February 2013 - Haskell-Cafe

A list of Haskell-related quotes?
by Petr Pudlák 06 Feb '13

06 Feb '13

Dear haskellers, over the time I've read many funny or inspiring quotes related to Haskell, but I forgot them later. For example I vaguely remember: - "What I really like about Haskell: It's completely unlike PHP." - "To learn Haskell your brain will have to get seriously rewired." Does anybody collect them or know about such a collection? Thanks, Petr Pudlak

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Re: [Haskell-cafe] How far compilers are allowed to go with optimizations?
by Artyom Kazak 06 Feb '13

06 Feb '13

Ouch, forgot the Cafe. Would you object to this particular optimisation (replacing an algorithm with an entirely different one) if you were guaranteed that the space behaviour would not change?

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Next Meetup
by Christopher Olah 05 Feb '13

05 Feb '13

Hey All, I think we were planning on meeting on the second Wednesday of this month (Feb 13) but Hacklab has a members meeting that day. How do people feel about the 14th or 15th? Chris

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CfP: OdHac (Haskell Hackathon)
by Roman Cheplyaka 05 Feb '13

05 Feb '13

------------------------------------------------------------------------ OdHac International Haskell Hackathon May 3-5, 2013 Odessa, Ukraine http://haskell.org/haskellwiki/OdHac Co-organized with Provectus IT ------------------------------------------------------------------------ We are pleased to announce the upcoming Haskell Hackathon! The event will be held over 3 days, May 3-5, in Odessa, Ukraine. This is a great opportunity to meet your fellow haskellers in real life, find new contributors for your project, improve existing libraries and tools or even start new ones! To attend, please register at http://bit.ly/OdHacReg. Please propose projects at http://www.haskell.org/haskellwiki/OdHac/Projects Consider participating in our accommodation program: http://www.haskell.org/haskellwiki/OdHac/Accommodation

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Video! Duncan Coutts on Cloud Haskell
by Theo 05 Feb '13

05 Feb '13

Back in October 2012 Well-Typed and Haskell expert Duncan Coutts delivered a talk on 'Cloud Haskell' at the 2K12 edition of the Haskell eXchange. Cloud Haskell takes Erlang's successful approach to distributed concurrency and implements it in Haskell as a library. We will look at what this means and what possibilities it opens up. You should also get a flavour of what distributed programming in Haskell is like. The initial Cloud Haskell idea and a prototype implementation were introduced last year. Since then we have been working on a new from-scratch implementation with a focus on robustness and flexibility Watch the video on the Skills Matter website - http://bit.ly/VB9tcy

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Re: [Haskell-cafe] FFI - Approaches to C/C++
by Casey Basichis 05 Feb '13

05 Feb '13

Hi Ertugrul, I'm not entirely sure what you mean. I'm intending on using Ogre for GUI - for which there is the Hogre bindings, but after emailing the DEV about it, I didn't get the impression from his advice that I should be using it for production code. Here is what he suggested: "It depends, really. Hogre is good for running Ogre from within Haskell, but it has its limitations. The number one thing people have been struggling with is handling input with hogre - there's Hois (Haskell wrapper for OIS) but it's not perfect (it misses input events), and the other option is having to write some C++ glue. Hogre is a solid proof of concept and you can do some demos with it, but if you're e.g. writing a game it might be a bit of a struggle. In the end it's about how much you value being able to write code in Haskell (or how allergic to C++ you are)." I'm on iOS so I imagine those difficulties are compounded. I am using several other C++ libraries for which there are no existing bindings and no Haskell alternative packages that are even remotely close. Are you suggesting it would be better to write all my own FFI bindings for all the needed libraries? Everything I read suggests that Haskells strengths are in transformation and that interaction is not its strong suit. I am interested in your thoughts and I am open to whatever, but you are the first to suggest that the mix is a bad idea. Thanks, Casey >>* I'm working on a project in Haskell and C++ where the former is the*>>* brains and the latter is for UI, interaction etc.* >That's a rather odd choice. Not exactly answering your question, but >questioning your project decisions, why would you do UI and interaction >in C++? You have the necessary Haskell bindings and libraries to write >everything cleanly in Haskell. > > >Greets, >Ertugrul

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haskell build phase is very slow
by Junior White 04 Feb '13

04 Feb '13

Hi Cafe, I came from the C/C++ world, recently I play with a haskell editor named yi-editor, I find haskell build phase is very slow: 1.Compile one .hs file is slow 2. When change a little, it will recompile many many files Compare to c, compile a c source file seems much quick then compile a haskell source file. And if i change a .c file, it only recompile the file i changed, and relink, it's awesome. How can i make my build phase more quick? Thanks!

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<package>-inplace is shadowed by package <package>-<hexstring>
by Alexander Bernauer 04 Feb '13

04 Feb '13

Hi I am trying to write criterion benchmarks for the pretty library. Unfortunately, building the benchmark executable fails at some point during the development with the following error message: ---8<--- <command line>: cannot satisfy -package-id pretty-1.1.1.1-inplace: pretty-1.1.1.1-inplace is shadowed by package pretty-1.1.1.1-7bd0114e9691fca3d3447fc0133701cf --->8--- I don't understand the cause of the error, let alone what I am supposed to do next. Any help is much appreciated. Here are the steps that lead to the above quoted error. Sorry, if this is not the smallest counter example possible. As I said, I hardly understand what is going on. (the two patch files mentioned are attached to this email, virthualenv is version 0.2.1) ---8<--- git clone https://github.com/haskell/pretty.git cd pretty git apply /tmp/0001-hello-world-setup.patch export PATH=/opt/ghc-7.4.2/install/bin:/opt/haskell-platform-2012.4.0.0/install/bin:$PATH ~/.cabal/bin/virthualenv source .virthualenv/bin/activate cabal configure --user cabal build cabal install cabal install criterion cabal configure --user --enable-benchmarks cabal build git apply /tmp/0002-replaced-example-with-real-benchmark.patch cabal install language-c cabal configure --user --enable-benchmarks cabal build # error --->8--- So the first build of the benchmark executable works, but the second one "suddenly" fails. Executing "cabal build -v" next yields ---8<--- $ cabal build -v creating dist/build creating dist/build/autogen Building pretty-1.1.1.1... Preprocessing library pretty-1.1.1.1... Building library... creating dist/build /opt/ghc-7.4.2/install/bin/ghc --make -package-name pretty-1.1.1.1 -hide-all-packages -fbuilding-cabal-package -package-conf /home/alex/tmp/pretty/.virthualenv/ghc_pkg_db -i -idist/build -isrc -idist/build/autogen -Idist/build/autogen -Idist/build -optP-include -optPdist/build/autogen/cabal_macros.h -odir dist/build -hidir dist/build -stubdir dist/build -package-id base-4.5.1.0-66f22db3dfcd87541c9c7e50e7095d26 -O -Wall -fwarn-tabs -XHaskell98 -XCPP -XBangPatterns Text.PrettyPrint Text.PrettyPrint.HughesPJ Linking... /usr/bin/ar -r dist/build/libHSpretty-1.1.1.1.a dist/build/Text/PrettyPrint.o dist/build/Text/PrettyPrint/HughesPJ.o /usr/bin/ar: creating dist/build/libHSpretty-1.1.1.1.a /usr/bin/ld -x --hash-size=31 --reduce-memory-overheads -r -o dist/build/HSpretty-1.1.1.1.o dist/build/Text/PrettyPrint.o dist/build/Text/PrettyPrint/HughesPJ.o Registering pretty-1.1.1.1... /opt/ghc-7.4.2/install/bin/ghc-pkg update - --global --user --package-conf=/home/alex/tmp/pretty/.virthualenv/ghc_pkg_db --package-conf=dist/package.conf.inplace Preprocessing benchmark 'bench-pretty' for pretty-1.1.1.1... Building benchmark bench-pretty... creating dist/build/bench-pretty creating dist/build/bench-pretty/bench-pretty-tmp /opt/ghc-7.4.2/install/bin/ghc --make -o dist/build/bench-pretty/bench-pretty -hide-all-packages -fbuilding-cabal-package -package-conf /home/alex/tmp/pretty/.virthualenv/ghc_pkg_db -package-conf dist/package.conf.inplace -i -idist/build/bench-pretty/bench-pretty-tmp -ibench -idist/build/autogen -Idist/build/autogen -Idist/build/bench-pretty/bench-pretty-tmp -optP-include -optPdist/build/autogen/cabal_macros.h -odir dist/build/bench-pretty/bench-pretty-tmp -hidir dist/build/bench-pretty/bench-pretty-tmp -stubdir dist/build/bench-pretty/bench-pretty-tmp -package-id base-4.5.1.0-66f22db3dfcd87541c9c7e50e7095d26 -package-id criterion-0.6.2.1-5ae981935ea0c9773e0df464b5922b27 -package-id language-c-0.4.2-fe58279e43af097994ce7b7010785c69 -package-id pretty-1.1.1.1-inplace -O -O -XHaskell98 bench/Bench.hs <command line>: cannot satisfy -package-id pretty-1.1.1.1-inplace: pretty-1.1.1.1-inplace is shadowed by package pretty-1.1.1.1-7bd0114e9691fca3d3447fc0133701cf (use -v for more information) --->8--- What does this mean? What am I doing wrong? How can I fix this? Greetings, Alex

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Text.PrettyPrint.HughesPJ is sloooow (and wl-pprint-text is fast)
by Johannes Waldmann 04 Feb '13

04 Feb '13

I was running into serious performance problems when printing moderately sized Doc and Xml data (HaXml goes via Doc). So I replace Text.PrettyPrint.HughesPJ with Text.PrettyPrint.Leijen.Text, and patched the HaXml printer in the same way. Now it is running much faster. This confirms some of the comments here: http://stackoverflow.com/questions/9761507/which-pretty-print-library If you want to see for yourself, here is a test case. It constructs and prints a document tree with about 10^4 nodes, rendered to an Xml document with 10^6 (nonblank) chars: https://github.com/jwaldmann/haskell-tpdb/blob/master/test/speed.hs Of the 4 output methods (fin the main program), only one takes < 1 second. Rendering via HughesPJ needs extra stack (!) and takes about 20 seconds. Rendering via Text.XML.HaXml.ByteStringPP seems much slower still (!) (ghc-7.6.2, pretty-1.1.1.0, HaXml-1.23.3, wl-pprint-text-1.1.0.0, amd64, fedora 18, kernel 3.7.4)

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Problems with code blocks in the description field in a .cabal file
by Josef Svenningsson 04 Feb '13

04 Feb '13

Hi, I'm putting together a cabal package and I'd like to have some code examples in my description file. In particular I would like to have a code block containing markdown containing a code block of Haskell, like this: > ~~~{ .haskell } > module Main where > > main = putStrLn "Hello World!" > ~~~ When I put the above code in my .cabal file and do `cabal haddock --executables` I get the following error: haddock: failed to parse haddock prologue from file: dist/doc/html/codeExtract/codeExtract/haddock-prolog31969.txt In general I can provoke the parse error from haddock whenever I have something inside curly braces. So the error seems to stem from haddock. I've tried to track down what happens inside haddock but I've run out steam. I'd like to know if there is anything I can do to be able to write something like the above as part of the description in my .cabal file. Thanks, Josef

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