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Last time, we implemented a bowling game scorer by using a Tardis. If you aren’t yet familiar with the Tardis’s interface, then I recommend you check out the explanation on Hackage. (tl;dr it’s a State monad with get and put, … Continue reading →

submitted by forseti_
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Hi cafe, I use symbols all the time when manipulating code. I vacillate between using stringtable-atom, symbol, and simple-atom. Unfortunately: - Stringtable-atom is has a broken build right now (GHC 7.6). (Also I've had some crashes with it in the past.) - simple-atom has dependency upper bounds that restrict it to GHC <= 7.0 - "symbol" has a design flaw, which is that it exposes the constructor for Symbol, which reveals the (nondeterministic) unique Int IDs. I.e. it is not "SafeHaskell". I submitted a pull request to relax simple-atom, but perhaps there are other packages people use with which I am not aware? Thanks, -Ryan _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe< at >haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe

submitted by whitehatguy
[link] [19 comments]

I use a number of different programming languages, so I have Haskell Platform, Strawberry Perl, Node.js, RVM, and Git Bash installed at the same time. I've noticed that compiling packages with C dependencies (e.g. using node-gyp during "npm install node-mhash", or doing "cpan install PAR::Packer") often crashes during the build process with a popup: The procedure entry point __gxx_personality_sj0 could not be located in the dynamic link library libstdc++-6.dll. As Roderich Schupp points out<https://rt.cpan.org/Public/Bug/Display.html?id=84949>, it appears that the different libstdc++-6.dll's are interfering with one another. Haskell Platform comes with one, Vagrant comes with one, GIMP comes with one, MinGW comes with one, and Strawberry Perl comes with two! Objdump seems to indicate that Haskell Platform's DLL is the one to blame. $ find /c/ -name libstdc++-6.dll 2>/dev/null /c/DevKit/mingw/bin/libstdc++-6.dll /c/Program Files/GIMP 2/bin/libstdc++-6.dll /c/Program Files/Haskell Platform/2012.4.0.0/mingw

Introduction

So, last thursday I escaped Belgium for a bit and travelled to Odessa to attend OdHac, a Haskell Hackathon organised there by Roman and hosted by Provectus IT.

Odessa is a really sweet city. One thing I noticed is that while some of the buildings seem to be in a deplorable condition from the outside, they actually turn out to be very nice once you’re indoors! This was for example the case for the hostel I was staying in. The contrast is also seen elsewhere in the city, with brand new appartements next to ramshackle, desolated houses.

Picture by Simon Meier

This is, however, not the case for the very centre of the city – around the famous Potemkin Stairs. This neighbourhood is absolutely amazing.

Picture by some random Ukranian guy

Hakyll at OdHac

At the Hackathon, I did a small presentation about Hakyll on friday, and some awesome people decided to help me improve Hakyll a bit this weekend. We were able to implement some exciting features.

Working on Hakyll, picture by Roman Cheplyaka

If-else conditionals in templates

We added some functionality to the Hakyll templates which you allows you to check if a certain value is defined. We chose to use the same syntax as Pandoc, to further ease integration:

<h1>$title$</h1> $if(author)$ <em>by $author$</em> $endif$

We also support if-else-endif. On the plane back, I also took the time to implement $foreach$ and $partial$.

Teasers

Teasers allow you to write a short introduction for a blogpost, and make it easy to reproduce this introduction on another page together with a “Read more” link. We decided to implement the convention used in Wordpress, which means you define your teasers using the following simple format:

--- title: Some post --- This is the introduction. <!--more--> The rest of the post... Pagination

We also started to work on a generic Pagination module. It’s not finished yet but it should be possible to clean this up and package it by the end of the week. I’m quite excited about this feature because lots of people have requested it in the past.

Additionally, we did some performance improvements and fixed a bug or two. All in all, a very productive and fun Hackathon! I hope to package up all these changes and push them to Hackage soon.

Thanks for contributing to Hakyll, Alexey Smirnov, Anton Dubovik, Dmitriy Shamatrin, Ivan Veselov and Pavel Poukh! And, of course, thanks for organizing, Roman!

Some time ago a friend asked for a good introductory work on Category theory. I never did answer his question to my satisfaction, as the stuff I picked up on the subject was here and there as I needed it, and I thought there was never any succinct introductory work.

Well, I thought wrongly.

http://en.wikipedia.org/wiki/Categories_for_the_Working_Mathematician

Above link ... links to the seminal summa, available for you if you wish to pursue this delightful area of research into expressivity in mathematics.

Also, of course, there's the working-quantum-physicist's introduction at:

http://math.ucr.edu/home/baez/categories.html

Having a working knowledge of quantum computation is not necessary, probably not even helpful, but a very nice introduction is Quantum Computation and Quantum Information by Nielsen and Chuang, if you wish to see the source from where I got to categories and Category Theory.

Dr. Baez's work starts off lightly and playfully, but then gets pretty deep pretty quickly, as he goes into the Groupoid/Topoid theoretical application of Category Theory, but that's to be understood, as quantists are always concerned about (super-)symmetries, and I, not so much, as I look for the more practical application of Categories in Monoids and the Relational Calculus, but there it is.

I do, of course, have more advanced works on this topic if you wish to research further, and there's always this blog, where I look at the logical implications of cat theory (heh: 'logical' 'implications' ... Math humor).  There is, e.g., an introductory article on monads and their computational application at:

http://logicaltypes.blogspot.com/2011/09/monads-in-java.html

I've been using Python for over 3 years now and PHP for about 2-3 before that. I touched on Haskell at uni and then tried again a few months ago. This time I'm really taking a proper stab at it and trying out Euler problems.

I'm up to number 7 and starting to get the hang of making programs but I've found a problem. My programs are slow. Dead slow.

Problem 3 involves finding the 10,001st prime number. My Python implementation takes 7 seconds and my Haskell implementation takes 42.

I was under the impression that Haskell would generally be faster than Python for number crunching, even if not we're talking a big factor of difference. This suggests very strongly to me I'm trying to solve the problem the wrong way with Haskell (I had the same issue moving from PHP to Python). Could you take a look at the two sets of code below and let me know how I could have better designed the program?

https://gist.github.com/Teifion/5536277

submitted by Teifion
[link] [37 comments]

===================================================================== 2nd Call for papers 15th International Symposium on Principles and Practice of Declarative Programming PPDP 2013 Special Issue of Science of Computer Programming (SCP) Madrid, Spain, September 16-18, 2013 (co-located with LOPSTR 2013) http://users.ugent.be/~tschrijv/PPDP2013/ ====================================================================== EXTENDED SUBMISSION DEADLINE: JUNE 13, 2013 PPDP 2013 is a forum that brings together researchers from the declarative programming communities, including those working in the logic, constraint and functional programming paradigms, but also embracing a variety of other paradigms such as visual programming, executable specification languages, database languages, and knowledge representation languages. The goal is to stimulate research in the use of logical formalisms and method

===================================================================== 2nd Call for papers 15th International Symposium on Principles and Practice of Declarative Programming PPDP 2013 Special Issue of Science of Computer Programming (SCP) Madrid, Spain, September 16-18, 2013 (co-located with LOPSTR 2013) http://users.ugent.be/~tschrijv/PPDP2013/ ====================================================================== EXTENDED SUBMISSION DEADLINE: JUNE 13, 2013 PPDP 2013 is a forum that brings together researchers from the declarative programming communities, including those working in the logic, constraint and functional programming paradigms, but also embracing a variety of other paradigms such as visual programming, executable specification languages, database languages, and knowledge representation languages. The goal is to stimulate research in the use of logical formalisms and method

Have you taught a course using Hutton's textbook on Programming in Haskell? If so, please read on! As part of the national assessment of universities in the UK that takes place every 5-6 years, I'm producing a case study on the impact of the book on student and professional training. The case study will include a number of quotes from academic and industrial users who have used the book for teaching purposes. If you have taught a course using the book any time from January 2008 onwards, and would be willing to provide a short quote (2-3 sentences) for the case study, that would be very much appreciated. It doesn't matter if you are no longer teaching the course or are not currently using the book. If you are interested, drop me an email and I'll explain what's involved. Many thanks, Graham Hutton

Have you taught a course using Hutton's textbook on Programming in Haskell? If so, please read on! As part of the national assessment of universities in the UK that takes place every 5-6 years, I'm producing a case study on the impact of the book on student and professional training. The case study will include a number of quotes from academic and industrial users who have used the book for teaching purposes. If you have taught a course using the book any time from January 2008 onwards, and would be willing to provide a short quote (2-3 sentences) for the case study, that would be very much appreciated. It doesn't matter if you are no longer teaching the course or are not currently using the book. If you are interested, drop me an email and I'll explain what's involved. Many thanks, Graham Hutton

(apologies for multiple copies) * DEADLINE EXTENSION: Paper submission deadline is now May 14th! (instead of May 8th) ========================================================================= Call for Papers Tenth International Workshop on Constraint Handling Rules CHR 2013 http://dtai.cs.kuleuven.be/CHR/CHR2013/ Berlin (Germany), July 13th, 2013 (co-located with the 3rd Intl Summer School on CHR) ========================================================================= Introduction The CHR 2013 Workshop will be held on July 13th, 2013 in Berlin (Germany) at the occasion of the 3rd International Summer School on CHR. More information on the venue and the co-located summer school can be found on the summer school website (http://met.guc.edu.eg/CHR2013/). The Constraint Handling Rules (CHR) language has become a major declara- tive s

CALL FOR PAPERS - MEMOCODE 2013 (NOTE: NEW EXTENDED DATES for PAPERS and DESIGN CONTEST) Eleventh ACM/IEEE International Conference on Formal Methods and Models for Codesign http://www.memocode-conference.com 18-20 October 2013, Portland, Oregon, USA Co-located with DIFTS and FMCAD SCOPE The eleventh ACM/IEEE MEMOCODE conference focuses on research and developments in methods, tools, and architectures for the design of hardware/software systems. MEMOCODE seeks submissions that present novel formal methods and design techniques to create, refine, and verify complex hardware/software systems and to tackle the tight constraints on timing, power, costs, reliability and security that these systems face. We also invite application-oriented papers, and especially encourage submissions that highlight the tools and design perspective of formal methods and models, including success as well as failure stories, constructive analysis thereof, and demonstrations of hardware/software codesign. Techniques may range

submitted by gnuvince
[link] [30 comments]

Have you taught a course using Hutton's textbook on Programming in Haskell? If so, please read on!

As part of the national assessment of universities in the UK that takes place every 5-6 years, I'm producing a case study on the impact of the book on student and professional training. The case study will include a number of quotes from academic and industrial users who have used the book for teaching purposes.

If you have taught a course using the book any time from January 2008 onwards, and would be willing to provide a short quote (2-3 sentences) for the case study, that would be very much appreciated. It doesn't matter if you are no longer teaching the course or are not currently using the book. If you are interested, drop me an email and I'll explain what's involved.

Many thanks,

Graham Hutton graham.hutton@nottingham.ac.uk

submitted by grahamhutton
[link] [2 comments]

Whats new in Spark will look the activity in the Spark commit logs every week and attempt to summarize what new features and bug fixes have occurred. This not intended to summarize everything, mostly things that might be useful to application developers. Without further ado lets get started: 

• zipPartions was added to the Scala & Java APIs. zipPartions joins an up to 4 RDDs using a user supplied function. It requires that all of the RDDs have the same number of partitions with no such requirement on size within each partition. https://github.com/mesos/spark/commit/c9c4954d994c5ba824e71c1c5cd8d5de531caf78 https://github.com/mesos/spark/commit/c9c4954d994c5ba824e71c1c5cd8d5de531caf78 
• unPersist() was added to the Scala & Java APIs allow the removal of an RDD from persistence once it is no longer needed. https://github.com/mesos/spark/commit/93091f6936262a4006d875bf69b3f8c31c291617
•  Bugfix was added to validate that local directories can be created when being added. https://github.com/mesos/spark/commit/c9c4954d994c5ba824e71c1c5cd8d5de531caf78
• Spark’s block UI manager had a bug with Spark Streaming blocks which was fixed https://spark-project.atlassian.net/browse/SPARK-740 https://github.com/mesos/spark/commit/538ee755b41585c638935a93ec838b635149f659
• The shuffle writer now looks at spark.shuffle.file.buffer.kb to determine the buffer to use. Previously the default buffer was 8kb which could cause a lot of unnecessary disk seeks, and the new default is 100kb. https://github.com/mesos/spark/commit/1055785a836ab2361239f0937a1a22fee953e029 

That is all that I found interesting in skimming this weeks commit logs, if I missed something important feel free to let me know :)

I'm presently a Vim zealot and am interested. The idea of being able to config my editor the same way I do XMonad sounds really effing awesome.

This post is me just trying to gauge the current interest and/or size of the community, since it's unclear.

submitted by the_lemma
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submitted by sclv
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This summer, spend some quality time with your favorite technology in our 2013 summer programming contest!

The Lisp community is awarding prizes for demonstrating interesting and useful programs, technologies and art using any LISP-based technology.

Lisp, prizes, what's not to like?