March 2013 - Haskell-Cafe

Announcement - HGamer3D - 0.2.1 - why netwire
by Peter Althainz 02 Apr '13

02 Apr '13

Peter Althainz wrote: > Dear All, > > I'm happy to announce release 0.2.1 of HGamer3D, the game engine with > Haskell API, featuring FRP based API and FRP based GUI. The new FRP API > is based on the netwire package. Currently only available on Windows: > http://www.hgamer3d.org. Nice work! Of course, I have to ask: what influenced your choice of FRP library in favor of netwire instead of reactive-banana ? Best regards, Heinrich Apfelmus -- http://apfelmus.nfshost.com Hi Heinrich good question, actually I need to thank you for your excellent tutorials on FRP and GUI on the WEB. I tried the version of reactive-banana without switches as the first FRP framework to have contact with and I liked its simplicity and the cool introduction around Excel cells you gave on the Web. HGamer3D is my personal way to get more insight into FP and Haskell especially and from the beginning I wanted to have a FRP API to try it with game examples. So your intro on FRP and the examples were very helpful with that. After reading a lot on the web it became clear, that currently reactive-banana and netwire are good candidates to start with. So why in the end I decided to use netwire for the binding? It's some personal things and I do not claim to have done a proper evaluation or comparison. I also cannot judge on performance or other relevant topics. Having said that, I can give you some points why I choosed netwire: - The cool simplicity of reactive-banana API seems to have suffered a little bit after the introduction of the switch functionality. - After getting around Monads and Applicative by great help of "Learning a Haskell for great good" I was shocked to see, there is even more to learn, when I detected Arrows. So I started to look at it and discovered some nice tutorials for Arrows. - What struck me was introduction of netwire author Ertugrul Söylemez on Arrows and the explanations of local state, which can be kept into an arrow. Since I was also curious on OOP and FP and game state handling, actually this raised some interest. So I think this "Arrows keep local state" argument was the killer feature. But also behaviours keep local state and maybe I got misguided here. - I then did some trials with netwire and I felt it's a quite comprehensive and nice API, so I got started with that. regards Peter

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cabal install pandoc
by Roger Mason 01 Apr '13

01 Apr '13

Hello, I installed ghc (7.6.2) on an Arch Linux machine. I'm trying to install pandoc via cabal but it fails: ... Configuring text-0.11.2.3... Warning: This package indirectly depends on multiple versions of the same package. This is highly likely to cause a compile failure. package deepseq-1.3.0.1 requires array-0.4.0.1 package text-0.11.2.3 requires array-0.4.0.1 Building text-0.11.2.3... Preprocessing library text-0.11.2.3... <command line>: cannot satisfy -package-id array-0.4.0.1-db49bb8b0087ae85b5875d4c0cc12874 (use -v for more information) Failed to install text-0.11.2.3 ... There are then errors for other packages that depend on 'text' or 'array'. I will be grateful for any help. Thanks, Roger This electronic communication is governed by the terms and conditions at http://www.mun.ca/cc/policies/electronic_communications_disclaimer_2012.php

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graphical editor links ?
by Luc TAESCH 01 Apr '13

01 Apr '13

I am designing some graphical editor ( visio - dia like) and would be interested to hear any pointer to help me think on the architecture of this, in term of data structure/ EDSL/ persistence/ paradigm (FP/ FRP/...) for the different "layers of abstraction " I may see , like rendering libraries ( gtk/wx..)<-> model of the diagram<-> semantics ( this is a state diag/ archimate / mind mapping , i.e. what the glyph and lines means ) <-> persistence Any help & pointers welcomed ! ( and which place is best to discuss this ?) Luc

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Haskell SBV Package with Z3
by J. J. W. 31 Mar '13

31 Mar '13

Dear all, I have a small question regarding the installation of the SBV package. I first installed the SBV 2.10 package with cabal with the following instructions: cabal install sbv Next I installed the Z3 theorem prover and adding the path to my system variables (Windows 7 x64). Next I tested whether I could find it by opening cmd.exe and then typing z3, I get an error message of Z3, so I can safely assume the system can find it. (I added the path to the bin of Z3, I have not included the include directory, I see no reason why I should add a path to this directory, but maybe I am wrong). I ran the program: SBVUnitTests. However it had some errors in the beginning and afterwards a few failures. Having no idea how to fix this, I continued to check whether I can get the SBV to work. So I started to execute the SBV package: ghci -XScopedTypeVariables ghci> :m Data.SBV ghci> prove $ \(x::SWord8) -> x `shiftL` 2 .== 4*x Now this should return Q.E.D., however it returned the following: An error occured. Failed to complete the call to z3 Executable: "C:\\Program Files\\z3-4.3.0-x64\\bin\\z3.exe Options: /in /smt2 Exit code: 0 Solver output: =========================================================== ; :smt.mbqi ; :pp.decimal_precision =========================================================== Giving up.. It does seems like that the Z3 has a normal output, however not a result. Can someone help me to figure out what I actually did wrong? I am using Z3 version 4.3.0, SBV 2.10 and GHCi 7.4.2 Thank you for your help! Yours sincerely, Jun Jie

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Organising code in FRP
by luc taesch 31 Mar '13

31 Mar '13

I am just learning FRP ( via reactive-banana) . so possibly opening a topic already mentionned , apologises in advance, and pointers welcomed. I am wondering about "code structuration" ? ie spagetti code for the network 1/ in a non trivial FRP applicaiton, how to manage "modulatity" or structuration of the Network ? ( most of the example I scanned are toy-size). I ca imagine it may not be trvial to find its way around in a large setup ... 2/ what about the separation of "layers". I mean fine, we extract the reactive ness from the GUI, and separate the layout of widgets from the behaviors of these great, but is it to then mingle the UI with the "business part" ( say in banking), and the infrastructure side ( say persistence, comms, transactionnality, etc) in other words, how tdoes the nice abstraction developped ( module/ interface / categoty patterns, monad, etc) coexsit with a netork of FRP event and behaviors ? Any prior art on this ? ( and which place si best to discuss this ?)

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Specialized Computer Architecture - A Question
by OWP 31 Mar '13

31 Mar '13

Hi, I was reading the paper "A History of Haskell: being lazy with class" ( http://www.haskell.org/haskellwiki/History_of_Haskel) and came on a section (I 2.1) which briefly explained the work people did on making non-von Neumann architectures. It concluded by saying "Much (but not all) of this architecturally oriented work turned out to be a dead end, when it was later dis- covered that good compilers for stock architecture could outper- form specialised architecture. But at the time it was all radical and exciting." These "stock architectures", were they really so good that they out performed the specialized ones on it's own merits or was this mainly due to Moore's Law on transistors? In other words, suppose we separate Moore's Law from the stock architecture, would it still outperform the specialized ones? Thank you for any response

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Threadscope 0.2.2 goes in segmentation fault on Mac Os X 10.8.3
by Alfredo Di Napoli 31 Mar '13

31 Mar '13

Hi Cafè, I've tried installing threadscope, but when I run it from console with "threadscope" I get a laconic segmentation fault. Some info to help the debugging: * Installed gtk via brew * gtk-demo runs correctly * I'm using Mac Os X 10.8.3 * Running gtk and threadscope through a virtual environment (provided by hsenv) * Using XQuartz 2.7.4 I know it's a bit difficult to debug this way, I can try debugging with gdb if it can help. Cheers, A.

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[ANN] hoodle-0.2
by Ian-Woo Kim 30 Mar '13

30 Mar '13

Hi, all, Pen note-taking program hoodle, which is being developed entirely in haskell, is updated to version 0.2. The previous version was 0.1.1. About what is hoodle, please refer to http://ianwookim.org/hoodle The changes in this version are - hoodle data format updated. now hoodle document has a unique id. - linking between documents implemented - vertical space inserting tool implemented - a widget introduced for panning and zooming - drag and drop linking implemented - drag and drop image embedding implemented - poppler pdf support is mandatory - pdf can be embedded in a file - toolbox ui reflects current hoodle state more correctly - slimmer select box design - several rendering glitches fixed Note that poppler is mandatory for hoodle (in the previous versions, poppler support was optional). One needs to install poppler-glib before installing hoodle. After gtk2hs and poppler installed, installing hoodle should be simply > cabal install hoodle As for the detail information about wacom tablet support, please read installation page on the webpage. If you were using the previous versions of hoodle, you will find this version gives you much smoother experience and many interesting improvements. (especially adding vertical space tool and pan-zoom widget ) Enjoy~ best, Ian-Woo Kim

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Idea: Source maps for GHC's -pgmF
by Christopher Done 29 Mar '13

29 Mar '13

Here's an idea. For the -pgmF flag, because compile errors become really obscure and line numbers rendered unhelpful, why don't we use source maps as recently done for JavaScript in the browser? Info: https://wiki.mozilla.org/DevTools/Features/SourceMap https://docs.google.com/document/d/1U1RGAehQwRypUTovF1KRlpiOFze0b-_2gc6fAH0… Here is an example I experimented with the Fay (Haskell→JS compiler): https://dl.dropbox.com/u/62227452/Screenshots/Screenshot%20from%202012-09-2… This shows the original source code and a backtrace of an exception thrown in JavaScript. We can use Mozilla/Google's format: http://hackage.haskell.org/package/sourcemap Though it's kind of an obscure format because it's aimed at being small, but if it's already been done, why not? Otherwise a simple JSON format is probably sufficient. It could be used both in GHC's compilation, pattern match exceptions, and even in debugger stepping, if desired. Provided with, e.g. -pgmFsm foo.map. This would make things like the XML mode or other syntactical extensions feel quite natural and not awkward in GHC's error messages. What say you, -pgmF users and GHC hackers? Ciao!

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Monad.Reader #22 call for copy
by Edward Z. Yang 29 Mar '13

29 Mar '13

Call for Copy: The Monad.Reader - Issue 22 -------------------------------------------- Another ICFP submission deadline has come and gone: why not celebrate by submitting something to The Monad.Reader? Whether you're an established academic or have only just started learning Haskell, if you have something to say, please consider writing an article for The Monad.Reader! The submission deadline for Issue 22 will be: **Saturday, June 1** The Monad.Reader ~~~~~~~~~~~~~~~~ The Monad.Reader is a electronic magazine about all things Haskell. It is less formal than journal, but somehow more enduring than a wiki- page. There have been a wide variety of articles: exciting code fragments, intriguing puzzles, book reviews, tutorials, and even half-baked research ideas. Submission Details ~~~~~~~~~~~~~~~~~~ Get in touch with me if you intend to submit something -- the sooner you let me know what you're up to, the better. Please submit articles for the next issue to me by e-mail (ezyang(a)mit.edu) Articles should be written according to the guidelines available from http://themonadreader.wordpress.com/contributing/ Please submit your article in PDF, together with any source files you used. The sources will be released together with the magazine under a BSD license. If you would like to submit an article, but have trouble with LaTeX please let me know and we'll work something out.

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