- Haskell-Cafe - Haskell.org

Re: [Haskell-cafe] How to get a file path to the program invoked?
by dokondr 01 Dec '11

01 Dec '11

To be precise, $0 always contains the path to the program called. You are right, this path will change depending on location from which the program was called. So $0 is OK for my case, while current directory is unrelated. Try this: #!/bin/sh echo "Arg 0: $0" echo "All Parameters: [$@]" Again, any way to get the same functionality in GHC? On Thu, Dec 1, 2011 at 10:32 PM, Giovanni Tirloni <gtirloni(a)sysdroid.com>wrote: > On Thu, Dec 1, 2011 at 5:26 PM, dokondr <dokondr(a)gmail.com> wrote: > >> On the contrary, standard shell variable $0 - contains a full path to the >> program location in the directory structure, no matter from what directory >> the program was called. >> >> > Are you sure? > > $ zero.sh > ./zero.sh > > $ ./zero.sh > ./zero.sh > > $ /home/gtirloni/zero.sh > /home/gtirloni/zero.sh > > > > -- > Giovanni > > >

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Hackage down!
by Edgar Gomes Araujo 01 Dec '11

01 Dec '11

Hi everybody, Is hackage.haskell.org down? I'm trying to access it but no answer, no ping response (timeout) , nothing. Is somebody else facing the same problem? Cheers, Edgar Gomes

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Poll: Do you want a mascot?
by heathmatlock 01 Dec '11

01 Dec '11

Question: Do you want a mascot? Answers: Yes No -- This is an attempt to figure out if this idea is going anywhere.

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Ann: Netwire 3.0.0
by Ertugrul Söylemez 01 Dec '11

01 Dec '11

Hello there, Netwire 3.0.0 is out: <http://hackage.haskell.org/package/netwire> Overview -------- Netwire is a library for high performance functional reactive programming, which calls its signal functions 'wires'. It solves the classic problems of FRP through a number of simple concepts: * It is based on an automaton arrow (similar to Yampa), so performance problems like time leaks become local. Getting high FRP performance is the art of writing good primitive automata, which is simple enough. * Wire inhibition (ArrowZero), combination (ArrowPlus) and choice (ArrowChoice) make switching combinators entirely obsolete. * Events are based on inhibition, so non-happened events take no CPU time. * Very simple internal representation: Writing custom primitive wires is easy. Since Netwire is developed mainly with libraries in mind, its internals are exposed entirely. If you need a wire that is not predefined, just write an addon. * Finally Netwire comes with a large set of predefined wires. This new version comes along with a major API change (hence the new major version number) -- hopefully the last one. The main change is that the Wire type is now a data family. This gives the flexibility of Netwire 2 with the high performance of Netwire 1. We are back to 600k FPS now for moderately complicated wires. =) Changes ------- Major changes and new features include: * Wire is now a data family. Most wire features are now addons through type classes, and every arrow can provide its own version of them, which is optimized for their respective internal representation. Mainly you get back the high performance monad-based wires from Netwire 1. * Nondeterministic wires (see below). * New wire transformers for supplying a clock, concurrent wires, and memoization/caching. * Improved ArrowLoop instance: Inhibition is now allowed inside of 'rec', as long as it doesn't break data dependencies. If it does, you get a useful error message now instead of a fatal pattern match failure. Minor changes: * Measuring FPS without disturbing performance: avgFpsInt. * The 'execute' wire is back. * More convenient wire stepping and testing functions. * Often you don't care about an event's value: gotEvent. Nondeterministic wires ---------------------- Now that Wire is a data family, you can have efficient nondeterministic wires by using a Kleisli-wrapped logic monad as the base arrow: import Control.Monad.Logic type MyWire = Wire e (Kleisli (LogicT IO)) Now you can use branching in a MyWire computation: x <- swallow branch -< [1..100] This will split the wire session into 101 branches at the first instant (it will always branch into a single inhibiting wire). Suppose you have an HTTP bot. You can now read URLs from a file and branch into an own wire for each URL: url <- swallow (branch <<< execute) -< fmap lines (readFile "urls.txt") quitWith <<< myBot -< url Performance ----------- Netwire 3 easily outperforms Netwire 2 by a factor of 10-30. Usually you will work with wire arrows on top of a Kleisli arrow. Now that Wire is a data family you can have an efficient representation of that, which gets along entirely without the Kleisli constructor wrapping. Now the main bottleneck is the monadic actions performed. This is very satisfactory. Greets, Ertugrul -- nightmare = unsafePerformIO (getWrongWife >>= sex) http://ertes.de/

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List fusion of nested lists
by Joachim Breitner 01 Dec '11

01 Dec '11

Dear Cafe, I’m trying to exploit list fusion as provided by GHC (build/foldr). One function that I want to get fusable is this, it splits a list of integeres into maximal monotonous subsequences: streaks :: [Integer] -> [[Integer]] streaks [] = [] streaks (x:xs) = let (this,rest) = oneStreak (x:xs) in this:streaks rest oneStreak :: [Integer] -> ([Integer], [Integer]) oneStreak [x] = ([x],[]) oneStreak l@(x:y:_) = splitWhile2 (\a b -> a `compare` b == x `compare` y) l splitWhile2 :: (Integer -> Integer -> Bool) -> [Integer] -> ([Integer], [Integer]) splitWhile2 p [x] = ([x],[]) splitWhile2 p (x:y:xs) | p x y = let (s,r) = splitWhile2 p (y:xs) in (x:s,r) | otherwise = ([x],y:xs) Now I’d like to implement streaks in terms of build and foldr such that it is subject to list fusion. Especially, when used in concatMap (streaks . func) :: [X] -> [[Integer]] where func :: X -> [Integer] is implemented with buildr, this should ideally remove all intermediate lists. Can this be done with list fusion at all? How would I go about it? If the above example is too complicated, known how it would work for Data.List.group would help me already a lot. Greetings, Joachim -- Joachim "nomeata" Breitner mail(a)joachim-breitner.de | nomeata(a)debian.org | GPG: 0x4743206C xmpp: nomeata(a)joachim-breitner.de | http://www.joachim-breitner.de/

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ANNOUNCE: data-timeout - 64-bit timeouts of nanosecond precision
by Mikhail Vorozhtsov 01 Dec '11

01 Dec '11

Hi. I grew up tired of counting milliseconds, so I wrote a small library[1] that allows me to specify time units for timeouts and convert between them. The library also provides wrapped versions of 'timeout' and 'threadDelay' functions: > threadDelay $ 1 # Minute + 30 # Second Nanosecond precision seems to be enough for RTS and POSIX calls and it also provides a good range for 64-bit representation: > maxBound :: Timeout 30500 w 3 d 23 h 34 m 33 s 709 ms 551 us 615 ns One thing that might disappoint some people is that I chose unsigned underlying type (Word64), which means that "infinite" timeouts cannot be represented. I think "negative" timeouts essentially are performance warts (a way of packing `Maybe Word63` into Word64) that muddle equality and I recommend using `Maybe Timeout` whenever timeout is optional. [1] http://hackage.haskell.org/package/data-timeout

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Munich December Haskell Meeting
by Heinrich Hördegen 01 Dec '11

01 Dec '11

Dear all, on our last meeting, we decided to set up a doodle poll to determine the date of our December's get-together: http://www.doodle.com/x6x4sgnemc35myq3 If you want to join, vote! There are also new dates available for next year's meetings (with rotating week-days): http://www.haskell-munich.de/dates Have a nice December, Heinrich -- -- hoerdegen(a)funktional.info www.funktional.info --

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Using Data,TypeLevel.Num
by Richard O'Keefe 01 Dec '11

01 Dec '11

I'd like to write a small module using Data.TypeLevel.Num. It has type level constants, variables, addition, and maximum, which is pretty much all I need. But I've never used it before, and there's one thing I want to do that I don't understand how to do. val :: Nat t => t -> Int val _ = t as an Int e.g., if x :: D8 then val x = 8. The "value-level reflection functions" in Data.TypeLevel.Num.Ops all seem to be 'undefined'.

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Haskell Weekly News: Issue 209
by Daniel Santa Cruz 01 Dec '11

01 Dec '11

Welcome to issue 209 of the HWN, a newsletter covering developments in the Haskell community. This release covers two weeks, from November 13 to 26, 2011. You can find the HTML version at: http://contemplatecode.blogspot.com/2011/11/haskell-weekly-news-issue-209.h… Announcements By now I'm sure you've heard about Da the lamb. [1] http://goo.gl/WF2o7 Sean Leather annouced that the next Dutch functinal programming day will take place on January 6, 2012, at the university campus "De Uithof" of Utrecht University. [2] http://goo.gl/IfVK8 Ganesh Sittampalam announced that the haskell.org committee for 2011-12 has been formed. [3] http://goo.gl/YFFsa New and Updated Projects * Gtk2Hs (Axel Simon; 0.12.2) Adjustments to Gtk2Hs to work with GHC 7.x.x. Also, looking for a part-time maintainer. [4] http://goo.gl/52M56 * iteratee-compress (Maciej Marcin Piechotka; 0.3.0.0) Provides compressing and decompressing enumerators. [5] http://goo.gl/tRAkg * Netwire (Ertugrul Soeylemez; 2.0.0) Complete rewrite. [6] http://goo.gl/HMCG8 * SBV (Levent Erkok; 0.9.22) [7] http://goo.gl/pSXGb * graphviz (Ivan Lazar Miljenovic; 2999.12.0.4). [8] http://goo.gl/JNVSV * SmallCHeck (Roman Cheplyaka; 0.5) [9] http://goo.gl/8njoh * OpenCL (Luis Cabellos; 1.0.2.2) Better error handling. [10] http://goo.gl/fphJN * clientsession (Michael Snoyman; 0.7.3.4) Major performance enhancement. [11] http://goo.gl/hCqrf Quotes of the Week * dmwit: Let's not make things better, I haven't put enough lipstick on the worse version yet. * mike-burns: Oh good, a semantic argument. Goodnight. * companion_cube: why bother with complicated abstractions like monads, when you can enjoy the taste of the sun on your skin? * applicative: clearly the trouble with haskell is plain: no inbuild syntactic support for quaternions. Wonder if *fortress* has it. * elliott: "with a lot of unicode" is like agda's @faq. "yes, agda can do that with a lot of unicode!" * [shachaf] mauke: EBCDIC? [mauke] shachaf: ah, the data encryption standard invented by IBM? * Tiwazz: It's called "Berp" because that's the sound Haskell makes after it devours a live Python. Top Reddit Stories * Typeclassopedia moved to the Haskell wiki Domain: byorgey.wordpress.com, Score: 72, Comments: 8 On Reddit: [12] http://goo.gl/pbHqr Original: [13] http://goo.gl/tWM0P * New project to support SIMD vector instructions in GHC (x86 SSE & AVX, ARM's NEON etc) Domain: hackage.haskell.org, Score: 62, Comments: 18 On Reddit: [14] http://goo.gl/JRj3o Original: [15] http://goo.gl/OcFCG * GHC 7.4 branched, what's in for Christmas? Domain: haskell.org, Score: 54, Comments: 16 On Reddit: [16] http://goo.gl/ZUN1e Original: [17] http://goo.gl/qWIhq * How to read Haskell like Python Domain: blog.ezyang.com, Score: 52, Comments: 7 On Reddit: [18] http://goo.gl/3cVXY Original: [19] http://goo.gl/nNhDI * xmonad-0.10 released! Domain: hackage.haskell.org, Score: 51, Comments: 15 On Reddit: [20] http://goo.gl/U5rry Original: [21] http://goo.gl/SIFuB * Roy - language with Hindley-Milner type system and monads that compiles to javascript Domain: roy.brianmckenna.org, Score: 43, Comments: 9 On Reddit: [22] http://goo.gl/RLK8S Original: [23] http://goo.gl/dzx8N * The Universe of Discourse : Triples and Closure and Monads Domain: blog.plover.com, Score: 42, Comments: 13 On Reddit: [24] http://goo.gl/7EDJX Original: [25] http://goo.gl/iPLnN * ANN: happstack-lite. A simpler, friendlier version of the Happstack Haskell Web Framework. What do you think? Domain: happstack.blogspot.com, Score: 35, Comments: 12 On Reddit: [26] http://goo.gl/Ii6Ch Original: [27] http://goo.gl/5wSZJ * HN/SPL - a better way to do your boring C++ job (written in Haskell) Domain: code.google.com, Score: 35, Comments: 16 On Reddit: [28] http://goo.gl/VxqIN Original: [29] http://goo.gl/9aAeZ * Fast lookup tables in haskell Domain: tab.snarc.org, Score: 34, Comments: 10 On Reddit: [30] http://goo.gl/mzgyw Original: [31] http://goo.gl/4VnrX * What Yesod Got Right Domain: yesodweb.com, Score: 34, Comments: 12 On Reddit: [32] http://goo.gl/eZhhK Original: [33] http://goo.gl/Li4mY Top StackOverflow Questions * What is a monad in FP, in categorical terms? votes: 30, answers: 7 Read on SO: [34] http://goo.gl/sC7PD * Haskell vs JVM performance [closed] votes: 24, answers: 6 Read on SO: [35] http://goo.gl/olA8g * Are there any Haskell techniques for mixed (part structure, part unmodified text) parsing & rewriting? votes: 24, answers: 1 Read on SO: [36] http://goo.gl/jRydd * STArray documentation for newbies and State/ST related questions votes: 17, answers: 1 Read on SO: [37] http://goo.gl/nw8eH * Should I avoid using Monad fail? votes: 15, answers: 3 Read on SO: [38] http://goo.gl/ruh7s * Effects of monomorphism restriction on type class constraints votes: 15, answers: 2 Read on SO: [39] http://goo.gl/QRbTh * Folding, function composition, monads, and laziness, oh my? votes: 14, answers: 2 Read on SO: [40] http://goo.gl/gped5 * Type error when ascribing a valid forall type to a let-bound variable votes: 13, answers: 2 Read on SO: [41] http://goo.gl/oyx0a * How do I organize my pure functions with my monadic actions idiomatically votes: 13, answers: 3 Read on SO: [42] http://goo.gl/6tByj * Is foldl ever preferable to its strict cousin, foldl'? votes: 13, answers: 2 Read on SO: [43] http://goo.gl/jFIe4 Until next time, Daniel Santa Cruz References 1. http://comments.gmane.org/gmane.comp.lang.haskell.cafe/93887 2. http://comments.gmane.org/gmane.comp.lang.haskell.general/19025 3. http://comments.gmane.org/gmane.comp.lang.haskell.general/19031 4. http://comments.gmane.org/gmane.comp.lang.haskell.general/19019 5. http://comments.gmane.org/gmane.comp.lang.haskell.libraries/16591 6. http://comments.gmane.org/gmane.comp.lang.haskell.cafe/93860 7. http://comments.gmane.org/gmane.comp.lang.haskell.cafe/93866 8. http://comments.gmane.org/gmane.comp.lang.haskell.cafe/93956 9. http://comments.gmane.org/gmane.comp.lang.haskell.cafe/94014 10. http://comments.gmane.org/gmane.comp.lang.haskell.cafe/94103 11. http://comments.gmane.org/gmane.comp.lang.haskell.yesod/941 12. http://byorgey.wordpress.com/2011/11/26/typeclassopedia-v2-moving-my-effort… 13. http://www.reddit.com/r/haskell/comments/mq2nr/typeclassopedia_moved_to_the… 14. http://hackage.haskell.org/trac/ghc/wiki/SIMD 15. http://www.reddit.com/r/haskell/comments/mbpoi/new_project_to_support_simd_… 16. http://www.haskell.org/pipermail/cvs-ghc/2011-November/068352.html 17. http://www.reddit.com/r/haskell/comments/mm68o/ghc_74_branched_whats_in_for… 18. http://blog.ezyang.com/2011/11/how-to-read-haskell/ 19. http://www.reddit.com/r/haskell/comments/mc2mw/how_to_read_haskell_like_pyt… 20. http://hackage.haskell.org/package/xmonad-0.10 21. http://www.reddit.com/r/haskell/comments/mhzu8/xmonad010_released/ 22. http://roy.brianmckenna.org/ 23. http://www.reddit.com/r/haskell/comments/mp245/roy_language_with_hindleymil… 24. http://blog.plover.com/math/monad-closure.html 25. http://www.reddit.com/r/haskell/comments/mfsfz/the_universe_of_discourse_tr… 26. http://happstack.blogspot.com/2011/11/ann-happstack-lite-friendly.html 27. http://www.reddit.com/r/haskell/comments/mcjoz/ann_happstacklite_a_simpler_… 28. http://code.google.com/p/inv/ 29. http://www.reddit.com/r/haskell/comments/mldzq/hnspl_a_better_way_to_do_you… 30. http://tab.snarc.org/posts/haskell/2011-11-15-lookup-tables.html 31. http://www.reddit.com/r/haskell/comments/mh1ox/fast_lookup_tables_in_haskel… 32. http://www.yesodweb.com/blog/2011/11/got-right 33. http://www.reddit.com/r/haskell/comments/mi4r7/what_yesod_got_right/ 34. http://stackoverflow.com/questions/8221395/what-is-a-monad-in-fp-in-categor… 35. http://stackoverflow.com/questions/8185282/haskell-vs-jvm-performance 36. http://stackoverflow.com/questions/8198808/are-there-any-haskell-techniques… 37. http://stackoverflow.com/questions/8197032/starray-documentation-for-newbie… 38. http://stackoverflow.com/questions/8163852/should-i-avoid-using-monad-fail 39. http://stackoverflow.com/questions/8270548/effects-of-monomorphism-restrict… 40. http://stackoverflow.com/questions/8249958/folding-function-composition-mon… 41. http://stackoverflow.com/questions/8190431/type-error-when-ascribing-a-vali… 42. http://stackoverflow.com/questions/8234162/how-do-i-organize-my-pure-functi… 43. http://stackoverflow.com/questions/8235797/is-foldl-ever-preferable-to-its-…

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Haskell Platform 64 bit
by Philippe Sismondi 30 Nov '11

30 Nov '11

I just tried to install the Haskell Platform 64-bit on OS X Snow Leopard 10.6.8. The install fails with "an error". This is all I see in /var/log/install.log: 11-11-25 6:22:01 PM Installer[53992] The Installer encountered an error that caused the installation to fail. Contact the software manufacturer for assistance. Is it known to be broken? I find something in haskell-cafe archives from last spring about a such a problem, but I don't know where to look for anything more recent. I may be blind, but I cannot see anything in the tickets under "known problems". I have been successfully running the 32-bit version for quite a while, but have begun to run into problems with linking haskell stuff against various 64-bit macports libraries. - Phil -

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Re: [Haskell-cafe] containers-deepseq?
by John Lato 29 Nov '11

29 Nov '11

> Message: 22 > Date: Tue, 29 Nov 2011 12:18:41 +0200 > From: Michael Snoyman <michael(a)snoyman.com> > Subject: Re: [Haskell-cafe] containers-deepseq? > > By the way, this is the part of situation that cabal-src is coming to > solve, and it *is* solved... except that the result is a lot of > re-compiling. How is cabal-src different from cabal-dev? John

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minor refactoring problem
by Martin DeMello 29 Nov '11

29 Nov '11

I have the following functions: makePair :: (String, String) -> IO PairBox parseFile :: String -> [(String, String)] importFile :: Editor -> String -> IO () importFile ed path = do s <- readFile path ps <- mapM (\x -> makePair (x, "")) (lines s) es <- return $ V.fromList ps writeIORef ed es loadFile :: Editor -> String -> IO () loadFile ed path = do s <- readFile path ps <- mapM makePair (parseFile s) es <- return $ V.fromList ps writeIORef ed es The problem is that loadFile and importFile are so similar it seems a shame not to combine them somehow, but anything I can think of doing leaves the code looking more rather than less messy. Any nice ideas? martin

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Re: [Haskell-cafe] minor refactoring problem
by Martin DeMello 29 Nov '11

29 Nov '11

On Tue, Nov 29, 2011 at 2:54 AM, Martin DeMello <martindemello(a)gmail.com> wrote: > On Tue, Nov 29, 2011 at 2:29 AM, Holger Siegel <holgersiegel74(a)yahoo.de> wrote: >> >> fromRawFile, fromSavedFile :: String -> IO [PairBox] >> fromRawFile = mapM (\x -> makePair (x, "")) . lines >> fromSavedFile = mapM makePair . parseFile >> >> setEditor :: Editor -> [PairBox] -> IO () >> setEditor ed = writeIORef ed . V.fromList >> >> importFile, loadFile :: Editor -> String -> IO () >> importFile ed = readfile >=> fromRawFile >=> setEditor >> loadFile ed = readfile >=> fromSavedFile >=> setEditor > > Wow, very nice! First time I've truly grasped what >=> is good for. > I'll need to go see where else I can use it in my code. Quick question: what's the difference between importFile ed = readfile >=> fromRawFile >=> setEditor ed and importFile = readfile >=> fromRawFile >=> setEditor that the former compiles but the latter doesn't? martin > > martin >

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containers-deepseq?
by Michael Snoyman 29 Nov '11

29 Nov '11

Hi all, Since the release of deepseq 1.2, we've had a bit of a problem: when using the newest versions of packages on Hackage, there is no NFData instance available for the containers types. When GHC 7.4 comes out with its newer version of containers, this will be addressed, but we'll still have problems for users of older GHC releases. I'd like to suggest a solution: a new package called containers-deepseq. Using conditional compilation, it will provide an orphans NFData instance for all containers types when deepseq >= 1.2 and containers < 0.5. Packages (e.g., aeson) would then depend on containers-deepseq and simply import the module whenever they rely on the NFData instances. When GHC 7.4 comes out, the package will essentially be a no-op. Does this make sense? Michael

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Overloaded Strings as default
by Daniel Díaz Casanueva 29 Nov '11

29 Nov '11

Hi Cafe, I only feel curious about what would be the consequences of becoming the Overloaded Strings feature (currently, an extension) to be default in Haskell. This is not a proposal. I just want to know what pros and cons there are. Thanks!

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(no subject)
by Willem Obbens 29 Nov '11

29 Nov '11

Hello, I get this error when I try to derive an instance of the Show typeclass: Abc.hs:21:60: Couldn't match expected type `Vector' with actual type `[Point]' In the first argument of `show'', namely `xs' In the second argument of `(++)', namely `show' xs' In the second argument of `(++)', namely `", " ++ show' xs'Failed, modules loaded: none. Here's the faulty code: newtype Point = Point Intinstance Show Point where show (Point a) = [chr $ a + 48] data Vector = Vector [Point]instance Show Vector where show (Vector ys) = let show' (Vector [z]) = show z show' (Vector (x:xs)) = show x ++ ", " ++ show' xs show' (Vector []) = [] in "(" ++ show' ys ++ ")" What I'm trying to do, is to print out a vector like "Vector [Point 1, Point 2, Point 3]" as "(1, 2, 3)".My question is: what should I change in order to make it work? Best regards, William

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Built-in LLVM exception handling
by Gregory Crosswhite 29 Nov '11

29 Nov '11

Purely out of curiosity, would it be more efficient for GHC to use the new built-in exception handling instructions in LLVM? http://blog.llvm.org/2011/11/llvm-30-exception-handling-redesign.html Cheers, Greg

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Drawing charts over a lot of data
by Eugene Kirpichov 28 Nov '11

28 Nov '11

Hi cafe, Are there any (possibly unfinished?) libraries dedicated to drawing charts over large amounts of data? I mean, such amounts that you don't want to store the whole set of input data in memory and instead you prefer to do one or a few passes over the input, calling the library's drawing functions for each data point. I'm currently using the excellent Chart package http://hackage.haskell.org/package/Chart , but it seems to require quite a bit of work to become usable in this mode (I haven't looked really deep yet). So, I'd be happy if someone pointed me to an existing package (I didn't find one on hackage) or if someone expressed interest in making Chart avoid having the whole input in memory. -- Eugene Kirpichov Principal Engineer, Mirantis Inc. http://www.mirantis.com/ Editor, http://fprog.ru/

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PADL 2012 Call for Participation
by Claudio Russo 28 Nov '11

28 Nov '11

Call for Participation ====================== 14th International Symposium on Practical Aspects of Declarative Languages (PADL 2012) http://research.microsoft.com/~crusso/padl12 Philadelphia, Pennsylvania, USA, January 23-24, 2012 Co-located with ACM POPL'12 You are cordially invited to PADL'12. PADL is a forum for researchers and practitioners to present original work emphasizing novel applications and implementation techniques for all forms of declarative concepts, including functional, logic and constraints. PADL'12 is sponsored by Association for Logic Programming with cooperation of ACM SIGPLAN and support by Microsoft Research. Registration ============ To register for PADL'12, please follow the instructions at: https://regmaster3.com/2012conf/POPL12/register.php The early registration deadline is December 24, 2011. The registration fee will cover a copy of the symposium proceedings, refreshments, and an informal dinner. Hotel Information ================= PADL will be co-located with POPL at the Sheraton Society Hill Hotel in Philadelphia. Please visit POPL's web site to make reservations at the special conference rate. Program ======= The symposium will include invited talks by Boon Thau Loo and Don Stewart, and 19 technical papers selected from 41 submissions. The preliminary program is as follows: Invited Talk (9:00-10:00) * Boon Thau Loo Recent Advances in Declarative Networking Break (10:00-10:30) Session 1: Applications (10:30-12:00) * Mayer Goldberg and Guy Wiener A Declarative Approach for Software Modeling * Sergio Antoy and Michael Hanus Contracts and Specifications for Functional Logic Programming * Pedro M. Martins, Julie A. McCann and Susan Eisenbach The Environment as an Argument Lunch (not provided) (12:00-13:30) Session 2: Logic Programming (13:30-15:30) * Yuliya Lierler, Shaden Smith, Mirek Truszczynski and Alex Westlund Weighted-Sequence Problem: ASP vs CASP and Declarative vs Problem-Oriented Solving * Marcello Balduccini and Yuliya Lierler Practical and Methodological Aspects of the Use of Cutting-Edge ASP Tools * Christian Theil Have and Henning Christiansen Efficient tabling of structured data using indexing and program transformation * Dario Campagna, Beata Sarna-Starosta and Tom Schrijvers Optimizing Inequality Joins in Datalog with Approximated Constraint Propagation Break (15:30-16:00) Session 3: Parallelism and Concurrency (16:00-17:30) * Elvira Albert, Puri Arenas and Miguel Gomez-Zamalloa Symbolic Execution of Concurrent Objects in CLP * Pablo Chico De GuzmÃ¡n, Amadeo Casas, Manuel Carro and Manuel Hermenegildo A Segment-Swapping Approach for Executing Trapped Computations * Michael Lesniak Palovca: Describing and Executing Graph Algorithms in Haskell Informal PADL Dinner (Place: TBA) Tuesday, January 24, 2012 Breakfast (8:00-9:00) Invited Talk (9:00-10:00) * Don Stewart Make Things Now! Pragmatic Functional Programming in Haskell Break (10:00-10:30) Session 4: Domain Specific Languages I (10:30-12:00) * Kenny Zhu, Kathleen Fisher and David Walker LearnPADS++: Incremental Inference of Ad Hoc Data Formats * Jeroen Bransen, Arie Middelkoop, Atze Dijkstra and S. Doaitse Swierstra The Kennedy-Warren algorithm revisited: ordering Attribute Grammars * Nicholas Coleman Distributed Policy Specification and Interpretation with Classified Advertisements Lunch (not provided) (12:00-13:30) Session 5: Domain Specific Languages II (13:30-15:30) * Andy Gill and Bowe Neuenschwander Handshaking in Kansas Lava using Patch Logic * Daniel Winograd-Cort, Hai Liu and Paul Hudak Virtualizing Real-World Objects in FRP * Edwin Brady and Kevin Hammond Resource-safe Systems Programming with Embedded Domain Specific Languages * David Broman and Henrik Nilsson Node-Based Connection Semantics for Equation-Based Object-Oriented Modeling Languages Break (15:30-16:00) Session 6: Numerics (16:00-17:00) * Paul Tarau A Declarative Specification of Tree-based Symbolic Arithmetic Computations * Vincent St-Amour, Sam Tobin-Hochstadt, Matthew Flatt and Matthias Felleisen Typing the Numeric Tower

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Proposed change to mime-mail
by Erik Hesselink 28 Nov '11

28 Nov '11

Hi all, I've found and solved a problem with mime-mail, and Michael Snoyman asked me to send a request for feedback to -cafe, so here goes. In short, the issue is with address headers containing 'special' (non-ascii) characters. In mime-mail, these are automatically encoded according to RFC 2047. However, the email address part of an address header is not allowed to be encoded. My patch adds 'from', 'to', 'cc' and 'bcc' fields to the Mail data type, and creates correct headers from these fields. This does make the Mail type a bit larger, so I've also added a smart constructor with initializes these fields with empty lists (only 'from' is required). For more details, see my initial bug report [1] and my patches in the pull request [2]. If you have any comments on this change, please let me know. Regards, Erik [1] https://github.com/snoyberg/mime-mail/issues/5 [2] https://github.com/snoyberg/mime-mail/pull/6

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Reminder Haskell Munich
by Heinrich Hördegen 28 Nov '11

28 Nov '11

Dear all, just a reminder for our monthly Haskell get-together in Munich, Cafe Puck, tomorrow (Tuesday, 29th, 19h30). If you will join and didn't already click the button, you can do it here: http://www.haskell-munich.de/dates Have a nice day, Heinrich -- -- hoerdegen(a)funktional.info www.funktional.info --

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Haskellers.com polls (specifically, the mascot question)
by Michael Snoyman 28 Nov '11

28 Nov '11

Hi all, I've just added the polls feature to Haskellers.com, and created an initial poll about mascots[1]. Let me know if there are any issues. Michael PS: I've also added Google+ profile link support, just go to your edit profile page and paste in the link. [1] http://www.haskellers.com/poll/1

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Mascot Poll Results
by heathmatlock 28 Nov '11

28 Nov '11

Haskellers.com poll: Yes 52 votes (50%), 22 verified votes (53%) No 51 votes (49%), 19 verified votes (46%) Email: Yes 14 (64%) No 8 (36%) Seems a bit divided. -- Heath Matlock +1 256 274 4225

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Current Haskell report URL
by Tom Murphy 28 Nov '11

28 Nov '11

Is there a reason that the Haskell 2010 report is in a subdirectory of haskell.org/onlinereport (which currently points to the Haskell98 standard)? http://www.haskell.org/onlinereport/ -- Haskell98 http://www.haskell.org/onlinereport/haskell2010/ -- Haskell2010 If it's for historical reasons - because books etc. use this URL for the 98 standard, then I'd highly recommend making a new directory called "currentreport" or something (if there isn't one already). The current impression that we give is that Haskell98 is the current standard, and Haskell2010 isn't compiler-supported. amindfv / Tom

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ANNOUNCE: clientsession-0.7.3.4 (performance enhancement)
by Michael Snoyman 27 Nov '11

27 Nov '11

Hi all, tl;dr: randomIV is now much faster, API is the same, upgrade ASAP to avoid painful slowdowns. Version 0.7 of clientsession brought with it a much enhanced encryption and hashing algorithm, courtesy of Felipe Lessa. Beginning with this version, you now need to provide an Initialization Vector (IV) for encrypting cookies, and these IVs need to be randomly generated. To start off with, we simply used the getIVIO[1] function to generate these values. Recently, some Yesod users reported that version 0.9 of Yesod no longer lived up to previous benchmarks. After some research, I determined that the slowdown came from the call to randomIV in clientsession. The initial fix was simply to disable this call when it wasn't used, but it was still a significant slowdown for most users of Yesod. Over the past few days, Felipe and I put together a significantly more efficient version of randomIV. getIVIO simply opens up /dev/urandom on each request, which involves I/O. As a result, the average run time of the function in our testing was 1.686ms. Instead, our new code initializes with a call to /dev/urandom for the base randomness. It then uses AES encryption to work as a cryptographic random number generator for generating successive IVs. Additionally, every 1000 calls (we'll probably change that number over time), it spawns a new thread to reseed the generator from /dev/urandom again. The result is a function that takes 7.144764 us, aka 236 times faster. Thanks for the initial reporters who commented on the slowdown in Yesod. If you install the newest clientsession and rerun the benchmarks, you should see *significantly* better results. Michael [1] http://hackage.haskell.org/packages/archive/crypto-api/0.8/doc/html/Crypto-…

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XML modification
by Andrew Coppin 25 Nov '11

25 Nov '11

Hi guys. I've got a folder with about 80 XML files in it. I want to take each file and make specific modifications to it. (Mostly just finding specific attributes and changing their values to make then all consistent.) Now I guess it wouldn't take me /that/ long to code something from scratch. But does anybody have a better suggestion for tools or libraries that might be useful?

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blaze-textual-native and aeson-native are being deprecated
by Michael Snoyman 25 Nov '11

25 Nov '11

Hi all, In the last Yesod release, we created two new packages: blaze-textual-native and aeson-native. These were direct forks of their source packages, with just two changes: blaze-textual-native did not include a double-conversion dependency, and aeson-native depended on blaze-textual-native instead of blaze-textual. The reason for all this is that there is a GHC bug which prevents C++ code from working correctly with GHCi and Template Haskell[1]. Bryan recently released a new version of blaze-textual which no longer uses double-conversion by default (it's still available with compile-time flags if you want the extra speed and don't need TH/GHCi), and as a result, we are very happy to be deprecating the native siblings. Fortunately, there are not that many packages on Hackage using these libraries; in fact, the only packages for which I'm not a maintainer are dingo-core, dingo-widgets and hledger-web. However, since these are Yesod dependencies, I'm guessing many Yesod users reference aeson-native in their site cabal files. Technically speaking, switching from aeson-native to aeson in a library should constitute a major version bump. However, in this case, I think we want these deprecated packages to die as quickly as possible. So my plan is to switch all of my packages from using aeson-native to aeson some time next week. The result will likely be broken builds for some people; all you'll need to do is edit your cabal file and replace aeson-native with aeson (likewise for blaze-textual). Are there any objections to this course of action, or better ideas on how to handle the situation? Michael [1] Please don't ask me for details, I don't know them. And for all I know, the bug has already be fixed in newer GHCs.

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FGL custom node identification (Label -> Node lookup)
by Thomas DuBuisson 24 Nov '11

24 Nov '11

All, The containers library has a somewhat primitive but certainly useful Data.Graph library. Building a graph with this library simultaneously results in the lookup functions: m1 :: Vertex -> (node, key, [key]) m2 :: key -> Maybe Vertex (where 'key' is like FGL's 'label' but is assumed to be unique) This is exactly what I wanted when building and analyzing a call graph in FGL. To that end, I started making a graph type that tracked label to Node mappings, wrapping Data.Graph.Inductive.Gr, and assuming the labels are all unique. The classes for such a graph actually aren't possible. The ability to build a mapping from a node's 'label' to the 'Node' requires extra context (ex: Hashable, Ord, or at least Eq), but such context can not be provided due to the typeclass construction. Is there any chance we can change the Graph and DiaGraph classes to expose the type variables 'a' and 'b'? class Graph gr a b where ... class (Graph gr) => DynGraph gr a b where ... This would allow instances to provide the needed context: instance (Hashable a, Hashable b) => Graph UniqueLabel a b where ... buildGraph = ... some use of containers libraries that require context ... ... lookupNode :: Hashable a => UniqueLabel a b -> a -> Node -- etc Cheers, Thomas P.S. Please do educate me if I simply missed or misunderstood some feature of FGL.

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ANN: OpenCL 1.0.2.2 package
by Luis Cabellos 24 Nov '11

24 Nov '11

Hello, all. I update the OpenCL package with a better error handle using Control.Exception. Thanks all comments in the previous version, and issues in github. # Where to get it * Hackage page (http://hackage.haskell.org/package/OpenCL) * Repository (https://github.com/zhensydow/opencl) * Bugs (https://github.com/zhensydow/opencl/issues) # Changes: * Changed LICENSE to BSD3 * Changed error from 'IO (Either CLError a)' to IO a + CLError exceptions * Added creation of programs using precompiled binaries (added example program) * Better documentation. Thanks, Luis Cabellos

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Re: [Haskell-cafe] type level strings?
by oleg＠okmij.org 24 Nov '11

24 Nov '11

Evan Laforge has defined > data Thing { > thing_id :: ThingId > , thing_stuff :: Stuff > } > newtype ThingId = ThingId String and wishes to statically preclude binary operations with things that have different ThingIds. However, Things and their Ids can be loaded from files and so cannot be known to the compiler. He wished for type-level strings -- which is what the enclosed code gives. When we've got two Things loaded from two different files we must do a run-time check to see if these two things have in fact the same ThingId. That is inevitable. The question is how frequently do we have to make such a test? One approach is to do such a ruin-time test on each binary operation on things. The original Thing above was of that approach: > instance Monoid Thing where > mappend (Thing id1 stuff1) (Thing id2 stuff2) > | id1 /= id2 = error "..." > | otherwise = Thing id1 (stuff1 `mappend` stuff2) Every time we mappend things, we must check their ids. It has been suggested to use existentials. We get the the following code: > maybeAppend :: Exists Thing -> Exists Thing -> Maybe (Exists Thing) > maybeAppend (Exists t1) (Exists t2) = > case thing_id t1 `equal` thing_id t2 of > Just Refl -> Just $ Exists (t1 `mappend` t2) > Nothing -> Nothing How different is this from the original mappend? Every time we wish to mappend two things, we have to do the run-time test of their ids! We added phantom times, existentials, GADTs -- and got nothing in return. No improvement to the original code, and no static guarantees. When we have to mappend things several times, it seems optimal to do the run-time ID check only once (we have to do that check anyway) and then mappend the results without any checks, and with full static assurance that only Identical things are mappended. The enclosed code implements that approach. The instance for Monoid makes patent only things with the same id may be mappended. Moreover, there is no run-time id check, and we do not have to think up the id to give to mempty. The test does read two things from a `file' (a string) and does several operations on them. The run-time test is done only once. The ideas of the code are described in the papers with Chung-chieh Shan on lightweight static capabilities and implicit configurations. {-# LANGUAGE RankNTypes, ScopedTypeVariables #-} module Thing where import Data.Monoid import Data.Char -- The data constructor Thing should not be exported newtype Thing id = Thing{ thingStuff :: Stuff } type Stuff = [Int] -- or any monoid class IDeal id where get_id :: id -> String -- The user should use make_thing make_thing :: IDeal id => id -> Stuff -> Thing id make_thing _ t = Thing t -- It is statically assured that only things with the same id -- may be mappended. Moreover, there is no run-time id check -- And we do not have to think up the id to give to mempty instance Monoid (Thing id) where Thing t1 `mappend` Thing t2 = Thing (t1 `mappend` t2) mempty = Thing mempty instance IDeal id => Show (Thing id) where show (Thing t) = show $ (get_id (undefined::id),t) -- A statically-known Id (just in case) data Id1 = Id1 instance IDeal Id1 where get_id _ = "Id1" -- Reading a thing from a file (or at least, a string) data DynId id = DynId instance Nat id => IDeal (DynId id) where get_id _ = int_to_str $ nat (undefined::id) read_thing :: String -> (forall id. IDeal id => Thing id -> w) -> w read_thing str k = reify_ideal i (\iD -> k (make_thing iD t)) where (i,t) = read str -- Run-time equality check -- If id and id' are the same, cast the second to the same id eqid_check :: forall id id'. (IDeal id, IDeal id') => Thing id -> Thing id' -> Maybe (Thing id) eqid_check _ (Thing t) | get_id (undefined::id) == get_id (undefined::id') = Just (Thing t) eqid_check _ _ = Nothing test file1 file2 = read_thing file1 (\t1 -> read_thing file2 (\t2 -> do_things t1 t2)) where -- A run-time test is inevitable, but it is done only once do_things t1 t2 | Just t2' <- eqid_check t1 t2 = do_things' t1 t2' do_things _ _ = error "bad things" -- Now it is assured we have the same id -- we can do things many times do_things' :: IDeal id => Thing id -> Thing id -> String do_things' t1 t2 = show $ mempty `mappend` t1 `mappend` t2 `mappend` t2 `mappend` t1 t1 = test "(\"id1\",[1,2])" "(\"id1\",[3,4])" -- "(\"id1\",[1,2,3,4,3,4,1,2])" t2 = test "(\"id1\",[1,2])" "(\"id2\",[3,4])" -- "*** Exception: bad things -- Reifying strings to types -- They say String kinds are already in a GHC branch. -- Edward Kmett maintains a Hackage package for these sort of things -- Assume ASCII for simplicity str_to_int :: String -> Integer str_to_int "" = 0 str_to_int (c:t) = fromIntegral (ord c) + 128 * str_to_int t int_to_str :: Integer -> String int_to_str = loop "" where loop acc 0 = reverse acc loop acc n | (n',c) <- quotRem n 128 = loop (chr (fromIntegral c) : acc) n' data Z = Z data S a = S a data T a = T a class Nat a where nat :: a -> Integer instance Nat Z where nat _ = 0 instance Nat a => Nat (S a) where nat _ = 1 + nat (undefined::a) instance Nat a => Nat (T a) where nat _ = 2 * nat (undefined::a) reify_integer :: Integer -> (forall x. Nat x => x -> w ) -> w reify_integer 0 k = k Z reify_integer n k | even n = reify_integer (n `div` 2) (\x -> k (T x)) reify_integer n k = reify_integer (n-1) (\x -> k (S x)) reify_ideal :: String -> (forall x. IDeal x => x -> w) -> w reify_ideal str k = reify_integer (str_to_int str) (k . dynid) where dynid :: x -> DynId x dynid = undefined tr1 = reify_integer 10 nat tr2 = int_to_str $ reify_integer (str_to_int "id1") nat

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Munich Haskell Meeting
by Heinrich Hördegen 24 Nov '11

24 Nov '11

Dear all, next week on Tuesday, 29 November, our monthly Haskell get-together will be held at Cafe Puck in Munich. Starting time is 19h30. Please feel free to join us. We are always happy to see someone new. There have been lots of people last time and we did not have enough tables. Therefore, if you plan to join us, please go to this page and hit the button. This well help to reserve places: http://www.haskell-munich.de/dates There is also the question, what to do in December. Any suggestions? We hope to see you soon, Heinrich -- -- hoerdegen(a)funktional.info www.funktional.info --

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Last CFP: 12th International Workshop on Language Descriptions, Tools, and Applications (LDTA 2012)
by Emilie Balland 24 Nov '11

24 Nov '11

LDTA 2012 Call for Papers 12th International Workshop on Language Descriptions, Tools, and Applications www.ldta.info Tallinn, Estonia March 31 & April 1, 2012 an ETAPS workshop LDTA is an application and tool-oriented workshop focused on grammarware - software based on grammars in some form. Grammarware applications are typically language processing applications and traditional examples include parsers, program analyzers, optimizers and translators. A primary focus of LDTA is grammarware that is generated from high-level grammar-centric specifications and thus submissions on parser generation, attribute grammar systems, term/graph rewriting systems, and other grammar-related meta-programming tools, techniques, and formalisms are encouraged. LDTA is also a forum in which theory is put to the test, in many cases on real-world software engineering challenges. Thus, LDTA also solicits papers on the application of grammarware to areas including, but not limited to, the following: - program analysis, transformation, generation, and verification, - implementation of Domain-Specific Languages, - reverse engineering and re-engineering, - refactoring and other source-to-source transformations, - language definition and language prototyping, and - debugging, profiling, IDE support, and testing. Note that LDTA is a well-established workshop similar to other conferences on (programming) language engineering topics such as SLE and GPCE, but is solely focused on grammarware. Paper Submission ------------------------- LDTA solicits papers in the following categories. - research papers: original research results within the scope of LDTA with a clear motivation, description, analysis, and evaluation. - short research papers: new innovative ideas that have not been completely fleshed out. As a workshop, LDTA strongly encourages these types of submissions. - experience report papers: description of the use of a grammarware tool or technique to solve a non-trivial applied problem with an emphasis on the advantages and disadvantages of the chosen approach to the problem. - tool demo papers: discussion of a tool or technique that explains the contributions of the tool and what specifically will be demonstrated. Each submission must clearly state in which of these categories it falls, and must not be published or submitted elsewhere. Papers are to use the standard LaTeX article style and the authblk style for affiliations; a sample of which is provided at www.ldta.info. Research and experience papers are limited to 15 pages, tool demonstration papers are limited to 10 pages, and short papers are limited to 6 pages. The final version of the accepted papers will, pending approval, be published in the ACM Digital Library and will also be made available during the workshop. Please submit your abstract and paper using EasyChair at http://www.easychair.org/conferences/?conf=ldta2012. The authors of each submission are required to give a presentation at LDTA 2011 and tool demonstration paper presentations are intended to include a significant live, interactive demonstration. The authors of the best papers will be invited to write a journal version of their paper which will be separately reviewed and, assuming acceptance, be published in journal form. As in past years this will be done in a special issue of the journal Science of Computer Programming (Elsevier Science). Invited Speaker --------------------- Janis Voigtländer (University of Bonn, Germany). Important Dates --------------------- Abstract submission: Nov. 28, 2011 Full paper submission: Dec. 5, 2011 Author notification: Jan. 20, 2012 Camera-ready papers: Feb. 05, 2012 LDTA Workshop: Mar. 31 - Apr. 1, 2012 LDTA Tool Challenge ----------------------------- The 2011 Workshop pioneered the LDTA Tool Challenge where tool developers were invited to develop solutions to a range of language processing tasks over a simple but evolving set of imperative programming languages. We expect a challenge to form part of LDTA every two years. The 2012 workshop will feature presentations devoted to a de-brief of the 2011 challenge, based on the paper currently being prepared by challenge participants. Program Committee --------------------------- Suzana Andova, Eindhoven University of Technology, The Netherlands (co-chair) Anya Helene Bagge, University of Bergen, Norway Kyung-Goo Doh, Hanyang University, Ansan, South Korea Jeff Gray, University of Alabama, USA Görel Hedin, Lund Institute of Technology, Sweden Zoltán Horváth, Eötvös Loránd University, Budapest, Hungary Zhenjiang Hu, National Institute of Informatics, Japan Roberto Ierusalimschy, Pontifícia Universidade Católica do Rio de Janeiro, Brazil Ivan Kurtev, University of Twente, The Netherlands Marjan Mernik, University of Maribor, Slovenia Nate Nystrom, University of Lugano, Switzerland João Saraiva, Universidade do Minho, Braga, Portuga Sylvain Schmitz, Ecole Normale Supérieure de Cachan, France Anthony Sloane, Macquarie University, Australia (co-chair) Robert Tairas, Inria, France Laurence Tratt, King's College London, UK Vadim Zaytsev, Centre for Mathematics & Computer Science, The Netherlands Organizing Committee ------------------------------ Anya Helene Bagge, University of Bergen, Norway Emilie Balland, INRIA, France Steering Committee --------------------------- Mark van den Brand, Eindhoven University of Technology, The Netherlands Görel Hedin, Lund University, Sweden Tony Sloane, Macquarie University, Australia Eric Van Wyk, University of Minnesota, United States

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Polls on Haskellers.com
by Michael Snoyman 24 Nov '11

24 Nov '11

I noticed the recent thread about mascots, and trying to get accurate polling information. Don't consider this email to say I think we need safeguards against a poll on mascots (are people *really* trying to rig the election on this???), but I thought this might be a good features for Haskellers.com. Since we already have the "verified account" issue, we could use that to break down polls. More specifically, anyone would be allowed to vote, and then you could review results for verified users only, all logged in users, or theoretically even not-logged-in users (not sure how I feel about this one). If people would use this feature, I think I can add it next week. Michael

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type level strings?
by Evan Laforge 24 Nov '11

24 Nov '11

So suppose I have a simple data type: > data Thing { > thing_id :: ThingId > , thing_stuff :: Stuff > } > newtype ThingId = ThingId String Stuff is a Monoid, and Things need to be combined as well, so: > instance Monoid Thing where > mappend (Thing id1 stuff1) (Thing id2 stuff2) > | id1 /= id2 = error "..." > | otherwise = Thing id1 (stuff1 `mappend` stuff2) > mempty = Thing $ (ThingId "dummy value?") mempty So clearly both the error and the "dummy value?" are not very nice (and mappend would need a special hack to treat the dummy as compatible with everything). I'd like to be able to lift that ID up to the type level, and then I don't have to worry about incompatible IDs and the mempty can figure out the ID from the type. Now if ThingId were a natural, I gather there's a new GHC feature for type level naturals that can do this kind of thing. Of course any string could be encoded into a large natural, but the resulting type errors would be less than readable. There is probably also a way to encode type level strings in the same way as the traditional way for type level naturals, e.g. 'data A; ... data Z;' and then a type encoding for lists. But I'm guessing that would also lead to excessive compilation times and crazy type errors. In any case, I don't think this can work even if I used naturals instead of ints, because it seems to me I can't write a function '(NatI n) => ThingId -> Thing n' without a statically knowable constant value for 'n'. Otherwise, the value has magically disappeared into the type system and I can't expect to get it back after types are erased. So I need a runtime value for the ThingId, but it still seems like it should be possible to do something better than the 'error' and "dummy value?". Maybe there's a completely different way to ensure that incompatible Things can't be mappended. Any ideas?

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Quickcheck research
by Macías López 24 Nov '11

24 Nov '11

Hello: I'm a Master's student in Computer Science. I have to make a project involving some research, I'm very interested in Quickcheck and I wonder if there are some areas which need work or if there is some potential research topic related to it. In particular I know that Erlang Quickcheck has been worked on a lot and has some features like state machines or C bindings which may be useful to the Haskell community. I would appreciate any directions. Cheers, Macías López.

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Re: [Haskell-cafe] Quickcheck research
by Jonathan Fischoff 23 Nov '11

23 Nov '11

> which makes me think that Arbitrary isn't the right set of > abstractions for controlling coverage of the value space. I agree with you Wren. I think what is needed is a library for expressing the distribution of values for a given type. I can see several ways of specifying distributions, directly (exponential, normal, etc), qualitative constraints (a tuple where each value is less then the next), constraints on moments (MaxEnt), etc, there are many ways that are not mutually exclusive. There are other ways to improve quickcheck. Writing arbitrary instance could be made more declarative. The process of describing an indicator function that fully determines the set of values that are valid for my type, and writing the sequence of steps necessary to make the function efficient could be separated. Combinatorial species and symbolic combinatorics are too possibilities to simplify the creation of arbitrary functions. There might be way go from list of functions to an generator. Something like make_arb :: [a -> Bool] -> Gen a That is psuedo code, since you can't reify a function. But that would be the idea, although I don't think it would work in all cases. Also, the current quickcheck workflow is to run it until a example of valid input fails a test. When this happens the example should be used in a regression. Creating unit tests automatically from failed quickcheck cases would be a time saver. Additionally the right type mutation of testing would be a great addition to quickcheck. -Jonathan

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"lambda.fm" How can I use this to help the Haskell community?
by Ben Wright 23 Nov '11

23 Nov '11

A while back I somehow managed to get the domain name, "lambda.fm" and I am simply creating this post to get some ideas from the community on what it could be used for to help the FP community. So tell me what you think.

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Re: [Haskell-cafe] A Mascot
by John Lato 23 Nov '11

23 Nov '11

> From: Michael Orlitzky <michael(a)orlitzky.com> > > On 11/22/11 16:52, heathmatlock wrote: >> Wasn't planning on it, but I saw some emails on the topic, so I worked >> on what I presented earlier: > > Anyway, creative design-by-committee is doomed, so my advice is to > ignore this and all other advice =) +1 (The knight is my favorite, but Da for Mascot regardless)

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Fwd: XML modification
by Dmitry Olshansky 23 Nov '11

23 Nov '11

Personally I prefer xml-enumerator. You can work with xml-stream or with DOM through cursor (like XPath). I think that in your case working with stream is preferrable. You can just make an Enumeratee like >import qualified Data.Enumerator.List as EL > myEnum = EL.map f > where > f (EventBeginElement n ats) = ... -- parse attributes > f e = e 2011/11/23 Andrew Coppin <andrewcoppin(a)btinternet.com> > Hi guys. > > I've got a folder with about 80 XML files in it. I want to take each file > and make specific modifications to it. (Mostly just finding specific > attributes and changing their values to make then all consistent.) > > Now I guess it wouldn't take me /that/ long to code something from > scratch. But does anybody have a better suggestion for tools or libraries > that might be useful? > > ______________________________**_________________ > Haskell-Cafe mailing list > Haskell-Cafe(a)haskell.org > http://www.haskell.org/**mailman/listinfo/haskell-cafe<http://www.haskell.org/mailman/listinfo/haskell-cafe> >

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PEPM'12 Call for participation
by Simon Thompson 23 Nov '11

23 Nov '11

ACM SIGPLAN 2012 Workshop on Partial Evaluation and Program Manipulation http://www.program-transformation.org/PEPM12 January 23-24, 2012. Philadelphia, PA, USA (co-located with POPL'12) Call For Participation Online registration is open at https://regmaster3.com/2012conf/POPL12/register.php Early registration deadline is December 24, 2011 The PEPM Symposium/Workshop series brings together researchers and practitioners working in the broad area of program transformation, which spans from refactoring, partial evaluation, supercompilation, fusion and other metaprogramming to model-driven development, program analyses including termination, inductive programming, program generation and applications of machine learning and probabilistic search. PEPM focuses on techniques, supporting theory, tools, and applications of the analysis and manipulation of programs. In addition to the presentations of regular research papers, the PEPM program includes tool demonstrations and `short paper' presentations of exciting if not fully polished research. PEPM has established a Best Paper award. The winner will be announced at the workshop. INVITED TALKS Compiling Math to High Performance Code Markus Pueschel (ETH Zuerich, Switzerland) http://www.inf.ethz.ch/~markusp/index.html Specification and verification of meta-programs Martin Berger (University of Sussex, UK) http://www.informatics.sussex.ac.uk/users/mfb21/ ACCEPTED PAPERS Regular research papers: Naoki Kobayashi, Kazutaka Matsuda and Ayumi Shinohara. Functional Programs as Compressed Data Kazutaka Matsuda, Kazuhiro Inaba and Keisuke Nakano. Polynomial-Time Inverse Computation for Accumulative Functions with Multiple Data Traversals Dana N. Xu. Hybrid Contract Checking via Symbolic Simplification Susumu Katayama. An Analytical Inductive Functional Programming System that Avoids Unintended Programs Roberto Giacobazzi, Neil Jones and Isabella Mastroeni. Obfuscation by Partial Evaluation of Distorted Interpreters Michael Gorbovitski, Yanhong A. Liu, Scott Stoller and Tom Rothamel. Composing Transformations for Instrumentation and Optimization Elvira Albert, Jesus Correas Fernandez, German Puebla and Guillermo Roman-Diez. Incremental Resource Usage Analysis Takumi Goto and Isao Sasano. An approach to completing variable names for implicitly typed functional languages Martin Hirzel and Bugra Gedik. Streams that Compose using Macros that Oblige Vlad Ureche, Tiark Rompf, Arvind Sujeeth, Hassan Chafi and Martin Odersky. StagedSAC: A Case Study in Performance-Oriented DSL Development Markus Degen, Peter Thiemann and Stefan Wehr. The Interaction of Contracts and Laziness Surinder Kumar Jain, Chenyi Zhang and Bernhard Scholz. Translating Flowcharts to Non-Deterministic Languages Francisco Javier Lopez-Fraguas, Enrique Martin-Martin and Juan Rodriguez-Hortala. Well-typed Narrowing with Extra Variables in Functional-Logic Programming Geoff Hamilton and Neil Jones. Superlinear Speedup by Distillation: A Semantic Basis Short papers: Jacques Carette and Aaron Stump. Towards Typing for Small-Step Direct Reflection Janis Voigtlaender. Ideas for Connecting Inductive Program Synthesis and Bidirectionalization Tool demonstration papers: Edvard K. Karlsen, Einar W. Hoest and Bjarte M. Oestvold. Finding and fixing Java naming bugs with the Lancelot Eclipse plugin Adriaan Moors, Tiark Rompf, Philipp Haller and Martin Odersky. Scala-Virtualized Elvira Albert, Puri Arenas, Samir Genaim, Miguel Gomez-Zamalloa and German Puebla. COSTABS: A Cost and Termination Analyzer for ABS 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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Why does GHC not warn about unnamed uninitialized fields?
by Eelis van der Weegen 23 Nov '11

23 Nov '11

Today I noticed that GHC is more concerned (when using -Wall) about uninitialized fields when those fields have names: data A = A {a::Integer} data B = B Integer x :: A x = A{} -- Gives a nice warning: "Fields of `A' not initialised: a" y :: B y = B{} -- No warning! Is this on purpose? If so, what is the rationale? The context in which I encountered this boils down to the following: {-# LANGUAGE RecordWildCards #-} data C = C {c::Integer} f :: C -> C f C{..} = C{..} g :: C -> Integer g (C i) = i main :: IO () main = print (g (f (C 3))) This code worked fine (and printed "3"), until I made C's Integer nameless. This made it crash with following runtime error instead: T: T.hs:6:11-15: Missing field in record construction The crash and error are perfectly understandable, but it would have been more helpful if GHC had warned about this at compile-time! The reason it didn't, though, is because of its aforementioned cavalier attitude towards uninitialized fields that don't have names... :-) (I'm using GHC 7.0.4.) Cheers, Eelis

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PEPM 2012: Call for participation
by oleg＠okmij.org 23 Nov '11

23 Nov '11

ACM SIGPLAN 2012 Workshop on Partial Evaluation and Program Manipulation http://www.program-transformation.org/PEPM12 January 23-24, 2012. Philadelphia, PA, USA (co-located with POPL'12) Call For Participation Online registration is open at https://regmaster3.com/2012conf/POPL12/register.php Early registration deadline is December 24, 2011 The PEPM Symposium/Workshop series brings together researchers and practitioners working in the broad area of program transformation, which spans from refactoring, partial evaluation, supercompilation, fusion and other metaprogramming to model-driven development, program analyses including termination, inductive programming, program generation and applications of machine learning and probabilistic search. PEPM focuses on techniques, supporting theory, tools, and applications of the analysis and manipulation of programs. In addition to the presentations of regular research papers, the PEPM program includes tool demonstrations and `short paper' presentations of exciting if not fully polished research. PEPM has established a Best Paper award. The winner will be announced at the workshop. INVITED TALKS Compiling Math to High Performance Code Markus Pueschel (ETH Zuerich, Switzerland) http://www.inf.ethz.ch/~markusp/index.html Specification and verification of meta-programs Martin Berger (University of Sussex, UK) http://www.informatics.sussex.ac.uk/users/mfb21/ ACCEPTED PAPERS Regular research papers: Naoki Kobayashi, Kazutaka Matsuda and Ayumi Shinohara. Functional Programs as Compressed Data Kazutaka Matsuda, Kazuhiro Inaba and Keisuke Nakano. Polynomial-Time Inverse Computation for Accumulative Functions with Multiple Data Traversals Dana N. Xu. Hybrid Contract Checking via Symbolic Simplification Susumu Katayama. An Analytical Inductive Functional Programming System that Avoids Unintended Programs Roberto Giacobazzi, Neil Jones and Isabella Mastroeni. Obfuscation by Partial Evaluation of Distorted Interpreters Michael Gorbovitski, Yanhong A. Liu, Scott Stoller and Tom Rothamel. Composing Transformations for Instrumentation and Optimization Elvira Albert, Jesus Correas Fernandez, German Puebla and Guillermo Roman-Diez. Incremental Resource Usage Analysis Takumi Goto and Isao Sasano. An approach to completing variable names for implicitly typed functional languages Martin Hirzel and Bugra Gedik. Streams that Compose using Macros that Oblige Vlad Ureche, Tiark Rompf, Arvind Sujeeth, Hassan Chafi and Martin Odersky. StagedSAC: A Case Study in Performance-Oriented DSL Development Markus Degen, Peter Thiemann and Stefan Wehr. The Interaction of Contracts and Laziness Surinder Kumar Jain, Chenyi Zhang and Bernhard Scholz. Translating Flowcharts to Non-Deterministic Languages Francisco Javier Lopez-Fraguas, Enrique Martin-Martin and Juan Rodriguez-Hortala. Well-typed Narrowing with Extra Variables in Functional-Logic Programming Geoff Hamilton and Neil Jones. Superlinear Speedup by Distillation: A Semantic Basis Short papers: Jacques Carette and Aaron Stump. Towards Typing for Small-Step Direct Reflection Janis Voigtlaender. Ideas for Connecting Inductive Program Synthesis and Bidirectionalization Tool demonstration papers: Edvard K. Karlsen, Einar W. Hoest and Bjarte M. Oestvold. Finding and fixing Java naming bugs with the Lancelot Eclipse plugin Adriaan Moors, Tiark Rompf, Philipp Haller and Martin Odersky. Scala-Virtualized Elvira Albert, Puri Arenas, Samir Genaim, Miguel Gomez-Zamalloa and German Puebla. COSTABS: A Cost and Termination Analyzer for ABS

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Decision procedure for foldr/foldl/foldl'?
by David Fox 22 Nov '11

22 Nov '11

Does anyone have a quick way to decide which of the fold functions to use in a given situation? There are times when I would like to find out which to use in the quickest way possible, rather than reading a long explanation of why each one behaves the way it does.

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Is SmallCheck maintained?
by Roman Cheplyaka 22 Nov '11

22 Nov '11

Hi Cafe, Does anyone currently work on Test.SmallCheck? I see the following problems: 1. SC doesn't have a repository, issue tracker etc. 2. It is not integrated with popular test frameworks 3. API should be better documented I'm willing to work on the above problems, but wanted to check first if someone's already working on them or at least has a repository. I already wrote to Colin Runciman but got no response. -- Roman I. Cheplyaka :: http://ro-che.info/

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FLOPS 2012: 2nd call for papers
by Tom Schrijvers 22 Nov '11

22 Nov '11

Second Call For Papers ===================== *Eleventh International Symposium on Functional and Logic Programming (FLOPS 2012)* May 23-25, 2012 Kobe, Japan [http://www.org.kobe-u.ac.jp/flops2012/] _Submission deadline : December 9, 2011_ FLOPS is a forum for research on all issues concerning declarative programming, including functional programming and logic programming, and aims to promote cross-fertilization and integration between the two paradigms. Previous FLOPS meetings were held in Fuji Susono (1995), Shonan Village (1996), Kyoto (1998), Tsukuba (1999), Tokyo (2001), Aizu (2002), Nara (2004), Fuji Susono (2006), Ise (2008), and Sendai (2010). Topics ====== FLOPS solicits original papers in all areas of functional and logic programming, including (but not limited to): - Declarative Pearls: new and excellent declarative programs with illustrative applications. - Language issues: language design and constructs, programming methodology, integration of paradigms, interfacing with other languages, type systems, constraints, concurrency and distributed computing. - Foundations: logic and semantics, rewrite systems and narrowing, type theory, proof systems. - Implementation issues: compilation techniques, memory management, program analysis and transformation, partial evaluation, parallelism. - Applications: case studies, real-world applications, graphical user interfaces, Internet applications, XML, databases, formal methods and model checking. The proceedings will be published as an LNCS volume. The proceedings of the previous meeting (FLOPS 2010) were published as LNCS 6009. PC co-Chairs ============ - Tom Schrijvers (Ghent University, Belgium) - Peter Thiemann (University of Freiburg, Germany) PC Members ========== - Salvador Abreu (University of Evora, Portugal) - Thorsten Altenkirch (University of Nottingham, UK) - Sebastian Brand (NICTA, Australia) - Giuseppe Castagna (CNRS Univ Paris 7, France) - Sebastian Fischer (Germany) - Marco Gavanelli (University of Ferrara, Italy) - Joxan Jaffar (National University of Singapore, Singapore) - Barry Jay (University of Sydney, Australia) - Andy King (University of Kent, UK) - Claude Kirchner (INRIA, France) - Neelakantan R. Krishnaswami (Microsoft Cambridge, UK) - Yulya Lierler (University of Kentucky, USA) - Keiko Nakata (Tallinn University of Technology, Estonia) - Peter Schneider-Kamp (University of Southern Denmark, Denmark) - Olin Shivers (Northeastern University, USA) - Paul Tarau (University of Northern Texas, USA) - Kazunori Ueda (Waseda University, Japan) - Meng Wang (Chalmers Technical University, Sweden) General Chair and Local co-Chairs ================================= - Naoyuki Tamura (Kobe University, Japan) - Mutsunori Banbara (Kobe University, Japan) - Katsutoshi Hirayama (Kobe University, Japan) Submission ========== Submissions must be unpublished and not submitted for publication elsewhere. Work that already appeared in unpublished or informally published workshops proceedings may be submitted. Submissions should fall into one of the following categories: - Regular research papers: they should describe new results and will be judged on originality, correctness, and significance. - System descriptions: they should contain a link to a working system and will be judged on originality, usefulness, and design. Submissions must be written in English and can be up to 15 pages long, though pearls are typically considerably shorter. Authors are required to use LaTeX2e and the Springer llncs class file, available at [http://www.springer.de/comp/lncs/authors.html] Regular research papers should be supported by proofs and/or experimental results. In case of lack of space, this supporting information should be made accessible otherwise (e.g., a link to a web page, or an appendix). Papers should be submitted electronically at [https://www.easychair.org/conferences/?conf=flops2012] Important Dates =============== - Submission deadline : December 9, 2011 - Author notification : February 3, 2012 - Camera-ready copy : March 2, 2012 Place and Related Events ======================== Takikawa Memorial Hall, Kobe University, 1-1 Rokkodai, Nada, Kobe 657-8501 Japan. The 23rd International Conference on Rewriting Techniques and Applications (RTA 2012) and satellite workshops including WFLP 2012 will be held in the week after FLOPS at Nagoya, Japan. Some Previous FLOPS =================== - FLOPS 2010, Sendai: [http://www.kb.ecei.tohoku.ac.jp/flops2010/] - FLOPS 2008, Ise: [http://www.math.nagoya-u.ac.jp/~garrigue/FLOPS2008/] - FLOPS 2006, Fuji Susono: [http://hagi.is.s.u-tokyo.ac.jp/FLOPS2006/] Sponsors ======== - Japan Society for Software Science and Technology (JSSST) SIGPPL In Cooperation with =================== - ACM SIGPLAN - Asian Association for Foundation of Software (AAFS) - Association for Logic Programming (ALP)

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FLOPS 2012: 2nd call for papers
by Tom Schrijvers 22 Nov '11

22 Nov '11

-- prof. dr. ir. Tom Schrijvers Programming Languages Group Department of Applied Mathematics and Computer Science University of Ghent Krijgslaan 281 S9 9000 Gent Belgium Phone: +32 9 264 4805 http://users.ugent.be/~tschrijv/

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Interpreter with Cont
by oleg＠okmij.org 22 Nov '11

22 Nov '11

I would recommend Ralf Hinze's ICFP00 Pearl Deriving Backtracking Monad Transformers http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.34.4164 He starts with a monad transformer expressed as a free term algebra, and shows step-by-step how to transform it to a more efficient context-passing style. He deals with exceptions and backtracking rather than IO; the ideas are quite similar though.

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FW: [Haskell] Job Opportunity at Parallel Scientific
by Simon Peyton-Jones 22 Nov '11

22 Nov '11

I'm taking the liberty of forwarding this super-relevant advert to Haskell Cafe in case any readers read the Cafe but not the main Haskell mailing list. Simon From: haskell-bounces(a)haskell.org [mailto:haskell-bounces@haskell.org] On Behalf Of Peter Braam Sent: 21 November 2011 22:23 To: haskell Subject: [Haskell] Job Opportunity at Parallel Scientific Parallel Haskell Programmers Parallel Scientific, LLC is a Boulder, CO based early stage, but funded startup company working in the area of scalable parallelization for scientific and large data computing. We are implementing radically new software tools for the creation and optimization of parallel programs benefiting applications and leveraging modern systems architecture. We build on our mathematical knowledge, cutting edge programming languages and our understanding of systems software and hardware. We are currently working with the Haskell development team and major HPC laboratories world wide on libraries and compiler extensions for parallel programming. Parallel Scientific was founded by Dr Peter Braam in 2010. Peter formerly taught mathematics and computer science at Oxford and Carnegie Mellon. Then he contributed file systems to Linux and invented Lustre (which provides storage to 9 of the top 10 systems in the world). He ran several successful startups, and Parallel Scientific is run by an very experienced management team and board. Successful candidates can in some cases work remotely and will work in a modern virtual environment. We provide training in advanced processes for software design and implementation and domain specific knowledge. Required skills: * Very strong background in computer science or mathematics * Experience with Haskell * Knowledge of systems programming and operating systems functionality * Knowledge of system architectures, such as high performance networking, memory architectures, multi and manycore CPUs and GPGPUs * Experience with performance tuning of parallel or concurrent algorithms * Experience designing and implementing concurrent or parallel programs Experience in one or more of the following areas is desirable: * Experience with Haskell compiler technology * In depth knowledge of core Haskell libraries for parallel programming (NDP, REPA etc) * Experience in the area of middleware algorithms for data flow programming, graphs, cloud based data analytics, or sparse matrices * Domain specific knowledge in scientific programming areas related to irregular and sparse problems, e.g. data analytics using graph analysis, genomics, tightly connected numerical analysis * Experience with performance tuning for parallel applications on multi core systems (e.g. with the Intel toolkit), for GPGPU's using Cuda/OpenCL or with MPI/OpenMP on clusters of SMPs To apply, please send a resume to jobs(a)parsci.com<mailto:jobs@parsci.com>.

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ST not strict enough?
by Jason Dusek 22 Nov '11

22 Nov '11

Hi All, I'm having some trouble with memory usage in rebuilding a ByteString with some sequences escaped. I thought I'd try vectors. However, it seems that even a relatively simple function, one that places all the bytes of a ByteString in to a vector, uses a great deal of memory. I've pulled this function out into a mini-module for testing: https://github.com/solidsnack/arx/blob/ST/Rebuild.hs#L37 On a one megabyte input, it peaks at ~38M of memory: :; dd if=/dev/zero bs=1M count=1 | ./rebuildprof +RTS -s ... 38,724,208 bytes maximum residency (5 sample(s)) 1,983,720 bytes maximum slop 76 MB total memory in use (0 MB lost due to fragmentation) ... %GC time 61.3% (61.5% elapsed) A heap profile by type, with -hy, shows a linear rise in ST items -- up to ~26M -- and then a linear decrease. It would stand to reason that, with sufficient strictness, the memory allocated to ST would stay constant and small. Should I be annotating my functions with strictness, for the vector reference, for example? Should I be using STUArrays, instead? -- Jason Dusek () ascii ribbon campaign - against html e-mail /\ www.asciiribbon.org - against proprietary attachments

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Job Opportunity at Parallel Scientific
by Peter Braam 21 Nov '11

21 Nov '11

Parallel Haskell Programmers Parallel Scientific, LLC is a Boulder, CO based early stage, but funded startup company working in the area of scalable parallelization for scientific and large data computing. We are implementing radically new software tools for the creation and optimization of parallel programs benefiting applications and leveraging modern systems architecture. We build on our mathematical knowledge, cutting edge programming languages and our understanding of systems software and hardware. We are currently working with the Haskell development team and major HPC laboratories world wide on libraries and compiler extensions for parallel programming. Parallel Scientific was founded by Peter Braam in 2010. Peter formerly taught mathematics and computer science at Oxford and Carnegie Mellon. Then he contributed file systems to Linux and invented Lustre (which provides storage to 9 of the top 10 systems in the world). He ran several successful startups, and Parallel Scientific is run by an very experienced management team and board. Successful candidates can in some cases work remotely and will work in a modern virtual environment. We provide training in advanced processes for software design and implementation and domain specific knowledge. Required skills: - Very strong background in computer science or mathematics - Experience with Haskell - Knowledge of systems programming and operating systems functionality - Knowledge of system architectures, such as high performance networking, memory architectures, multi and manycore CPUs and GPGPUs - Experience with performance tuning of parallel or concurrent algorithms - Experience designing and implementing concurrent or parallel programs Experience in one or more of the following areas is desirable: - Experience with Haskell compiler technology - In depth knowledge of core Haskell libraries for parallel programming (NDP, REPA etc) - Experience in the area of middleware algorithms for data flow programming, graphs, cloud based data analytics, or sparse matrices - Domain specific knowledge in scientific programming areas related to irregular and sparse problems, e.g. data analytics using graph analysis, genomics, tightly connected numerical analysis - Experience with performance tuning for parallel applications on multi core systems (e.g. with the Intel toolkit), for GPGPU's using Cuda/OpenCL or with MPI/OpenMP on clusters of SMPs To apply, please send a resume to jobs(a)parsci.com.

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