September 2011 - Haskell-Cafe

Parsing workflow
by Nils Schweinsberg 21 Jan '12

21 Jan '12

Hi! I'm having a really hard time to write a correct parser for a small language I've developed. I have been trying to write a parser using parsec, but always get a lot of error messages like "unexpected "\n", expected ..., new-line or..." when trying to run the parser. Then I read about the happy parser and really liked the separation of lexing the text into tokens and parsing the actual logic behind those tokens. Since I couldn't get familiar with the lexer "alex" I gave up on the alex-happy-approach again and went back to parsec. But with that lexer->parser idea on my mind, my parser currently looks a lot like a lexer. So I came up with the idea of using a combination of parsec and happy, where I generate a list of tokens for my text via parsec and analyse it with happy. My questions would be: - Is this a valid approach? - What is your workflow on parsing complex data structures? - What about performance? Since my project is going to be an interpreted language parsing performance might be interesting aswell. I've read that happy is in general faster than parsec, but what if I combine both of them as I said above? I guess that parsing a simple list of tokens without any nested parser structures would be pretty fast? - Do you have any other ideas on how to improve my parser? - What are your general thoughts on happy vs. parsec? Thanks for any replies, Nils

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Proposal to incorporate Haskell.org
by Don Stewart 16 Dec '11

16 Dec '11

Hello everyone. The haskell.org committee[1], in the interest of the long-term stability of the open source Haskell community infrastructure, has decided to incorporate haskell.org as a legal entity. This email outlines our recommendation, and seeks input from the community on this decision. The committee's proposal is that haskell.org incorporate as an entity under the Software Freedom Conservancy umbrella organization (the same group that Darcs joined recently): http://sfconservancy.org/ If we proceed with this move, haskell.org will be a legal entity, and registered as a non-profit, allowing us to more directly accept (US tax-deductible) donations, and to invest in assets that benefit the Haskell open source community. We welcome your feedback on the proposal attached below. -- Don Stewart (on behalf of the Haskell.org committee) ------------------------------------------------------------------------ = A proposal for the incorporation of Haskell.org = In recent years, haskell.org has started to receive assets, e.g. money from Google Summer Of Code, donations for Hackathons, and a Sparc machine for use in GHC development. We have also started spending this money: in particular, on hosting haskell.org itself. There is also interest in running fundraising drives for specific things such as Hackathon sponsorship and hosting fees. However, haskell.org doesn't currently exist as a legal entity, meaning that these assets have had to be held on our behalf by other entities, such as Galois and various universities. This leads to tricky situations, with no-one being sure who should decide how the haskell.org assets can be used. To solve these problems, we propose that haskell.org applies to become a member project of the Software Freedom Conservancy (SFC) <http://conservancy.softwarefreedom.org/>. The SFC is a non-profit organization that provides free financial and administrative services to open source projects. Additionally, it has 501(c)(3) status, meaning donations from the US are tax-deductible. The SFC would hold haskell.org's money and other assets, and would be able to accept donations on behalf of haskell.org. The haskell.org committee, as described here [2], will make decisions on spending assets and other decisions related to governing the non-profit. Before proceeding, we are inviting input from the community in the form of specific objections or queries regarding the plan. We've tried to answer some of the most likely questions: Q: Does this mean that my Haskell project must now be covered by a copyleft licence such as GPL? A: No, but Haskell projects using haskell.org resource should use an Open Source licence <http://www.opensource.org/licenses/alphabetical>. Q: Will it still be possible to use community.h.o to host non-open-source material, such as academic papers? A: An overall minority of such content, as is the current situation, is not a problem. Q: Will it still be possible to have job ads on the haskell.org mailing lists and website? A: Yes. Q: Will this affect our ability to host the Haskell Symposium <http://www.haskell.org/haskell-symposium/> and Industrial Haskell Group<http://industry.haskell.org/> webpages within haskell.org? A: No. Q: What will be the relationship between haskell.org and other organizations such as the Haskell Symposium and Industrial Haskell Group? A: Those organisations will continue to exist as separate entities. Q: If an umbrella non-profit organisation "The Haskell Foundation" was created, would haskell.org be able to join it? A: Yes. It's likely that in such a scenario, the Haskell Foundation would become the owner of the haskell.org domain name, with the cost divided between the members. The entity that is part of the SFC would be renamed "community.haskell.org" in order to avoid confusion. [1]: http://www.haskell.org/haskellwiki/Haskell.org_committee [2]: http://www.haskell.org/haskellwiki/Haskell.org_committee#Operation

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Hexpat: Lazy I/O problem with huge input files
by Aleksandar Dimitrov 10 Dec '11

10 Dec '11

Hello Haskell Cafe, I really hope this is the right list for this sort of question. I've bugged the folks in #haskell, they say go here, so I'm turning to you. I want to use Hexpat to read in some humongous XML files (linguistic corpora,) since it's the only Haskell XML library (I could find) that takes ByteStrings as input. I stumbled on a problem when using one of the examples from the docs of Text.XML.Expat.Tree. The "cookbook recipe" there suggests *first* processing the data, and only then looking into the parser error to see if there has been an error. I understand this should prevent the parse tree from being fully evaluated before use. Unfortunately, that is not what happens on my system (ghc 6.12.1, if that's of importance.) This is the code from the docs, that I modified to read files: > import Text.XML.Expat.Tree > import System.Environment (getArgs) > import Control.Monad (liftM) > import qualified Data.ByteString.Lazy as C >· > -- This is the recommended way to handle errors in lazy parses > main = do > f <- liftM head getArgs >>= C.readFile > let (tree, mError) = parse defaultParseOptions f > print (tree :: UNode String) >· > -- Note: We check the error _after_ we have finished our processing > -- on the tree. > case mError of > Just err -> putStrLn $ "It failed : "++show err > Nothing -> putStrLn "Success!" Given a 42M test file, an invocation like this: % ghc --make -O2 Hexpat.hs % ./Hexpat input.xml > dump.xml will gobble up some 2Gigs of RAM (at least. I usually kill it before it starts thrashing the swap space, since that almost crashes my entire machine.) If I remove the last 3 lines: > import Text.XML.Expat.Tree > import System.Environment (getArgs) > import Control.Monad (liftM) > import qualified Data.ByteString.Lazy as C > > main = do > f <- liftM head getArgs >>= C.readFile > let (tree, mError) = parse defaultParseOptions f > print (tree :: UNode String) the same invocation and input file barely uses a megabyte or two of RAM and finishes really quickly. Why is that? Is this a mistake in the Hexpat docs, or am I doing something wrong? Lazy IO has always been a little bit of a mystery to me, and just when I thought I had it... Thanks for any help on the matter! Aleks

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doctest: Interpreter exited with an error: ExitFailure 127
by informationen 16 Nov '11

16 Nov '11

Hi, i have upgraded to doctest version 0.4.1. Now when i try to run the example from the webpage, i get: doctest: Interpreter exited with an error: ExitFailure 127 What's wrong here and how can i fix it? Kind regards Chris This is the content of Fib.hs: module Fib where -- | Compute Fibonacci numbers -- -- Examples: -- -- >>> fib 10 -- 55 -- -- >>> fib 5 -- 5 fib 0 = 0 fib 1 = 1 fib n = fib (n - 1) + fib (n - 2) main = do print $ fib 4

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haskell i18n best practices
by Paulo Pocinho 11 Oct '11

11 Oct '11

Hello list. I've been trying to figure a nice method to provide localisation. An application is deployed using a conventional installer. The end-user is not required to have the Haskell runtimes, compiler or platform. The application should bundle ready to use translation data. What I am after is simple; an intuitive way that an interested translator, with little knowledge of Haskell, can look at and create valid translation data. This is what I've been looking at lately. The first thing I noticed was the GNU gettext implementation for Haskell. The wiki page [1] has a nice explanation by Aufheben. The hgettext package is found here [2]. I don't know if this is a bad habit, but I had already separated the dialogue text in the code with variables holding the respective strings. At this time, I thought there could be some other way than gettext. Then I figured how to import localisation data, that the program loads, from external files. The data type is basically a tuple with variable-names associated with strings. This is bit like the file-embed package [3]. Still uncomfortable with i18n, I learned about the article "I18N in Haskell" in yesod blog [4]. I'd like to hear more about it. What is considered the best practice for localisation? -- [1] http://www.haskell.org/haskellwiki/Internationalization_of_Haskell_programs [2] http://hackage.haskell.org/packages/archive/hgettext/ [3] http://hackage.haskell.org/package/file-embed [4] http://www.yesodweb.com/blog/2011/01/i18n-in-haskell

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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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CAL or Frege as a Haskell replacement on JVM?
by Karel Gardas 04 Oct '11

04 Oct '11

Hello, since there is no Haskell compiler/interpreter for JVM yet (considering LambdaVM outdated), then the question for kind of Haskell replacement on this platform is either CAL[1] or Frege[2]. I'd like to ask here those who have used either of those languages for your experience with it/them, what's more similar to Haskell (at least from your point of view) and what you like more as a Haskell replacement on JVM. Thanks! Karel [1]: http://openquark.org/Welcome.html [2]: http://code.google.com/p/frege/

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ANN: Peggy 0.2.1
by Hideyuki Tanaka 02 Oct '11

02 Oct '11

Hello, all. I have released 'Peggy' a new parser generator . It is based on Parsing Expression Grammer (PEG) [1], and generates efficient packrat parsers. # Where to get it * Hackage page (http://hackage.haskell.org/package/peggy) * github repository (https://github.com/tanakh/peggy) * Some documents are at (http://tanakh.github.com/Peggy/) # Advantage * Simple and Powerful syntax * No shift/reduce conflict * Unlimited look-ahead * You don't need to prepare separated Scanner * Linear time complexity * Based on modern Haskell ecosystem (bytestring, text, ListLike, Monads, etc...) * Support to use and generate Quasi Quoters # Examples Here are few example of parsers: * http://tanakh.github.com/Peggy/example.html * https://github.com/tanakh/Peggy/blob/master/example/Json.hs There is a self defined parser of peggy syntax, used for bootstrapping: * https://github.com/tanakh/Peggy/blob/master/bootstrap/peggy.peggy Please try it and give me feedbacks! Thanks, [1]: http://en.wikipedia.org/wiki/Parsing_expression_grammar -- Hideyuki Tanaka

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ANNOUNCE: GA-1.0, a library for working with genetic algorithms
by Kenneth Hoste 01 Oct '11

01 Oct '11

Hello, I'm proud to announce the v1.0 release of GA [1], my library for working with genetic algorithms in Haskell. Source repo is available on github. [2] This is a major version bump compared to the previous v0.2 release, because the library is pretty mature now in my view. Major features: * flexible user-friendly API for working with genetic algorithms * Entity type class to let user define entity definition, scoring, etc. * abstraction over monad, resulting in a powerful yet simple interface * support for scoring entire population at once * support for checkpointing each generation, and restoring from last checkpoint * convergence detection, as defined by user * also available: random searching, user-defined progress output * illustrative toy examples included I'm happy to take any questions or suggestions that you might have. [1] http://hackage.haskell.org/package/GA [2] https://github.com/boegel/GA

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Build local-gc branch of GHC
by Andreas Voellmy 01 Oct '11

01 Oct '11

Hi, I've been trying to get and build a branch of ghc that includes the new local GC algorithm ( http://www.haskell.org/pipermail/cvs-ghc/2011-June/062748.html) but I haven't been able to build it successfully. Here is what I've done: 1. Got the latest source tree using these commands: $ git clone http://darcs.haskell.org/ghc.git/ $ cd ghc $ ./sync-all --testsuite get 2. Use 'fingerprint' script to get the state of the repository for the branch mentioned in the web page I mentioned above. A fingerprint file based on the announcement above fails due to some problem with binary and haddock change sets not being found. So I modified the fingerprint to use the latest versions for binary and deleted the change for haddock entirely. I ran this command: ./utils/fingerprint/fingerprint.py restore -f local-gc.fp and my local-gc.fp fingerprint file contains this: .|ab5aad587de8e3d9dde539982ae728b33e5bca50 ghc-tarballs|e7b7b152083f7c3e3559e557a239757d41ac02a6 libraries/Cabal|6f01f56a2702b50e2da909566c4a01622cb2ca7f libraries/Win32|0cf603103e9ad3fccd862171ba5e689b87930622 libraries/array|e4b4e2e0a79f4138bdff4f10d263436b0155f449 libraries/base|be2750a0a11b919fb03cc070074e430f88bdfa90 libraries/binary|376797487651cf995bd52458ce1f7d7a283341b3 libraries/bytestring|cab9d8566fba8611598f14fb4f2ac7b8d4aae75b libraries/containers|592f6d9da9090e8d53432f22a01bb117fea2246c libraries/deepseq|91e8a93b15ed32af3941f81e927291a023feb369 libraries/directory|3a0f2e2cb94c3e4f346023acc7201409d2876ed8 libraries/extensible-exceptions|a667b48d0cb6469b6611cb516d16836aa002e782 libraries/filepath|92d211a2752fe8827582ae0d97efd18722ad3d87 libraries/ghc-prim|7fcfc880853fa399c9468049aeb14e6eadb9eae5 libraries/haskeline|125ee5bba59fa9ac2fd77aa3922c30dffc11b7b5 libraries/haskell2010|f90687bee55adfd693fe460f2ab4bc270a7f97e3 libraries/haskell98|eb655b0317665acb9670025480b4af4465bc8f55 libraries/hoopl|0febb7f04ff4326bd120fc75549845e5e9678d72 libraries/hpc|fce8babbc3f60fb195d84545753dc342422ab8e1 libraries/integer-gmp|2567c97aaa467cb676a6ecc2cf840c92ee1cb6ec libraries/integer-simple|c3e9c0268b4d59895829e429d1ac767e6041b06a libraries/mtl|a748dfa2770af1d348dfaa8ad6955b25b4935711 libraries/old-locale|7f09f55ea3011c17c526805f099394a05ec9c3fe libraries/old-time|6aae8dc2f13cef6ab48c5436c6c0e7c1b5ae3f51 libraries/parallel|f82611fac439236e22a057cd555bb9fe393597b0 libraries/pretty|e00aa7e0f82fc6f13ad85f1b3a27f53efe473e60 libraries/process|d1c2999473ba0d4ceafdc6da309debca83f91abe libraries/random|ba8cb1b9fdfddeb29fdfedd8612c8ce85a987af8 libraries/stm|ccc6d74872916e5de7747df4cc61f64de64be591 libraries/template-haskell|acd4c3292d0f7a222a1f4f426054e4732a809fc8 libraries/terminfo|f4476f1881085b74dbe65cf4a4561e8fb34017d4 libraries/unix|c9a0bf119ce343b291bef77828066339e94fb64d libraries/utf8-string|d28cd1fbd4ebaaa0608c070bd02ed72dc9b70399 libraries/xhtml|9a4d7d64d0491a1844d5b5759275b029ccd1e2cd nofib|6d3ea16e56bd99d060e778fab3583aa67a6b50d4 testsuite|6560613138d61afddd0d8d428254370f8dfdb4cd utils/hsc2hs|c46eed44ce96f1719334ffb190eddf63695bc553 3. I then run $perl boot $./configure This succeeds telling me that it will be building ghc version 7.1.20110606. 4. Run make and it fails with this output: + test -f mk/config.mk.old + cp -p mk/config.mk mk/config.mk.old touch -r mk/config.mk.old mk/config.mk + test -f mk/project.mk.old + cp -p mk/project.mk mk/project.mk.old touch -r mk/project.mk.old mk/project.mk + test -f compiler/ghc.cabal.old + cp -p compiler/ghc.cabal compiler/ghc.cabal.old touch -r compiler/ghc.cabal.old compiler/ghc.cabal ===--- building phase 0 make -r --no-print-directory -f ghc.mk phase=0 phase_0_builds libraries/dph/ghc.mk:116: *** dph_th_deps(v,seq): libraries/dph/dph-base_dist-install_GHCI_LIB not defined!. Stop. make: *** [all] Error 2 5. I don't know how to fix this, so I tried deleting libraries/dph. Then I run make again, and get a ways through the build, and then get this error: "inplace/bin/ghc-stage1" -M -dep-makefile libraries/vector/dist-install/build/.depend-v-p-dyn.haskell.tmp -dep-suffix p -dep-suffix dyn -include-pkg-deps -H32m -O -package-name vector-0.8 -hide-all-packages -i -ilibraries/vector/. -ilibraries/vector/dist-install/build -ilibraries/vector/dist-install/build/autogen -Ilibraries/vector/dist-install/build -Ilibraries/vector/dist-install/build/autogen -Ilibraries/vector/include -Ilibraries/vector/internal -optP-DVECTOR_BOUNDS_CHECKS -optP-include -optPlibraries/vector/dist-install/build/autogen/cabal_macros.h -package base-4.3.1.0 -package primitive-0.4.0.1 -O2 -XHaskell98 -XCPP -XDeriveDataTypeable -O2 -no-user-package-conf -rtsopts -odir libraries/vector/dist-install/build -hidir libraries/vector/dist-install/build -stubdir libraries/vector/dist-install/build -hisuf hi -osuf o -hcsuf hc libraries/vector/./Data/Vector/Internal/Check.hs libraries/vector/./Data/Vector/Fusion/Util.hs libraries/vector/./Data/Vector/Fusion/Stream/Size.hs libraries/vector/./Data/Vector/Fusion/Stream/Monadic.hs libraries/vector/./Data/Vector/Fusion/Stream/Monadic/Safe.hs libraries/vector/./Data/Vector/Fusion/Stream.hs libraries/vector/./Data/Vector/Fusion/Stream/Safe.hs libraries/vector/./Data/Vector/Generic/Mutable.hs libraries/vector/./Data/Vector/Generic/Mutable/Safe.hs libraries/vector/./Data/Vector/Generic/Base.hs libraries/vector/./Data/Vector/Generic/New.hs libraries/vector/./Data/Vector/Generic/New/Safe.hs libraries/vector/./Data/Vector/Generic.hs libraries/vector/./Data/Vector/Generic/Safe.hs libraries/vector/./Data/Vector/Primitive/Mutable.hs libraries/vector/./Data/Vector/Primitive/Mutable/Safe.hs libraries/vector/./Data/Vector/Primitive.hs libraries/vector/./Data/Vector/Primitive/Safe.hs libraries/vector/./Data/Vector/Storable/Internal.hs libraries/vector/./Data/Vector/Storable/Mutable.hs libraries/vector/./Data/Vector/Storable.hs libraries/vector/./Data/Vector/Unboxed/Base.hs libraries/vector/./Data/Vector/Unboxed/Mutable.hs libraries/vector/./Data/Vector/Unboxed/Mutable/Safe.hs libraries/vector/./Data/Vector/Unboxed.hs libraries/vector/./Data/Vector/Unboxed/Safe.hs libraries/vector/./Data/Vector/Mutable.hs libraries/vector/./Data/Vector/Mutable/Safe.hs libraries/vector/./Data/Vector.hs libraries/vector/./Data/Vector/Safe.hs libraries/vector/Data/Vector/Fusion/Util.hs:4:14: Unsupported extension: Trustworthy make[1]: *** [libraries/vector/dist-install/build/.depend-v-p-dyn.haskell] Error 1 make: *** [all] Error 2 I deleted this library too, but my build errors just continued. After resolving a bunch of build errors in Haskell libraries, I started getting errors in the C files in the rts directory. While I could go on fixing these problems, it seems likely that I went wrong somewhere early on. Does anyone see where I went wrong? Did I use the various tools (git, sync-all, fingerprint, boot, configure, make) in the right order and way? Regards, Andreas

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