October 2011 - Haskell-Cafe

Re: [Haskell-cafe] ANNOUNCE: HaTeX 3 - First release
by Daniel Díaz Casanueva 06 Oct '11

06 Oct '11

It seems there is an error in the hackage URL's. Working URL's: http://hackage.haskell.org/package/HaTeX http://hackage.haskell.org/package/HaTeX-meta Sorry!

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ANNOUNCE: HaTeX 3 - First release
by Daniel Díaz Casanueva 06 Oct '11

06 Oct '11

Hello, folks! I have just released HaTeX 3 to Hackage: http://hackage.haskell.org/HaTeX It is a first version, not well documented yet, but now you can test it with a simple "cabal install hatex". What is HaTeX? HaTeX consists in a set of combinators which allow you to build LaTeX code, following the LaTeX syntax in a type-safe manner. This allows you to build programs which generates LaTeX code automatically for any purpose you can figure out. Further reading about HaTeX 3: * http://deltadiaz.blogspot.com/2011/09/hatex-3-previous-notes.html * http://deltadiaz.blogspot.com/2011/10/hatex-3-two-styles.html I wanted to make the release before end the proper documentation because: 1) This allow people to test the library (and hence, help me to build the documentation if any feedback comes). 2) I am too busy currently and I can't expend to HaTeX the time I'd like. The library may need some improvements, but it worked well for my own tests. With HaTeX, I uploaded the HaTeX-meta package. This package is needed if you want to develope a subset of the HaTeX modules, because they are automatically generated by this application. Anyway, there are notes in the API reference warning this. HaTeX-meta in Hackage: http://hackage.haskell.org/HaTeX-meta A continously updated version of the source code from these packages can be found at: http://dhelta.net/hprojects/HaTeX/code http://dhelta.net/hprojects/HaTeX-meta/code Thanks for reading, Daniel Díaz.

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How to install haddock with ghc-7.2.1?
by Paulo Pocinho 06 Oct '11

06 Oct '11

Hi list. Installing haddock fails with ghc-7.2.1. How do I get to install it along with all dependencies? C:\>cabal install haddock Resolving dependencies... Downloading ghc-paths-0.1.0.8... [1 of 1] Compiling Main ( C:\Users\user\AppData\Local\Temp\ghc-paths-0.1.0.86336\ghc-pths-0.1.0.8\Setup.hs, C:\Users\user\AppData\Local\Temp\ghc-paths-0.1.0.86336\ghc-paths-0.1.0.8\dis \setup\Main.o ) Linking C:\Users\user\AppData\Local\Temp\ghc-paths-0.1.0.86336\ghc-paths-0.1.0.8\dist\setup\setup.exe ... Configuring ghc-paths-0.1.0.8... Building ghc-paths-0.1.0.8... Preprocessing library ghc-paths-0.1.0.8... [1 of 1] Compiling GHC.Paths ( GHC\Paths.hs, dist\build\GHC\Paths.o ) Registering ghc-paths-0.1.0.8... Installing library in C:\Users\user\AppData\Roaming\cabal\ghc-paths-0.1.0.8\ghc-7.2.1 Registering ghc-paths-0.1.0.8... Downloading xhtml-3000.2.0.4... Configuring xhtml-3000.2.0.4... Preprocessing library xhtml-3000.2.0.4... Building xhtml-3000.2.0.4... [ 1 of 15] Compiling Text.XHtml.BlockTable ( Text\XHtml\BlockTable.hs, dist\build\Text\XHtml\BlockTable.o ) Implicit import declaration: base:Prelude can't be safely imported! The package (base) the module resides in isn't trusted. cabal: Error: some packages failed to install: haddock-2.9.4 depends on xhtml-3000.2.0.4 which failed to install. xhtml-3000.2.0.4 failed during the building phase. The exception was: ExitFailure 1

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Science, FRP and Haskell
by Tom Nielsen 06 Oct '11

06 Oct '11

Dear cafe, I am please to announce that our paper on using FRP (and Haskell!) in physiological experimentation and analysis has now been published in Journal of the Royal Society Interface. Since most people on this list probably don't read that journal on a regular basis, I thought a quick note to the list would be appropriate. The full PDF is available here: http://rsif.royalsocietypublishing.org/cgi/reprint/rsif.2011.0616?ijkey=vFo… If this link doesn't work, just email me for a copy. I'll provide a brief summary here: -The main point of the paper is that there is a large conceptual overlap between FRP and the observation and analysis of physiological data. We show that many different quantities map on to Signals or Events (we introduce a third type scheme, Durations, similar to Events but with a start and an end time). These types can be used not only for data but also for meta-data. In fact, we make no distinction between the two. -We have developed a non-embedded functional programming language with first-class signals and events for executing experiments defined as functional reactive programs. A key innovation is that differential equations can be introduced by pattern matching on the derivative of a signal. One back-end supports the execution of some programs under a real-time (LXRT) environment. -We have carried out two non-trivial neurophysiology experiments to demonstrate the generality, concision and practical usefulness of our approach. -All code used for data acquisition, stimulus generation and presentation, analysis and producing figures was written in Haskell or in programming languages implemented in Haskell. I stress that the paper is about ideas and does not describe a mature software package. I am reimplementing a lot of those ideas and integrating them with Bayesian inference, such that we can analyse data in terms of physical, probabilistic models. This more mature language is called BAYSIG. here is the code described in the paper, in all it's messiness: https://github.com/glutamate/bugpan The repository for BAYSIG is here https://github.com/glutamate/baysig Both of these packages depend on a couple of unreleased cabal packages that can be found in my github account. Regards, Tom

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How to mark a package obsolete on Hackage?
by Geoffrey Mainland 06 Oct '11

06 Oct '11

How does one mark a package obsolete on Hackage? For example, monads-fd no longer appears on the main web page listing available packages, but it still exists on Hackage (but is marked obsolete [1]). I have several package that are similarly obsolete due to mtl2 and would like to flag them appropriately. Thanks, Geoff [1] http://hackage.haskell.org/package/monads-fd

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Haskell Weekly News: Issue 202
by Daniel Santa Cruz 05 Oct '11

05 Oct '11

Welcome to issue 202 of the HWN, a newsletter covering developments in the Haskell community. This release covers the week of September 25 to October 1, 2011. New and Updated Projects * ParserFunction (Enzo Fabrizio; 0.0.5) Provides utilities for parsing and evaluating mathematical expressions. [1] http://goo.gl/xNOe1 * flexiwrap (Iain Alexander; 0.1.0) Also updates to related packages: data-type, function-combine, and flexiwrap-smallcheck. [2] http://goo.gl/dN0ew * crypto-api-tests (Thomas DuBuisson) These tests have been split out into their own package. Tests now use the test-framework package. [3] http://goo.gl/7kUIV * hledger (Simon Michael; 0.16) Stability/bugfix/polish release. [4] http://goo.gl/hW085 * GA (Kenneth Hoste; 1.0) Major version bump to this genetic algorithms package. [5] http://goo.gl/NoAl4 Quotes of the Week * glguy: lazy evaluation is best 50% of time because there are 2 cases, the cases where it is the best and the cases where it is not the best * Cale: Computing lengths is admitting defeat * syntaxfree: Many people think the core ideas behind Haskell [snip] In the Deep Complex Universe some Gnomes were having Tangling problems. Wadler & friends solved their problems and as a reward the Tangled Gnomes gave them the Secret of Haskell * monochrom: How do I extract the IO out of IO String? Top Reddit Stories * GHC-specific alias analysis for LLVM Domain: blog.omega-prime.co.uk, Score: 74, Comments: 4 On Reddit: [6] http://goo.gl/kNXp9 Original: [7] http://goo.gl/851qj * GHC Projects for All Domain: dterei.blogspot.com, Score: 45, Comments: 2 On Reddit: [8] http://goo.gl/X3jpJ Original: [9] http://goo.gl/FpnUP * The Evolution of a Haskell Programmer Domain: willamette.edu, Score: 41, Comments: 17 On Reddit: [10] http://goo.gl/4WQyK Original: [11] http://goo.gl/gbNsH * Stanford CS240h, Functional Systems in Haskell course materials available on GitHub Domain: github.com, Score: 29, Comments: 3 On Reddit: [12] http://goo.gl/5aL1X Original: [13] http://goo.gl/EEflc * Introduction to programming with shift and reset (Tutorial by Oleg) Domain: okmij.org, Score: 29, Comments: 1 On Reddit: [14] http://goo.gl/Ogsjo Original: [15] http://goo.gl/xvVmQ * A few Haskell notes from the Strange Loop conference Domain: serpentine.com, Score: 27, Comments: 2 On Reddit: [16] http://goo.gl/qx4qn Original: [17] http://goo.gl/nplIs * Par Monad Slides from CUFP Domain: community.haskell.org, Score: 27, Comments: 0 On Reddit: [18] http://goo.gl/pFkgw Original: [19] http://goo.gl/Ax4bW * Slides from the CUFP 2011 Snap Framework Tutorial Domain: gregorycollins.net, Score: 23, Comments: 0 On Reddit: [20] http://goo.gl/uVrlv Original: [21] http://goo.gl/myRYa * Haskell Job Opportunity at Sensor Sense Domain: self.haskell, Score: 22, Comments: 1 On Reddit: [22] http://goo.gl/PpSdW Original: [23] http://goo.gl/PpSdW * Slides from my Haskell Implementors Workshop talk Domain: blog.johantibell.com, Score: 20, Comments: 3 On Reddit: [24] http://goo.gl/sgmzC Original: [25] http://goo.gl/BT4H0 Top StackOverflow Questions * Learning Haskell with a view to learning Scala votes: 23, answers: 4 Read on SO: [26] http://goo.gl/8BnAv * Why are the functions making Vector an instance of Functor, Monad, Applicative, Alternative, Foldable and Traversable slow? votes: 11, answers: 2 Read on SO: [27] http://goo.gl/F8sph * Strategies in Scala votes: 10, answers: 1 Read on SO: [28] http://goo.gl/NzUiU * What's the smoothest way to update haskell platform to latest? votes: 8, answers: 2 Read on SO: [29] http://goo.gl/EnG7p * Does Haskell have an equivalent to Sage? votes: 8, answers: 3 Read on SO: [30] http://goo.gl/v7oE8 * Haskell syntax for 'or' in case expressions votes: 7, answers: 3 Read on SO: [31] http://goo.gl/Akl9D * Is operator && strict in Haskell? votes: 6, answers: 3 Read on SO: [32] http://goo.gl/TLe86 Until next time, Daniel Santa Cruz References 1. http://permalink.gmane.org/gmane.comp.lang.haskell.general/18942 2. http://permalink.gmane.org/gmane.comp.lang.haskell.general/18943 3. http://permalink.gmane.org/gmane.comp.lang.haskell.cafe/92700 4. http://permalink.gmane.org/gmane.comp.finance.ledger.hledger/521 5. http://permalink.gmane.org/gmane.comp.lang.haskell.cafe/92746 6. http://blog.omega-prime.co.uk/?p=135 7. http://www.reddit.com/r/haskell/comments/kwaee/ghcspecific_alias_analysis_f… 8. http://dterei.blogspot.com/2011/09/ghc-project-for-all.html 9. http://www.reddit.com/r/haskell/comments/kwm0g/ghc_projects_for_all/ 10. http://www.willamette.edu/~fruehr/haskell/evolution.html 11. http://www.reddit.com/r/haskell/comments/kv610/the_evolution_of_a_haskell_p… 12. https://github.com/bos/stanford-cs240h 13. http://www.reddit.com/r/haskell/comments/kvjda/stanford_cs240h_functional_s… 14. http://okmij.org/ftp/continuations/index.html#tutorial 15. http://www.reddit.com/r/haskell/comments/kxg3o/introduction_to_programming_… 16. http://www.serpentine.com/blog/2011/09/27/the-strange-loop-conference-was-a… 17. http://www.reddit.com/r/haskell/comments/ktscd/a_few_haskell_notes_from_the… 18. http://community.haskell.org/~simonmar/slides/CUFP.pdf 19. http://www.reddit.com/r/haskell/comments/ky3cw/par_monad_slides_from_cufp/ 20. http://gregorycollins.net/posts/2011/10/01/cufp-tutorial-slides 21. http://www.reddit.com/r/haskell/comments/kxkex/slides_from_the_cufp_2011_sn… 22. http://www.reddit.com/r/haskell/comments/kt5g4/haskell_job_opportunity_at_s… 23. http://www.reddit.com/r/haskell/comments/kt5g4/haskell_job_opportunity_at_s… 24. http://blog.johantibell.com/2011/09/slides-from-my-haskell-implementors.html 25. http://www.reddit.com/r/haskell/comments/kti89/slides_from_my_haskell_imple… 26. http://stackoverflow.com/questions/7594337/learning-haskell-with-a-view-to-… 27. http://stackoverflow.com/questions/7583403/why-are-the-functions-making-vec… 28. http://stackoverflow.com/questions/7574937/strategies-in-scala 29. http://stackoverflow.com/questions/7546949/whats-the-smoothest-way-to-updat… 30. http://stackoverflow.com/questions/7556053/does-haskell-have-an-equivalent-… 31. http://stackoverflow.com/questions/7603509/haskell-syntax-for-or-in-case-ex… 32. http://stackoverflow.com/questions/7612580/is-operator-strict-in-haskell

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ANN: hit a reimplementation of git storage in haskell.
by Vincent Hanquez 05 Oct '11

05 Oct '11

Hi Haskellers, I just want to announce the hit project [1], which is a reimplementation of low level git operations to read *AND* write to a git repository. It support reading from anything i threw at it (loose objects, packed objects, deltas), a subset of revisions specifier (man gitrevisions), and writing new objects (blob, tree, commit, tag). I don't necessarily want to re-implement git itself (although patches welcome if someone want to go in this direction), and as such the project is a bit of a toy to investigate git storage (for another project of mine) and superseeding my own libgit project (for yet another project). Yet it should be completely functional and have good performance. A few word of the implementation: it's very IO based at the moment; The way things are done by git, doesn't necessarily cope with pure and nice stuff if performance need to follow. That said it should still be easier to understand than reading the git source :-) Any comments welcome, [1] http://hackage.haskell.org/package/hit/ -- Vincent

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Cabal rebuilding all of the C++ code for wxHaskell
by DukeDave 05 Oct '11

05 Oct '11

Hi all, I've been trying to resolve a compile time issue[1] with wxHaskell, and I thought I'd throw it open to see if anyone on cafe can help. Here's the crux of the issue: The Setup.hs for wxcore (the major component of wxHaskell) uses "simpleUserHooks", overriding only "confHook". However there is also "cleanHook", which is defined by simpleUserHooks to be: cleanHook = \p _ _ f -> clean p f, If you consult the source for clean[2] you'll see that it tries to "remove the whole dist/ directory rather than tracking exactly what files we created in there". I presume that's why we have to do a full re-build every time? To try and circumvent this I modified the definition of "main" in Setup.hs to this: main = defaultMainWithHooks simpleUserHooks { confHook = myConfHook, cleanHook = (\_ _ _ _ -> return ())} Unfortunately it still seems to re-build all the C++ on each 'install' from cabal. Not sure why? Dave, [1] http://sourceforge.net/mailarchive/message.php?msg_id=28099997 [2] Taken from http://www.haskell.org/ghc/docs/6.10.4/html/libraries/Cabal/src/Distributio… -- Cleaning clean :: PackageDescription -> CleanFlags -> IO () clean pkg_descr flags = do let distPref = fromFlag $ cleanDistPref flags notice verbosity "cleaning..." maybeConfig <- if fromFlag (cleanSaveConf flags) then maybeGetPersistBuildConfig distPref else return Nothing -- remove the whole dist/ directory rather than tracking exactly what files -- we created in there. chattyTry "removing dist/" $ do exists <- doesDirectoryExist distPref when exists (removeDirectoryRecursive distPref) -- these live in the top level dir so must be removed separately removeRegScripts -- Any extra files the user wants to remove mapM_ removeFileOrDirectory (extraTmpFiles pkg_descr) -- If the user wanted to save the config, write it back maybe (return ()) (writePersistBuildConfig distPref) maybeConfig where removeFileOrDirectory :: FilePath -> IO () removeFileOrDirectory fname = do isDir <- doesDirectoryExist fname isFile <- doesFileExist fname if isDir then removeDirectoryRecursive fname else if isFile then removeFile fname else return () verbosity = fromFlag (cleanVerbosity flags)

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what happens to ()'s from Core?
by John Lato 05 Oct '11

05 Oct '11

Hello, I'm working on a small EDSL, and I think I've finally managed to get GHC to compile it to good core. Basically, it allows for the creation of expressions like: > g = 0.5*x + 0.1*y which is then compiled to a tuple (related work: CCA, stream fusion) > exists s. (s, s -> Double -> (s,Double)) I also have a function 'mapAccumL :: (V.Unbox a, V.Unbox b) => (s -> a -> (s,b)) -> s -> V.Vector a -> V.Vector b'. Basic usage would be similar to: > import qualified Data.Vector.Unboxed as V > > main = do > let (gs, gf) = $(compile [] g) > ys = mapAccumL gf gs $ V.enumFromTo (1::Double) 5 > print ys For 'g' as above, I currently get 's :: (((), ()), Double)', which is expected. GHC produces the following core for the inner loop, which looks pretty good to me: letrec { $s$wa_s2OL [Occ=LoopBreaker] :: () -> () -> GHC.Prim.Double# -> GHC.Prim.Int# -> GHC.Prim.State# (Control.Monad.Primitive.R:PrimStateST s_a1Y9) -> (# GHC.Prim.State# s_a1Y9, () #) [LclId, Arity=5, Str=DmdType LLLLL] $s$wa_s2OL = \ _ _ (sc2_s2Oq :: GHC.Prim.Double#) (sc3_s2Or :: GHC.Prim.Int#) (sc4_s2Os :: GHC.Prim.State# (Control.Monad.Primitive.R:PrimStateST s_a1Y9)) -> case GHC.Prim.<# sc3_s2Or rb1_a2EV of _ { GHC.Types.False -> (# sc4_s2Os, GHC.Unit.() #); GHC.Types.True -> let { x#_a2aI [Dmd=Just L] :: GHC.Prim.Double# [LclId, Str=DmdType] x#_a2aI = GHC.Prim.+## (GHC.Prim.*## (GHC.Prim.indexDoubleArray# rb2_a2EW (GHC.Prim.+# rb_a2EU sc3_s2Or)) 0.5) (GHC.Prim.*## sc2_s2Oq 0.1) } in $s$wa_s2OL GHC.Unit.() GHC.Unit.() x#_a2aI (GHC.Prim.+# sc3_s2Or 1) ((GHC.Prim.writeDoubleArray# @ (Control.Monad.Primitive.PrimState (GHC.ST.ST s_a1Y9)) arr#_a29n sc3_s2Or x#_a2aI (sc4_s2Os `cast` (GHC.Prim.State# (Sym (Control.Monad.Primitive.TFCo:R:PrimStateST <s_a1Y9>)) :: GHC.Prim.State# (Control.Monad.Primitive.R:PrimStateST s_a1Y9) ~ GHC.Prim.State# (Control.Monad.Primitive.PrimState (GHC.ST.ST s_a1Y9))))) `cast` (GHC.Prim.State# (Control.Monad.Primitive.TFCo:R:PrimStateST <s_a1Y9>) :: GHC.Prim.State# (Control.Monad.Primitive.PrimState (GHC.ST.ST s_a1Y9)) ~ GHC.Prim.State# (Control.Monad.Primitive.R:PrimStateST s_a1Y9))) }; } in So my question is, what happens to the ()'s after this stage? Since they're not used, and also expressed as literals in core (both in the recursive case and the original call site of $s$wa_s2OL, is the backend smart enough to get rid of them completely? Thanks for any advice, John L.

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Really Simple explanation of Continuations Needed
by Mark Spezzano 05 Oct '11

05 Oct '11

Hi, Can someone please give me a _lucid_ and _simple_ explanation of exactly how continuations can be used in Haskell? I've already had a look at most of the tutorials and explanations on the web, but I'm still confused. Continuations and CPS have me baffled. (I have most of the Haskell textbooks and even these are sketchy on Continuations) I don't understand the notion of the Cont monad and how it can be used for multitasking, backtracking and interrupting computations. I understand that functions take in a (continuation) function that represents the work remaining to do, but al of the explanations on the web and in technical papers seems to trip over themselves in explaining the fundamentals to a CPS-newbie. If anyone could explain such concepts to me in unambiguous, clear English then this would be very helpful. Thanks in advance for your help, Mark

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