- Haskell-Cafe - Haskell.org

[Haskell-cafe] hopefully, a very quick question about ByteString lib
by Iain Barnett 27 Oct '09

27 Oct '09

[1 of 1] Compiling Main ( sha1.lhs, interpreted ) import qualified Data.ByteString as B main = B.getLine >>= B.putStrLn Ok, modules loaded: Main. *Main> :main *** Exception: no buffering And just to make sure it's not something to do with GHCi or anything like that main = getLine >>= putStrLn [1 of 1] Compiling Main ( sha1.lhs, interpreted ) Ok, modules loaded: Main. *Main> :main hello hello Why am I getting an error when using the ByteString library? Iain

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ANN: haskell-mode 2.5
by Svein Ove Aas 27 Oct '09

27 Oct '09

Fellow Haskellers, I'm happy to announce the release of haskell-mode 2.5. * By web: http://projects.haskell.org/haskellmode-emacs/ * By darcs: http://code.haskell.org/haskellmode-emacs/ Furthermore, there is a change of maintainer; if you have issues, you should now contact me instead of Stefan Monnier. haskell-mode 2.5 ============= I was uncertain whether to mark this a minor or major release. On the one hand, very little has changed in core functionality. On the other, a new minor mode for indentation has been added: haskell-indentation.el, written by Kristof Bastiaensen. It will be familiar to those of you who have been tracking the CVS repository; there are only minor bug-fixes relative to the last version to be uploaded there. For the rest of you: haskell-indentation.el is an intelligent indentation mode in the style of haskell-indent.el, with a few changes to improve usability. Specifically, instead of a tab cycle, backspace is now used to reduce the nesting level, while tab will increase it. The behaviour is otherwise substantially the same; only valid nestings will be considered. It can be turned on by adding (add-hook 'haskell-mode-hook 'turn-on-haskell-indentation) to your .emacs file, as described in the README. As usual, it is mutually exclusive with the two other indentation modes. Known bugs: * Occasionally, the haskell-indentation parser will get stuck on what it considers to be invalid haskell code, and refuse to accept your commands; this includes, mainly, haskell-newline-and-indent. To avoid annoyance, if you bind RET to haskell-newline-and-indent, you should bind M-RET to plain newline. -- Svein Ove Aas

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Is there a null statement that does nothing?
by michael rice 27 Oct '09

27 Oct '09

It looks like both the THEN and the ELSE in an IF expression must each have an expression. What's a graceful way to do nothing in either or both slots, kind of like the Fortran CONTINUE statement. --mr ================ [michael@localhost ~]$ ghci GHCi, version 6.10.3: http://www.haskell.org/ghc/ :? for help Loading package ghc-prim ... linking ... done. Loading package integer ... linking ... done. Loading package base ... linking ... done. Prelude> if (1==1) then else <interactive>:1:15: parse error on input `else' Prelude> if (1==1) then True else <interactive>:1:24: parse error (possibly incorrect indentation) Prelude> if (1==1) then True else False True Prelude>

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ANN: WFLP2010 2nd CFP: LNCS + invited speaker + abstract due Nov 9
by Pablo Nogueira 27 Oct '09

27 Oct '09

******************************************************************** Second Call For Papers 19th International Workshop on Functional and (Constraint) Logic Programming Madrid, Spain, January 17, 2010 http://babel.ls.fi.upm.es/events/wflp2010/ ********* colocated with Principles of Programming Languages POPL 2010 http://www.cse.psu.edu/popl/10/ ******************************************************************** IMPORTANT DATES Abstract Submission: November 9, 2009 Full Paper Submission: November 15, 2009 Acceptance Notification: December 15, 2009 Preliminary Proceedings: January 5, 2010 Workshop: January 17, 2010 SCOPE The aim of the Workshop on Functional and (Constraint) Logic Programming is to bring together researchers interested in functional programming and (constraint) logic programming with special emphasis on the integration of both paradigms and of other declarative programming extensions. It promotes the cross-fertilizing exchange of ideas and experiences among researchers and students from the different communities interested in the foundations, applications, and combinations of high-level declarative programming languages and related areas. The previous WFLP editions are: WFLP 2009 (Brasilia, Brazil), WFLP 2008 (Siena, Italy), WFLP 2007 (Paris, France), WFLP 2006 (Madrid, Spain), WCFLP 2005 (Tallinn, Estonia), WFLP 2004 (Aachen, Germany), WFLP 2003 (Valencia, Spain), WFLP 2002 (Grado, Italy), WFLP 2001 (Kiel, Germany), WFLP 2000 (Benicassim, Spain), WFLP'99 (Grenoble, France), WFLP'98 (Bad Honnef, Germany), WFLP'97 (Schwarzenberg, Germany), WFLP'96 (Marburg, Germany), WFLP'95 (Schwarzenberg, Germany), WFLP'94 (Schwarzenberg, Germany), WFLP'93 (Rattenberg, Germany), and WFLP'92 (Karlsruhe, Germany). LOCATION WFLP 2010 will be held on January 17, 2010 in Madrid, Spain, colocated with the 37th ACM SIGACT-SIGPLAN Symposium on Principles of Programming Languages (POPL 2010). WFLP 2010 solicits papers in all areas of functional and (constraint) logic programming, including but not limited to: * Foundations: formal semantics, logic variables, binding and abstract syntax, rewriting and narrowing, unification, constraint solving, dynamics, type theory, meta-theory, effects, etc. * Language Design: security, services, modules, type systems, multi-paradigm languages, concurrency and distribution, objects, libraries, generic programming, interoperability, etc. * Implementation: abstract machines, parallelism, compile-time and run-time optimizations, foreign-language interfaces, memory management, multi-threading, exploiting parallel hardware, etc. * Transformation and Analysis: abstract interpretation, specialization, partial evaluation, program transformation, program calculation, program proof, meta-programming, generative programming, etc. * Software Development: algorithms, data structures, design patterns, components and composition, specification, proof assistants, verification and validation, model checking, debugging, testing, profiling, tracing, etc. * Paradigm Integration: integration of declarative programming with other paradigms or features such as imperative, object-oriented, aspect-oriented, concurrent, real-time programming, event-driven architectures, etc. * Applications: education, industry, commercial uses, domain-specific languages, visual/graphical user interfaces, embedded systems, WWW applications, XML processing, artificial intelligence, knowledge representation and machine learning, deductive databases, advanced programming environments and tools, etc. SUBMISSIONS and PROCEEDINGS Authors are invited to submit papers presenting original unpublished work. Papers must be at most 15 pages long. Exceptionally, authors may surpass the page limit by providing well-marked appendices intended as reviewing aids. Appendices will not appear in the final publication. Submission categories include regular research papers, system descriptions, and short papers describing on-going work (at most 8 pages). Submissions must be formatted in Lecture Notes in Computer Science (LNCS) style. This requirement needs not apply to appendices. Papers should be submitted in pdf format electronically via the web-based submission site http://www.easychair.org/conferences/?conf=wflp2010 Preliminary proceedings will be available at the workshop. Selected authors will be invited to submit a full version of their papers after the workshop. Contributions accepted for the post-workshop proceedings will be published in Springer's Lecture Notes in Computer Science series. INVITED SPEAKER Mariangiola Dezani (University of Torino, Italy) PROGRAM CHAIR Julio Marino (Universidad Politecnica de Madrid, Spain) PROGRAM COMMITTEE Maria Alpuente (Universidad Politecnica de Valencia, Spain) Sergio Antoy (Portland State University, USA) Bernd Brassel (CAU Kiel, Germany) Olaf Chitil (Univ. of Kent, UK) Rachid Echahed (CNRS-IMAG, France) Santiago Escobar (Universidad Politecnica de Valencia, Spain) Moreno Falaschi (Universita di Siena, Italy) Murdoch Gabbay (Heriot-Watt University, UK) Maria Garcia de la Banda (Monash University, Australia) Victor Gulias (Lambdastream SL, Spain) Michael Hanus (CAU Kiel, Germany) Herbert Kuchen (Univ. of Muenster, Germany) Francisco Lopez-Fraguas (Universidad Complutense de Madrid, Spain) James Lipton (Wesleyan University, USA) Mircea Marin (Univ. of Tsukuba, Japan) Juan Jose Moreno-Navarro (Ministry of Science & Innovation, Spain) Brigitte Pientka (McGill University, Canada)

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A 3 line program --> Reid, Don, Daniel
by Philippos Apolinarius 27 Oct '09

27 Oct '09

Thank you for your help. I am sure that you are right as to the cause of the problem. However, I do not know what I should do to solve it. The Haskell program is generated by LaTeX macros. It is useless to import System.IO.UTF8. I did it. The system keeps producing the same error. What I need is to configure GHC to accept input from any editor, or text generating tool (like TeX). I suppose it is not very difficult to do it, since all other languages have it. I mean, Haskell is the only language where I cannot type a common word like "façade" without running into trouble. I will send you a slightly more complete program, so you can analyse the problem. One has two programs in Tex, and an example. The first file is haskell.gen and it defines the macro \haskell{} % Store in file haskell.gen % Last change 2007-05-23 \newcount\evalFilecount \evalFilecount=0 {\gdef\haskellSetup{% \csname newwrite\endcsname\progPort \immediate\openout\progPort H\jobname.hs % \immediate\write\progPort{module H\jobname}% \immediate\write\progPort{where}% \newlinechar=`\^^M% \newlinechar=`\^^M% }% } \newcommand{\haskell}{\begingroup \ifx\progPort\UNDEFINED \haskellSetup\fi% \catcode`\^^M=12 \haskellGen } \newcommand{\haskellGen}[1]{% \immediate\write\progPort{#1}% \endgroup } %end of file haskell.gen The second file is hask.ell and it defines \eval{}. It is slightly more complex than the previous one. Still, it is very simple. % Store in file hask.ell % Last change 2007-05-23 \newcount\evalFilecount \evalFilecount=0 {\gdef\evalSetup{% \csname newwrite\endcsname\outPort % Port name \immediate\openout\outPort \jobname.hs % \newlinechar=`\^^M% \immediate\write\outPort{import H\jobname}% \newlinechar=`\^^M% \immediate\write\outPort{import IO}% \newlinechar=`\^^M% \immediate\write\outPort{main= do }% \newlinechar=`\^^M% }% } \newcommand{\eval}{\begingroup \ifx\outPort\UNDEFINED \evalSetup\fi \global\advance\evalFilecount by 1 \edef\evalAuxFile{\jobname-G-H-C\the\evalFilecount}% \immediate\write\outPort { outh <- openFile "\evalAuxFile.ghc" { WriteMode;} }% {\immediate\openin0=\evalAuxFile.ghc \ifeof0 \immediate\closein0 \else \input \evalAuxFile.ghc \fi}% \catcode`\^^M=12 \evalBody } \newcommand{\evalBody}[1]{% \immediate\write\outPort{#1}% \immediate\write\outPort{ hClose outh;}% \endgroup } %end of file hask.ell Below, there is an example of how to use the above macros. Store it in file tudin.tex. \documentclass[12pt]{article} \usepackage[latin1]{inputenc} \usepackage[brazil]{babel} \usepackage{makeidx} \usepackage{wrapfig} \usepackage{pictexwd} \title{Calling Haskell from \LaTeX} \author{Philippos Apolinarius} \date{} \begin{document} \maketitle \input haskell.gen \input hask.ell % load \eval \eval{ hPutStrLn outh "Hello, facade!" } \eval{ hPutStrLn outh (show (fat 6)) } \haskell{ fat n | n<1= 1 fat n= n*fat(n-1) } \end{document} In order to use these examples, do the following: 1 --- Apply latex to tudin.tex: C:\hastex> latex tudin.tex 2 --- You have generated file tudin.hs and Htudin.hs. Execute tudin.hs: C:\hastex> runghc tudin.hs This action will generate two files: tudin-G-H-C1.ghc, and tudin-G-H-C2.ghc. There is one file for each instance of \eval{}. 3 --- If you run latex tudin.tex again, it will load these two files, and insert the results of the Haskell programs into the resulting pdf or dvi files. C:\hastex> latex tudin.tex My friend has a lot of complex Clean libraries that she uses to generate postscript images of her designs. The trouble is that she needs to compile Clean souce code generated by the two LaTeX macros. SInce Clean needs two files per module (implementation module and definition module), the two LaTeX macros are quite complex. Clean looks a lot like Haskell. Therefore, I believe that she will not have any difficulty in translating the code to Haskell. It is true that input/output is different in Clean and Haskell. However, input/output can be centered in the main function. Unhappily she needs to write all those French, Swiss, Italian and Spanish names, like façade, Antoní Gaudi, Xenákes, etc. BTW, if you discover how to use strings in Haskell, one could write Haskell-café, instead of Haskell-cafe. __________________________________________________________________ Looking for the perfect gift? Give the gift of Flickr! http://www.flickr.com/gift/

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RE: ANN: GPipe-TextureLoad 1.0.0 and GPipe 1.0.3
by Tobias Bexelius 27 Oct '09

27 Oct '09

I accidently missed a spot in the latest GPipe bugfix, this is fixed in version 1.0.4 that I've just uploaded. Sorry for that. /Tobias Bexelius From: tobias_bexelius(a)hotmail.com To: haskell-cafe(a)haskell.org; haskell(a)haskell.org; hopengl(a)haskell.org Subject: ANN: GPipe-TextureLoad 1.0.0 and GPipe 1.0.3 Date: Mon, 26 Oct 2009 22:37:01 +0100 I've uploaded a new version of GPipe as well as a utility package for loading textures. GPipe 1.0.3: * Fixes a major bug in the shader generation GPipe-TextureLoad 1.0.0: * Helps loading GPipe textures from file. It is based on the stb-image package, and supports subsets of the JPG, PNG, TGA, BMP and PSD formats. kolla in resten av Windows LiveT. Inte bara e-post - Windows LiveT är mycket mer än din inkorg. Mer än bara meddelanden _________________________________________________________________ Hitta kärleken nu i vår! http://dejting.se.msn.com/channel/index.aspx?trackingid=1002952

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ANN: GPS package on Hackage
by Thomas DuBuisson 27 Oct '09

27 Oct '09

FYI I've fixed up the GPS package [1] (not previously announced) so it now has a correct distance calculation, new addVector function, and a separate module for the KML export functionality. This is just something I pretty up if/when I need it; let me know if you find it useful and I'll be more likely to maintain it. Features: For Coordinates (single points) Distance, heading and vector calculations Typeclass interface that allows other coordinate schemes (ex: MGRS) to be developed Path distance computation Minimum distance between distinct paths (trivial, computationally expensive) For locations (a point at a given time) and trails (lists of locations) Speed calculation Path smoothing Rest location filtering Basic KML exporting is also available in Data.GPS.KML TODO * Some day I'll have a GPS logger and make a parser for the NEMA format. * Fix or eliminate KML exporting. This should be a different package and is currently an ugly hack. * Add a path intersection algorithm * Make Data.GPS.MGRS Thomas [1] http://hackage.haskell.org/package/gps

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tips on installing System.Console.Readline
by Michael Mossey 27 Oct '09

27 Oct '09

Before I ask my main question, incidentally has anyone noticed that the GHCI prompt, on Windows XP, now has auto-completion! (since 6.10) Awesome! I'm trying to install System.Console.Readline on Windows XP. I need to have GNU readline installed first, which I did (by multiple methods). But running 'cabal install readline' it reports that readline is not found. Obviously I need to set a path or environment variable... can anyone help? Thanks, Mike

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ANNOUNCE: xmonad 0.9 is now available!
by Don Stewart 26 Oct '09

26 Oct '09

http://xmonad.org The xmonad dev team is pleased to announce xmonad 0.9! We think this is a great release. The headlines: * Actions.SpawnOn: Windows go to the workspace they were launched on, even if you're no longer viewing that workspace. Especially handy for slow-launching applications like Firefox * Actions.GridSelect: graphically go to, select, do things with windows, workspaces, prompts ... * Many new window layouts: http://is.gd/4BzAI * Many new scriptable actions: http://is.gd/4BzCN * Focus changes across screens with mouse movement, no longer requiring a click, even for empty workspaces. * Improved xmobar/dzen statusbar functions, easier to use, more compositional * New --restart command line flag to restart a running xmonad process. * Supports for multi-module local configuration files * Support for user-defined X event handling * xmonad comes with 180 extensions for enhancing functionality * Over 3000 commits have been made to the project. Extensive change logs: http://haskell.org/haskellwiki/Xmonad/Notable_changes_since_0.8 About: xmonad is a leading tiling window manager, known for its lightness, reliability, extensibility and efficiency. It supports true multiheaded tiling, and rich, rapid customisation. It is also highly portable, running on regular desktops, laptops, netbooks, phones, game consoles, the OLPC, and more. Features: * Very stable, fast, small and simple. * Automatic window tiling and management * First class keyboard support: a mouse is unnecessary * Full support for tiling windows on multi-head displays * Full support for floating, tabbing and decorated windows * Full support for Gnome and KDE utilities * XRandR support to rotate, add or remove monitors * Per-workspace layout algorithms * Per-screens custom status bars * Compositing support * Powerful, stable customisation and reconfiguration * Large extension library * Excellent, extensive documentation * Large, active development team, support and community Get it! Information, screenshots, documentation, tutorials and community resources are available from the xmonad home page: http://xmonad.org The 0.9 release, and its dependencies, are available from hackage.haskell.org: http://hackage.haskell.org/package/xmonad xmonad packages are available in pretty much every package system, including. Debian, Gentoo, Arch, Ubuntu, OpenBSD, NetBSD, FreeBSD, Gobo, NixOS, Source Mage, Slackware and 0.9 packages will appear in coming days (some are already available). On the fly updating to xmonad 0.9 is supported, without losing your session! You can even use cabal-install: $ cabal update $ cabal install xmonad-0.9 $ cabal install xmonad-contrib-0.9 $ xmonad --recompile mod-q Extensions: xmonad comes with a huge library of extensions (now around 15 times the size of xmonad itself), contributed by viewers like you. Extensions allow for all sorts of functionality and enhancements to the window manager, via Haskell in your config file. For more information on using and writing extensions see the webpage. The library of extensions is available from hackage: http://hackage.haskell.org/cgi-bin/xmonad-contrib Full documentation for using and writing your own extensions: http://xmonad.org/documentation.html This release brought to you by the xmonad dev team: Spencer Janssen Don Stewart Adam Vogt Brent Yorgey Daniel Wagner Devin Mullins Daniel Schoepe Braden Shepherdson Nicolas Pouillard Roman Cheplyaka Gwern Branwen Lukas Mai Featuring code contributions from over 80 developers: Aaron Denney Jason Creighton Alec Berryman Alex Tarkovsky Alexandre Buisse Andrea Rossato Austin Seipp Bas van Dijk Ben Voui Brandon Allbery Chris Mears Christian Thiemann Clemens Fruhwirth Daniel Neri Anders Engstrom Dave Harrison David Glasser David Lazar Dmitry Kurochkin Dominik Bruhn Dougal Stanton Eric Mertens Ferenc Wagner Jan Vornberger Hans Philipp Annen Ivan Tarasov Ivan Veselov Jamie Webb Jeremy Apthorp Malebria Joachim Breitner Joachim Fasting Joe Thornber Joel Suovaniemi Juraj Hercek Justin Bogner Kai Grossjohann Karsten Schoelzel Klaus Weidner Mathias Stearn Mats Jansborg Matsuyama Tomohiro Michael Fellinger Michael Sloan Miikka Koskinen Neil Mitchell Nelson Elhage Nick Burlett Quentin Moser Nils Anders Danielsson Peter De Wachter Robert Marlow Sam Hughes Shachaf Ben-Kiki Shae Erisson Simon Peyton Jones Stefan O'Rear Tom Rauchenwald Valery V. Vorotyntsev Will Farrington Yaakov Nemoy timthelion Rickard Gustafson Trevor Elliott Ian Zerny Ivan Miljenovic Marco e Silva Michal Janeczek David Roundy Wirt Wolff Max Rabkin Sean Escriva Norbert Zeh Alexey Khudyakov Ismael Carnales Luis Cabellos Konstantin Sobolev Dmitry Astapov Andres Salomon Aleksandar Dimitrov Ilya Portnov Michal Trybus Travis Hartwell As well as the support of many others on the #xmonad and #haskell IRC channels, and the wider Haskell and window manager communities. Thanks to everyone for their support!

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ANN: GPipe-TextureLoad 1.0.0 and GPipe 1.0.3
by Tobias Bexelius 26 Oct '09

26 Oct '09

I've uploaded a new version of GPipe as well as a utility package for loading textures. GPipe 1.0.3: * Fixes a major bug in the shader generation GPipe-TextureLoad 1.0.0: * Helps loading GPipe textures from file. It is based on the stb-image package, and supports subsets of the JPG, PNG, TGA, BMP and PSD formats. _________________________________________________________________ Hitta kärleken nu i vår! http://dejting.se.msn.com/channel/index.aspx?trackingid=1002952

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Fortran mixed mode arithmetic expressions -> Haskell
by michael rice 26 Oct '09

26 Oct '09

Translating Fortran mixed mode arithmetic expressions into Haskell is quite a challenge. Believe it or not c=10.**(11-int(alog10(r)+10)) translates to let c = (**) 10.0 $ fromIntegral $ subtract 11 $ truncate $ (+) (logBase 10.0 r) 10.0 I finally broke the expression below into two parts (k1 & k2) to ease translation. I get it that Haskell is expecting to subtract two Integers and is instead being given an Integer and a Double. What must I do to make this work? Are there any guidelines for doing this kind of translation work? Michael ================ Prelude> let mm = 2 Prelude> let k1 = 3*mm+2 Prelude> let k2 = (/) 150 119 Prelude> let k = k1 - k2 <interactive>:1:13: Couldn't match expected type `Integer' against inferred type `Double' In the second argument of `(-)', namely `k2' In the expression: k1 - k2 In the definition of `k': k = k1 - k2 Prelude> :t 150/119 150/119 :: (Fractional t) => t Prelude>

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any haskellers in chicago? Impromptu lakeview meetup tomorrow (tuesday) evening.
by Thomas Hartman 26 Oct '09

26 Oct '09

I'm visiting chicago, and found one other haskeller interested in a haskell meetup tomorrow 7:30 pm lakeview cafe intelligentsia. email thomashartman1 at gmail if you'd like to hook up! this is a relaxed occasion with no fixed agenda other than birds of a feather flocking home. thomas.

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ANN: attempt-0.0.0
by Michael Snoyman 26 Oct '09

26 Oct '09

Hello, I'm happy to announce the first release of the attempt package[1]. It is meant to solve the "how should I represent a failure" issue. It is based on extensible exceptions and provides a monad, a monad transformers and helper functions to replace many standard, unsafe functions like head. This release should be considered unstable as the API is still open to some change, but is quite usable. I have a blog post [2] which includes an example walk through of how to use this library. It covers most of what is available. Comments are most welcome. I would like this to be a suitable replacement for the ubiquitous Maybe, (Either String) and ad-hoc Result data types so often used to report a failure. I'd be very happy to improve the package for the general community. Michael [1] http://hackage.haskell.org/cgi-bin/hackage-scripts/package/attempt [2] http://blog.snoyman.com/2009/10/25/introduction-to-attempt-error-reporting-…

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ANN: HoleyMonoid-0.1
by Martijn van Steenbergen 26 Oct '09

26 Oct '09

Hello! I'm happy to announce the first release of HoleyMonoid, a datatype that helps you build monoids with holes in them. The holes are filled in later using normal function application. For example: > > let holey = now "x = " > . later show > . now ", y = " > . later show > > run holey 3 5 > "x = 3, y = 5" The library is available on Hackage: http://hackage.haskell.org/package/HoleyMonoid Thanks to David Menendez for the name and Sjoerd Visscher for help with rewriting and simplifying. :-) Martijn.

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example of PortMidi use
by erik flister 26 Oct '09

26 Oct '09

hey mike- i think the trouble with your program is that it sends all the events as fast as possible and then terminates -- it is insensitive to their timestamps. probably portmidi's buffer receives them all, starts the first one, and then is destroyed before ever emitting the corresponding off message, leaving the first note hung. i've just been learning haskell and have been using portmidi as a vehicle. here's a demo i've been working on, it seems to work well. it uses Data.Heap (http://hackage.haskell.org/package/heap) as a priority queue to manage the timestamp scheduling and allow you to schedule events nonmonotonically (portmidi expects you to handle this). it also shows how to use the random generator i noticed you asked about. http://code.google.com/p/h1ccup/source/browse/trunk/theory/haskell/src/PMTe… i would really appreciate any style/design critiques that anyone could offer! some specific q's: 1) the 'addNote' function has a local predicate 'match', which winds up being called on every member in the queue twice -- but memoizing it would be hard because it is used by the heap's higher order functions ('filter' and 'partition'). how should i handle this? can i expect/rely on any auto-memoizing? 2) because a noteOff event in midi turns off a note no matter how many previous noteOns occurred, 'addNote' needs to be careful to not schedule a noteOff during a previously scheduled note, and remove any previously scheduled noteOff that would prematurely cut off the new note. the alg is a little tricky and it would be nice to "prove" its correctness -- and there are enough degrees of freedom that QuickCheck would not explore the relevant corner cases. how would one approach this from a curry-howard perspective? 3) i would like the most natural possible musical EDSL, but currently have to write things like 'Dotted $ Triplet $ NoteDur Eighth' rather than 'Dotted Triplet Eighth'. it would be worse if i added a layer of symbols to prevent arbitrary nesting and ordering of 'Dotted' and 'Triplet'. can this be addressed? 4) threadDelay seems to have a resolution of 10ms. isn't that awfully high? (i'm on OSX 10.5.8, ghc 6.10.3). could this possibly because i forkIO the producer, but not the consumer (only the consumer threadDelays)? 5) ski on #haskell wrote 'asksTo' for me (see http://tunes.org/~nef//logs/haskell/09.08.06) -- but it is not as polymorphic as we'd like -- it only works for ReaderT's instead of all MonadReader's. 'asksTo' is for accessing more than one MVar simultaneously inside a ReaderT, one needs to avoid nesting liftIO's (see http://hpaste.org/fastcgi/hpaste.fcgi/view?id=7915) why not allow nested liftIO's, and if there is a good reason, is there a more general solution than asksTo? 6) i would (neurotically) like to work under 'default ()', but this causes zillions of problems that i can't figure out. is there a good strategy for getting all your numbers to work polymorphically? 7) i want to write as paradigmatically as possible, so style advice is very helpful! i've tried to follow the guidelines from the wiki. i didn't see any opportunities to define a new monad, but maybe there are some? the 'addNote' and 'drain' functions, which do the queueing and dequeuing, seem uglier than necessary -- any way to decompose them better? -e On Wed, 14 Oct 2009, Michael Mossey wrote: > Can someone give me an example of Sound.PortMidi use? I'm having trouble. > This program has bugs---makes sound only intermittently, and seems to have > set up some kind of loop that is sending midi messages continuously even > after terminating the program: import Sound.PortMidi import Foreign.C msgs = [ (0::CULong,PMMsg 0x9c 0x40 0x40) , (500, PMMsg 0x8c 0x40 0x40) , (1000, PMMsg 0x9c 0x41 0x40) , (1500, PMMsg 0x8c 0x41 0x40) ] main = do let deviceId = 12 initialize >>= print getDeviceInfo deviceId >>= print startTime <- time let evts = map (\(t,msg) -> PMEvent msg (t+startTime)) msgs result <- openOutput deviceId 10 case result of Right err -> putStrLn ("After open: " ++ show err) Left stream -> do result <- writeEvents stream evts putStrLn ("After write: " ++ show result) close stream return () terminate >>= print

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Re: ghci can't find Paths_ module created by cabal
by Thomas Hartman 26 Oct '09

26 Oct '09

from my bash hints file: thartman@ubuntu:~/haskellInstalls/gitit>thartman_ghci_with_data_files Loading a package with data files in ghci See http://neilmitchell.blogspot.com/2008/02/adding-data-files-using-cabal.html Snip: The above method works well after a program has been installed, but is harder to work with while developing a program. To alleviate these problems, we can add our own Paths module to the program, for example: module Paths_hoogle where getDataFileName :: FilePath -> IO FilePath getDataFileName = return Place this module alongside all the other modules. While developing the program our hand-created Paths module will be invoked, which says the data is always in the current directory. When doing a Cabal build, Cabal will choose its custom generated Paths module over ours, and we get the benefits of Cabal managing our data. 2009/10/21 Robin Green <greenrd(a)greenrd.org>: > I'm trying to run cabal-install in ghci so I can run it under the ghci > debugger. However I try it, though, I always get one of these two > errors: > > /src/greenrd/darcs/cabal-install/Main.hs:70:17: > Could not find module `Paths_cabal_install': > Use -v to see a list of the files searched for. > Failed, modules loaded: none. > > or > > <command line>: > Could not find module `Main': > Use -v to see a list of the files searched for. > > -- > Robin > _______________________________________________ > Libraries mailing list > Libraries(a)haskell.org > http://www.haskell.org/mailman/listinfo/libraries >

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How come pattern match does not recognize this code style?
by Magicloud Magiclouds 26 Oct '09

26 Oct '09

Hi, In case of this: case bala of [ bala , bala , bala ] -> bala bala bala _ -> bala ghc 6.10.4 would fail to compile, because of the wrong indent of line ", bala". -- 竹密岂妨流水过山高哪阻野云飞

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ANN: GlomeVec, IcoGrid
by Jim Snow 26 Oct '09

26 Oct '09

I just uploaded two packages to hackage. The first package [1] is the vector library used by my haskell ray-tracer, Glome, which has been neglected of late. It's one of the first things I ever wrote in Haskell, so some of the code looks a little strange to me now, but it works pretty well for a wide variety of computational geometry tasks. I also included a perlin noise implementation. I released GlomeVec so that I would have a reasonable vector library to work off of for my other project, which is the IcoGrid library [2]. IcoGrid (Icosahedron Grid) is a library for dealing with grids of hexagons and pentagons wrapped around a sphere. Individual grid cells are identified by an integer, and the library can find all the neighbors of a given cell, it can find all the places where three cells intersect at a point, and it can also tell you where in 3-D space the center of the cell is. (The cells are positioned on the surface of a sphere with unit 1.) The one very useful function I haven't implemented yet is, given an arbitrary point, find the cell that the point "belongs" in. I posted a screenshot on the Haskell wiki [3] showing an OpenGL application I wrote that uses IcoGrid. My initial goal was to write some sort of simple environmental simulator that can eventually be made into a game. The grid turned out to be a pretty big project by itself, so I turned it into a stand-alone library. Both libraries have haddock docs, but they aren't showing up on hackage. Is there a trick to tell hackage it needs to generate docs, or do I just need to wait for a cron job to run? -jim [1] http://hackage.haskell.org/package/GlomeVec [2] http://hackage.haskell.org/package/IcoGrid [3] http://www.haskell.org/haskellwiki/IcoGrid

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Re: What is the current state of affairs with supercompilation?
by Peter A. Jonsson 25 Oct '09

25 Oct '09

Hi Eugene, here are some answers: > I'm mainly interested in the following: > - What supercompilers do exist, except for the ones mentioned above? We have prototype implementations of supercompilers for both GHC and the Timber compiler, but they are not yet in a suitable form for public inspection. Neil Mitchell has the source code to Supero available on his homepage [1], which I think uses yhc as frontend and ghc as backend. > - What academic organizations do research in the area? Looking at where the authors of some publications on supercompilation were at the time of the publication gives some hints: - University of York: Neil Mitchell, Colin Runciman - University of Copenhagen: Morten Heine Sørensen, Robert Glück, Jens Peter Secher, Neil Jones - University of Liverpool: Alexei Lisitsa - Russian Academy of Sciences: Sergei Romanenko, Ilya Klyuchnikov - Luleå University of Technology: myself and Johan Nordlander > - What papers should be read by someone eager to learn about > supercompilation and maybe to make research contributions? If you are interested in program optimization, here's two pointers: - A Positive Supercompiler [2] - An Algorithm of Generalization in Positive Supercompilation.[3] Combine these two and you have a positive supercompiler for a first- order functional language, using the notation that is familiar to the functional programming community. More recent work on program optimization: - Neil's thesis [4] - There's a number of tutorials available from the group at University of Copenhagen, all worth a read. Alexei Lisitsa, Sergei Romanenko, and Ilya Klyuchnikov have used supercompilation to do verification: - Verification as a parameterized testing (experiments with the SCP4 supercompiler). [5] - Proving the equivalence of higher-order terms by means of supercompilation. [6] > - What are some solved problems and some open problems in > supercompilation? The algorithms are quite well-studied with respect to correctness. There's less material available on actual implementations, and how to get them to perform well. I haven't seen anything discussing code explosion and similar practical issues. I don't think anyone has mechanically verified the correctness of supercompilation. This is by no means an exhaustive list of everything, but it's something to start with. I hope it helps. Kind Regards, Peter [1] http://community.haskell.org/~ndm/supero/ [2] ftp://ftp.diku.dk/pub/diku/semantics/papers/D-300.ps.gz [3] http://citeseerx.ist.psu.edu/viewdoc/download? doi=10.1.1.49.1869&rep=rep1&type=pdf [4] http://community.haskell.org/~ndm/thesis/ [5] http://www.springerlink.com/content/c8623847257w22j9/ [6] http://pat.keldysh.ru/~roman/doc/Klyuchnikov,Romanenko-2009-- Proving.the.Equivalence.of.Higher- Order.Terms.by.Means.of.Supercompilation.pdf

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unix pkg on cygwin
by Ben Fitzgerald 25 Oct '09

25 Oct '09

Hi just starting out on haskell so thought I'd try and install a few packages. from unix-2.3.2.0: $ runhaskell Setup.hs configure checking target system type... i686-pc-cygwin configure: creating ./config.status config.status: creating unix.buildinfo config.status: creating include/HsUnixConfig.h Setup.hs: Missing dependency on a foreign library: * Missing header file: HsUnix.h * Missing C library: dl This problem can usually be solved by installing the system package that provides this library (you may need the "-dev" version). If the library is already installed but in a non-standard location then you can use the flags --extra-include-dirs= and --extra-lib-dirs= to specify where it is. The file is part of the pkg I'm trying to build: $ find . -name HsUnix.h ./include/HsUnix.h I would not expect to have to include $CWD/include normally when building a pkg but even using --extra-include-dirs does not work. I've followed the setup guide here: http://hackage.haskell.org/trac/ghc/wiki/Building/Windows/Cygwin Any help appreciated! Regards, Ben

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bit of a noob question
by spot135 24 Oct '09

24 Oct '09

Ok maybe a noob question, but hopefully its an easy one. This is what I've got so far: test :: x->[a] -> (b,[b]) test x arrlist = let test1 = x a = filter (\n -> fst n == test1) arrlist test2 = map snd a in (test1, [test2]) so basically I have a list say [(a,1),(a,2),(a,3),(b,1),(b,2)] etc So I give the function a x value (a or b) in this case and it return (a,[1,2,3]) which is all gravy But, Is there a way that i dont have to supply the a or b ie i call the function and it gives me the list [(a,[1,2,3]),(b,[1,2])... I presume i need another layer of recursion but I cant figure out how to do it. Any help would be gratefully received :-) -- View this message in context: http://www.nabble.com/bit-of-a-noob-question-tp26043671p26043671.html Sent from the Haskell - Haskell-Cafe mailing list archive at Nabble.com.

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Re: [Haskell] ANN: quickcheck-poly - Automating QuickCheck for polymorphic/overloaded properties in a small world of types
by Henning Thielemann 24 Oct '09

24 Oct '09

Ahn, Ki Yung schrieb: > Often times QuickCheck properties are polymophic/overloaded without > giving a monomorphic type signature. But there can be several types > that you are interested. You can write scripts that check all the types > you are interested annotating the generic property for each different > monotype, which is a tedious work to do. Here, I automated this via > hint (a Haskell Interpreter Library). How it works is it first asks a > type of a property to the Haskell interpreter and gets a type string, > identifies type variables that start with lowercase alphabet, generate > all possible substitution that may or may not be a correct type, stick > the type string to the property name as a signature and collect only the > meaningful types, and then finally run quickCheck over each meaningful > types. The example below clearly illustrates what it does. Maybe you could write a block of quickCheck tests, that shall be run on different types. tests :: a -> IO () tests x = do quickCheck (\y -> law1 (y `asTypeOf x)) ... allTests = tests (undefined :: Int) tests (undefined :: Double)

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A 3-line program that does not work
by Philippos Apolinarius 24 Oct '09

24 Oct '09

I have a friend who is an architect. I asked her why she does not use Haskell, since she is fond of functional programming. She writes her scripts in Clean, and needs to compile them before using them to generate postscript diagrams. In Haskell, I told her, she could use runghc, and skip the compilation step. She told me that she would consider switching to Haskell, and skipping the compilation step, if I could tell her how to write "façade" in Haskell. C:\ghc\hastex>runghc tudin.hs tudin.hs:10:19: lexical error in string/character literal (UTF-8 decoding error) After browsing the Internet, I noticed that a many of people are having the same problem. Could someone tell me what is wrong with my friend's program? import System.IO main= do outh <- openFile "garb.tsm" WriteMode hPutStrLn outh "A façade is the exterior of a building" hClose outh I would appreciate a "normal" solution, that is, I would like to type the text in any editor, or generate it with LaTeX macros, and compile it using ghc. __________________________________________________________________ Make your browsing faster, safer, and easier with the new Internet Explorer® 8. Optimized for Yahoo! Get it Now for Free! at http://downloads.yahoo.com/ca/internetexplorer/

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Re: [Haskell-beginners] using quickcheck for blackbox testing for 3rd party apps.
by Daniel Fischer 24 Oct '09

24 Oct '09

Am Dienstag 13 Oktober 2009 18:04:52 schrieb Brent Yorgey: > Brent > > * Some smart-alecks might pipe up with something about unsafePerformIO > here. But that's not a cure, it's more like performing an emergency > tracheotomy with a ballpoint pen. Quote of the month!

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STM semantics
by Paolino 24 Oct '09

24 Oct '09

I have a doubt that this code works like I want because actual STM implementation exposes its effects import Control.Concurrent import Control.Concurrent.STM main = do c <- atomically $ newTChan :: IO (TChan ()) r <- atomically $ newTVar False forkIO $ do atomically $ do r0 <- readTVar r case r0 of True -> return () False -> readTChan c myThreadId >>= killThread threadDelay 1000000 atomically (writeTVar r True) The thread stops on readTChan, but exits when I change the TVar, which happens before the readTChan. Should I trust this is the correct STM behaviour , and will not change in different implementations ? thanks paolino

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How do I uninstall GHC on a Mac running Snow Leopard?
by R J 24 Oct '09

24 Oct '09

What's the cleanest way to fully uninstall GHC on a Mac running Snow Leopard? Running Library/Frameworks/GHC.framework/Tools/Uninstaller from an account with admin privileges produced the following, surprising error message: > GHC.framework installer must be run with admin privileges> Prefix command by 'sudo'> logout > [Process completed] Thanks as always. _________________________________________________________________ Windows 7: Simplify your PC. Learn more. http://www.microsoft.com/Windows/windows-7/default.aspx?ocid=PID24727::T:WL…

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What is the current state of affairs with supercompilation?
by Eugene Kirpichov 24 Oct '09

24 Oct '09

Hi. I became intrigued with supercompilation; what is the current state of affairs with it? I know that there exist experimental supercompilers for Java and REFAL. I know of the existence of jhc and its follower lhc, although I don't know quite well what they can and what they can't. I know that ghc is probably going to have a supercompiler inside. I, again, don't know how broads the plans are. I'm mainly interested in the following: - What supercompilers do exist, except for the ones mentioned above? - What academic organizations do research in the area? - What papers should be read by someone eager to learn about supercompilation and maybe to make research contributions? - What are some solved problems and some open problems in supercompilation? -- Eugene Kirpichov Web IR developer, market.yandex.ru

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Haskell Weekly News: Issue 136 - October 24, 2009
by jfredett＠gmail.com 24 Oct '09

24 Oct '09

--------------------------------------------------------------------------- Haskell Weekly News http://sequence.complete.org/hwn/20091024 Issue 136 - October 24, 2009 --------------------------------------------------------------------------- Welcome to issue 136 of HWN, a newsletter covering developments in the [1]Haskell community. Short one this week, I have GREs today, so I've spent more time aggregating GRE knowledge rather than Haskell news. Till next week, Haskellers, The Haskell Weekly News! Announcements PastePipe -- a CLI for hpaste instances. Rogan Creswick [2]announced a new version of PastePipe, a library which reads from stdin and posts it to an hpaste instance (defaulting to hpaste.org) haskell-src-exts-1.2.0. Niklas Broberg [3]announced a major release of haskell-src-exts. Several breaking changes, a few (ideally) backwards compatable changes. See the post for all the details. mecha-0.0.0. Tom Hawkins [4]announced a very cool new DSL in Haskell for Constructive Solid Modelling. GPipe 1.02 and Vec-Transform 1.0.1. Tobias Bexelius [5]announced new versions of these packages, only a few API changes Data.Stream 0.4. Wouter Swierstra [6]announced a very delicate change to Data.Stream involving irrefutable patterns. Specifically added them in functions which produce new streams from old. strptime bindings. Eugene Kirpichov [7]announced bindings to strptime. cereal-0.2. Trevor Elliott [8]announced a new version of the cereal library, a variation on the `binary` package which provides strict parsing. quickcheck-poly. Ki Yung Ahn [9]announced a package for testing polymorphic functions automatically. 2nd CFP: JSC Special Issue on Automated Verification and Specification of Web Systems. demis [10]announced a special issue of the Journal of Symbolic Computation. The issue contains articles relating to Automated Specification and Verification of Web Systems. qtHaskell-1.1.3. David Harley [11]announced a new version of qtHaskell. Discussion Is there in Haskell the eval function? Waldemar Biernacki [12]asked about an `eval` function for Haskell. What's this pattern called? Martijn van Steenbergen [13]asked about a common pattern for an simple EDSL AST-like type. Problems with Haskell. Philippos Apolinarius [14]forwarded his response to a [15]Clean programmer who planned a move to Haskell upon fears of Clean being around for the long term. A very nice read. Statically checked binomail heaps? Maciej Kotowicz [16]talked about his implementation of Statically Checked Binomial Heaps in Haskell Blog noise [17]Haskell news from the [18]blogosphere. Blog posts from people new to the Haskell community are marked with >>>, be sure to welcome them! * Mikael Vejdemo Johansson (Syzygy-): [19][MATH198] Lecture 5 is up. * JP Moresmau: [20]Releasing my code on the unsuspecting public (EclipseFP). * Neil Brown: [21]Benchmarking STM with Criterion. * Galois, Inc: . * Brent Yorgey: [22]Typeclassopedia in Japanese!. * Neil Brown: [23]An early look at ThreadScope, a tool for profiling concurrent and parallel Haskell programs. * FP-Syd: [24]Sydney FP Group: FP-Syd #19.. * Michael Snoyman: [25]Monadic pairs and Kleisli arrows. * Martijn van Steenbergen: [26]Transforming polymorphic values. * Manuel M T Chakravarty: [27]Multicore Haskell Now!. * Don Stewart (dons): [28]Multicore Haskell Now! ACM Reflections | Projections 2009. * Dan Piponi (sigfpe): [29]What Category do Haskell Types and Functions Live In?. * Manuel M T Chakravarty: [30]Don Stewart's talk on Domain Specific Languages and Haskell. Quotes of the Week * Veinor: I program in austere haskell. I name all my variables a, a', a'', a''', etc * ddarius: releases network version 127.0.0.1 * Berengal: 'Bobby Boolean felt horrible. What did he ever do to the other values? He was just a simple bit, a simple answer to a simple question! Suddenly he felt his insides churn; he felt an exception coming on! Oh no! What should he do, now that he was outside of IO?' * Berengal: '"Go away! You're not like us!" the other values yelled. "You're impure! Impure! Impure! Impure!" they started chanting.' * dpratt71: <dpratt71> so I read somewhere that the unofficial motto of Haskell was "avoid success at all costs"... <Baughn> dpratt71: Yeah. We failed. * Warrigal: Note to self: don't do maximum [1..]. * mauke: the first and foremost task of a haskell compiler is to break haskell programs * ksf: ...premature generalisation is the root of all procrastination. * jimi_hendrix: that took longer than it should have, but it feels so pure * ddarius: Unfortunately, the logic programming community has this unhealthy death grip on Prolog. About the Haskell Weekly News New editions are posted to [31]the Haskell mailing list as well as to [32]the Haskell Sequence and [33]Planet Haskell. [34]RSS is also available, and headlines appear on [35]haskell.org. To help create new editions of this newsletter, please see the information on [36]how to contribute. Send stories to jfredett . at . gmail . dot . com. The darcs repository is available at darcs get [37]http://patch-tag.com/r/jfredett/HWN2/pullrepo HWN2 . References Visible links 1. http://haskell.org/ 2. http://article.gmane.org/gmane.comp.lang.haskell.cafe/65222 3. http://article.gmane.org/gmane.comp.lang.haskell.cafe/65219 4. http://article.gmane.org/gmane.comp.lang.haskell.cafe/65134 5. http://article.gmane.org/gmane.comp.lang.haskell.cafe/65119 6. http://article.gmane.org/gmane.comp.lang.haskell.cafe/65116 7. http://article.gmane.org/gmane.comp.lang.haskell.cafe/65061 8. http://article.gmane.org/gmane.comp.lang.haskell.cafe/65043 9. http://article.gmane.org/gmane.comp.lang.haskell.general/17586 10. http://article.gmane.org/gmane.comp.lang.haskell.general/17585 11. http://article.gmane.org/gmane.comp.lang.haskell.general/17583 12. http://thread.gmane.org/gmane.comp.lang.haskell.cafe/65153 13. http://thread.gmane.org/gmane.comp.lang.haskell.cafe/65148 14. http://thread.gmane.org/gmane.comp.lang.haskell.cafe/65014 15. http://clean.cs.ru.nl/ 16. http://thread.gmane.org/gmane.comp.lang.haskell.cafe/64998 17. http://planet.haskell.org/ 18. http://haskell.org/haskellwiki/Blog_articles 19. http://blog.mikael.johanssons.org/archive/2009/10/math198-lecture-5-is-up/ 20. http://jpmoresmau.blogspot.com/2009/10/releasing-my-code-on-unsuspecting.ht… 21. http://chplib.wordpress.com/2009/10/21/benchmarking-stm-with-criterion/ 22. http://byorgey.wordpress.com/2009/10/20/typeclassopedia-in-japanese/ 23. http://chplib.wordpress.com/2009/10/19/an-early-look-at-threadscope/ 24. http://www.mega-nerd.com/erikd/Blog/FP-Syd/fp-syd-19.html 25. http://blog.snoyman.com/2009/10/19/monadic-pairs-and-kleisli-arrows/ 26. http://martijn.van.steenbergen.nl/journal/2009/10/18/transforming-polymorph… 27. http://justtesting.org/post/216085196 28. http://donsbot.wordpress.com/2009/10/17/multicore-haskell-now-acm-reflectio… 29. http://blog.sigfpe.com/2009/10/what-category-do-haskell-types-and.html 30. http://justtesting.org/post/215438784 31. http://www.haskell.org/mailman/listinfo/haskell 32. http://sequence.complete.org/ 33. http://planet.haskell.org/ 34. http://sequence.complete.org/node/feed 35. http://haskell.org/ 36. http://haskell.org/haskellwiki/HWN 37. http://patch-tag.com/r/jfredett/HWN2/pullrepo%20HWN2 Hidden links: 38. http://www.galois.com/blog/2009/10/20/crenshaw-simplex/

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What does :*: mean again?
by Günther Schmidt 23 Oct '09

23 Oct '09

Günther

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ANN: haskell-src-exts-1.2.0
by Niklas Broberg 23 Oct '09

23 Oct '09

Fellow Haskelleers, I'm pleased to announce the release of haskell-src-exts-1.2.0! * On hackage: http://hackage.haskell.org/package/haskell-src-exts * Via cabal: cabal install haskell-src-exts * Darcs repo: http://code.haskell.org/haskell-src-exts Version 1.2.0 is a new major release, following the PVP, as it contains a few backwards-incompatible changes, as well as some major changes that are supposedly backwards-compatible in theory, but as much of it is new and untested in practice there may be some regressions (bugs). The main new thing in 1.2.0 is the integration of the Annotated machinery into the package proper, for instance all parsing is now handled by the fully location-aware parser. haskell-src-exts-1.2.0: ==================== * Language.Haskell.Exts.Annotated.Simplify provides translation from an annotated AST to the old simple AST. * Behind-the-scenes integration of the new exact parser and lexer to do all parsing (using the above mentioned simplifier if the old AST version is requested). * All syntactic nodes now derive Eq, Ord and Show. * Pretty instance for SrcSpan. * Top-level expressions are now treated as implicit TH splice declarations (as per GHC HEAD). Note that this incurs a non-backwards-compatible change to the AST. * Empty data declarations may now have explicit kind annotations. * AST (and Pretty/Exact) support for kind variables (not yet parser support). * Error messages now extensively use prettyPrint instead of show for AST elements and locations, leading to way neater messages. * Bug fix to not crash ungracefully when encountering type equality predicates in proper types. * Liberalise line comments (as per GHC) to allow a line comment on the last line of a source file. Please help me test and report! Grab a darcs version, put your source files in the Test/examples dir, and go cabal test (in the top dir). Any failing cases not due to CPP or literate source files (for the exact-printer), please report to the trac: http://trac.haskell.org/haskell-src-exts Cheers, /Niklas

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Announcing: PastePipe -- a CLI for hpaste instances
by Rogan Creswick 23 Oct '09

23 Oct '09

I'm happy to announce PastePipe (v1.3)! PastePipe reads from stdin and publishes whatever it reads to the hpaste instance of your choice (defaulting to hpaste.org) This makes it trivial to..... * post a file to hpaste.org: `cat <file> | pastepipe' * turn a terminal into a pastebin window: 'pastepipe' (ctrl-d to close & send) * upload error output as a paste: 'faultyProgram | pastepipe -t "faultyProgram error output" -l bash' * paste to a local hpaste instance: 'pastepipe --uri http://my.local.hpaste/fastcgi/hpaste.fgci/' * add a title, select different languages, specify a user name, etc... see pastepipe --help for details. PastePipe will output the resulting url for your new paste to stdout, so you can script it, or just copy / paste that as you need. Availability: ------------------------------------------------------------------------------------------------------- It is available on Hackage (so you can 'cabal install PastePipe'): http://hackage.haskell.org/package/PastePipe The project for pastepipe is hosted at Google Code, with the source in mercurial: Homepage (issue tracker, etc): http://code.google.com/p/pastepipe/ Mercurial repo: hg clone https://pastepipe.googlecode.com/hg/ pastepipe --------------------------------------------------------------------------------------------------------------- Please let me know of any bugs / feature requests / etc. (or just post them to the issue tracker.) Thanks! Rogan

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Re: \Statically checked binomail heaps?
by Okasaki, C. DR EECS 23 Oct '09

23 Oct '09

Maciej Kotowicz asked about implementing binomial heaps using types to enforce the shape invariants. I dug up an old email from 1998 talking about how to do this with nested types, and posted it to my blog: http://okasaki.blogspot.com/2009/10/binomial-queues-as-nested-type.html -- Chris

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Help me improve design of my project.
by Andy Stewart 23 Oct '09

23 Oct '09

Hi all, I develop some Haskell IDE, below is screenshots: http://farm4.static.flickr.com/3483/3947340553_933df88a22_o.png http://farm3.static.flickr.com/2628/3952175905_9295a7421a_o.png http://farm3.static.flickr.com/2544/3957610799_70fab5eb57_o.png http://farm3.static.flickr.com/2703/4016163374_493e3738c7_o.png Below is source code. You only can compile it with darcs version of gtk2hs. The simple usage is press `F4` open terminal, then press `F7` to type file-path for open. Now is really simple, now i haven't stable time maintain project, so i will opensource my project when i have stable time. Okay, question is, IORefObject module and most module reference each other, so i will got `recursive reference problem` (looks how many .hs-boot in my project). So anyone can help me improve design to split IORefObject and other modules, make them less depend? Thanks, -- Andy

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FW: Free Pizza, C++, and Haskell
by Simon Peyton-Jones 23 Oct '09

23 Oct '09

You may enjoy this interesting blog post by Bartosz Milewski about understanding C++ template metaprogramming by starting with Haskell. http://bartoszmilewski.wordpress.com/2009/10/21/what-does-haskell-have-to-d… Bartosz gave the talk at the Northwest C++ users group; the video for the talk will be linked eventually on the NWCPP website: http://nwcpp.org/ Simon

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Time Typeable Instances
by John Goerzen 23 Oct '09

23 Oct '09

Hugo Gomes wrote: > The Glorious Glasgow Haskell Compilation System, version 6.10.4 > with old-time-1.0.0.2 and time-1.1.2.4 > > This is a standard haskell platform on a windows xp. Cabal install > didn't work complaining about missing instances of typeable for posix > time and other datatypes, yet, after removing the macros (thus, adding > those instances), hdbc and convertible compiled and installed fine. > > Removing the macros might be a bit overkill, probably finetuning them so > that they add only the necessary instances for typeable in ghc > 610 > might be a better solution. I'm going to CC haskell-cafe on this because I am confused. Hugo, can you confirm what version of convertible you have? Back on May 21, I started a thread [1] on haskell-cafe complaining that GHC 6.10.3 included a newer time that included instances of Typeable for NominalDiffTime and UTCTime. This broke my code, which had manually defined instances for these types, as they were needed. Things got complicated, as only time's minor version number got incremented (x.x.x.Y) [2]. Cabal can't test against that version number. I wanted my code to work with old and new versions of GHC. Since testing against the version of time was impossible, I did the next best thing: tested against the version of GHC. #if __GLASGOW_HASKELL__ >= 610 -- instances added in GHC 6.10.3 #else instance Typeable NominalDiffTime where typeOf _ = mkTypeName "NominalDiffTime" instance Typeable UTCTime where typeOf _ = mkTypeName "UTCTime" #endif Also, in the .cabal, there is a build-depends on time>=1.1.2.4. Now, that would break for GHC 6.10.1 and 6.10.2 users, but will work for 6.10.3 and above, or 6.8 and below. Or so I thought. Now I'm getting complaints from people using 6.10.4 saying that there are now missing instances of Typeable with time 1.1.2.4. 1) Did the Typeable instances get dropped again from time? 2) What exactly should I do so this library compiles on GHC 6.8 and 6.10.x? I'm looking at the darcs repo for time and don't see the instances ever getting dropped. [1] http://osdir.com/ml/haskell-cafe@haskell.org/2009-05/msg00982.html [2] http://osdir.com/ml/haskell-cafe@haskell.org/2009-05/msg00985.html .... later addendum .... so it appears that what's happening here is that GHC 6.10.3 extralibs included time 1.1.3, but then haskell-platform standardized on 1.1.2.4. This is pretty annoying -- that haskell-platform would standardize on a version older than what shipped with a GHC release -- but I guess I can work around it by restricting my build-dep to be time < 1.1.3 and re-adding the instances. Does this sound right? > > > On Tue, Oct 13, 2009 at 2:51 AM, John Goerzen <jgoerzen(a)complete.org > <mailto:jgoerzen@complete.org>> wrote: > > Hugo Gomes wrote: > > Hi, > > > > convertible and hdbc packages fail to compile in my standard > instalation > > of the haskell platform. I think this has to do with those "if ghc >= > > 610" macros on the typeable instances for some datatypes. I > removed them > > and now they work fine... > > > > > > > > > What version of GHC and time do you have? > > -- John > >

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Newbie has trouble using QuickCheck
by steenreem 23 Oct '09

23 Oct '09

Hello. I have made a simple test.hs file that imports the module QuickCheck. However, when I load this module in ghci, it says that the module QuickCheck is not found. I have looked in my haskell platform folder and find the folder "QuickCheck 1.2.0.0". I also tried to :set -package QuickCheck. This added QuickCheck to the list of loaded packages. However when loading my test module it still says "Could not find module QuickCheck". Locations searched were "QuickCheck.hs" and "QuickCheck.lhs" What's wrong? Thanks, Remy. -- View this message in context: http://www.nabble.com/Newbie-has-trouble-using-QuickCheck-tp26024248p260242… Sent from the Haskell - Haskell-Cafe mailing list archive at Nabble.com.

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ANN: Data.Stream 0.4
by Wouter Swierstra 23 Oct '09

23 Oct '09

I'm happy to announce a new release of the Data.Stream library. http://hackage.haskell.org/package/Stream The only change with the previous version has been to add irrefutable patterns to several function definitions. This is rather delicate design decision: too many irrefutable patterns could result in thunks not being evaluated; too few irrefutable patterns could cause your functions diverge. As a rule of thumb I've chosen only to use irrefutable patterns in functions that produce streams from streams. The operations that observe finite information (a prefix, the element at index i, etc.) do not have have irrefutable patterns and force evaluation to weak head normal form. I've uploaded a new version to Hackage. I'd be interested to hear if any existing code takes a performance hit as a result of these changes. Wouter

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What's this pattern called?
by Martijn van Steenbergen 23 Oct '09

23 Oct '09

Bonjour café, > data ExprF r > = Add r r > | Sub r r > | Mul r r > | Div r r > | Num Int This is a well-known pattern that for example allows nice notation of morphisms. But what is it called? I've heard fixed-point view, open datatypes and some others, but I'm curious where this pattern comes up in literature and what it is called there. Thanks, Martijn.

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TimeZone bug?
by Magicloud Magiclouds 23 Oct '09

23 Oct '09

Hi, As we know, "CST" could mean both +8 or -6 time zone. So I got a problem. In the same envoironment. When a ZonedTime is shown, I got "xxxxx CST". Now it means +8 time zone. Then I read it, stupidly, it turns into -6 time zone. How could I fix this? I am using ghc 6.10.4 in rhel 5. -- 竹密岂妨流水过山高哪阻野云飞

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Lazy problem ?
by zaxis 23 Oct '09

23 Oct '09

"ssqHitNum.txt" contains data as below: 6 7 18 24 30 32 9 4 12 20 25 28 29 16 3 5 11 12 31 32 11 2 9 13 15 19 24 3 5 17 21 25 27 32 14 5 9 15 21 26 31 13 12 16 25 26 27 31 05 ... good_ssq_red:: IO [Int] good_ssq_red = withFile "ssqHitNum.txt" ReadMode (\h -> do { samp <- fmap str2Ints $ hGetContents h; print samp; --without this line, the result will always [1..16] return $ statis samp; }) statis :: [Int] -> [Int] statis samp = take 16 $ map (\(a,b) -> a) $ sortBy (\a b-> if (snd a >= snd b) then LT else GT) $ times4n where times = map (\n -> (foldl (\acc x -> if x==n then acc+1 else acc) 0 samp)) [1..33] times4n = map (\n -> (n,times!!(n-1))) [1..33] Does it mean that the sampe will not be evalued with `print samp` line ? thanks! -- View this message in context: http://www.nabble.com/Lazy-problem---tp26021845p26021845.html Sent from the Haskell - Haskell-Cafe mailing list archive at Nabble.com.

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Time and space complexity of "take k . sort"
by Paul Johnson 23 Oct '09

23 Oct '09

This question on StackOverflow asked about how to find the largest 100 items in a very long list: http://stackoverflow.com/questions/1602998/fastest-way-to-obtain-the-larges… I replied that you could do it with something like this (but here taking the k smallest to strip out some irrelevant complications): > takeLargest k = take k . sort Because "sort" is lazily evaluated this only does enough sorting to find the first k elements. I guess the complexity is something like O(n*k*log(k)). But of equal practical interest is the space complexity. The optimum algorithm is to take the first k items, sort them, and then iterate through the remaining items by adding each item to the sorted list and then throwing out the highest one. That has space complexity O(k). What does the function above do? Paul.

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why cannot i get the value of a IORef variable ?
by zaxis 23 Oct '09

23 Oct '09

> let aaa = unsafePerformIO $ newIORef [] > writeIORef aaa [1,2,3] > readIORef aaa [(),(),()] sincerely! -- View this message in context: http://www.nabble.com/why-cannot-i-get-the-value-of-a-IORef-variable---tp26… Sent from the Haskell - Haskell-Cafe mailing list archive at Nabble.com.

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NetSnmp problem.
by Magicloud Magiclouds 23 Oct '09

23 Oct '09

Hi, I am trying to use NetSnmp to get some information from my switch. And I met this problem. After initialize, I used snmpWalk to get some information, and dealed with it. Everything is fine. Then I sleep for 5 mins. SnmpWalk again. But this time, all asnValues were unsupported format, which broke my dealing process. Why? I am sure my switch and OID, bluh bluh bluh are correct. They worked in ruby script. -- 竹密岂妨流水过山高哪阻野云飞

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cvs.haskell.org down? haskell-mode abandoned?
by Svein Ove Aas 22 Oct '09

22 Oct '09

Attempting to update haskell-mode, I've been getting authorization failures from the cvs.haskell.org pserver. I thought this might have some connection to the recent disk crash, and as nobody uses cvs anymore, it could have been overlooked. In any case, I need it fixed before I can work on haskell-mode. Preferably by migrating haskell-mode over to cvs. :-) On a different note, I've been unable to contact the apparent current maintainer of haskell-mode, while in a state of having a useful patch. Though it may already have made it to cvs, with me simply being unable to check that.. actually, who *is* the current maintainer? The last release was Dec. 2007. -- Svein Ove Aas

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Is there in Haskell the eval function?
by Waldemar Biernacki 22 Oct '09

22 Oct '09

Hello! I have a very stupid question. Sorry for that! Is there the eval function like in imperative languages? I'd like to write an application which has to be compiled to exec file. It is neccessary to performe some additional procedures which are unknown at the moment of the compilition. Regards wb.

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Simple but interesting (for me) problem
by michael rice 22 Oct '09

22 Oct '09

There's a thread on the plt-scheme list about creating a function of NO arguments named NEXT that just returns the number of times it's been called, a piece of cake in Scheme, but how would one do this in Haskell? Would the best approach be to use a State monad? Michael

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How can i safely change the value of specified key ?
by zaxis 22 Oct '09

22 Oct '09

aaa <- newIORef ([]::[(Int,Int)]) writeIORef aaa [(1,1),(2,2),(3,3)] then if i want to change aaa to [(1,1),(2,222),(3,3)] , what's the best way ? re-write aaa is not permitted. Sincerely! -- View this message in context: http://www.nabble.com/How-can-i-safely-change-the-value-of-specified-key---… Sent from the Haskell - Haskell-Cafe mailing list archive at Nabble.com.

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ANN: mecha-0.0.0
by Tom Hawkins 22 Oct '09

22 Oct '09

A few months ago, I started toying with a few alternative pump designs to power our hydraulic hybrids. After not being able to secure a ProE license, I searched for a free solid modeler to sketch out a few ideas. To my surprise, their are practically no open source 3D CAD packages available. So I created Mecha, DSL for constructive solid modeling. Mecha's geometry is based on octrees, which makes it easy to perform set operations on solids, as well as volumetric calculations such as center-of-mass, moments of inertia, and of course, total volume. Drawbacks of octrees include consuming a lot of memory and the loss of some surface information. To address the later, Mecha carries forward surface points and normals to the leaf nodes of the octree to assist in rendering, such that solids don't look like they're made from a bunch of LEGOS. Note this is a very early release. The only thing Mecha can do at the moment is draw a pretty blue ball -- well it can also zoom and pan on a pretty blue ball (mouse wheel). Establishing a primitive API and building a primitive library must be finished before Mecha an do anything useful. Any comments and suggestions are welcome. http://tomahawkins.org/

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pretty printing with comments
by Pasqualino "Titto" Assini 22 Oct '09

22 Oct '09

Hi, Is there any simple way of pretty printing haskell source code while preserving the comments? I am looking at the haskell-src-ext library. It can parse files with comments and it can pretty print but, for what I can see it cannot do both :-) (prettyPrint won't work on the structure returned by parseFileWithComments). Thanks, titto

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Real World Haskell Chapter 19 and GHC 6.10
by Michael Mossey 22 Oct '09

22 Oct '09

The examples in the "error handling" chapter (19) of RWH don't run under GHC 6.10. For instance, an example might be main = handle (\_ -> putStrLn "error") (print $ 5 `div` 0) Trying to load this results in "amigous type variable 'e' in the constraint: 'Exception e' arising from a use of 'handle' etc etc. I was able to fix this via the ludicrously complex: main2 = (handle :: (SomeException -> IO ()) -> IO () -> IO ()) (\_ -> putStrLn "Error calculating result") (print $ 5 `div` 0) Is there a more concise way to use "handle", or can someone point me to a tutorial that might explain the changes in 6.10 and in a general way how to get the RWH examples to run? Thanks, Mike

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