- Haskell-Cafe - Haskell.org

Re: [Haskell-cafe] ANNOUNCE : Leksah 0.12.1.2 (fixes some metadata issues)
by Hilco Wijbenga 21 Jun '12

21 Jun '12

On 20 June 2012 18:22, Oliver Batchelor <saulzar(a)gmail.com> wrote: > Check the error given by cairo. > > cabal install cairo-0.12.3.1 Well, it wasn't cairo that was the problem but ... > You probably need to put the .cabal/bin in your PATH, so that the > tools such as c2hs can run. ... indeed, adding .cabal/bin to my PATH allowed the install to finish successfully. Why doesn't cabal abort when a package fails to install? Why doesn't it die if .cabal/bin isn't on the PATH? (Surely, that's easy to test for?)

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relocation R_X86_64_PC32 against undefined symbol
by Henning Thielemann 20 Jun '12

20 Jun '12

Just for the record: I compiled with GHC and got the linker error: /usr/bin/ld: dist/build/.../Module.dyn_o: relocation R_X86_64_PC32 against undefined symbol `..._xyz1_closure' can not be used when making a shared object; recompile with -fPIC Problem was that I forgot to declare Module in the Cabal description.

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[Word8] -> FilePath using ghc's file system encoding
by Joey Hess 20 Jun '12

20 Jun '12

I found myself writing the code below today, and thought I'd write to see if there's a better way, perhaps one that doesn't use unsafePerformIO. A sample use case for this is a program that reads a FilePath from a Handle, and then operates on that file on disk. GHC uses a special encoding for FilePaths that cleanly roundtrips invalid utf8, but for that to work, the FilePath must be read using that encoding too. Neglecting to do that would result in a program that worked for most filenames, but failed on edge case non-utf8 encoded filenames. Another way to deal with this problem is to first hSetEncoding using GHC.IO.Encoding.getFileSystemEncoding, and then read from the Handle using hGetLine, which applies the encoding to the data it reads. However, in this case I needed to use ByteString to read from the Handle, and so needed a way to convert from a ByteString to a FilePath. (Using RawFilePath would be another approach, but reworking my program to use it isn't practical.) Anyway, it seems there should be a pure way to encode a string with GHC's filesystem encoding. ----- import qualified GHC.Foreign as GHC import qualified GHC.IO.Encoding as Encoding import System.IO.Unsafe import Data.Bits.Utils -- from MissingH {- Converts a [Word8] to a FilePath, encoding using the filesystem encoding. - - w82c produces a String, which may contain Chars that are invalid - unicode. From there, this is really a simple matter of applying the - file system encoding, only complicated by GHC's interface to doing so. -} {-# NOINLINE encodeW8 #-} encodeW8 :: [Word8] -> FilePath encodeW8 w8 = unsafePerformIO $ do enc <- Encoding.getFileSystemEncoding GHC.withCString Encoding.char8 (w82s w8) (GHC.peekCString enc) -- see shy jo

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Problem with plugins
by Timo von Holtz 20 Jun '12

20 Jun '12

Hi, I'm currently working on extending the hascat Server. My problem is, that for whatever odd reason it will only work on GHC < 7.0 or alternatively if I execute it with runghc or in ghci. If I compile it with GHC>=7.0 and execute it, then I get this: $ ~/.cabal/bin/hascat config.xml Installing "Root" at / hascat: /home/tvh/.cabal/lib/plugins-1.5.2.1/ghc-7.4.1/HSplugins-1.5.2.1.o: unknown symbol `ghczm7zi4zi1_ErrUtils_zdsinsertzugo3_info' hascat: unloadObj: can't find `/usr/lib/ghc/binary-0.5.1.0/HSbinary-0.5.1.0.o' to unload user error (unloadObj: failed) Installing "Hascat Server Info" at /ServerInfo/ hascat: /home/tvh/.cabal/lib/hascat-system-0.2/ghc-7.4.1/HShascat-system-0.2.o: unknown symbol `base_DataziMaybe_Nothing_closure' hascat: unloadObj: can't find `/usr/lib/ghc/Cabal-1.14.0/HSCabal-1.14.0.o' to unload user error (unloadObj: failed) Installing "Hascat Application Manager" at /Manager/ hascat: /home/tvh/.cabal/lib/hascat-system-0.2/ghc-7.4.1/HShascat-system-0.2.o: unknown symbol `base_DataziMaybe_Nothing_closure' hascat: unloadObj: can't find `/usr/lib/ghc/Cabal-1.14.0/HSCabal-1.14.0.o' to unload user error (unloadObj: failed) Installing "Hascat Application Deployer" at /Deployer/ hascat: /usr/lib/haskell-packages/ghc/lib/zlib-0.5.3.3/ghc-7.4.1/HSzlib-0.5.3.3.o: unknown symbol `base_GHCziForeignPtr_ForeignPtr_con_info' hascat: unloadObj: can't find `/usr/lib/ghc/Cabal-1.14.0/HSCabal-1.14.0.o' to unload user error (unloadObj: failed) Waiting for connections on port 8012 Is there a way to make this work? Greetings Timo

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Re: [Haskell-cafe] Again, version conflicting problem with cabal-install
by Jason Dagit 20 Jun '12

20 Jun '12

In my experience the diamond of death is typically because: * You install package A that uses C-0.1 * Someone uploads C-0.2 to hackage * Later you 'cabal update', this does not rebuild A to use C-0.2, even though it could. * You install package B that uses C, and cabal builds it with C-0.2 * Now you want to build D that uses A and B, but A requires C-0.1 and B requires C-0.2, even though they could be rebuilt to use the same C. Typically, the constraints on A, B, and D would all accept the same version of C. Except that when they were compiled separately and C changed between building A and B, then the compiled versions become fixed on C-0.1 and C-0.2. It's true that it won't solve it in all cases, but in my experience using cabal-dev made the problem go away. I hope that clarifies. Jason On Fri, Feb 3, 2012 at 7:33 AM, Magicloud Magiclouds <magicloud.magiclouds(a)gmail.com> wrote: > Well, cabal-dev could not resolve the conflict of "the diamond". > Because the conflict is "depending different version at the SAME > time". > > On Fri, Feb 3, 2012 at 9:20 PM, Jason Dagit <dagitj(a)gmail.com> wrote: >> On Thu, Feb 2, 2012 at 9:54 PM, Magicloud Magiclouds >> <magicloud.magiclouds(a)gmail.com> wrote: >>> Hello, >>> As I recalled, ghc works in staticly link mode. So after one library >>> is compiled, all its build dependencies are useless. Lost, changed, >>> wheresoever, it does not matter. >>> Then why the problem of version conflicting exists? >> >> I'm not sure, but for me this problem has gone away by using cabal-dev >> to build everything. >> >> Jason > > > > -- > 竹密岂妨流水过 > 山高哪阻野云飞 > > And for G+, please use magiclouds#gmail.com.

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Lazy producing a list in the strict ST monad
by Nicu Ionita 19 Jun '12

19 Jun '12

Hi, I'm trying to produce a list in the strict ST monad. The documentation of ST says that the monad is strict in the state, but not in the values. So I expect that, when returning a list, I get back only the Cons (with 2 unevaluated thunks). Now, when I need the first element (head), this will be evaluated (with whatever actions are necessary in the ST universe) and the tail is again a Cons with unevaluated parts. Internally my list is stored in a vector, and the elements are generated phasewise, each phase generating 0 or more elements in the vector, and a fuction splitMove is driving this process (see code below). I would expect that the first phase triggers, generates some moves, then (after these are consumed from the list) the next phase triggers generating the next few moves and so on. But when I trace the phases (Debug.Trace.trace) I get all the trace messages in front of the first move: Moves for fen: rnbqkbnr/pp3ppp/4p3/2pp4/3P4/2NQ4/PPP1PPPP/R1B1KBNR w After move generation... 0 >= 0 : next phase 3 >= 3 : next phase 3 >= 3 : next phase 42 >= 42 : next phase 44 >= 44 : next phase d4c5 g1f3 g1h3 c3b1 ... This seems not to be just an unhappy combination between trace and ST, as also the program without trace is beeing slower than the same implemented with plain lists, which is hard to believe (in many cases the move list is not consumed to the end). I wonder if my expectation is wrong, but I don't find a way to do this. Here is the (incomplete) code: produceList ... = runST $ do ml <- newMList ... listMoves ml -- Transforms a move list to a list of moves - lazy listMoves :: MList s -> ST s [Move] listMoves ml = do sm <- splitMove ml case sm of Just (m, ml') -> do rest <- listMoves ml' return $ m : rest Nothing -> return [] -- Split the first move from the move list and return it together with -- the new move list (without the first move). Return Nothing if there -- is no further move splitMove :: MList s -> ST s (Maybe (Move, MList s)) splitMove ml | mlToMove ml >= mlToGen ml = do mml <- trace trm $ nextPhase ml case mml of Nothing -> return Nothing Just ml' -> splitMove ml' | otherwise = do m <- U.unsafeRead (mlVec ml) (mlToMove ml) case mlCheck ml ml m of Ok -> return $ Just (m, ml1) Skip -> splitMove ml1 Delay -> splitMove ml1 { mlBads = m : mlBads ml } where ml1 = ml { mlToMove = mlToMove ml + 1 } trm = show (mlToMove ml) ++ " >= " ++ show (mlToGen ml) ++ " : next phase"

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Re: [Haskell-cafe] [Haskell-beginners] Function application versus function composition performance
by KC 19 Jun '12

19 Jun '12

A good functional programming language has a good "code algebra" after parsing to which algebraic transformations can be applied for optimization. For example, reducing the need for generating intermediate data structures. See: fusion. On Tue, Jun 19, 2012 at 3:01 PM, Matt Ford <matt(a)dancingfrog.co.uk> wrote: > Hi All, > > My last question got me thinking (always dangerous): an expression > that doubles a list and takes the 2nd element (index 1), I assume, > goes through the following steps. > > double (double [1,2,3,4]) !! 1 > double ( 1*2 : double [2,3,4]) !! 1 > 1*2*2 : double ( double [2,3,4] ) !! 1 > 1*2*2 : double ( 2*2 : double [3,4] ) !! 1 > 1*2*2 : 2*2*2 : double ( double [3,4] ) !! 1 > 2*2*2 > 8 > > Up until the element requested all the proceeding elements have to > have the expression formed as Haskell process the calculation. > > Now, I want to compare this to using function composition > > ( double . double ) [ 1 ,2, 3, 4 ] !! 1 > > This is the bit I'm unsure of - what does the composition look like. > It is easy to see that it could be simplified to something like: > > ( double . double) (x:xs) = x*4 : (double . double) xs > > This would mean the steps could be written > > (double . double) [ 1,2,3,4 ] !! 1 > (1*4 : (double.double) [2,3,4]) !! 1 > (1*4 : 2*4 : (double.double) [ 3,4 ]) !! 1 > 2*4 > 8 > > Ignoring the start and end steps, it will be half the number of steps > compared to the application version. Significant then, over long > lists. > > So is this true, are composite functions simplified in Haskell in > general so that they may have improved performance over function > application? > > I've seen posts on the internet that say it's a matter of style only: > > http://stackoverflow.com/questions/3030675/haskell-function-composition-and… > . > But my reasoning suggests it could be more than that. > > Perhaps, function application is similarly optimised - maybe by > replacing all functions applications with composition and then > simplifying? Or maybe the simplifying/optimisation step never > happens? As you can see I'm just guessing at things :-) But it's > nice to wonder. > > Many thanks for any pointers, > > Matt. > > _______________________________________________ > Beginners mailing list > Beginners(a)haskell.org > http://www.haskell.org/mailman/listinfo/beginners > -- -- Regards, KC

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Haskell Implementors' Workshop 2012, Second CFT
by Johan Tibell 19 Jun '12

19 Jun '12

Call for Talks ACM SIGPLAN Haskell Implementors' Workshop http://haskell.org/haskellwiki/HaskellImplementorsWorkshop/2012 Copenhagen, Denmark, September 14th, 2012 The workshop will be held in conjunction with ICFP 2012 http://www.icfpconference.org/icfp2012/ Important dates Proposal Deadline: 10th July 2012 Notification: 27th July 2012 Workshop: 14th September 2012 The Haskell Implementors' Workshop is to be held alongside ICFP 2012 this year in Copenhagen, Denmark. There will be no proceedings; it is an informal gathering of people involved in the design and development of Haskell implementations, tools, libraries, and supporting infrastructure. This relatively new workshop reflects the growth of the user community: there is a clear need for a well-supported tool chain for the development, distribution, deployment, and configuration of Haskell software. The aim is for this workshop to give the people involved with building the infrastructure behind this ecosystem an opportunity to bat around ideas, share experiences, and ask for feedback from fellow experts. We intend the workshop to have an informal and interactive feel, with a flexible timetable and plenty of room for ad-hoc discussion, demos, and impromptu short talks. Scope and target audience ------------------------- It is important to distinguish the Haskell Implementors' Workshop from the Haskell Symposium which is also co-located with ICFP 2012. The Haskell Symposium is for the publication of Haskell-related research. In contrast, the Haskell Implementors' Workshop will have no proceedings -- although we will aim to make talk videos, slides and presented data available with the consent of the speakers. In the Haskell Implementors' Workshop, we hope to study the underlying technology. We want to bring together anyone interested in the nitty-gritty details behind turning plain-text source code into a deployed product. Having said that, members of the wider Haskell community are more than welcome to attend the workshop -- we need your feedback to keep the Haskell ecosystem thriving. The scope covers any of the following topics. There may be some topics that people feel we've missed, so by all means submit a proposal even if it doesn't fit exactly into one of these buckets: * Compilation techniques * Language features and extensions * Type system implementation * Concurrency and parallelism: language design and implementation * Performance, optimisation and benchmarking * Virtual machines and run-time systems * Libraries and tools for development or deployment Talks ----- At this stage we would like to invite proposals from potential speakers for a relatively short talk. We are aiming for 20 minute talks with 10 minutes for questions and changeovers. We want to hear from people writing compilers, tools, or libraries, people with cool ideas for directions in which we should take the platform, proposals for new features to be implemented, and half-baked crazy ideas. Please submit a talk title and abstract of no more than 200 words to: johan.tibell(a)gmail.com We will also have a lightning talks session which will be organised on the day. These talks will be 2-10 minutes, depending on available time. Suggested topics for lightning talks are to present a single idea, a work-in-progress project, a problem to intrigue and perplex Haskell implementors, or simply to ask for feedback and collaborators. Organisers ---------- * Lennart Augustsson (Standard Chartered Bank) * Manuel M T Chakravarty (University of New South Wales) * Gregory Collins - co-chair (Google) * Simon Marlow (Microsoft Research) * David Terei (Stanford University) * Johan Tibell - co-chair (Google)

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Call for Papers: STVR Special Issue on Tests and Proofs
by Achim D. Brucker 19 Jun '12

19 Jun '12

Apologies for duplicates. CALL FOR PAPERS STVR Special Issue on Tests and Proofs http://lifc.univ-fcomte.fr/tap2012/stvr/ The Software Testing, Verification & Reliability (STVR) journal (http://www3.interscience.wiley.com/journal/13635/home) invites authors to submit papers to a Special Issue on Tests and Proofs. Background ========== The increasing use of software and the growing system complexity make focused software testing a challenging task. Recent years have seen an increasing industrial and academic interest in the use of static and dynamic analysis techniques together. Success has been reported combining different test techniques such as model-based testing, structural testing, or concolic testing with static techniques such as program slicing, dependencies analysis, model-checking, abstract interpretation, predicate abstraction, or verification. This special issue serves as a platform for researchers and practitioners to present theory, results, experience and advances in Tests and Proofs (TAP). Topics ====== This special issue focuses on all topics relevant to TAP. In particular, the topics of interest include, but are not limited to: * Program proving with the aid of testing techniques * New challenges in automated reasoning emerging from specificities of test generation * Verification and testing techniques combining proofs and tests * Generation of test data, oracles, or preambles by deductive techniques such as: theorem proving, model checking, symbolic execution, constraint logic programming, SAT and SMT solving * Model-based testing and verification * Automatic bug finding * Debugging of programs combining static and dynamic analysis * Transfer of concepts from testing to proving (e.g., coverage criteria) and from proving to testing * Formal frameworks for test and proof * Tool descriptions, experience reports and evaluation of test and proof * Case studies combining tests and proofs * Applying combination of test and proof techniques to new application domains such as validating security procotols or vulnerability detection of programs * The processes, techniques, and tools that support test and proof Submission Information ====================== The deadline for submissions is 17th December, 2012. Notification of decisions will be given by April 15th, 2013. All submissions must contain original unpublished work not being considered for publication elsewhere. Original extensions to conference papers - identifing clearly additional contributions - are also encouraged unless prohibited by copyright. Submissions will be refereed according to standard procedures for Software Testing, Verification and Reliability. Please submit your paper electronically using the Software Testing, Verification & Reliability manuscript submission site. Select "Special Issue Paper" and enter "Tests and Proofs" as title. Important Dates: ================ * Paper submission: December 17, 2012 * Notification: April 15, 2013 Guest Editors ============= * Achim D. Brucker, SAP Research, Germany http://www.brucker.ch/ * Wolfgang Grieskamp, Google, U.S.A. http://www.linkedin.com/in/wgrieskamp * Jacques Julliand, University of Franche-Comté, France http://lifc.univ-fcomte.fr/page_personnelle/accueil/8 -- Dr. Achim D. Brucker, SAP Research, Vincenz-Priessnitz-Str. 1, D-76131 Karlsruhe Phone: +49 6227 7-52595, http://www.brucker.ch

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How do people still not understand what FP is about? What are we doing wrong?
by Ben Kolera 18 Jun '12

18 Jun '12

Saw this float by in twitter, and it made me a bit sad. Obviously this is still a large misunderstanding of FP in the larger programming community and it make me wonder what we FP enthusiasts are doing wrong to not get the message out to people. "Programming languages that require random senseless voodoo to get an effect are awesome. Let's make programming hard through poor design." [1] The sad thing about this is that the inverse of this has more truth to it; that "languages that allow people to intersperse side effects anywhere in their computation without thought are flawed by design and allow programmers to do stupid things that hinder the composability, thread safety and ability to reason of/about their code". Has anyone had any experience / success with convincing people that the "senseless voodoo" is actually a boon rather than a bane? Is it even worth trying to convince people so set in their ways? ( Sorry if this is even too off-topic for the cafe. Just needed a place to vent my frustration at this. ) Cheers, Ben [1] https://twitter.com/cwestin63/status/214793627170390018

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