- Haskell-Cafe - Haskell.org

GHC 7.6.2 introduces <<loop>> in UUAGC
by Jeroen Bransen 07 Mar '13

07 Mar '13

Hi all, The uuagc package [1] works fine with GHC versions 7.4.* and 7.6.1. However, with GHC 7.6.2 the binary still compiles but runs into an infinite loop at runtime. To reproduce, do: cabal install uuagc && touch tmp.ag && uuagc tmp.ag With GHC versions < 7.6.2 this succeeds and creates a (rather boring) file tmp.hs, while with GHC 7.6.2 this displays: uuagc: <<loop>> I suspect that this is related to strictness annotations, which exist in many places in the UUAGC source code (which itself is also preprocessed by the UUAGC system). In the release notes I cannot find anything related to strictness which could introduce this, so would anyone have a clue on where to look? Has there been a longstanding bug in the UUAGC source code which only now surfaces? Or is it a bug introduced in GHC 7.6.2 where something is a bit too strict? Regards, Jeroen Bransen [1] http://hackage.haskell.org/package/uuagc

1 1

Re: [Haskell-cafe] Announce: Leksah 0.13.2.0 (still a bit experimental)
by Hamish Mackenzie 07 Mar '13

07 Mar '13

I am not able to reproduce this on my Ubuntu 12.10 VM. What version of GHC are you using? Do you have anything in your ~/.ghci file? What command are you running? Does putStrLn "Hello World" work? What is the active .cabal project? The GHCi interface is sensitive to changes in the way GHCi formats it output, so it is a bit fragile. Some things that will currently break it are... * Anything that tries to read input on stdin * :set prompt (Leksah uses the prompt to detect when the output finishes) I added some tests a while back to try to catch issues running GHCi. Can you please try this... cd leksah/vendor/leksah-server cabal install --enable-tests --force-reinstall You should see this near the end... Running 1 test suites... Test suite test-tool: RUNNING... Test suite test-tool: PASS Test suite logged to: dist/test/leksah-server-0.13.0.0-test-tool.log 1 of 1 test suites (1 of 1 test cases) passed. Thanks, Hamish On 7 Mar 2013, at 08:48, Alejandro Toribio Bello Ruiz <alejandro.bello67(a)gmail.com> wrote: > Leksah 0.13.2 compiled successfully on Ubuntu 12.10 following the new instructions on .travis.yml, but arise the old problem where the GHCi integration break when the first command set is from the debug scratch pane. This bug was fixed on Leksah 0.12.1.3. What happened? This issue is very import for my students. Would be very grateful if you fix this bug. > > Regards > > El viernes, 1 de marzo de 2013 23:04:59 UTC-5, Hamish escribió: > 12.10 uses webkit 1.10 so the -fwebkit1.8 was probably tripping it up. > > I have updated webkit so that webkit 1.8 is detected automatically and > updated the .travis.yml file. > > Please try again. > > On 23 Feb 2013, at 06:20, alejandr...@gmail.com wrote: > >> I compiled Leksah 0.13.2 using Ubuntu 12.04 (I followed the instructions on .travis.yml). It was OK, but when I tried to compile with Ubuntu 12.10, I got the following error: >> >> Building webkit-0.12.5... >> Preprocessing library webkit-0.12.5... >> gtk2hsC2hs: Errors during expansion of binding hooks: >> >> webkit1.8/Graphics/UI/Gtk/WebKit/DOM/File.chs:17: (column 14) [ERROR] >> >>> Unknown identifier! >> Cannot find a definition for `webkit_dom_file_get_file_name' in the header file. >> webkit1.8/Graphics/UI/Gtk/WebKit/DOM/File.chs:23: (column 16) [ERROR] >> >>> Unknown identifier! >> Cannot find a definition for `webkit_dom_file_get_file_size' in the header file. >> >> Can you help me, please? >> >> Alejandro T. Bello Ruiz >> >> >> -- >> You received this message because you are subscribed to the Google Groups "leksah" group. >> To unsubscribe from this group and stop receiving emails from it, send an email to leksah+un...@googlegroups.com. >> For more options, visit https://groups.google.com/groups/opt_out. >> >> > > > -- > You received this message because you are subscribed to the Google Groups "leksah" group. > To unsubscribe from this group and stop receiving emails from it, send an email to leksah%2Bunsubscribe(a)googlegroups.com. > For more options, visit https://groups.google.com/groups/opt_out. > >

1 0

GSOC application level
by Mateusz Kowalczyk 07 Mar '13

07 Mar '13

Greetings, It seems that the Haskell community consistently participates in the Google Summer of Code project. I (and probably many others) am interested in taking part in one of such projects but I have a question in regards to the expertise. I know that this year's projects aren't up yet but by looking at the past results, the expertise required seems to vary pretty widely. Can someone that has been around for a bit longer comment on what level of experience with Haskell and underlying concepts is usually expected from candidates? Are applications discarded simply based on the applicant not having much previous experience in the target area? What is the level of the competition for places on the projects? It's not my first week of meddling with Haskell (and studying the ideas behind it) but I can't say that I would be able to confidently take on any project that might be put out. I do however realise that the project is open to students so I don't imagine the requirements specify something like couple of years with type theory research either. Any insight about the topic is appreciated. I'd much rather flip bits than do labour this summer and if it can be done using the language I'm interested in, even better! -- Mateusz K.

3 2

ANNOUNCE: Start Ajhc project with forking jhc.
by Kiwamu Okabe 07 Mar '13

07 Mar '13

Hi all. I am a user of jhc Haskell compiler. Jhc can compile Haskell code to micro arch such as Cortex-M3. I have written LED blinking demo for Cortex-M3 with jhc. Very fun! https://github.com/ajhc/demo-cortex-m3 http://www.youtube.com/watch?v=3R9sogReVHg And I created many patches for jhc. But...I think that the upstream author of jhc, John Meacham, can't pull the contribution speedy, because he is too busy. It's difficult that maintain many patches without any repositories, for me. Then, I have decided to fork jhc, named Ajhc. # pain full... http://ajhc.github.com/ I will feedback Ajhc's big changes to jhc mailing list. Or I am so happy if John joins Ajhc project. Regards, -- Kiwamu Okabe

4 4

Haskell Weekly News: Issue 261
by Daniel Santa Cruz 07 Mar '13

07 Mar '13

Welcome to issue 261 of the HWN, an issue covering crowd-sourced bits of information about Haskell from around the web. This issue covers the week of February 24 to March 02, 2013. Quotes of the Week * EvilMachine: I always picture some poor mutant guy whose every body part looks alike in the deepest depths of the dark ages going to the doc, and being told he has ‚monomorphism‚. * pmk: the last time i asked GHC to compile a function with forty (.)'s in a row, it took over an hour Top Reddit Stories * Some draft chapters of "Parallel and Concurrent Programming in Haskell" available online for comment Domain: self.haskell, Score: 79, Comments: 40 On Reddit: [1] http://goo.gl/emvnI Original: [2] http://goo.gl/emvnI * Hulk: A Haskell IRC server - Nice example of real world monad without IO Domain: chrisdone.com, Score: 62, Comments: 18 On Reddit: [3] http://goo.gl/CR986 Original: [4] http://goo.gl/RhjG6 * Hole-driven Haskell Domain: matthew.brecknell.net, Score: 59, Comments: 52 On Reddit: [5] http://goo.gl/5ctnJ Original: [6] http://goo.gl/NqJVi * Chasing a Space Leak in Shake: Profiling, reduction, digging thru stacks Domain: neilmitchell.blogspot.com, Score: 46, Comments: 11 On Reddit: [7] http://goo.gl/cO86j Original: [8] http://goo.gl/v09x6 * Haskell patterns ad nauseam Domain: yaxu.org, Score: 39, Comments: 2 On Reddit: [9] http://goo.gl/dapAz Original: [10] http://goo.gl/hPW6y * Cross Compiling for iOS with GHC Domain: hackage.haskell.org, Score: 35, Comments: 18 On Reddit: [11] http://goo.gl/3uzjR Original: [12] http://goo.gl/Kw0Pe * From Set Theory to Type Theory Domain: golem.ph.utexas.edu, Score: 35, Comments: 8 On Reddit: [13] http://goo.gl/HaPN4 Original: [14] http://goo.gl/LUi5f * EclipseFP 2.5.0 released: cabal-dev support, import cleaning, and more Domain: jpmoresmau.blogspot.fr, Score: 31, Comments: 0 On Reddit: [15] http://goo.gl/lR6Tc Original: [16] http://goo.gl/JJzBz * Michael Snoyman's overview of the new conduit 1.0, on School of Haskell Domain: haskell.fpcomplete.com, Score: 31, Comments: 11 On Reddit: [17] http://goo.gl/aFbw1 Original: [18] http://goo.gl/ObEHA * How is Haskell tackling the multicore problem? - Simon Marlow Domain: youtube.com, Score: 28, Comments: 5 On Reddit: [19] http://goo.gl/qOKlJ Original: [20] http://goo.gl/HVddu * Generics and Protocol Buffers... now on Hackage Domain: breaks.for.alienz.org, Score: 28, Comments: 5 On Reddit: [21] http://goo.gl/WqIyn Original: [22] http://goo.gl/J9NKB * Demonstrating tidal - haskell music patterns in action Domain: blog.lurk.org, Score: 24, Comments: 5 On Reddit: [23] http://goo.gl/4ddqI Original: [24] http://goo.gl/Ift8y * GHC iOS Packages Domain: github.com, Score: 23, Comments: 5 On Reddit: [25] http://goo.gl/PONjI Original: [26] http://goo.gl/6D3Gz * SoH tutorial: a regular expression matcher using continuations Domain: haskell.fpcomplete.com, Score: 22, Comments: 4 On Reddit: [27] http://goo.gl/toQpy Original: [28] http://goo.gl/BZ1xI * [nyc-haskell] Greg Wright - A Purely Symbolic Effort in Mathematics Domain: vimeo.com, Score: 22, Comments: 6 On Reddit: [29] http://goo.gl/jNybI Original: [30] http://goo.gl/Q8pq8 * ANN: clckwrks 0.16 Haskell blog/CMS platform released. Includes a screencast demonstrating clckwrks features. Domain: clckwrks.com, Score: 20, Comments: 2 On Reddit: [31] http://goo.gl/Tp92p Original: [32] http://goo.gl/zV7Sj Top StackOverflow Questions * Do Hask or Agda have equalisers? votes: 23, answers: 2 Read on SO: [33] http://goo.gl/k74C9 * Prove idempotency of type-level disjunction votes: 17, answers: 2 Read on SO: [34] http://goo.gl/wsFUL * Internal representation of Haskell lists? votes: 16, answers: 2 Read on SO: [35] http://goo.gl/TCGDk * GHC Generating Redundant Core Operations votes: 15, answers: 1 Read on SO: [36] http://goo.gl/d9zWP * eliminating repetition in cabal files votes: 14, answers: 0 Read on SO: [37] http://goo.gl/2StJ9 * Translate from monad to applicative votes: 12, answers: 3 Read on SO: [38] http://goo.gl/IbSUi * Memoizing multiplication votes: 10, answers: 2 Read on SO: [39] http://goo.gl/EXvUk * Most efficient way to seek around in a large file votes: 9, answers: 1 Read on SO: [40] http://goo.gl/C9FGp * Does Haskell optimizer utilize memoization for repeated function calls in a scope? votes: 9, answers: 3 Read on SO: [41] http://goo.gl/3qDPQ * Existential type in higher order function votes: 9, answers: 1 Read on SO: [42] http://goo.gl/YfalJ * Haskell `ncurses` library votes: 9, answers: 2 Read on SO: [43] http://goo.gl/w7vKf Until next time, +Daniel Santa Cruz References 1. http://www.reddit.com/r/haskell/comments/195app/some_draft_chapters_of_para… 2. http://www.reddit.com/r/haskell/comments/195app/some_draft_chapters_of_para… 3. http://chrisdone.com/posts/hulk-haskell-irc-server 4. http://www.reddit.com/r/haskell/comments/194ngx/hulk_a_haskell_irc_server_n… 5. http://matthew.brecknell.net/posts/2013/02/26/hole-driven-haskell/ 6. http://www.reddit.com/r/haskell/comments/19aj9t/holedriven_haskell/ 7. http://neilmitchell.blogspot.com/2013/02/chasing-space-leak-in-shake.html 8. http://www.reddit.com/r/haskell/comments/197ax4/chasing_a_space_leak_in_sha… 9. http://yaxu.org/haskell-patterns-ad-nauseam/ 10. http://www.reddit.com/r/haskell/comments/19e2ln/haskell_patterns_ad_nauseam/ 11. http://hackage.haskell.org/trac/ghc/wiki/Building/CrossCompiling/iOS 12. http://www.reddit.com/r/haskell/comments/19cq83/cross_compiling_for_ios_wit… 13. http://golem.ph.utexas.edu/category/2013/01/from_set_theory_to_type_theory.… 14. http://www.reddit.com/r/haskell/comments/19igl8/from_set_theory_to_type_the… 15. http://jpmoresmau.blogspot.fr/2013/02/eclipsefp-250-released.html 16. http://www.reddit.com/r/haskell/comments/199smc/eclipsefp_250_released_caba… 17. https://haskell.fpcomplete.com/school/pick-of-the-week/conduit-overview 18. http://www.reddit.com/r/haskell/comments/19akp3/michael_snoymans_overview_o… 19. https://www.youtube.com/watch?v=Mu6JjZsIdu8 20. http://www.reddit.com/r/haskell/comments/19eh7e/how_is_haskell_tackling_the… 21. http://breaks.for.alienz.org/blog/2013/02/28/generics-and-protocol-buffers-… 22. http://www.reddit.com/r/haskell/comments/19et3i/generics_and_protocol_buffe… 23. http://blog.lurk.org/demonstrating-tidal/ 24. http://www.reddit.com/r/haskell/comments/19jq16/demonstrating_tidal_haskell… 25. https://github.com/kaoskorobase/ghc-ios-cabal-scripts 26. http://www.reddit.com/r/haskell/comments/19gufd/ghc_ios_packages/ 27. https://haskell.fpcomplete.com/user/pbv/a-regular-expression-matcher 28. http://www.reddit.com/r/haskell/comments/199523/soh_tutorial_a_regular_expr… 29. https://vimeo.com/60737699 30. http://www.reddit.com/r/haskell/comments/19fp85/nychaskell_greg_wright_a_pu… 31. http://clckwrks.com/page/view-page-slug/10/ann--clckwrks-0-16---now-built-w… 32. http://www.reddit.com/r/haskell/comments/19a393/ann_clckwrks_016_haskell_bl… 33. http://stackoverflow.com/questions/15047775/do-hask-or-agda-have-equalisers 34. http://stackoverflow.com/questions/15180557/prove-idempotency-of-type-level… 35. http://stackoverflow.com/questions/15063115/internal-representation-of-hask… 36. http://stackoverflow.com/questions/15095902/ghc-generating-redundant-core-o… 37. http://stackoverflow.com/questions/15179316/eliminating-repetition-in-cabal… 38. http://stackoverflow.com/questions/15123552/translate-from-monad-to-applica… 39. http://stackoverflow.com/questions/15080399/memoizing-multiplication 40. http://stackoverflow.com/questions/15052905/most-efficient-way-to-seek-arou… 41. http://stackoverflow.com/questions/15084162/does-haskell-optimizer-utilize-… 42. http://stackoverflow.com/questions/15125522/existential-type-in-higher-orde… 43. http://stackoverflow.com/questions/15176015/haskell-ncurses-library 44. https://plus.google.com/105107667630152149014/about

1 0

Commercial Users of Functional Programming: Call for tutorials
by Simon Thompson 06 Mar '13

06 Mar '13

Commercial Users of Functional Programming Call for tutorials Commercial Users of Functional Programming (CUFP) is an annual meeting co-located with the International Conference on Functional Programming which this year will take place in Boston, MA, USA on 22-24 September 2013. CUFP aims to bridge the gap between academia and users applying functional programming in practice. CUFP provides high-quality practical tutorials covering state-of-the-art techniques and tools for functional programming. We are seeking proposals for half-day tutorials to be presented during the first two days of the meeting, 22 and 23 September, with the main CUFP session on 24 September. Among the suggested topics for tutorials are: - Introductions to functional programming languages: in the past we have had introductions to Clojure, Erlang, F#, Haskell, ML, OCaml, Scala, Scheme and others. - Applying functional programming in particular areas, including the web, high-performance computing, finance. - Tools and techniques supporting state of the art functional programming. Tutorial proposals should address the following points - Title - Abstract (about 100 words) - Goals: by the end of this tutorial you will be able to … - Intended audience: e.g. beginners, those with a working knowledge of X, … - Infrastructure required: For example, - will participants need access to a particular system? - can they be expected to have this on a laptop, or does it need to be provided by the meeting? and should be sent by email to - Francesco Cesarini: francesco(a)erlang-solutions.com - Simon Thompson: S.J.Thompson(a)kent.ac.uk by 31 March 2013. 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

1 0

ANNOUNCE: http-streams 0.3.1.0
by Andrew Cowie 06 Mar '13

06 Mar '13

Hey, I'd like to announce the initial release of http-streams, an HTTP client library using the Snap Framework's io-streams library to handle the streaming I/O. I blogged about it the background and API design here: http://blogs.operationaldynamics.com/andrew/software/haskell/http-streams-i… The SHA256 sum of http-streams-0.3.1.0.tar.gz as uploaded is: e0671f8eac83e9a4b092bdd7b03e69b80ac0417818b8dbc51d8604b769179bd3 Comments and feedback welcome. Cheers, AfC Sydney

1 0

ANNOUNCE: io-streams 1.0.0.0
by Gregory Collins 06 Mar '13

06 Mar '13

Hi all, After more than eight months of careful design and development, The Snap Framework team is happy to announce the first version of io-streams, a simple and easy-to-use library for doing streaming I/O in Haskell. The io-streams library is based around two basic types, InputStream a and OutputStream a, and three fundamental I/O primitives: -- read an item from an input stream read :: InputStream a -> IO (Maybe a) -- push an item back to an input stream unRead :: a -> InputStream a -> IO () -- write to an output stream write :: Maybe a -> OutputStream a -> IO () Streams can be transformed by composition and hooked together (using Kleisli composition) with a large set of provided combinators. Simple types and operations in the IO monad mean straightforward and simple exception handling and resource cleanup using Haskell standard library functions like bracket. The io-streams library comes with: - functions to use files, handles, concurrent channels, sockets, lists, vectors, and more as streams. - a plethora of combinators for wrapping and transforming streams, including compression and decompression using zlib, controlling precisely how many bytes are read from or written to a stream, buffering output using bytestring builders, folds, maps, filters, zips, etc. - support for parsing from streams using attoparsec. For first-time users, io-streams comes with an included tutorial in theSystem.IO.Streams.Tutorial module, written by Gabriel Gonzalez of “pipes” fame. The io-streams library is tested on GHC 7.0, 7.2, 7.4, and 7.6, and includes an extensive test suite with 100% function, statement, and branch coverage. We would like to acknowledge the financial assistance of Erudify AG, who graciously funded some of the documentation and development of the io-streams library. Many thanks are also due to Gabriel Gonzalez, Andrew Cowie, Johan Tibell, and Bas van Dijk for their helpful discussions, contributions, and review. For further details, you can read our release announcement here: http://snapframework.com/blog/2013/03/05/announcing-io-streams Cheers, G -- Gregory Collins <greg(a)gregorycollins.net>

4 3

OdHac: second call for participation
by Roman Cheplyaka 06 Mar '13

06 Mar '13

------------------------------------------------------------------------ OdHac International Haskell Hackathon May 3-5, 2013 Odessa, Ukraine http://haskell.org/haskellwiki/OdHac Co-organized with Provectus IT ------------------------------------------------------------------------ The international Haskell hackathon in Odessa is just two months away! To attend, please register at http://bit.ly/OdHacReg. ## Projects A big idea of this Hackathon is to concentrate the effort around a few important and established projects. Although participants are free to work on their own projects, it's more fun to work together! So far we've got two great projects: Hakyll and Fay http://www.haskell.org/haskellwiki/OdHac/Projects#Hakyll http://www.haskell.org/haskellwiki/OdHac/Projects#Fay Feel free to add new projects to the wiki! One project we'd love to see represented, because of its enormous value to the community, is Cabal. So far several core Cabal hackers have expressed willingness to offer help via IRC, but it would be great to have a Cabal expert on site. If you can coordinate the effort around Cabal and answer questions, and you're planning to come — please get in touch with me. ## Accommodation The Hackathon dates overlap with a series of holidays in Ukraine and neighbour countries, and Odessa is a popular tourist destination. So book early! We offer an accommodation program to make it simple for you: http://www.haskell.org/haskellwiki/OdHac/Accommodation

1 0

Library API design: functional objects VS type classes
by Rob Stewart 05 Mar '13

05 Mar '13

Hi, I have a question about API design for Haskell libraries. It is a simple one: functional object data structures encapsulating mutable state VS type classes encapsulating mutable state Here is a simple example. I present an API: using a type class `FooC`, and aso as a data structure `FooT`. Both are stateful, in the form of an MVar holding an Integer, with an operation `incrFoo` to increment this value by one, and another `readFoo` to read the Integer value. ----- import Control.Concurrent -- API approach 1: Using type classes class FooC a where mkFooC :: IO a readFooC :: a -> IO Int incrFooC :: a -> IO () newtype Bar = Bar (MVar Int) instance FooC Bar where mkFooC = newMVar 0 >>= \i -> return $ Bar i readFooC (Bar mv) = readMVar mv incrFooC (Bar mv) = modifyMVar_ mv $ \i -> return (i+1) -- API approach 2: Using direct field records data FooT a = FooT { readFooT :: IO a , incrFooT :: IO () } mkBar :: IO (FooT Int) mkBar = do mv <- newMVar 0 return FooT { readFooT = readMVar mv , incrFooT = modifyMVar_ mv $ \i -> return (i+1) } -- Tests the type class API testTypeClass :: IO () testTypeClass = do bar <- mkBar incrFooT bar incrFooT bar i <- readFooT bar print i -- prints 2 -- Tests the direct data structure API testDataStruct :: IO () testDataStruct = do bar <- (mkFooC :: IO Bar) incrFooC bar incrFooC bar i <- readFooC bar print i -- prints 2 ---- With that, I now ask: which is more common? Which is the better API design for a library? The APIs are almost identical. Under what conditions is the type classes preferred over the "mutable object" style data structure? There are two related resources that provides additional context here, that favour the functional objects approach: - Section 3.4 "Mutable Objects" in "Haskell's Overlooked Object System" http://goo.gl/gnZXL - A similar question (data structures vs type classes) in "Haskell Antipattern: Existential Typeclass" http://lukepalmer.wordpress.com/2010/01/24/haskell-antipattern-existential-… Thanks! -- Rob

4 3