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Haskell Weekly News: Issue 268
by Daniel Santa Cruz 31 May '13

31 May '13

Welcome to issue 268 of the HWN, an issue covering crowd-sourced bits of information about Haskell from around the web. This issue covers the week of May 12 to 25, 2013. Quotes of the Week * tikhonjelvis: the lesson is that the fix function exists to "fix" any type problems you may encounter * shachaf: The trouble with peano arithmetic is that it stops at 88. * Peaker: Python's dynamic nature adds slowness and unsafety, but doesn't actually make things more expressive * sj4nz: Programming in weakly-typed languages forever after will feel like working with punch cards. Send in your program to the nodejs interpreter and hope for a result to come back. * xplat: if you want to carry your machete all the time and not make people nervous, you need to constantly blaze trails * otters: heh, F# is just the unboxed version of F * quchen: This was the first time in months that I thought imperatively. Conclusion: 1. it complicated things, 2. it was refreshing * cmccann: I still kind of expect that the next standard will be haskell2017 or something, and all it will do is a minor change to lexical syntax of comments that fixes nothing but nevertheless breaks 20% of hackage. * cmccann: [on reimplementing cryptography in pure Haskell] writing in Haskell lets you use type safety to ensure that all the security holes you create are subtle instead of obvious. Top Reddit Stories * Haskell in Production [slides] Domain: mth.io, Score: 60, Comments: 114 On Reddit: [1] http://goo.gl/ldnv0 Original: [2] http://goo.gl/tMjTd * B-trees with GADTs Domain: matthew.brecknell.net, Score: 56, Comments: 6 On Reddit: [3] http://goo.gl/Sjf9U Original: [4] http://goo.gl/sQnYW * Yearly revisions to the Haskell language: who killed Haskell Prime? Domain: self.haskell, Score: 54, Comments: 19 On Reddit: [5] http://goo.gl/5GWKg Original: [6] http://goo.gl/5GWKg * Elm paper accepted at PLDI: Asynchronous FRP for GUIs! Domain: people.seas.harvard.edu, Score: 51, Comments: 4 On Reddit: [7] http://goo.gl/iYiyh Original: [8] http://goo.gl/98jft * The complete correctness of sorting [Agda] Domain: twanvl.nl, Score: 49, Comments: 5 On Reddit: [9] http://goo.gl/PLH6m Original: [10] http://goo.gl/RQGZn * Anatomy of an MVar operation Domain: blog.ezyang.com, Score: 47, Comments: 7 On Reddit: [11] http://goo.gl/7miao Original: [12] http://goo.gl/3ZHSI * Typing Haskell in Haskell Domain: web.cecs.pdx.edu, Score: 44, Comments: 34 On Reddit: [13] http://goo.gl/q1ghy Original: [14] http://goo.gl/M5csQ * STM in Haskell is better because of types Domain: joeyh.name, Score: 44, Comments: 8 On Reddit: [15] http://goo.gl/wj9Ab Original: [16] http://goo.gl/fmLM1 * Typed Template Haskell ready for testing in GHC Domain: haskell.org, Score: 44, Comments: 13 On Reddit: [17] http://goo.gl/he61y Original: [18] http://goo.gl/YJIZB * A detailed look at GHC's STM implementation from a non-GHC hacker Domain: fryguybob.github.io, Score: 38, Comments: 11 On Reddit: [19] http://goo.gl/pTp2c Original: [20] http://goo.gl/4oe3Y * New Haskell Communities and Activity Report (May 2013) is out Domain: haskell.org, Score: 37, Comments: 2 On Reddit: [21] http://goo.gl/P2kz1 Original: [22] http://goo.gl/YoIE4 * Three examples of problems with Lazy I/O Domain: newartisans.com, Score: 36, Comments: 31 On Reddit: [23] http://goo.gl/reKqZ Original: [24] http://goo.gl/ZagPt * Understanding the Yoneda Lemma Domain: fpcomplete.com, Score: 35, Comments: 48 On Reddit: [25] http://goo.gl/RUZ4h Original: [26] http://goo.gl/xbAJj * Simon Peyton Jones to keynote Haskell eXchange 2013! Domain: skillsmatter.com, Score: 35, Comments: 2 On Reddit: [27] http://goo.gl/DlfRt Original: [28] http://goo.gl/5lpwh * Greg Hale's "Functional programming elevator pitch" Domain: fpcomplete.com, Score: 34, Comments: 8 On Reddit: [29] http://goo.gl/gbhX3 Original: [30] http://goo.gl/QrrxP * FP Complete is looking for a Technical Sales Engineer and Support Specialist Domain: fpcomplete.com, Score: 32, Comments: 1 On Reddit: [31] http://goo.gl/nYNci Original: [32] http://goo.gl/VGCoa * A Typed Markup Language Based On Haskell Domain: blog.functorial.com, Score: 31, Comments: 9 On Reddit: [33] http://goo.gl/eLLjV Original: [34] http://goo.gl/wFxcv * Announcing: Snap Framework v0.12 Domain: snapframework.com, Score: 28, Comments: 2 On Reddit: [35] http://goo.gl/5wYLk Original: [36] http://goo.gl/KibyP * John Wiegley's "Understanding Continuations", on School of Haskell Domain: fpcomplete.com, Score: 27, Comments: 17 On Reddit: [37] http://goo.gl/ZT7d6 Original: [38] http://goo.gl/YitVR Top StackOverflow Questions * Why are if expressions frowned upon in Haskell? votes: 20, answers: 6 Read on SO: [39] http://goo.gl/NejhX * Haskell: `Map (a,b) c` versus `Map a (Map b c)`? votes: 19, answers: 3 Read on SO: [40] http://goo.gl/8f1hf * Why recursive `let` make space effcient? votes: 18, answers: 3 Read on SO: [41] http://goo.gl/QTLYQ * Should do-notation be avoided in Haskell? [duplicate] votes: 16, answers: 7 Read on SO: [42] http://goo.gl/MGiFr * Correspondence between type classes and grammar levels in the Chomsky hierarchy votes: 15, answers: 1 Read on SO: [43] http://goo.gl/LRJy2 * Calling Haskell from C# votes: 14, answers: 2 Read on SO: [44] http://goo.gl/n9QB1 * How do exceptions work in Haskell (part two)? votes: 13, answers: 1 Read on SO: [45] http://goo.gl/U2GDR * Can a monad be a comonad? votes: 11, answers: 5 Read on SO: [46] http://goo.gl/ESrc2 * Dynamic Programming Memoization in Haskell votes: 11, answers: 1 Read on SO: [47] http://goo.gl/Gp7c8 * Employing arrows to fold a list of tuples votes: 11, answers: 1 Read on SO: [48] http://goo.gl/shRWV Until next time, +Daniel Santa Cruz References 1. http://mth.io/talks/haskell-in-production/ 2. http://www.reddit.com/r/haskell/comments/1etssw/haskell_in_production_slide… 3. http://matthew.brecknell.net/post/btree-gadt/ 4. http://www.reddit.com/r/haskell/comments/1efuog/btrees_with_gadts/ 5. http://www.reddit.com/r/haskell/comments/1esmhj/yearly_revisions_to_the_has… 6. http://www.reddit.com/r/haskell/comments/1esmhj/yearly_revisions_to_the_has… 7. http://people.seas.harvard.edu/~chong/pubs/pldi13-elm.pdf 8. http://www.reddit.com/r/haskell/comments/1eie6m/elm_paper_accepted_at_pldi_… 9. http://twanvl.nl/blog/agda/sorting 10. http://www.reddit.com/r/haskell/comments/1exv2t/the_complete_correctness_of… 11. http://blog.ezyang.com/2013/05/anatomy-of-an-mvar-operation/ 12. http://www.reddit.com/r/haskell/comments/1eostu/anatomy_of_an_mvar_operatio… 13. http://web.cecs.pdx.edu/~mpj/thih/TypingHaskellInHaskell.html 14. http://www.reddit.com/r/haskell/comments/1e6s68/typing_haskell_in_haskell/ 15. http://joeyh.name/blog/entry/the_newinwheezy_game:_STM/ 16. http://www.reddit.com/r/haskell/comments/1e8ow9/stm_in_haskell_is_better_be… 17. http://www.haskell.org/pipermail/ghc-devs/2013-May/001255.html 18. http://www.reddit.com/r/haskell/comments/1egfra/typed_template_haskell_read… 19. http://fryguybob.github.io/STM-Commentary/ 20. http://www.reddit.com/r/haskell/comments/1ejgjo/a_detailed_look_at_ghcs_stm… 21. http://haskell.org/communities/05-2013/html/report.html 22. http://www.reddit.com/r/haskell/comments/1e601k/new_haskell_communities_and… 23. http://newartisans.com/2013/05/three-examples-of-problems-with-lazy-io 24. http://www.reddit.com/r/haskell/comments/1e8k3k/three_examples_of_problems_… 25. https://www.fpcomplete.com/user/bartosz/understanding-yoneda 26. http://www.reddit.com/r/haskell/comments/1eelao/understanding_the_yoneda_le… 27. http://skillsmatter.com/event/scala/haskell-exchange/te-7391 28. http://www.reddit.com/r/haskell/comments/1ewq54/simon_peyton_jones_to_keyno… 29. https://www.fpcomplete.com/user/imalsogreg/functional-programming-elevator-… 30. http://www.reddit.com/r/haskell/comments/1ewvhm/greg_hales_functional_progr… 31. https://www.fpcomplete.com/page/product_specialist 32. http://www.reddit.com/r/haskell/comments/1ezeng/fp_complete_is_looking_for_… 33. http://blog.functorial.com/posts/2013-05-18-Typed-Markup-Language.html 34. http://www.reddit.com/r/haskell/comments/1elhj2/a_typed_markup_language_bas… 35. http://snapframework.com/blog/2013/05/15/snap-0.12-released 36. http://www.reddit.com/r/haskell/comments/1ef3kt/announcing_snap_framework_v… 37. https://www.fpcomplete.com/user/jwiegley/understanding-continuations 38. http://www.reddit.com/r/haskell/comments/1e977w/john_wiegleys_understanding… 39. http://stackoverflow.com/questions/16572446/why-are-if-expressions-frowned-… 40. http://stackoverflow.com/questions/16613032/haskell-map-a-b-c-versus-map-a-… 41. http://stackoverflow.com/questions/16632143/why-recursive-let-make-space-ef… 42. http://stackoverflow.com/questions/16726659/should-do-notation-be-avoided-i… 43. http://stackoverflow.com/questions/16607637/correspondence-between-type-cla… 44. http://stackoverflow.com/questions/16615641/calling-haskell-from-c-sharp 45. http://stackoverflow.com/questions/16678165/how-do-exceptions-work-in-haske… 46. http://stackoverflow.com/questions/16551734/can-a-monad-be-a-comonad 47. http://stackoverflow.com/questions/16585741/dynamic-programming-memoization… 48. http://stackoverflow.com/questions/16676758/employing-arrows-to-fold-a-list… 49. https://plus.google.com/105107667630152149014/about

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Re: [Haskell-cafe] using a win32 dll (Happy too soon)
by Brandon Allbery 31 May '13

31 May '13

On Thu, May 30, 2013 at 3:15 AM, Kees Bleijenberg < k.bleijenberg(a)lijbrandt.nl> wrote: > argument. The dll is in the PATH. I don't understand why it needs the -L > argument. I'll figure this out later. If I use -lglasPng.dll (additional > .dll) it doesn't work either. > Unix has standard places to install and search for libraries; Windows doesn't, and almost every library that doesn't come with your build system will need at least one -L option to tell the linker where to find it. As I mentioned in my first message, it looks for multiple file names with -l: first it tries a .dll, then it tries a .lib (static library or import library for older DLLs). It does this mechanically; if you also include the .dll suffix, then it looks for library.dll.dll and library.dll.lib, which is almost certainly wrong. -- brandon s allbery kf8nh sine nomine associates allbery.b(a)gmail.com ballbery(a)sinenomine.net unix, openafs, kerberos, infrastructure, xmonad http://sinenomine.net

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Re: [Haskell-cafe] [haskell.org Google Summer of Code 2013] Approved Projects
by Stephen Tetley 31 May '13

31 May '13

Similarly (to some degree), in the ML world John Reppy had a very nice system that employed user customization via combinators rather than inference to generate application/library specific FFIs, see: http://people.cs.uchicago.edu/~jhr/papers/2006/gpce-fig.pdf On 29 May 2013 18:57, Jason Dagit <dagitj(a)gmail.com> wrote: > Are you folks aware of the work on this topic by Tristan Ravitch? > https://github.com/travitch/foreign-inference > > Jason > > _______________________________________________ > Haskell-Cafe mailing list > Haskell-Cafe(a)haskell.org > http://www.haskell.org/mailman/listinfo/haskell-cafe

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ANN stm-chans 2.1 / 3.0
by wren ng thornton 31 May '13

31 May '13

-------------------------------------------- -- stm-chans 2.1 / 3.0 -------------------------------------------- The stm-chans package offers a collection of channel types, similar to Control.Concurrent.STM.{TChan,TQueue} but with additional features. -------------------------------------------- -- Changes (since 2.0.0) -------------------------------------------- By popular demand, the functions newBroadcastTMChan{,IO} have been added. However, these rely on newBroadcastTChan{,IO} which are only available in stm >= 2.4 and do not appear to be replicable using the public API of stm < 2.4. Thus, the minimum version of stm is now 2.4, which obviates all the compatibility modules. Version 2.1.0 adds the new functions and issues deprecation warnings about using the compatibility modules. This version is just to help people transition. If you can use this version without warnings (i.e., you don't use the Compat modules directly) then you should be able to use version 3.0 as well. Version 3.0 removes the compatibility modules. -------------------------------------------- -- Long description -------------------------------------------- In particular stm-chans offers the following data types: * Control.Concurrent.STM.TBChan: Bounded FIFO channels. When the channel is full, writers will block/retry. This ensures that the writers do not get too far ahead of the readers, which helps to make sure that memory and cpu resources are used responsibly. * Control.Concurrent.STM.TMChan: Closeable FIFO channels. * Control.Concurrent.STM.TMQueue: Closeable FIFO queues. Like TChan (Maybe a) but with a monotonicity guarantee that once Nothing is returned all future reads will be Nothing as well. * Control.Concurrent.STM.TBMChan: Bounded Closeable FIFO channels. * Control.Concurrent.STM.TBMQueue: Bounded Closeable FIFO queues. Combines the capabilities of TBChan and TMChan. -------------------------------------------- -- Links -------------------------------------------- Homepage: http://code.haskell.org/~wren/ Hackage: http://hackage.haskell.org/package/stm-chans Darcs: http://community.haskell.org/~wren/stm-chans Haddock (Darcs version): http://community.haskell.org/~wren/stm-chans/dist/doc/html/stm-chans -- Live well, ~wren

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Re: [Haskell-cafe] using a win32 dll (Happy too soon)
by Brandon Allbery 31 May '13

31 May '13

On Thu, May 30, 2013 at 11:46 AM, Kees Bleijenberg < k.bleijenberg(a)lijbrandt.nl> wrote: > Brandon, thanks again for your explanation > Are you sure about the non existing search order for dynamic loaded dll’s? > I.e. > http://msdn.microsoft.com/en-us/library/windows/desktop/ms682586(v=vs.85).a… there is a search order, starting with the current directory (I think). > There is a search order. What I said is that there are no standard locations to install things. That is, every library package stows stuff in its own directory structure and no compiler can possibly know all the places it needs to look to find every library off in its own directory. > I don’t understand why the linker needs to see the dll anyway. Because it's better to catch "that symbol doesn't exist" at build time instead of throwing an ugly error at runtime, among other things. > possible in Delphi. Is Haskell dynamic loading more limited? > There are ways to do that kind of dynamic linking; this is not one of them. C and C++ don't automatically dynload the way you're thinking either, because you should test for the DLL you're distributing (you are distributing it, right, not forcing the end user on a wild goose chase to find their own copy of the DLL, hoping it's the right/compatible version, and figure out where to put it so your program will run?) being the right one *when you build the program*, not defer that test until it is run. If you think about it, this is very similar to doing your type checking at compile time instead of runtime. If you want lazy type checking, why are you using Haskell? If you want lazy library checking, why are you using a compiler? -- brandon s allbery kf8nh sine nomine associates allbery.b(a)gmail.com ballbery(a)sinenomine.net unix, openafs, kerberos, infrastructure, xmonad http://sinenomine.net

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Re: [Haskell-cafe] Problem with compilation on MAC OS X
by Simon Thompson 30 May '13

30 May '13

Thanks - unfortunately it breaks cabal-install too! S. On 30 May 2013, at 13:28, Artyom Kazak <artyom.kazak(a)gmail.com> wrote: > Apparently, Agda has been broken by the recent decision to remove 'catch', which had already been deprecated for some time, from Prelude. You can fix the source yourself, or wait for a new release. > > On May 30, 2013 3:04 PM, "Simon Thompson" <s.j.thompson(a)kent.ac.uk> wrote: > Simon Thompson | Professor of Logic and Computation School of Computing | University of Kent | Canterbury, CT2 7NF, UK s.j.thompson(a)kent.ac.uk | M +44 7986 085754 | W www.cs.kent.ac.uk/~sjt

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Problem with compilation on MAC OS X
by Simon Thompson 30 May '13

30 May '13

New machine, latest version of the Haskell Platform for 64 bit Mac OS X. In trying to build a new version of cabal-install and also of Agda I get variants of the same error dist/build/autogen/Paths_Agda.hs:21:13: Not in scope: `catch' any thoughts on what I am doing wrong? I have XCode command line tools installed. Thanks! Simon T. Simon Thompson | Professor of Logic and Computation School of Computing | University of Kent | Canterbury, CT2 7NF, UK s.j.thompson(a)kent.ac.uk | M +44 7986 085754 | W www.cs.kent.ac.uk/~sjt

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Re: [Haskell-cafe] using a win32 dll (Happy too soon)
by Brandon Allbery 30 May '13

30 May '13

On Wed, May 29, 2013 at 9:40 AM, Kees Bleijenberg < k.bleijenberg(a)lijbrandt.nl> wrote: > If I compile with ghc --make testGlasPng.hs –lglasPng I get: ….\ld.exe: > cannot find –lglasPng. Collect 2: ld returned 1 exit status. > > ** > > Ld can’t find lglasPng (with the l in front, does it trim the l?). Why? > Okay I try > It's reproducing the thing passed to it, rather than outputting both the dll and implib versions that it actually looks for. Same happens on unixlikes where it's looking for a .so/.dylib/whatever or a .a. **** > > ghc --make testGlasPng.hs –L<path to glasPng.dll> I get: > Not quite right; -L identifies a *directory* to search, then you must specify the actual filename afterward. > **** > > testGlasPng.o: fake: (.text + 0x82) :undefined reference to > ‘getPngVersion@0’. I think it has found the > This just means it can't find the symbol; it does not mean it necessarily found the DLL. > I run ghc on a 64 bits computer. The dll is 32 bits. Is that the problem? > That can certainly be a problem, yes, and is likely why it wasn't found with the first one. But it's not so much what kind of machine you are on, as what kind of ghc you are using: a 64-bit ghc cannot link 32-bit libraries, and vice versa. But a 32-bit ghc and toolchain will work fine on a 64-bit system, aside from not linking 64-bit DLLs. -- brandon s allbery kf8nh sine nomine associates allbery.b(a)gmail.com ballbery(a)sinenomine.net unix, openafs, kerberos, infrastructure, xmonad http://sinenomine.net

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ANN: yi-0.6.7
by Dmitry Ivanov 30 May '13

30 May '13

Hello Cafe After about a year we've released a new version of Yi, text editor written and extensible in Haskell. Please have a look, hopefully you can find something interesting for you, whether you are emacs, vim or $(your-favorite-editor) fan. Changelog is available at https://github.com/yi-editor/yi/blob/master/CHANGELOG We currently lack active maintainers for Pango and Cocoa frontends, Emacs emulation and some smaller modules. Contributors in these areas are especially welcome. Also we have almost no user-level documentation compared to other editors, so if someone new to yi would set it up to his liking and share the experience on wiki or his blog or somewhere else, that would also be a very nice contribution. Places to dicuss using and developing yi: mailing list: https://groups.google.com/group/yi-devel issue tracker: https://github.com/yi-editor/yi/issues IRC channel: #yi@freenode (it's very slow compared to #haskell, please don't quit after 10 mins) Regards, Dmitry

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ANN: hsbencher-1.1, with Fusion Table upload
by Ryan Newton 30 May '13

30 May '13

I'm pleased to announce a new benchmarking framework, HSBencher. It's an early prototype, but it's flexible, extensible and uploads benchmark data to Google Fusion Tables. Right now the fusion table upload depends on a pre-release version of "handa-gdata" (0.6.2), which you can get at one of these locations: https://code.google.com/p/hgdata/ https://github.com/rrnewton/hgdata_mirror (It should be released soon.) Here's a blog post explaining HSBencher's usage: http://parfunk.blogspot.com/2013/05/towards-cloud-based-crowd-sourced.html Hackage: http://hackage.haskell.org/package/hsbencher Github (see README) https://github.com/rrnewton/hsbencher

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