October 2011 - Haskell-Cafe

Will changing associativity of enumerator's ($=) affect anyone? (also: enumerator mailing list)
by John Millikin 23 Oct '11

23 Oct '11

A user recently suggested changing the associativity of ($=) from [[ infixr 0 ]] to [[ infixl 1 ]]. This allows the following expressions to be equivalent: run $ enumerator $$ enumeratee =$ enumeratee =$ iteratee run $ enumerator $= enumeratee $$ enumeratee =$ iteratee run $ enumerator $= enumeratee $= enumeratee $$ iteratee Although this is technically a backward-incompatible change, I feel it's small enough that it could go in a minor release *if nobody depends on the current behavior*. So, if anybody using 'enumerator' will have code broken by this change, please speak up. If I don't hear anything in a week or so, I'll assume it's all clear and will cut the new release. ------------------------- Second, I was asked whether there's a mailing list for enumerator stuff. To my knowledge there isn't, so I started one on librelist. To subscribe and/or post, send an email to haskell.enumerator(a)librelist.com . Archives are available at http://librelist.com/browser/haskell.enumerator/ . I plan to make release announcements there (for releases not important enough for haskell-cafe), and it might be useful for general discussion.

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SpecConstr message while compiling
by Daniel Díaz Casanueva 23 Oct '11

23 Oct '11

Hi, cafe! I wrote a program and had the following message while compiling (with -O2): SpecConstr Function `addOc{v s6RL} [lid]' has four call patterns, but the limit is 3 Use -fspec-constr-count=n to set the bound Use -dppr-debug to see specialisations What it means? Is it bad? It only happens when compiling with -O2. addOc is a local function (defined in a where clause). If it helps, here is the definition: addOc x [] = [(x,1)] addOc x ((y,n):ys) = if x == y then (y,n+1) : ys else (y,n) : addOc x ys I want to know if there is something wrong or a I don't need to take care about this. Thanks in advance, Daniel Díaz.

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Problem installing svgcairo
by Roly Perera 23 Oct '11

23 Oct '11

Hi, I'm having a problem installing svgcairo with Cabal, which I need for something else. I don't know what's going on, but something (maybe a C preprocessor, judging by Google search results) barfs with the complaint: ./Graphics/Rendering/Cairo/SVG.chs:209:28: error: missing binary operator before token "(" I can't find the file SVG.chs on my system to inspect this line, but perhaps I'm looking in the wrong place. Has anyone encountered this? Am I perhaps using the wrong version of Cairo or Gtk? Any suggestions welcome. thanks Roly ====== $ cabal install svgcairo Resolving dependencies... [1 of 2] Compiling SetupWrapper ( /tmp/svgcairo-0.12.125554/svgcairo-0.12.1/SetupWrapper.hs, /tmp/svgcairo-0.12.125554/svgcairo-0.12.1/dist/setup/SetupWrapper.o ) [2 of 2] Compiling Main ( /tmp/svgcairo-0.12.125554/svgcairo-0.12.1/Setup.hs, /tmp/svgcairo-0.12.125554/svgcairo-0.12.1/dist/setup/Main.o ) Linking /tmp/svgcairo-0.12.125554/svgcairo-0.12.1/dist/setup/setup ... [1 of 2] Compiling Gtk2HsSetup ( Gtk2HsSetup.hs, dist/setup-wrapper/Gtk2HsSetup.o ) [2 of 2] Compiling Main ( SetupMain.hs, dist/setup-wrapper/Main.o ) Linking dist/setup-wrapper/setup ... Configuring svgcairo-0.12.1... Preprocessing library svgcairo-0.12.1... ./Graphics/Rendering/Cairo/SVG.chs:209:28: error: missing binary operator before token "(" gtk2hsC2hs: Error during preprocessing chs file cabal: Error: some packages failed to install: svgcairo-0.12.1 failed during the building phase. The exception was: ExitFailure 1

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Web API attempt: Thrift + Evernote API -- apparent brick wall: HTTPS support
by Ryan Newton 23 Oct '11

23 Oct '11

Hi all, An old fogey here -- new to this world of web APIs / rpc over HTTP. I was thinking that since Thrift supports Haskell that it wouldn't be to hard to plug my Haskell program into the Thrift-based Evernote API to upload notes to the cloud. The first step to do that would be to authenticate: http://www.evernote.com/about/developer/api/evernote-api.htm#_Toc297053064 Uh, oh! Trouble already. You must use THttpClient to connect using HTTPS! It looks like the Thrift library for Haskell doesn't offer that option (plain HttpClient only). Presumably because the package HTTP doesn't support https? http://stackoverflow.com/questions/3988115/haskell-network-browser-https-co… Is there a way that libcurl could be used to provide THttpClient? I don't know enough to say... More generally, my problem is that it hard to figure out how to use Thrift from Haskell. Simple examples like this are helpful: http://mortenib.wordpress.com/2009/10/29/thrift-and-haskell/ But the Thrift library itself lacks full Haddock documentation: http://hackage.haskell.org/package/Thrift-0.6.0 And the generated Thrift code doesn't restrict its export lists to give you a hint as to what the "entry points" are. This is not to blame the thrift authors. They have N languages to support! But for someone with some extra time from the Haskell community, it seems like there would be some good return-on-investment for effort spent cleaning up the Haskell Thrift support. Maybe this is what Christian Lavoie is already doing? (http://hackage.haskell.org/package/thrift) Cheers, -Ryan P.S. One final note in the language-interop department. Since OCaml is supported by SWIG, Haskell should be too! Manuel's caveats notwithstanding: http://www.haskell.org/pipermail/c2hs/2003-May/000016.html

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Data.Vector.Mutable.mapM
by Joachim Breitner 23 Oct '11

23 Oct '11

Hi, I’m consdering to change some performance critical code from Vector to MVector, hopefully avoiding a lot of copying and garbage collecting. But it seems that the Data.Vector.Mutable interface at http://hackage.haskell.org/packages/archive/vector/0.9/doc/html/Data-Vector… is quite limited; e.g. I am missing simple functions having type modifyM :: PrimMonad m => (a -> m a) -> MVector (PrimState m) a -> m () that would do something with each element in the vector. Is this an indication that such use is actually not desired, or is it just the case that nobody has developed that yet? Thanks, 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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hackage and cabal test support: why does it claim I have no type field when I do?
by Doug Burke 22 Oct '11

22 Oct '11

I've just been updating my code to take advantage of the test support in Cabal. I have it so that cabal configure --enable-tests cabal build cabal test works. However, when I try to upload to hackage, I get cabal upload -c dist/swish-0.6.2.0.tar.gz Checking dist/swish-0.6.2.0.tar.gz... Error: dist/swish-0.6.2.0.tar.gz: 400 Error in upload 400 Error in upload line 271: The 'type' field is required for test suites. The available test types are: exitcode-stdio-1.0 and here are the relevant lines from the cabal file: 267 if flag(developer) 268 ghc-options: -Werror 269 ghc-prof-options: -auto-all 270 271 Test-Suite test-builtinmap 272 type: exitcode-stdio-1.0 273 Hs-Source-Dirs: tests/ src/ 274 Main-Is: BuiltInMapTest.hs 275 Other-Modules: TestHelpers 276 As you can see, there's a type field for the Test-Suite and I don't see any obvious discrepancy with the information from the user's guide (http://www.haskell.org/cabal/users-guide/#test-suites) I also have Cabal-Version: >= 1.9.2 in the file; the full version can be found at https://bitbucket.org/doug_burke/swish/src/4545220d88e2/swish.cabal#cl-271 What am I doing wrong? Thanks in advance, Doug

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runStateT execution times measurement baffling
by thomas burt 22 Oct '11

22 Oct '11

Hello - I've been trying to measure execution time for some code I'm running with the StateT monad transformer. I have a function f :: StateT MyState IO a Now, I measure the time it takes to run an invocation of this function from beginning to end, i.e. f = do t0 <- getCurrentTime stuffToDo t1 <- getCurrentTime liftIO $ putStrLn (show $ diffUTCTime t1 t0) And also measure like this: g :: IO g = do t0 <- getCurrentTime (val,newState) <- runStateT f initialState t1 <- getCurrentTime putStrLn $ "outside: " ++ (show $ diffUTCTime t1 t0) Curiously, the times reported for "outside" are about 5-8 times as long. I should probably note that stuffToDo calls itself a few hundred times (and uses liftIO once per loop). Anyone with ideas on why runStateT apparently has so much overhead? By the way I'm using ghc-6.10.4 and Control.Monad.Trans.State.Strict. Thanks for any suggestions or advice. Thomas

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Haddock fails on ConfigFile, but why?
by Magnus Therning 22 Oct '11

22 Oct '11

Would love to get some help on making Haddock accept ConfigFile[1]. The error message is about as far from helpful as you can get ;) dist/build/tmp-15743/src/Data/ConfigFile/Monadic.hs:34:1: parse error on input `import' The author is informed but is as confused as me, it seems[2]. /M [1] http://hackage.haskell.org/package/ConfigFile [2] https://github.com/jgoerzen/configfile/issues/4 -- Magnus Therning OpenPGP: 0xAB4DFBA4 email: magnus(a)therning.org jabber: magnus(a)therning.org twitter: magthe http://therning.org/magnus Most software today is very much like an Egyptian pyramid with millions of bricks piled on top of each other, with no structural integrity, but just done by brute force and thousands of slaves. -- Alan Kay

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What is the etiquette for posting to multiple forums?
by Michael Litchard 21 Oct '11

21 Oct '11

I know it's bad form to post the same question to multiple mailing lists. But what about say, the beginner's mailing list and stackoverflow.com?

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ANN: OpenCL 1.0.1.3 package
by Luis Cabellos 21 Oct '11

21 Oct '11

Hello, all. I want to show you the OpenCL package. I have done this using Jeff Heard OpenCLRaw package, but I create a new one due the lack of updates of the former. # 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) * Examples (https://github.com/zhensydow/opencl/tree/master/examples) # Things: * I write it's high-level binding to OpenCL libraries, but only because I added more types to hide most of the alloc/free of the API, and hide the enums using c2hs enums. * The worst problem of the OpenCLRaw is the bad types it use, I learn to fix 32/64 bits issues with c2hs, and test it on linux machines. * Tested on Linux + NVidia only. * Jason Dagit is helping with Windows, OSX testing in own fork, also the call-conv fork in github has changes to work on Windows Please, Consider it's on experimental status but it works, I need lots of feedbacks for detect posible errors, Thanks,

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