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Haskell Weekly News: Issue 258
by Daniel Santa Cruz 14 Feb '13

14 Feb '13

Welcome to issue 258 of the HWN, an issue covering crowd-sourced bits of information about Haskell from around the web. This issue covers the week of February 03 to 09, 2013. Quotes of the Week * shachaf: The trouble with the lens rabbit hole is that there are a few of us here at the bottom, digging. * monochrom: "a monad is like drinking water from a bottle without human mouth touching bottle mouth" Top Reddit Stories * GHCi 7.4.2 is finally working on ARM Domain: luzhuomi.blogspot.com, Score: 49, Comments: 15 On Reddit: [1] http://goo.gl/yBh9o Original: [2] http://goo.gl/Kgx9R * Implementation of a Java Just In Time Compiler in Haskell Domain: blog.wien.tomnetworks.com, Score: 41, Comments: 15 On Reddit: [3] http://goo.gl/BjpX3 Original: [4] http://goo.gl/f1Qrh * I/O is pure Domain: chris-taylor.github.com, Score: 32, Comments: 41 On Reddit: [5] http://goo.gl/pYMXz Original: [6] http://goo.gl/9xeKd * Introduction to Haskell, Lecture 4 is Live (Pattern matching and Guards) Domain: shuklan.com, Score: 28, Comments: 7 On Reddit: [7] http://goo.gl/wvFO6 Original: [8] http://goo.gl/sKF5C * What makes comonads important? Domain: self.haskell, Score: 20, Comments: 41 On Reddit: [9] http://goo.gl/CqS7Z Original: [10] http://goo.gl/CqS7Z * OdHac, the Haskell Hackathon in Odessa Domain: haskell.org, Score: 18, Comments: 2 On Reddit: [11] http://goo.gl/ZumYI Original: [12] http://goo.gl/Pfuaq * NYC Haskell Meetup Video: Building a Link Shortener with Haskell and Snap Domain: vimeo.com, Score: 18, Comments: 3 On Reddit: [13] http://goo.gl/j42PG Original: [14] http://goo.gl/RRgsl * Evaluation-State Assertions in Haskell Domain: joachim-breitner.de, Score: 18, Comments: 6 On Reddit: [15] http://goo.gl/lMMT1 Original: [16] http://goo.gl/7eLI5 * A post about computational classical type theory Domain: queuea9.wordpress.com, Score: 17, Comments: 14 On Reddit: [17] http://goo.gl/r8DOO Original: [18] http://goo.gl/UIxIY * parellella has a forum board for haskell. anyone working in this direction? Domain: forums.parallella.org, Score: 13, Comments: 5 On Reddit: [19] http://goo.gl/BSfRd Original: [20] http://goo.gl/qLnG0 * Haskell Lectures - University of Virginia (Nishant Shukla) Domain: shuklan.com, Score: 13, Comments: 3 On Reddit: [21] http://goo.gl/CxTPI Original: [22] http://goo.gl/JkhXz * NYC Haskell Meetup Video: Coding and Reasoning with Purity, Strong Types and Monads Domain: vimeo.com, Score: 13, Comments: 2 On Reddit: [23] http://goo.gl/MmGZb Original: [24] http://goo.gl/Vj63w * Introducing fixed-points via Haskell Domain: apfelmus.nfshost.com, Score: 9, Comments: 34 On Reddit: [25] http://goo.gl/UuCc1 Original: [26] http://goo.gl/SCVJc Top StackOverflow Questions * Is spoon unsafe in Haskell? votes: 19, answers: 2 Read on SO: [27] http://goo.gl/6RDku * What general structure does this type have? votes: 17, answers: 4 Read on SO: [28] http://goo.gl/2GV0V * Why aren't Nums Ords in Haskell? votes: 14, answers: 2 Read on SO: [29] http://goo.gl/8Hrkn * Why does cabal install reinstall packages already in .cabal/lib votes: 12, answers: 1 Read on SO: [30] http://goo.gl/yMXCh * Free Monad of a Monad votes: 12, answers: 2 Read on SO: [31] http://goo.gl/kpV2q * Haskell pattern match “diverge” and ⊥ votes: 11, answers: 2 Read on SO: [32] http://goo.gl/VeRUJ * How can one make a private copy of Hackage votes: 11, answers: 2 Read on SO: [33] http://goo.gl/ZNAwL * Recursion Schemes in Agda votes: 9, answers: 1 Read on SO: [34] http://goo.gl/xtmqr Until next time, +Daniel Santa Cruz References 1. http://luzhuomi.blogspot.com/2013/02/ghci-742-is-finally-working-on-arm.html 2. http://www.reddit.com/r/haskell/comments/17zxgj/ghci_742_is_finally_working… 3. http://blog.wien.tomnetworks.com/2013/02/06/thesis/ 4. http://www.reddit.com/r/haskell/comments/17zqgr/implementation_of_a_java_ju… 5. http://chris-taylor.github.com/ 6. http://www.reddit.com/r/haskell/comments/1874at/io_is_pure/ 7. http://shuklan.com/haskell/lec04.html 8. http://www.reddit.com/r/haskell/comments/17y18q/introduction_to_haskell_lec… 9. http://www.reddit.com/r/haskell/comments/185k0s/what_makes_comonads_importa… 10. http://www.reddit.com/r/haskell/comments/185k0s/what_makes_comonads_importa… 11. http://www.haskell.org/pipermail/haskell-cafe/2013-February/106216.html 12. http://www.reddit.com/r/haskell/comments/17xxyf/odhac_the_haskell_hackathon… 13. http://vimeo.com/59109358 14. http://www.reddit.com/r/haskell/comments/185la5/nyc_haskell_meetup_video_bu… 15. https://www.joachim-breitner.de/blog/archives/590-Evaluation-State-Assertio… 16. http://www.reddit.com/r/haskell/comments/1870oe/evaluationstate_assertions_… 17. http://queuea9.wordpress.com/2012/11/05/canonize-this/ 18. http://www.reddit.com/r/haskell/comments/180uqv/a_post_about_computational_… 19. http://forums.parallella.org/viewforum.php?f=21 20. http://www.reddit.com/r/haskell/comments/180muq/parellella_has_a_forum_boar… 21. http://shuklan.com/haskell/index.html 22. http://www.reddit.com/r/haskell/comments/184r9v/haskell_lectures_university… 23. http://vimeo.com/59215336 24. http://www.reddit.com/r/haskell/comments/185li3/nyc_haskell_meetup_video_co… 25. http://apfelmus.nfshost.com/blog/2010/07/02-fixed-points-video/player.html 26. http://www.reddit.com/r/haskell/comments/186bi1/introducing_fixedpoints_via… 27. http://stackoverflow.com/questions/14710928/is-spoon-unsafe-in-haskell 28. http://stackoverflow.com/questions/14715811/what-general-structure-does-thi… 29. http://stackoverflow.com/questions/14690608/why-arent-nums-ords-in-haskell 30. http://stackoverflow.com/questions/14699269/why-does-cabal-install-reinstal… 31. http://stackoverflow.com/questions/14740213/free-monad-of-a-monad 32. http://stackoverflow.com/questions/14698414/haskell-pattern-match-diverge-a… 33. http://stackoverflow.com/questions/14758423/how-can-one-make-a-private-copy… 34. http://stackoverflow.com/questions/14699334/recursion-schemes-in-agda 35. https://plus.google.com/105107667630152149014/about

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searching the attic for lambada
by John Lask 13 Feb '13

13 Feb '13

I'm interested in resurrecting the idl generator from lambada: http://www.dcs.gla.ac.uk/mail-www/haskell/msg02391.html is the code out there in anyone's attic?

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ghc-mod and cabal targets
by Francesco Mazzoli 13 Feb '13

13 Feb '13

Hi, I have been using ghc-mod for a long time and I can’t give it up now, but I have an annoying problem. When I have a cabal file with a library and an executable depending on the library (for example here <https://github.com/bitonic/kant/blob/master/kant.cabal>), ghc-mod is not happy, complaining in every file that Error:<command line>: cannot satisfy -package kant Where ‘kant’ is the package that the cabal file defines with the library that the executable needs. Note that if I issue ‘cabal configure; cabal build’, everything goes smoothly. Did anybody stumble on the same problem? Thanks, Francesco

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Structured Graphs
by John Sharley 13 Feb '13

13 Feb '13

What are the prospects for Haskell supporting Structured Graphs as defined here? http://www.cs.utexas.edu/~wcook/Drafts/2012/graphs.pdf Is there an interest by developers of GHC in doing this? -John

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Problem installing cabal-dev
by David Turner 13 Feb '13

13 Feb '13

Hi, From a clean install of Haskell Platform 2012.4.0.0 (on Windows) I have issued just: > cabal update > cabal install cabal-install > cabal install cabal-dev The last command fails with: Resolving dependencies... In order, the following would be installed: tar-0.3.2.0 (new package) transformers-0.2.2.0 (new version) mtl-2.0.1.0 (new version) parsec-3.1.3 (reinstall) changes: mtl-2.1.2 -> 2.0.1.0 network-2.3.2.0 (new version) HTTP-4000.2.8 (new version) cabal-dev-0.9.1 (new package) cabal: The following packages are likely to be broken by the reinstalls: network-2.3.1.0 haskell-platform-2012.4.0.0 cgi-3001.1.7.4 HTTP-4000.2.5 Use --force-reinstalls if you want to install anyway. I *think* the problem is that cabal-dev has these dependencies: mtl >= 1.1 && < 2.1, transformers >= 0.2 && < 0.3, where the latest version of mtl and transformers are 2.1.2 and 0.3 respectively. At least, if I download the latest cabal-dev package and relax those upper bounds I can get it to install. The irony is, of course, that I'm trying to install cabal-dev to get me out of a totally unrelated dependencies hole! What should I do now? Cheers, -- David Turner Senior Consultant Tracsis PLC Tracsis PLC is a company registered in England and Wales with number 5019106.

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How far compilers are allowed to go with optimizations?
by Jan Stolarek 13 Feb '13

13 Feb '13

Hi all, some time ago me and my friend had a discussion about optimizations performed by GHC. We wrote a bunch of nested list comprehensions that selected objects based on their properties (e.g. finding products with a price higher than 50). Then we rewrote our queries in a more efficient form by using tree-based maps as indices over the data. My friend knows how to turn nested list comprehensions into queries that use maps and claims this could be automated. He argued that it would be fine if compiler did such an optimization automatically, since we can guarantee that both versions have exactly the same semantics and if they have the same semantics we are free to use faster version. From a functional point of view this is a good point, but nevertheless I objected to his opinion, claiming that if compiler performed such a high-level optimization - replace underlying data structure with a different one and turn one algorithm into a completely different one - programmer wouldn't be able to reason about space behaviour of a program. I concluded that such a solution should not be built into a compiler but instead turned into an EDSL. I would like to hear your opinion on this. How far a compiler can go with transforming code? I don't want to concentrate on discussing whether such an optimization is possible to implement from a technical point of view. What I'm interested in is whether such kind of high-level optimization could be accepted. Janek

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[Announcement] hArduino: Control your Arduino board from Haskell
by Levent Erkok 12 Feb '13

12 Feb '13

I'm happy to announce hArduino: a library that allows Arduino boards to be controlled directly from Haskell. hArduino uses the Firmata protocol ( http://firmata.org) to communicate with and control Arduino boards, making it possible to implement many controller projects directly in Haskell. Home page: http://leventerkok.github.com/hArduino/ Hackage: http://hackage.haskell.org/package/hArduino Some example programs: Blink the led: http://hackage.haskell.org/packages/archive/hArduino/latest/doc/html/System… Digital counter: http://hackage.haskell.org/packages/archive/hArduino/latest/doc/html/System… Control an LCD: http://hackage.haskell.org/packages/archive/hArduino/latest/doc/html/System… Short (4.5 mins) youtube video of the blink example: http://www.youtube.com/watch?v=PPa3im44t2g hArduino is work-in-progress: Patches, bug-reports, and feedback is most welcome. -Levent.

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arrow notation
by Ross Paterson 12 Feb '13

12 Feb '13

I'd like to hear from anyone who's using arrow notation as supported by GHC, because I'm planning a couple of changes to parts of it.

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[Announcement] HsLlvm v0.1: Using Hoopl to optimize LLVM Code
by Ning Wang 12 Feb '13

12 Feb '13

Hi all, It is my dream for years to be able to manipulate LLVM in type safe language. I has explored the possibility of reimplementing LLVM in Haskell with Hoopl and made a small step to realize this dream. I am writing to announce the release of HsLlvm v0.1, which is a pure Haskell implementation (Not LLVM C++ binding) of LLVM. It is available through the link below. https://github.com/mlite/HsLlvm Hightlight of this release: - Support LLVM 3.1 syntax - LLVM normalization - Dominator, mem2reg, DCE passes Project goals: - port all LLVM optimizations - provide functionalities to generate and manipulate LLVM code. Since LLVM is a complex IR and there are many sophisticated optimizations, this job won't be easy. Your contribution would be of value to eventually achieve this goal. Cheers, Ning

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Fwd: Google Summer of Code 2013
by Johan Tibell 11 Feb '13

11 Feb '13

Hi all, Summer of code has always been a good way for us to get some important work, that no one has time to do, done. I encourage everyone to come up with good summer of code projects so we have a good number when the time for students to apply comes around. Empirically projects that focus on existing infrastructure (e.g. Cabal) work well. They limit the scope enough for students to 1) make something that's impacts lots of people and 2) doesn't give them too much rope*. * Building something good from scratch requires lots of experience, something most students don't have, almost per definition. -- Johan ---------- Forwarded message ---------- From: Carol Smith <carols(a)google.com> Date: Mon, Feb 11, 2013 at 11:02 AM Subject: Google Summer of Code 2013 To: Google Summer of Code Announce < google-summer-of-code-announce(a)googlegroups.com> Hi all, We're pleased to announce that Google Summer of Code will be happening for its ninth year this year. Please check out the blog post [1] about the program and read the FAQs [2] and Timeline [3] on Melange for more information. [1] - http://google-opensource.blogspot.com/2013/02/flip-bits-not-burgers-google-… [2] - http://www.google-melange.com/gsoc/document/show/gsoc_program/google/gsoc20… [3] - http://www.google-melange.com/gsoc/events/google/gsoc2013 Cheers, Carol -- You received this message because you are subscribed to the Google Groups "Google Summer of Code Announce" group. To unsubscribe from this group and stop receiving emails from it, send an email to google-summer-of-code-announce%2Bunsubscribe(a)googlegroups.com. To post to this group, send email to google-summer-of-code-announce(a)googlegroups.com. Visit this group at http://groups.google.com/group/google-summer-of-code-announce?hl=en. For more options, visit https://groups.google.com/groups/opt_out.

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