June 2013 - Haskell-Cafe

Why isn't ArrowChoice a parent of of ArrowApply?
by Petr Pudlák 20 Jun '13

20 Jun '13

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Re: [Haskell-cafe] Remove Enum from Float and Double
by Doug McIlroy 19 Jun '13

19 Jun '13

> it's the entire Enum class which doesn't have a consistent or sensible semantics Yes, for a language with generally sound mathematical roots, Enum is an embarrassment. My pet peeve is that Rationals are enumerable, but not with Enum. And the differing lengths of [1,4..6] and [1.0,4.0..6.0] will shock even the non-mathematically inclined. Much of the craziness can be hidden if in place of [a..b] for nonintegral numeric types, one uses (map fromInteger [a..b]). Perhaps that should happen automatically. As for the horror mentioned at the end of the first paragraph, the language definition's oafish attempt to "get right" things like [0.0,0.1..1.0] needs major revision. Doug McIlroy

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GADTs and pattern matching
by Francesco Mazzoli 19 Jun '13

19 Jun '13

Hi list, I have stumbled upon a strange annoyance: {-# LANGUAGE GADTs #-} data Foo v where Foo :: Foo (Maybe v) -- This doesn't work foo1 :: a -> Foo a -> Int foo1 Nothing Foo = undefined foo1 (Just x) Foo = undefined -- This does foo2 :: a -> Foo a -> Int foo2 x Foo = foo2' x foo2' :: Maybe a -> Int foo2' Nothing = undefined foo2' (Just x) = undefined The first definition fails with the error Couldn't match expected type `a' with actual type `Maybe t0' `a' is a rigid type variable bound by the type signature for foo1 :: a -> Foo a -> Int at /tmp/foo_flymake.hs:8:9 In the pattern: Nothing In an equation for `foo1': foo1 Nothing Foo = undefined Now, GHC can clearly derive and use the type equalities correctly, given that the second definition works, but why can’t I pattern match directly? Thanks, Francesco

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ANNOUNCE: Ajhc 0.8.0.6 Release
by Kiwamu Okabe 19 Jun '13

19 Jun '13

We are happy to announce Ajhc 0.8.0.6. Major change on the release is supporting THREAD. Yeah! You can get Ajhc using "cabal install ajhc" command. Ajhc's project web site is found at http://ajhc.metasepi.org/. You find the source code at https://github.com/ajhc/ajhc/tags. Welcome sending any bugs or your ideas to https://github.com/ajhc/ajhc/issues. ## Good news * You can use forkOS interface on Ajhc. * Your program runs on pthread with compiling -fpthread option. See below. $ cat Main.hs import Control.Monad import Control.Concurrent main :: IO () main = do l <- putStrLn "Type some string and enter." >> getLine forkOS $ (forever $ putChar '*') forkOS $ (forever $ putStr l) forever $ putChar '.' $ ajhc -fpthread Main.hs $ ./hs.out ## Bad news * Ajhc guards critical section only for the runtime. * Example: StablePtr isn't guarded with lock. * Ajhc's thread can't share any objects without Ptr type. * And you may find funny pthread bugs. Please send us the report! ## Other changes * No more depend on DrIFT. * Add _JHC_JGC_LIMITED_NUM_GC_STACK flag to set number of limited gc_stack entries. * Add _JHC_JGC_FIXED_MEGABLOCK flag to set number of limited megablock entries. * Add compile flags -fcustomthread -fpthread -fnothread. * You can implement your own thread API for Ajhc, if you choose -fcustomthread. Enjoy! ;) - - - Metasepi team

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ANN: Nomyx 0.2 beta, the game where you can change the rules
by Corentin Dupont 19 Jun '13

19 Jun '13

Hello everybody! Here it comes, the second beta release [1] of Nomyx, the only game where You can change the rules!! This is an implementation of a Nomic [2] game in Haskell (I believe the first complete implementation of a Nomic game on a computer). In a Nomyxgame you can change the rules of the game itself while playing it. The players can submit new rules or modify existing ones, thus completely changing the behaviour of the game through time. The rules are managed and interpreted by the computer. They must be written in the Nomyx language, which is a subset of Haskell. At the beginning, the initial rules are describing: - how to add new rules and change existing ones. For example a unanimity vote is necessary to have a new rule accepted. - how to win the game. For example you win the game if you have 5 rules accepted. But of course even that can be changed! Here is a video introduction and first tutorial of the game: http://vimeo.com/58265498 The game is running here: www.nomyx.net:8000/Nomyx I have set up a forum where players can learn about Nomyx and discuss the rules they intend to propose: www.nomyx.net/forum The example file gives a lot of examples of rules that you can submit: www.nomyx.net:8000/src/Language/Nomyx/Examples.hs Changes from V0.1: - new login system: you can now login with your Google, Yahoo, Live Journal, Myspace, OpenId or Facebook accounts (thanks to happstack-authenticate)! - new DSL for voting (see below) - styling: rule code colorized, better settings and help - use cookies to store the user ID (as suggested on this mailing list) - new error system to handle exceptions in rules (with ErrorT) - use lenses I set up a little DSL to create elections (elect one of the players for a special role) or referendums (a yes/no question). You create in one line within Nomyx an vote with unanimity or majority, a quorum and different ballot systems. See here: http://www.nomyx.net/forum/viewtopic.php?f=3&t=1518 Let's test it! If you are interested, please go to this forum thread and we'll set up a small team to start a match! http://www.nomyx.net/forum/viewtopic.php?f=4&t=1517 The demo game is running here: www.nomyx.net:8000/Nomyx then select game "demo2". As the first player of the game, I changed the initial unanimity vote to a simple majority, with a minimum of 2 players voting. Having your new rules accepted will be easy! Let's see who will win :) Cheers, Corentin [1] http://hackage.haskell.org/package/Nomyx [2] www.nomic.net

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hand over maintenance of a package
by Corentin Dupont 19 Jun '13

19 Jun '13

Hi Cafe, How to hand over the maintenance of a hackage package? Thanks Corentin

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ML 2013: last call for presentations
by Daan Leijen 19 Jun '13

19 Jun '13

There are still a few days left to write a short talk proposal for the ML workshop 2013! Since there are no official proceedings, this is an ideal venue if you are working on a full submission for some other conference but want to talk about the work early on and get useful community feedback. Hope to see you there, -- Daan ACM SIGPLAN Workshop on ML Sunday, September 22, 2013, Boston MA (co-located with ICFP) http://research.microsoft.com/en-us/um/people/daan/mlworkshop2013 ======================================================================= The ML family of programming languages includes dialects known as Standard ML, OCaml, and F#. These languages have inspired a large amount of computer-science research, both practical and theoretical. This workshop aims to provide a forum where users, developers and researchers of ML languages and related technology can interact and discuss ongoing research, open problems and innovative applications. The ML workshop has adopted an informal model since 2010. It is a workshop with presentations selected from submitted abstracts. There are no published proceedings, so any contributions may be submitted for publication elsewhere. We hope that this format encourages the presentation of exciting (if unpolished) research and deliver a lively workshop atmosphere. SCOPE ----- We seek research presentations on topics related to ML, including but not limited to * Applications: case studies, experience reports, pearls, etc. * Extensions: higher forms of polymorphism, generic programming, objects, concurrency, distribution and mobility, semi-structured data handling, etc. * Type systems: inference, effects, overloading, modules, contracts, specifications and assertions, dynamic typing, error reporting, etc. * Implementation: compilers, interpreters, type checkers, partial evaluators, runtime systems, garbage collectors, etc. * Environments: libraries, tools, editors, debuggers, cross-language interoperability, functional data structures, etc. * Semantics: operational, denotational, program equivalence, parametricity, mechanization, etc. Three kinds of submissions will be accepted: Research Presentations, Experience Reports and Demos. * Research Presentations: Research presentations should describe new ideas, experimental results, significant advances in ML-related projects, or informed positions regarding proposals for next-generation ML-style languages. We especially encourage presentations that describe work in progress, that outline a future research agenda, or that encourage lively discussion. These presentations should be structured in a way which can be, at least in part, of interest to (advanced) users. * Experience Reports: Users are invited to submit Experience Reports about their use of ML languages. These presentations do not need to contain original research but they should tell an interesting story to researchers or other advanced users, such as an innovative or unexpected use of advanced features or a description of the challenges they are facing or attempting to solve. * Demos: Live demonstrations or short tutorials should show new developments, interesting prototypes, or work in progress, in the form of tools, libraries, or applications built on or related to ML. (Please note that you will need to provide all the hardware and software required for your demo; the workshop organizers are only able to provide a projector.) Each presentation should take 20-25 minutes, except demos, which should take 10-15 minutes. The exact time will be decided based on the number of accepted submissions. SUBMISSION INSTRUCTIONS ----------------------- Submissions should be at most two pages, in PDF format, and printable on US Letter or A4 sized paper. Submissions longer than half a page should include a one-paragraph synopsis suitable for inclusion in the workshop program. Submissions must be uploaded to the following website before the submission deadline (2013-06-21): https://www.easychair.org/conferences/?conf=ml2013 For any question concerning the scope of the workshop or the submission process, please contact the program chair (daan at microsoft.com) IMPORTANT DATES --------------- * Friday, June 21 : Submission * Monday, July 22 : Notification * Sunday, September 22: Workshop PROGRAM COMMITTEE ----------------- Daan Leijen (chair) (Microsoft Research, US) Jesse A. Tov (Harvard University, US) Derek Dreyer (MPI-SWS, Germany) Atsushi Ohori (Univ. of Tohoku, Japan) Lars Bergstrom (Univ. of Chicago, US) Jean Yang (MIT CSAIL, US) Gavin Bierman (Microsoft Research, Cambridge, UK) Tomas Petricek (Univ. of Cambridge, UK) Yukiyoshi Kameyama (Univ. of Tsukuba, Japan) Peter Thiemann (Univ. of Freiburg, Germany) STEERING COMMITTEE ------------------ Matthew Fluet (Chair, Rochester Institute of Technology) Alain Frisch (LexiFi) Jacques Garrigue (Nagoya University) Yaron Minsky (Jane Street) Greg Morrisett (Harvard University) Chung-chieh Shan (Indiana University) Anil Madhavapeddy (Cambridge University) Daan Leijen (Microsoft Research)

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[ANNOUNCE] Juicy.Pixels 3.1
by Vincent Berthoux 18 Jun '13

18 Jun '13

Hello, I'm pleased to announce the release of Juicy.Pixels 3.1 AKA. the "Squeezed juice" release Hackage : http://hackage.haskell.org/package/JuicyPixels GitHub : https://github.com/Twinside/Juicy.Pixels Change list : * Addition of Tiff reading : - 2, 4, 8, 16 bit depth reading (planar and contiguous for each) - CMYK, YCbCr, RGB, Paletted, Greyscale - Uncompressed, PackBits, LZW * Adding basic handling of 16bits pixel types * Some new tiny helper functions (nothing too fancy) * Performances : now between 2x and 3x of the performance of ImageMagick! (some benchmarks at https://soundofapixel.wordpress.com/2013/06/17/juicy-pixels-3-1/ ) Big thanks to Alp Mestanogullari and Jason Dagit who helped making this release possible. Vincent Berthoux

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Strange cabal failure
by Jacques Carette 18 Jun '13

18 Jun '13

In trying to install the lens package, it eventually tries to install transformers-compat-0.1.1.1 which in turn depends on transformers-0.3.0.0 -- however that asksk for transformers-0.3.0.0-3006d6ea13a2c10770bffd4de7a96dc9 which 1) is weird, and 2) doesn't exist!' What gives? Jacques

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Re: [Haskell-cafe] Promoting Haskell via Youtube movies
by Walter Askew 18 Jun '13

18 Jun '13

I think something like Erlang: The Movie is more Haskell's style: http://www.youtube.com/watch?v=uKfKtXYLG78

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