsletter covering developments in the Haskell community. This release covers the week of August 28 to September 3, 2011. Announcements Eric Y. Know released the 5th edition of the Parallel Haskell Digest. [1] http://goo.gl/Jqx01 New and Updated Projects * swapper (New - Roman Smrz) Provides a wrapper for functors, which allows their data to be automatically and transparently swapped to disk and loaded back when necessary. [2] http://goo.gl/CwojE * GA (New - Kenneth Hoste) Provides support for working with genetic algorithms in Haskell. [3] http://goo.gl/XjvFA * hledger[-web] (Update - Simon Michael) Bugfix update. [4] http://goo.gl/98ApM * bindings-DSL (Update - Mauricio CA) Provides a language to describe foreign interfaces on top of hsc2hs. [5] http://goo.gl/fFL4Y * hspec (Update - Trystan Spangler) This latest release includes a command line runner that can search through directory trees for specs and support for nested specs. [6] http://goo.gl/rVbF0 * EclipseFP (Update - JP Moresmau) New features and bugfixes. [7] http://goo.gl/dXS6t Quotes of the Week * dankna: I do [gui on osx] by writing a polyglot ObjC/Haskell program * maurer: I'd do it kmc style * hpc: your next challenge: write a definition of fix in java that fits in a twitter post * kmc: i leave for 3 seconds and you're all metaprogramming and shit * acowley: Haskellers are so abstract they can't even spell primitive * edwardk: i was happy that i had the 4th entry on google for a topic... but then i realized it was only for me, not for everyone that searches for it * kmc: oh, my suggestion was to hand off the fd's directly through a UNIX socket ... but that's probably silly ... i just like the fact that fd's can be passed through a unix socket * monochrom: "linear types change the world!" says Wadler. "Record updates change the type!" says Haskell. :) * gosu: Type parameters are covariant. This is not sound, and that does not matter. * Yitzchak Gale: I certainly wouldn't dream of dragging in type-level olegery, unsafe coercion, implicit parameters and other experimental extensions. Simplicity just works. Top Reddit Stories * 8 ways to report errors in Haskell revisited : Inside 233 Domain: blog.ezyang.com, Score: 51, Comments: 33 On Reddit: [8] http://goo.gl/RBcIL Original: [9] http://goo.gl/A2m2Z * Yesod 0.9 Released! A Massive Changelog explained. Domain: yesodweb.com, Score: 43, Comments: 6 On Reddit: [10] http://goo.gl/go7Zo Original: [11] http://goo.gl/dGoMa * EclipseFP 2.1.0 released, with Hoogle and HLint integration, and much more! Domain: jpmoresmau.blogspot.com, Score: 40, Comments: 42 On Reddit: [12] http://goo.gl/6E1QV Original: [13] http://goo.gl/mkx7g * And they say complexity has no philosophical implications Domain: scottaaronson.com, Score: 36, Comments: 9 On Reddit: [14] http://goo.gl/g97k3 Original: [15] http://goo.gl/9OGU7 * data Maybe -- harmful? Domain: blog.dbpatterson.com, Score: 29, Comments: 26 On Reddit: [16] http://goo.gl/fd2QC Original: [17] http://goo.gl/x4ibO * haskell-TLS framework progress report Domain: tab.snarc.org, Score: 29, Comments: 14 On Reddit: [18] http://goo.gl/Mdc8x Original: [19] http://goo.gl/UpyZ6 * I made a simple image upload site using haskell, sqlite3 and lighttpd. Check it out. Domain: self.haskell, Score: 27, Comments: 15 On Reddit: [20] http://goo.gl/vuF8E Original: [21] http://goo.gl/vuF8E * Manuel Chakravarty on Data Parallel Haskell Domain: vimeo.com, Score: 26, Comments: 2 On Reddit: [22] http://goo.gl/CLXJU Original: [23] http://goo.gl/jCf9w * Functional Programming Day : Oct 14th, Cambridge, UK SPJ & D Syme - early book. bef. Aug 31st Domain: fpday.net, Score: 18, Comments: 11 On Reddit: [24] http://goo.gl/wbIWr Original: [25] http://goo.gl/8OPgK * How does AwesomePrelude transform non-strict code to efficient strict code? Domain: self.haskell, Score: 18, Comments: 12 On Reddit: [26] http://goo.gl/VgIQt Original: [27] http://goo.gl/VgIQt * Composable MVCs (or UIs), a google talk by Conal Elliot Domain: youtube.com, Score: 18, Comments: 14 On Reddit: [28] http://goo.gl/9ekmO Original: [29] http://goo.gl/GDEkN Top StackOverflow Questions * Good examples of Not a Functor/Functor/Applicative/Monad? votes: 17, answers: 3 Read on SO: [30] http://goo.gl/F2q5y * Haskell: What monad did I just reinvent? votes: 17, answers: 4 Read on SO: [31] http://goo.gl/HCko4 * Why is Scalas type inference not as powerful as Haskells? votes: 17, answers: 4 Read on SO: [32] http://goo.gl/gvCF1 * Hard to understand Haskell memory allocation behaviour votes: 11, answers: 1 Read on SO: [33] http://goo.gl/X7HtB * Haskell on JVM? votes: 11, answers: 1 Read on SO: [34] http://goo.gl/Ra4kA * Implementations of spatial indexes in Haskell? votes: 11, answers: 1 Read on SO: [35] http://goo.gl/ThqRA * Does Haskell have variadic functions/tuples? votes: 9, answers: 3 Read on SO: [36] http://goo.gl/NLYCE * couldn't match expected type (Int -> Int -> Int) with actual type `(t0, t1, t2)' votes: 9, answers: 2 Read on SO: [37] http://goo.gl/5EmAS * What is the advantage of using a parser generator like happy as opposed to using parser combinators? votes: 9, answers: 3 Read on SO: [38] http://goo.gl/04s9n * manually defining boolean conjunction votes: 8, answers: 1 Read on SO: [39] http://goo.gl/FGbAj About the Haskell Weekly News To help create new editions of this newsletter, please send stories to dstcruz(a)gmail.com. Until next time, Daniel Santa Cruz References 1. http://permalink.gmane.org/gmane.comp.lang.haskell.cafe/92123 2. http://permalink.gmane.org/gmane.comp.lang.haskell.general/18903 3. http://permalink.gmane.org/gmane.comp.lang.haskell.general/18908 4. http://permalink.gmane.org/gmane.comp.finance.ledger.hledger/479 5. http://permalink.gmane.org/gmane.comp.lang.haskell.general/18909 6. http://permalink.gmane.org/gmane.comp.lang.haskell.general/18912 7. http://permalink.gmane.org/gmane.comp.lang.haskell.cafe/92150 8. http://blog.ezyang.com/2011/08/8-ways-to-report-errors-in-haskell-revisited/ 9. http://www.reddit.com/r/haskell/comments/jy34j/8_ways_to_report_errors_in_h… 10. http://www.yesodweb.com/blog/2011/08/announcing-yesod-0.9 11. http://www.reddit.com/r/haskell/comments/jy42c/yesod_09_released_a_massive_… 12. http://jpmoresmau.blogspot.com/2011/09/eclipsefp-210-released.html 13. http://www.reddit.com/r/haskell/comments/k2idm/eclipsefp_210_released_with_… 14. http://www.scottaaronson.com/blog/?p=103 15. http://www.reddit.com/r/haskell/comments/k2kuu/and_they_say_complexity_has_… 16. http://blog.dbpatterson.com/post/9528836599 17. http://www.reddit.com/r/haskell/comments/jxj8i/data_maybe_harmful/ 18. http://tab.snarc.org/post/2011/8/31/tls_progress/ 19. http://www.reddit.com/r/haskell/comments/k12g7/haskelltls_framework_progres… 20. http://www.reddit.com/r/haskell/comments/k2b10/i_made_a_simple_image_upload… 21. http://www.reddit.com/r/haskell/comments/k2b10/i_made_a_simple_image_upload… 22. http://vimeo.com/28477220 23. http://www.reddit.com/r/haskell/comments/k3x2l/manuel_chakravarty_on_data_p… 24. http://www.fpday.net/fpday2011/index.php 25. http://www.reddit.com/r/haskell/comments/jz592/functional_programming_day_o… 26. http://www.reddit.com/r/haskell/comments/k05fo/how_does_awesomeprelude_tran… 27. http://www.reddit.com/r/haskell/comments/k05fo/how_does_awesomeprelude_tran… 28. http://www.youtube.com/watch?v=faJ8N0giqzw 29. http://www.reddit.com/r/haskell/comments/k14k7/composable_mvcs_or_uis_a_goo… 30. http://stackoverflow.com/questions/7220436/good-examples-of-not-a-functor-f… 31. http://stackoverflow.com/questions/7223901/haskell-what-monad-did-i-just-re… 32. http://stackoverflow.com/questions/7234095/why-is-scalas-type-inference-not… 33. http://stackoverflow.com/questions/7247058/hard-to-understand-haskell-memor… 34. http://stackoverflow.com/questions/7261039/haskell-on-jvm 35. http://stackoverflow.com/questions/7270796/implementations-of-spatial-index… 36. http://stackoverflow.com/questions/7220953/does-haskell-have-variadic-funct… 37. http://stackoverflow.com/questions/7232375/couldnt-match-expected-type-int-… 38. http://stackoverflow.com/questions/7269025/what-is-the-advantage-of-using-a… 39. http://stackoverflow.com/questions/7220297/manually-defining-boolean-conjun…

1 0

Fwd: Is there any way to parametrize a value update using record syntax?
by David Barbour 07 Sep '11

07 Sep '11

forgot to CC list. ---------- Forwarded message ---------- From: David Barbour <dmbarbour(a)gmail.com> Date: 2011/9/6 Subject: Re: [Haskell-cafe] Is there any way to parametrize a value update using record syntax? To: Poprádi Árpád <popradi_arpad(a)freemail.hu> 2011/9/6 Poprádi Árpád <popradi_arpad(a)freemail.hu> > But it's ugly. Always the same, only the record selector has another > name. Is it possible to generalize it? > You can generalize using template haskell. I believe Oleg's HList already provides such mechanisms, so you don't need to do this yourself. If you're doing this a lot, try the HList package. (If not, just do the Also, I would say you've too tightly coupled your BigData to the MonadicEnv. I suggest you reduce it instead to: setX :: X -> BigData -> BigData setX x' bd = bd { dataX = x' } updX :: (X -> X) -> BigData -> BigData updX fx bd = bd { dataX = fx (dataX bd) } Then in your state monad you can use: modify (setX x') gets dataX And use of 'updX' is much more composable. That aside, from personal experience, I'm usually okay just using: modify (\ s -> s { dataX = x' }) in the few places I need it.

2 1

ghc-mtl and ghc-7.2.1
by José Romildo Malaquias 07 Sep '11

07 Sep '11

Hello. In order to compile ghc-mtl-1.0.1.0 (the latest released version) with ghc-7.2.1, I would apply the attached patch, which removes any references to WarnLogMonad. ghc-7.2.1 does not have the monad WarnLogMonad anymore. As I do not know the details of the GHC api, I am not sure if this is enough to use ghc-mtl with ghc-7.2.1. I want ghc-mtl in order do build lambdabot. Any thoughts? Romildo

2 1

Is there any way to parametrize a value update using record syntax?
by Poprádi Árpád 07 Sep '11

07 Sep '11

Hi all, i have a record with a lot of items used in a state monad. data BigData = BigData { data1 :: X , data2 :: X -- and so on } type MonadicEnv a = State BigData a I updates the fields in the computation with such functions: updateData1 :: X -> MonadicEnv() updateData1 d = do; env <- get; put env {data1 = d} updateData2 :: X -> MonadicEnv() updateData2 d = do; env <- get; put env {data2 = d} But it's ugly. Always the same, only the record selector has another name. Is it possible to generalize it? Thanks, Árpád

5 5

Data.IArray rant
by Evan Laforge 07 Sep '11

07 Sep '11

I never liked Data.IArray. Recently I had to deal with it again and it kind of touched off a bit of a rant: Array bounds are an inclusive range, which runs counter to almost all other uses of ranges, and for good reason. Length of an array is (high - low + 1). If you want to convert a list to an array it's 'IArray.listArray (0, length xs - 1) xs'. And if you forget to subtract one or add one it's likely to be a runtime crash. Off-by-one errors and runtime crashes... I've gotten accustomed to not having those in haskell! The vast majority of data types have their own set of monomorphic fuctions, and yet array all of the sudden wants to be an interface. That's nice and all, but who actually uses that interface? I recall there used to be a DiffArray and some other variants, but they were decried as being slow and appear to be gone now. So it appears that there's a complexity price paid to support different array types under the same interface, namely giant class contexts that can't be abstracted away and dependence on MPTCs... and appears to be unused. And then another price paid to support arbitrary indices... which I at least have never used. Maybe there is a field where arrays with strange index ranges like 5--20 are useful, but I always just want 0--length-1. Meanwhile, they lack basic features like concatenation. No Monoid instance. In fact, hardly any useful instances. The result is that my first contact with haskell arrays left me with the impression that they were complicated, hard to use, and designed for someone with different priorities than me. Of course, Data.Vector didn't exist back then, but if someone were new to haskell now I would recommend they skip Data.IArray and head straight for vector. If they wanted 2 dimensional arrays then I know there are some matrix libraries. Of course, sometimes IArray is hard to avoid, e.g. Data.Graph is just a type synonym for an array. I wrote a small library of graph utilities, and dealing with the arrays was back to awkward land. So... am I alone in this dislike of IArray? Or maybe someone can explain why it's actually a very useful interface? Admittedly vector is a mere 'cabal install' away, but array has a blessed status as a ghc bundled library and is likely to be the first place people will look, as well as the natural base for other data types that want an array, like Data.Graph. I know it's not as simple as "just debundle IArray" because it's a bootlib and presumably used in ghc itself, though I know there is support for reducing the set of bootlibs. There's also the whole mutable interface, which I haven't used, but maybe I'd like it more. I know the array stuff winds up integrated fairly deeply with ghc's unboxed arrays and whatnot, so there's a lot of detail I don't understand. I just know I dread going back to array using code while I tend to enjoy working with vector, bytestring, text, storablevector, etc.

7 10

Memoization of functions
by Michael Orlitzky 07 Sep '11

07 Sep '11

I'm working on a program where I need to compute a gajillion (171442176) polynomials and evaluate them more than once. This is the definition of the polynomial, and it is expensive to compute: > polynomial :: Tetrahedron -> (RealFunction Point) > polynomial t = > sum [ (c t i j k l) `cmult` (beta t i j k l) | i <- [0..3], > j <- [0..3], > k <- [0..3], > l <- [0..3], > i + j + k + l == 3] Currently, I'm storing the polynomials in an array, which is quickly devoured by the OOM killer. This makes me wonder: how much memory can I expect to use storing a function in an array? Is it possible to save some space through strictness? Does that question even make sense?

2 1

Re: [Haskell-cafe] Configuration Problem and Plugins
by M. George Hansen 06 Sep '11

06 Sep '11

On Sat, Sep 3, 2011 at 12:33 AM, Max Rabkin <max.rabkin(a)gmail.com> wrote: > On Sat, Sep 3, 2011 at 03:15, M. George Hansen <technopolitica(a)gmail.com> wrote: >> Greetings, >> >> I'm a Python programmer who is relatively new to Haskell, so go easy on me :) >> >> I have a program that uses (or will use) plugins to render output to >> the user in a generic way. I'm basing the design of the plugin >> infrastructure on the Plugins library, and have the following >> interface: >> >> data Renderer = Renderer { >> initialize :: IO (), >> destroy :: IO (), >> render :: SystemOutput -> IO () >> } > > How about having initialize return the render (and destroy, if > necessary) functions: > > initialize :: IO (SystemOutput -> IO ()) > > or > > initialize :: IO (SystemOutput -> IO (), IO()) > Thanks for your reply. That does seem like the best solution, I'll give it a try. -- M. George Hansen

2 1

EclipseFP fails to install
by Henk-Jan van Tuyl 06 Sep '11

06 Sep '11

L.S., I have installed Eclipse 3.7 and EclipseFP 2.1.0 on my Windows XP computer After trying to install EclipseFP in Eclipse, I got the following message: C:\Programs\Haskell Platform\2011.2.0.1\bin\ghc-pkg.exe dump --global cabal.0.6.0.exe: failed to parse output of 'ghc-pkg dump' What can I do about this? Regards, Henk-Jan van Tuyl -- http://Van.Tuyl.eu/ http://members.chello.nl/hjgtuyl/tourdemonad.html --

2 1

ANN: Netwire 1.2.0
by Ertugrul Soeylemez 06 Sep '11

06 Sep '11

Hello there, version 1.2.1 of netwire is out. New features include: * Completely reworked event system. Events are now solely based on signal inhibition, which turns out to be much more convenient and faster than AFRP's traditional approach using Maybe-wrapped values. Now instead of checking for the presence of an event, you simply assume that it happened. If it didn't happen, then the signal is inhibited and your wire is not run. This makes your code much simpler, because you get along almost entirely without switches. Example displaying a discrete clock updated at intervals of half a second: system :: forall m. Monad m => Wire m () String system = proc _ -> printf "%8.2f" ^<< hold discreteClock -< () where discreteClock :: Wire m () Double discreteClock = proc _ -> do t <- time -< () repeatedly -< (0.5, t) By using ArrowPlus or Alternative, you can handle the case, where the event did not happen, listening for alternative events or simply having a fallback. By using the various wire combinators you can hold, sample, keep or exhibit event values as shown above. * Lots and lots of Haddock documentation improvements. Now the inhibition and feedback behaviour of every builtin wire is documented. * Apropos feedback: Finally added an ArrowLoop instance, so you can now have recursive values in your wires. There is a catch though: Right now wires which produce values used recursively must not inhibit. There is an inherent problem handling the inhibition case, which you will observe as a pattern match error. Right now I don't have a solution for this problem, but I'm working on it. However, it may well be that it simply cannot be solved with my current internal wire representation. This is the price to pay for signal inhibition. To prevent (or rather catch) inhibition you can use the 'exhibit' or 'event' combinators. * Many small performance improvements. Simple signal networks go well beyond 35000 frames per second on my mobile Intel i7 with 1.7 GHz and their executables cost well less than 5 MiB RAM. The performance passes the 50k FPS mark on my i5 with 2.8 GHz at home. This is more than a 10x speedup compared to my last benchmark on the initial release of version 1.0.0 * Removed some of variations of existing wires and replaced them by wire combinators instead. For example 'executeOnce' and 'executeEvery' are gone. Instead you should use the normal 'execute' wire together with 'swallow', 'sample', 'hold' or other combinators. * Changed the semantics of all wires to support feedback. Now some wires support feedback right away, while for others you need a one-instant delay. The feedback behaviour of all wires is Haddock-documented, as noted. Enjoy and please give me as much feedback as possible. =) Greets, Ertugrul -- nightmare = unsafePerformIO (getWrongWife >>= sex) http://ertes.de/

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GHC/Cabal on AFS
by Tristan Ravitch 06 Sep '11

06 Sep '11

I have the Haskell Platform (and my home directory with my cabal-installed packages) installed on an AFS (a network filesystem) volume and have been noticing a strange issue. Whenever I install a package using cabal-install and it gets to a phase of the build where it needs to load a bunch of packages, the build fails without a useful error. Example: cabal-dev install yesod Resolving dependencies... Configuring yesod-core-0.9.1.1... Preprocessing library yesod-core-0.9.1.1... Preprocessing test suites for yesod-core-0.9.1.1... Building yesod-core-0.9.1.1... [ 1 of 15] Compiling Yesod.Internal.Session ( Yesod/Internal/Session.hs, dist/build/Yesod/Internal/Session.o ) [ 2 of 15] Compiling Paths_yesod_core (dist/build/autogen/Paths_yesod_core.hs, dist/build/Paths_yesod_core.o) [ 3 of 15] Compiling Yesod.Logger (Yesod/Logger.hs,dist/build/Yesod/Logger.o ) [ 4 of 15] Compiling Yesod.Internal.RouteParsing(Yesod/Internal/RouteParsing.hs,dist/build/Yesod/Internal/RouteParsing.o) [ 5 of 15] Compiling Yesod.Internal (Yesod/Internal.hs,dist/build/Yesod/Internal.o ) Loading package ghc-prim ... linking ... done. Loading package integer-gmp ... linking ... done. Loading package base ... linking ... done. Loading package bytestring-0.9.1.10 ... linking ... done. Loading package array-0.3.0.2 ... linking ... done. Loading package containers-0.4.0.0 ... linking ... done. Loading package deepseq-1.1.0.2 ... linking ... done. Loading package text-0.11.0.5 ... cabal: Error: some packages failed to install: yesod-0.9.1.1 depends on yesod-core-0.9.1.1 which failed to install. yesod-auth-0.7.1 depends on yesod-core-0.9.1.1 which failed to install. yesod-core-0.9.1.1 failed during the building phase. The exception was: ExitFailure 7 yesod-form-0.3.1 depends on yesod-core-0.9.1.1 which failed to install. yesod-json-0.2.1 depends on yesod-core-0.9.1.1 which failed to install. yesod-persistent-0.2.1 depends on yesod-core-0.9.1.1 which failed to install. If I keep re-running it, it will eventually succeed. It also always makes forward progress (the next attempt will get past text and a few more packages). It seems to be related to the state of the AFS cache; if all of the required packages are in the local AFS cache it usually just works. If the cache has just been flushed (due to other FS operations), this failure pretty much always shows up. Has anyone else experienced anything like this? Alternatively, does anyone have ideas on getting a more useful error message/tracking it down? I didn't see any relevant bugs filed yet, but I wanted to get more information before adding a report.

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Smarter do notation
by Daniel Peebles 05 Sep '11

05 Sep '11

Hi all, I was wondering what people thought of a smarter do notation. Currently, there's an almost trivial desugaring of do notation into (>>=), (>>), and fail (grr!) which seem to naturally imply Monads (although oddly enough, return is never used in the desugaring). The simplicity of the desugaring is nice, but in many cases people write monadic code that could easily have been Applicative. For example, if I write in a do block: x <- action1 y <- action2 z <- action3 return (f x y z) that doesn't require any of the context-sensitivty that Monads give you, and could be processed a lot more efficiently by a clever Applicative instance (a parser, for instance). Furthermore, if return values are ignored, we could use the (<$), (<*), or (*>) operators which could make the whole thing even more efficient in some instances. Of course, the fact that the return method is explicitly mentioned in my example suggests that unless we do some real voodoo, Applicative would have to be a superclass of Monad for this to make sense. But with the new default superclass instances people are talking about in GHC, that doesn't seem too unlikely in the near future. On the implementation side, it seems fairly straightforward to determine whether Applicative is enough for a given do block. Does anyone have any opinions on whether this would be a worthwhile change? The downsides seem to be a more complex desugaring pass (although still something most people could perform in their heads), and some instability with making small changes to the code in a do block. If you make a small change to use a variable before the return, you instantly jump from Applicative to Monad and might break types in your program. I'm not convinced that's necessary a bad thing, though. Any thoughts? Thanks, Dan

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The maximum/minimum asymmetry
by Mario Blažević 05 Sep '11

05 Sep '11

I was recently surprised to discover that the maximum and maximumBy functions always return the *last* maximum, while minimum and minimumBy return the *first* minimum in the list. The following GHCi session demonstrates this: $ ghci GHCi, version 7.2.1: http://www.haskell.org/ghc/ :? for help Loading package ghc-prim ... linking ... done. Loading package integer-gmp ... linking ... done. Loading package base ... linking ... done. Loading package ffi-1.0 ... linking ... done. Prelude> :module +Data.List Data.Ord Prelude Data.List Data.Ord> let list = [(1, 'B'), (1, 'A')] Prelude Data.List Data.Ord> maximumBy (comparing fst) list (1,'A') Prelude Data.List Data.Ord> minimumBy (comparing fst) list (1,'B') I would normally consider this kind of gratuitous asymmetry a bug, but seeing that these functions' implementations have been specified in the Haskell 98 Library Report, I guess they are now a permanent feature of the language. Can anybody explain the reason for this behaviour?

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Idiomatic usage of the fixpoint library
by Roman Cheplyaka 05 Sep '11

05 Sep '11

Hi, I'm looking for an example of idiomatic usage of the fixpoint library[1]. [1]: http://hackage.haskell.org/package/fixpoint-0.1.1 Here's what I managed to get: {-# LANGUAGE TypeFamilies, FlexibleContexts, UndecidableInstances, FlexibleInstances #-} import Data.Fixpoint newtype Expr = Expr { unExpr :: Pre Expr Expr } instance Functor (Pre Expr) => Fixpoint Expr where data Pre Expr a = Add a a | Const Int project = unExpr inject = Expr instance Functor (Pre Expr) where fmap f (Const x) = Const x fmap f (Add x1 x2) = Add (f x1) (f x2) eval = cata eval' where eval' (Const x) = x eval' (Add x1 x2) = x1 + x2 There are some issues with this code, compared to simply using newtype Fix f = In { out :: f (Fix f) } to build an Expr. 1. Since 'Pre' is a data (not type) family, we cannot simply make use of a functor defined elsewhere. We need to define the functor inside the instance declaration (or at least wrap an existing functor). 2. I wasn't able to derive the Functor instance, getting an error Derived instance `Functor (Pre Expr)' requires illegal partial application of data type family Pre In the data type instance declaration for `Pre' 3. Having to use UndecidableInstances makes me feel a bit uncomfortable. This makes me think that the intended usage is somewhat different. So, could someone give an example? -- Roman I. Cheplyaka :: http://ro-che.info/

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Lens with merge (Semigroup)
by Tony Morris 05 Sep '11

05 Sep '11

A regular Lens can be represented as follows: data CoState a = CoState (a -> b) a newtype Lens a b = Lens (a -> CoState b a) I once read about a lens representation that permits a general "merge" operation. I forget where I read it -- I think it was #haskell IRC. However, as I recall, perhaps incorrectly, the merge operation involves a Semigroup[1] and helps to overcome the fact that Lens is not an Arrow and so does not have a (&&&) operation. I am interested to know what this Lens operation is and the associated merge operation. [1] -- Approximate data SemigroupT f a = SemigroupT (a -> a -> f a) -- Tony Morris http://tmorris.net/

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Call for papers: Programming languages meets program verification
by Nikhil Swamy 05 Sep '11

05 Sep '11

PLPV 2012 The Sixth ACM SIGPLAN Workshop Programming Languages meets Program Verification 24th January, 2012 Philadelphia, USA (Affiliated with POPL 2012) http://research.microsoft.com/en-us/um/people/nswamy/plpv12 -------------------------------------------------------------------------------- Overview The goal of PLPV is to foster and stimulate research at the intersection of programming languages and program verification, by bringing together experts from diverse areas like types, contracts, interactive theorem proving, model checking and program analysis. Work in this area typically attempts to reduce the burden of program verification by taking advantage of particular semantic or structural properties of the programming language. Examples include dependently typed programming languages, which leverage a language's type system to specify and check richer than usual specifications or extended static checking systems which incorporate contracts with either static or dynamic contract checking. We invite submissions on all aspects, both theoretical and practical, of the integration of programming language and program verification technology. To encourage cross-pollination between different communities, we seek a broad scope for PLPV. In particular, submissions may have diverse foundations for verification (Type-based, Hoare-logic-based, Abstract Interpretation-based, etc.), target different kinds of programming languages (functional, imperative, object-oriented, etc.), and apply to diverse kinds of program properties (data structure invariants, security properties, temporal protocols, resource constraints, etc.). -------------------------------------------------------------------------------- Important Dates: Submission: 11th October, 2011 Notification: 8th November, 2011 Final Version: 15th November, 2011 Workshop: 24th January, 2012 -------------------------------------------------------------------------------- Submissions We seek submissions of up to 12 pages related to the above topics---shorter submissions are also welcome. Submissions may describe new work, propose new challenge problems for language-based verification techniques, or present a known idea in an elegant way (i.e., a pearl). Submissions should be prepared with SIGPLAN two-column conference format (http://www.sigplan.org/authorInformation.htm) Submitted papers must adhere to the SIGPLAN republication policy (http://www.sigplan.org/republicationpolicy.htm) Concurrent submissions to other workshops, conferences, journals, or similar forums of publication are not allowed. To submit a paper, access the submission site at http://www.easychair.org/conferences/?conf=plpv2012. -------------------------------------------------------------------------------- Publication Accepted papers will be published by the ACM and will appear in the ACM Digital library. -------------------------------------------------------------------------------- Program Committee Amal Ahmed Indiana University Lennart Augustsson Standard Chartered Koen Claessen Chalmers (co-chair) Martin Giese University of Oslo Daniel Licata Carnegie Mellon University Peter MÃ¼ller ETH Zurich Aleksandar Nanevski IMDEA Matthieu Sozeau INRIA Nikhil Swamy Microsoft Research (co-chair) David Walker Princeton University Dana Xu INRIA -------------------------------------------------------------------------------- Previous PLPVs: http://plpv.org

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Final CFP: PADL'12 - Practical Aspects of Declarative Languages 2012
by Claudio Russo 05 Sep '11

05 Sep '11

[Apologies if you receive multiple copies.] Final Call for Papers ===================== 14th International Symposium on Practical Aspects of Declarative Languages (PADL 2012) http://research.microsoft.com/~crusso/padl12 Philadelphia, Pennsylvania, USA, January 23-24, 2012 Co-located with ACM POPL'12 Abstract/Paper submission deadline: September 10th/17th, 2011 Conference Description ====================== Declarative languages build on sound theoretical bases to provide attractive frameworks for application development. These languages have been successfully applied to many different real-world situations, ranging from data base management to active networks to software engineering to decision support systems. New developments in theory and implementation have opened up new application areas. At the same time, applications of declarative languages to novel problems raise numerous interesting research issues. Well-known questions include designing for scalability, language extensions for application deployment, and programming environments. Thus, applications drive the progress in the theory and implementation of declarative systems, and benefit from this progress as well. PADL is a forum for researchers and practitioners to present original work emphasizing novel applications and implementation techniques for all forms of declarative concepts, including, functional, logic, constraints, etc. Topics of interest include, but are not limited to: * Innovative applications of declarative languages * Declarative domain-specific languages and applications * Practical applications of theoretical results * New language developments and their impact on applications * Declarative languages and Software Engineering * Evaluation of implementation techniques on practical applications * Practical experiences and industrial applications * Novel uses of declarative languages in the classroom * Practical extensions such as constraint-based, probabilistic, and reactive languages. PADL'12 welcomes new ideas and approaches pertaining to applications and implementation of declarative languages. In this occasion PADL is co-located, as traditionally, with ACM POPL, which will be held immediately following PADL, January 25-27. The symposium will be held in Philadelphia, Pennsylvania, USA. Important Dates and Submission Guidelines ========================================= Abstract Submission: September 10, 2011 Paper Submission: September 17, 2011 Notification: October 22, 2011 Camera-ready: November 5, 2011 Symposium: January 23-24, 2012 Authors should submit an electronic copy of the full paper in PDF using the Springer LNCS format. The submission will be done through EasyChair conference system. If electronic submission is impossible, please contact the program chairs for information on how to submit hard copies. All submissions must be original work written in English. Submissions must be unpublished and not submitted for publication elsewhere. Work that already appeared in unpublished or informally published workshops proceedings may be submitted. PADL'12 will accept both technical and application papers: * Technical papers must describe original, previously unpublished research results. Technical papers must not exceed 15 pages in Springer LNCS format. * Application papers are a mechanism to present important practical applications of declarative languages that occur in industry or in areas of research other than Computer Science. Application papers will be published in the Springer-Verlag conference proceedings, and will be presented in a separate session. Application papers are expected to describe complex and/or real-world applications that rely on an innovative use of declarative languages. Application descriptions, engineering solutions and real-world experiences (both positive and negative) are solicited. The limit for application papers is 6 pages in Springer LNCS format. Program Committee ================= Marcello Balduccini, Intelligent Systems Department, Kodak Research Labs Edwin Brady, University of St Andrews, Scotland Henning Christiansen, Roskilde University, Denmark Agostino Dovier, University of Udine, Italy Matthew Flatt, University of Utah, USA Gopal Gupta, University of Texas at Dallas, USA John Hughes, Chalmers University of Technology, Sweden; Quviq AB Gabriele Keller, University of New South Wales, Australia Lunjin Lu, Oakland University, USA Marc Pouzet, École normale supérieure, France Ricardo Rocha, University of Porto, Portugal Andreas Rossberg, Google Germany GmbH, Germany Claudio Russo, Microsoft Research Cambridge, UK (co-chair) Kostis Sagonas, Uppsala University, Sweden; NTUA, Greece Satnam Singh, Microsoft Research Cambridge, UK Zoltan Somogyi, University of Melbourne, Australia Eijiro Sumii, Tohoku University, Japan Terrance Swift, Universidade Nova de Lisboa, Portugal; Johns Hopkins University, USA Andrew Tolmach, Portland State University, USA Jan Wielemaker, University of Amsterdam, The Netherlands Roland Yap, National University of Singapore, Republic of Singapore Kwangkeun Yi, Seoul National University, Korea Neng-Fa Zhou, Brooklyn College, City University of New York, USA (co-chair) Contacts ======== For additional information about papers and submissions, please contact the Program Chairs: Claudio Russo Microsoft Research Cambridge,UK Email: crusso <AT> microsoft <DOT> com Neng-Fa Zhou Brooklyn College, The City University of New York, USA Email: zhou <AT> sci <DOT> brooklyn <DOT> cuny <DOT> edu With the Cooperation of ======================= The Association for Logic Programming (ALP) ACM SIGPLAN Microsoft Research, Cambridge ===================================

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Real CMS Application in Haskell
by Haisheng Wu 04 Sep '11

04 Sep '11

Hello guys, I googled for a real open source CMS application in Haskell but have no luck. So I'm wondering if Haskell is used very little in Web development area. Thanks. -Simon

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Enumeratee that generates data
by tsuraan 04 Sep '11

04 Sep '11

I'm trying to write a program whose network behaviour is analogous to a web proxy. A client connects to my server and gives me some data, my server connects to an upstream server and gives data to it, my server gets data from upstream, and gives data to the client. I'd like to write this using the enumerator library, since it seems like it should be possible to do that cleanly. Now, the guts of an echo server are pretty easy: runIteratee $ enumSocket cs sock $$ iterSocket sock That's just plain pretty. You can even put interesting data tranformations (Enumeratees) in there to make it behave a bit differently. What I'd like to do is have an Enumeratee that connects to the upstream server, forwards the request, and then uses one of the Data.Enumerator.List functions to generate a response that is the response from the upstream server. It doesn't look like this is possible though, since Enumeratees are pretty much one output per input. Is my basic model broken here? It's occurred to me that what I actually want to do is tie the enumSocket clientSock to an iterSocket upstreamSock, do the reverse, and then do two runIteratee calls (one in a forkIO, I guess?). That seems uglier, I'm not sure if there would be complications in making sure both Iteratees stop running correctly. Is that the right way to do, or am I just missing some capability that Enumeratees have?

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ANNOUNCE: Hs2lib-0.5.5
by Phyx 04 Sep '11

04 Sep '11

What is it? ======== A preprocessor and library which allow you to create dynamic libs from arbitrary annotated Haskell programs with one click. It also allows you to use the generated lib in C, C++ and C# just by including the generated header files. At a minimum it can be considered the inverse of c2hs. Where to get it? ============ You can get it from Hackage (http://hackage.haskell.org/package/Hs2lib) or by using cabal (cabal install Hs2lib). Documentation, Mailing List, Source, etc ======================= Go to http://mistuke.wordpress.com/category/hs2lib/ for information. Or for a tutorial http://www.scribd.com/doc/63918055/Hs2lib-Tutorial What's New? ========= - Currently Supported: * Autogerates free functions for any StablePtr used. * Added support for memory leak tracing with the --debug flag http://mistuke.wordpress.com/2011/08/09/tracing-lexer-memory-leaks/ * Fixed a bug in the library that caused an error in marshalling * No longer frees strings, in order to prevent heap corruptions on calls from c# * Fixed an issue with lists and type synonyms * Fixed an alignment issue with stdcall * Renamed the hs2c# pragma to hs2cs * Fixed an error in parsing pragmas * Fixed a majot marshalling bug having to do with lists of pointer types * Started on an implementation of an automatic test generator to test exported functions. * Re-arranged the namespaces generated in C#. Now Functions and types are put in different namespaces. - Not Currently supported: * Infix constructors * Control over the autogenerated free functions for StablePtr * Exporting of type/functions with the same name in different modules * Exporting polymorphic functions Details ===== A more detailed documentation will follow in the next few weeks. Why is the first version 0.4.8? -------------- This project has been in development for a very long time. Nearly two years on and off. It was developed mainly to facilitate the creation of Visual Haskell 2010. This is just the first public release of this tool.

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Any good topics for Master Thesis
by Haisheng Wu 04 Sep '11

04 Sep '11

Dear Haskellers, I'm a master student major of computer science and trying to find any topics for my master thesis. My mentor suggest me to find any topic I'm interested in. Therefore I'm thinking whether there are some topics related to FP and Haskell. Especially use such technology to solve problems rather than theory research. Appreciate any suggestions / ideas! -Simon

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ANN: EclipseFP 2.1.0 released
by JP Moresmau 03 Sep '11

03 Sep '11

Hello Haskellers, Version 2.1.0 of the EclipseFP project (Eclipse plugins for Haskell development) has been released. Based mainly on the work Alejandro Serrano did for his GSoC project, this release features a lot of enhancements: - A package/module browser - Hoogle integration: select a identifier in your code and jump to its hoogle definitions - HLint integration: jump directly to HLint errors and warnings - Profiling graphs: run an executable with profiling flags and its the resulting graphs - SourceGraph: generate SourceGraph reports - Better auto completion information And of course some bug fixes. Please go to http://eclipsefp.github.com/, the new website Alejandro designed for more information and installation instructions. Feedback welcome! -- JP Moresmau http://jpmoresmau.blogspot.com/

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Configuration Problem and Plugins
by M. George Hansen 03 Sep '11

03 Sep '11

Greetings, I'm a Python programmer who is relatively new to Haskell, so go easy on me :) I have a program that uses (or will use) plugins to render output to the user in a generic way. I'm basing the design of the plugin infrastructure on the Plugins library, and have the following interface: data Renderer = Renderer { initialize :: IO (), destroy :: IO (), render :: SystemOutput -> IO () } The program loads plugins at the start and runs the initialize function, and then enters the main loop where it repeatedly calls the render function with output to display. When the program exits the main loop, it calls the destroy function to clean up any resources used by the plugin. You can probably already see my problem: how do I pass initialization information created in the initialize function to the render function? I'm vaguely aware of some solutions to the typical "configuration problem", such as implicit arguments or explicitly passing the configuration data through the function call hierarchy. As far as I can tell, neither of these approaches would work because the program can't know at compile time what, if any, configuration data is used by the plugin. I suppose I could pass a Dynamic up the call chain and let the plugin decode it in the render function, but that seems a little kludgy to me. Any thoughts would be greatly appreciated. -- M. George Hansen

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ANN: hledger-web 0.15.1 (& hledger 0.15)
by Simon Michael 02 Sep '11

02 Sep '11

I've made a bugfix release of the hledger-web package, to fix build problems. hledger-web 0.15.1: * web: add missing Hledger.Web.Options to cabal file * web: tighten up dependencies to reduce build problems And here's another new dependency I forgot to mention: flot, the js charting library. The rest of this mail is a repeat of yesterday's announcement, since that one seriously confused google groups, gmane, and perhaps your mailreader (pro tip: don't re-edit old announcements with Mail.app's cmd-shift-d. :) -Simon Date: 2011/9/1 Subject: ANN: hledger 0.15 I'm pleased to announce hledger 0.15! This release includes work by Trygve Laugstøl, Dmitry Astapov, Clint Adams, Johann Klähn and myself. hledger is a library and set of user tools for working with financial data (or anything that can be tracked in a double-entry accounting ledger.) It is a haskell port and friendly fork of John Wiegley's Ledger. hledger provides command-line, curses and web interfaces, and aims to be a reliable, practical tool for daily use. Given a plain text file describing transactions of money or any other commodity, it will print the chart of accounts, account balances, or just the transactions you're interested in. It can also help you record new transactions, or convert CSV data from your bank. Home: http://hledger.org IRC: irc://irc.freenode.net/#ledger Install: cabal update; cabal install hledger [hledger-web hledger-vty hledger-chart hledger-interest] Platform-specific binaries, which are time-consuming to make and support, are now provided on request to financial donors - a great way to give back and help pay hosting costs! Best, -Simon Release notes for 0.15: * hledger's options are now modal, providing better help (using cmdargs) * hledger now lists and runs any hledger-* add-ons found in the user's path * case insensitivity of filter patterns has been fixed * parsing: `alias`/`end aliases` directives, for renaming accounts, are supported, like ledger's but a bit more powerful; also an `--alias` option for renaming on the fly * parsing: the `account` directive now preserves posting type (normal/virtual/balanced virtual) * parsing: the `pop` directive is supported as an alias for `end tag`, like ledger * parsing: `P` (historical price) directives can contain a (ignored) numeric time zone, like ledger * parsing: the leading `!` in directives is now optional and deprecated, like ledger * parsing: entries with a negative amount in the first posting now infer the correct balancing amount * parsing: bad date checking is more accurate * balance: collapsing of boring accounts to one line can be disabled with `--no-elide` * balance: fix a wrong precision regression from last release * convert: standard input can be converted * convert: an alternate rules file can be specified with `--rules` * convert: `account2-field` can be used when the CSV file specifies both accounts * convert: `description-field` can have a custom format and combine multiple CSV fields * convert: `in-field` and `out-field` support CSV files that use two amount columns * convert: don't fail when there's no default journal file * web: the web interface has been overhauled/cleaned up * web: account register views are now transaction-based, like gnucash etc., and show accurate historical balances when possible * web: simple balance charts are displayed (using flot) * web: more expressive and consistent search patterns, using a new matching engine * web: add form uses currently focussed account as default, redirects to itself, formats status messages better * web: sidebar now shows empty/boring accounts too * web: now uses warp and a newer yesod * api simplifications * importable Hledger, Hledger.Web, Hledger.Vty and Hledger.Chart modules * the basic reports are now provided by hledger-lib for easier reuse * new api use examples: `equity.hs`, `uniquify.hs` * some old base 3 support has been dropped * the old -s flag has been dropped Stats: Release contributors: Simon Michael, Trygve Laugstøl, Dmitry Astapov, Clint Adams, Johann Klähn 132 days, 314 commits, 18 end-user features and 6 end-user bugfixes since last release. 210 unit & functional tests and 55% unit test coverage (hledger, hledger-lib packages). 7642 lines of code (all packages).

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type profiling not helpful
by Ozgur Akgun 02 Sep '11

02 Sep '11

Cafe, Using "prog +RTS -M1G -hy" for my program prog, I generate a heap profile as documented in [1]. There is one big block in the output graph labelled with "*" though, which is not very helpful. The star character isn't even mentioned in the documentation, I wonder what it represents. Thanks in advance, [1] http://www.haskell.org/ghc/docs/latest/html/users_guide/prof-heap.html#rts-… -- Ozgur Akgun

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