October 2012 - Haskell-Cafe

Monad.Reader #21 call for copy
by Edward Z. Yang 20 Oct '12

20 Oct '12

Call for Copy: The Monad.Reader - Issue 21 -------------------------------------------- Whether you're an established academic or have only just started learning Haskell, if you have something to say, please consider writing an article for The Monad.Reader! The submission deadline for Issue 21 will be: **Tuesday, January 1** The Monad.Reader ~~~~~~~~~~~~~~~~ The Monad.Reader is a electronic magazine about all things Haskell. It is less formal than journal, but somehow more enduring than a wiki- page. There have been a wide variety of articles: exciting code fragments, intriguing puzzles, book reviews, tutorials, and even half-baked research ideas. Submission Details ~~~~~~~~~~~~~~~~~~ Get in touch with me if you intend to submit something -- the sooner you let me know what you're up to, the better. Please submit articles for the next issue to me by e-mail (ezyang(a)mit.edu) Articles should be written according to the guidelines available from http://themonadreader.wordpress.com/contributing/ Please submit your article in PDF, together with any source files you used. The sources will be released together with the magazine under a BSD license. If you would like to submit an article, but have trouble with LaTeX please let me know and we'll work something out.

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Getting PID of a child process
by Jason Dusek 19 Oct '12

19 Oct '12

Hi All, Using `System.Process.runInteractiveProcess', I can start a process and get a handle to it: runInteractiveProcess :: FilePath -> [String] -> Maybe FilePath -> Maybe [(String, String)] -> IO (Handle, Handle, Handle, ProcessHandle) For diagnostic purposes, I'd like to print the PID of the process attached to this handle -- how best to do that? -- Jason Dusek pgp // solidsnack // C1EBC57DC55144F35460C8DF1FD4C6C1FED18A2B

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Release Candidate 2: HP 2014.4.0.0
by Mark Lentczner 19 Oct '12

19 Oct '12

Haskellistas - The second release candidate of HP 2014.4.0.0 is now available: - Source tarball: haskell-platform-2012.4.0.0-rc2.tar.gz<http://ozonehouse.com/mark/platform/haskell-platform-2012.4.0.0-rc2.tar.gz> - Mac 32-bit installer: Haskell Platform 2012.4.0.0 32bit rc2 signed.pkg<http://ozonehouse.com/mark/platform/Haskell%20Platform%202012.4.0.0%2032bit…> Mac notes: This version is now digitally signed by me, and so will install without fuss on OS X 10.8. I'll put up 64-bit version soon. - Mark Changes since RC1: TODO ---- [x] update vector and primitive versions (they had a point release to fix a bad bug, and the fix was very very simple) [x] remove Build.hs - it did all its work by shelling out anyway! [x] main .cabal file should not have versions commented out [x] this will require a way to extract the list of packages that need to be part of the source release [x] why not also extract the list of packages needed for core.packages [x] fix to build.hs (ticket #195) [x] bugs in build.sh (ticket #197) [x] build instructions in the tarball (ticket #207) [x] merge in shared library patch (ticket #198) MAC TODO -------- [x] mac cabal script needs to quote things with $HOME or ~ in them (ticket #192) [x] If the cabal command is "update" then the wrapper script shouldn't do an update the first time through! [x] sign Mac installers (ticket #203)

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acid-state audit trail
by Richard Wallace 19 Oct '12

19 Oct '12

Hey all, I've been looking at acid-state as a possible storage backend for an application. It looks like it fits my needs pretty damn well, but one thing that I'm curious about is if it is possible to get a list of "update events". You can obviously query for the current state, but it's not immediately apparent if you can see the history of your values state. This is useful in some things, like providing audit trails and debugging. As well as being able to re-create state in a different form. I was also curious if the createCheckpoint function eliminates the state history or does it just create a snapshot, it's not apparent from the docs. Thanks, Rich

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Adding custom events to eventlog
by Janek S. 19 Oct '12

19 Oct '12

Dear list, I'm using ThreadScope to improve performance of my parallel program. It would be very helpful for me if I could place custom things in eventlog (e.g. "now function x begins"). Is this possible? Janek

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Erroneous interaction between DataKinds and ExistentialQuantification?
by Stefan Holdermans 19 Oct '12

19 Oct '12

I am almost sure this is a known issue, but I noticed some erroneous (?) interaction between datatype promotion and existential quantification. Consider the following program: {-# LANGUAGE DataKinds #-} {-# LANGUAGE ExistentialQuantification #-} {-# LANGUAGE GADTs #-} {-# LANGUAGE KindSignatures #-} module Test where data K = forall a. T a -- promotion gives 'T :: * -> K data G :: K -> * where D :: G (T []) -- kind error! I would expect the type checker to reject it, but GHC (version 7.6.1) compiles it happily. Is this indeed a (known) bug? On a related note: is there a way to promote a type that involves an existential type variable of a kind other than *? Thanks, Stefan

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Build GHC to i386 platform represent an error after run command "make bootstrapping-files"
by Chatsiri Ratana 19 Oct '12

19 Oct '12

Hello All, I using GHC for x86_64 platform compiles the GHC source in order to port code to the i386 platform. Steps for building GHC to i386 platform at link[1]. Configure before initial other steps as completed follow by $./configure --enable-hc-boot --build=i386-unknown-linux --host=i386-unknown-linux --target=i386-unknown-linux --with-gcc=/usr/bin/gcc --with-ld=/usr/bin/ld --with-nm=/usr/bin/nm --with-ghc=/usr/lib/ghc/bin/ghc ---------------------------------------------------------------------- Configure completed successfully. Building GHC version : 7.7.20120806 Build platform : i386-unknown-linux Host platform : i386-unknown-linux Target platform : i386-unknown-linux Bootstrapping from HC files. Using GCC : /usr/bin/gcc which is version : 4.6.3 Building a cross compiler : NO Porting to foreign arch : NO Alien script : ld : /usr/bin/ld Happy : () Alex : () Python : /usr/bin/python Perl : /usr/bin/perl dblatex : xsltproc : HsColour was not found; documentation will not contain source links Building DocBook HTML documentation : NO Building DocBook PS documentation : NO Building DocBook PDF documentation : NO ---------------------------------------------------------------------- Next step for making executable file by command "make bootstrapping-files". It's show an error such as below. $ make bootstrapping-files make -r --no-print-directory -f ghc.mk bootstrapping-files /usr/bin/find: `libraries/ghc-prim/dist-install/build': No such file or directory /usr/bin/find: `libraries/ghc-prim/dist-install/build': No such file or directory /usr/bin/find: `libraries/integer-gmp/dist-install/build': No such file or directory /usr/bin/find: `libraries/integer-gmp/dist-install/build': No such file or directory /usr/bin/find: `libraries/base/dist-install/build': No such file or directory /usr/bin/find: `libraries/base/dist-install/build': No such file or directory /usr/bin/find: `libraries/filepath/dist-install/build': No such file or directory /usr/bin/find: `libraries/filepath/dist-install/build': No such file or directory /usr/bin/find: `libraries/array/dist-install/build': No such file or directory /usr/bin/find: `libraries/array/dist-install/build': No such file or directory /usr/bin/find: `libraries/deepseq/dist-install/build': No such file or directory /usr/bin/find: `libraries/deepseq/dist-install/build': No such file or directory /usr/bin/find: `libraries/bytestring/dist-install/build': No such file or directory /usr/bin/find: `libraries/bytestring/dist-install/build': No such file or directory /usr/bin/find: `libraries/containers/dist-install/build': No such file or directory /usr/bin/find: `libraries/containers/dist-install/build': No such file or directory /usr/bin/find: `libraries/old-locale/dist-install/build': No such file or directory /usr/bin/find: `libraries/old-locale/dist-install/build': No such file or directory /usr/bin/find: `libraries/old-time/dist-install/build': No such file or directory /usr/bin/find: `libraries/old-time/dist-install/build': No such file or directory /usr/bin/find: `libraries/time/dist-install/build': No such file or directory /usr/bin/find: `libraries/time/dist-install/build': No such file or directory /usr/bin/find: `libraries/unix/dist-install/build': No such file or directory /usr/bin/find: `libraries/unix/dist-install/build': No such file or directory /usr/bin/find: `libraries/directory/dist-install/build': No such file or directory /usr/bin/find: `libraries/directory/dist-install/build': No such file or directory /usr/bin/find: `libraries/process/dist-install/build': No such file or directory /usr/bin/find: `libraries/process/dist-install/build': No such file or directory /usr/bin/find: `libraries/hpc/dist-boot/build': No such file or directory /usr/bin/find: `libraries/hpc/dist-boot/build': No such file or directory /usr/bin/find: `libraries/hpc/dist-install/build': No such file or directory /usr/bin/find: `libraries/hpc/dist-install/build': No such file or directory /usr/bin/find: `libraries/pretty/dist-install/build': No such file or directory /usr/bin/find: `libraries/pretty/dist-install/build': No such file or directory /usr/bin/find: `libraries/template-haskell/dist-install/build': No such file or directory /usr/bin/find: `libraries/template-haskell/dist-install/build': No such file or directory /usr/bin/find: `libraries/Cabal/Cabal/dist-boot/build': No such file or directory /usr/bin/find: `libraries/Cabal/Cabal/dist-boot/build': No such file or directory /usr/bin/find: `libraries/Cabal/Cabal/dist-install/build': No such file or directory /usr/bin/find: `libraries/Cabal/Cabal/dist-install/build': No such file or directory /usr/bin/find: `libraries/binary/dist-boot/build': No such file or directory /usr/bin/find: `libraries/binary/dist-boot/build': No such file or directory /usr/bin/find: `libraries/binary/dist-install/build': No such file or directory /usr/bin/find: `libraries/binary/dist-install/build': No such file or directory /usr/bin/find: `libraries/bin-package-db/dist-boot/build': No such file or directory /usr/bin/find: `libraries/bin-package-db/dist-boot/build': No such file or directory /usr/bin/find: `libraries/bin-package-db/dist-install/build': No such file or directory /usr/bin/find: `libraries/bin-package-db/dist-install/build': No such file or directory /usr/bin/find: `libraries/hoopl/dist-boot/build': No such file or directory /usr/bin/find: `libraries/hoopl/dist-boot/build': No such file or directory /usr/bin/find: `libraries/hoopl/dist-install/build': No such file or directory /usr/bin/find: `libraries/hoopl/dist-install/build': No such file or directory /usr/bin/find: `libraries/transformers/dist-install/build': No such file or directory /usr/bin/find: `libraries/transformers/dist-install/build': No such file or directory /usr/bin/find: `libraries/xhtml/dist-install/build': No such file or directory /usr/bin/find: `libraries/xhtml/dist-install/build': No such file or directory /usr/bin/find: `libraries/terminfo/dist-install/build': No such file or directory /usr/bin/find: `libraries/terminfo/dist-install/build': No such file or directory /usr/bin/find: `libraries/haskeline/dist-install/build': No such file or directory /usr/bin/find: `libraries/haskeline/dist-install/build': No such file or directory /usr/bin/find: `libraries/integer-gmp/dist-install/build': No such file or directory /usr/bin/find: `compiler/stage1/build': No such file or directory /usr/bin/find: `compiler/stage1/build': No such file or directory /usr/bin/find: `compiler/stage2/build': No such file or directory /usr/bin/find: `compiler/stage2/build': No such file or directory /usr/bin/find: `libraries/haskell98/dist-install/build': No such file or directory /usr/bin/find: `libraries/haskell98/dist-install/build': No such file or directory /usr/bin/find: `libraries/haskell2010/dist-install/build': No such file or directory /usr/bin/find: `libraries/haskell2010/dist-install/build': No such file or directory /usr/bin/find: `libraries/random/dist-install/build': No such file or directory /usr/bin/find: `libraries/random/dist-install/build': No such file or directory /usr/bin/find: `libraries/primitive/dist-install/build': No such file or directory /usr/bin/find: `libraries/primitive/dist-install/build': No such file or directory /usr/bin/find: `libraries/vector/dist-install/build': No such file or directory /usr/bin/find: `libraries/vector/dist-install/build': No such file or directory /usr/bin/find: `libraries/dph/dph-base/dist-install/build': No such file or directory /usr/bin/find: `libraries/dph/dph-base/dist-install/build': No such file or directory /usr/bin/find: `libraries/dph/dph-prim-interface/dist-install/build': No such file or directory /usr/bin/find: `libraries/dph/dph-prim-interface/dist-install/build': No such file or directory /usr/bin/find: `libraries/dph/dph-prim-seq/dist-install/build': No such file or directory /usr/bin/find: `libraries/dph/dph-prim-seq/dist-install/build': No such file or directory /usr/bin/find: `libraries/dph/dph-prim-par/dist-install/build': No such file or directory /usr/bin/find: `libraries/dph/dph-prim-par/dist-install/build': No such file or directory /usr/bin/find: `libraries/dph/dph-lifted-base/dist-install/build': No such file or directory /usr/bin/find: `libraries/dph/dph-lifted-base/dist-install/build': No such file or directory /usr/bin/find: `libraries/dph/dph-lifted-boxed/dist-install/build': No such file or directory /usr/bin/find: `libraries/dph/dph-lifted-boxed/dist-install/build': No such file or directory /usr/bin/find: `libraries/dph/dph-lifted-copy/dist-install/build': No such file or directory /usr/bin/find: `libraries/dph/dph-lifted-copy/dist-install/build': No such file or directory /usr/bin/find: `libraries/dph/dph-lifted-vseg/dist-install/build': No such file or directory /usr/bin/find: `libraries/dph/dph-lifted-vseg/dist-install/build': No such file or directory /bin/sh: 1: Syntax error: Unterminated quoted string make[1]: *** [includes/dist-derivedconstants/build/tmp/mkDerivedConstants] Error 2 make: *** [bootstrapping-files] Error 2 Who have strategies or methods for solving build step at here? [1] http://hackage.haskell.org/trac/ghc/wiki/Building/Porting Thank in advance Chatsiri Rattana -- :--------------------------------------------------------

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How to correctly benchmark code with Criterion?
by Janek S. 19 Oct '12

19 Oct '12

Dear list, during past few days I spent a lot of time trying to figure out how to write Criterion benchmarks, so that results don't get skewed by lazy evaluation. I want to benchmark different versions of an algorithm doing numerical computations on a vector. For that I need to create an input vector containing a few thousand elements. I decided to create random data, but that really doesn't matter - I could have as well use infinite lists instead of random ones. My problem is that I am not certain if I am creating my benchmark correctly. I wrote a function that creates data like this: dataBuild :: RandomGen g => g -> ([Double], [Double]) dataBuild gen = (take 6 $ randoms gen, take 2048 $ randoms gen) And I create benchmark like this: bench "Lists" $ nf L.benchThisFunction (L.dataBuild gen) The question is how to generate data so that its evaluation won't be included in the benchmark. I already asked this question on StackOverflow ( http://stackoverflow.com/questions/12896235/how-to-create-data-for-criterio… ) and got answer to use evaluate + force. After spending one day on testing this approach I came to conclusion that doing this does not seem to influence results of a benchmark in any way (I did stuf like unsagePerformIO + delayThread). On the other hand I looked into sources of criterion and I see that the benchmark code is run like this: evaluate (rnf (f x)) I am a Haskell newbie and perhaps don't interpret this correctly, but to me it looks as though criterion did not evaluate the possibly non-evaluated parameter x before running the benchmark, but instead evaluates the final result. Can someone provide an explanation on how this exactly works and how should I write my benchmarks so that results are correct? Janek

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ANNOUNCE: apphointments - A simple functional calendar
by Steffen Schuldenzucker 18 Oct '12

18 Oct '12

Dear Café, I just wrote myself a small (~ 200 LOC) calendar application today. https://bitbucket.org/rainmaker/apphointments Comments/Patches welcome. From the readme: apphointments - A simple functional calendar ============================================ This is a "UI = Code" calendar application: You create an event by writing code that defines it. To see what's up next, you create a "report", i.e. a summary of the events in a certain time range such as 'thisWeek'. This is done by haskell functions again from GHCi or ghc -e. See example.hs. Using just haskell instead of our own language or GUI allows great flexibility in both defining events and generating reports. See e.g. the 'lecture' combinator from Apphointments.Util. Status ------ Works for me, but has no features yet. See TODO. Credits ------- Created by Steffen Schuldenzucker <sschuldenzucker(a)uni-bonn.de>

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Fwd: hdbc parametrized select
by Wilfried van Asten 18 Oct '12

18 Oct '12

This was not sent to the cafe since I used the wrong from address. ---------- Forwarded message ---------- From: Asten, W.G.G. van (Wilfried, Student M-CSC) <w.g.g.vanasten(a)student.utwente.nl> Date: Thu, Oct 18, 2012 at 12:27 PM Subject: Re: [Haskell-cafe] hdbc parametrized select To: s9gf4ult(a)gmail.com Cc: haskell-cafe(a)haskell.org To my knowledge you can combine execute and the fetch functions like this: find conn id = do stmt <- prepare conn "SELECT * FROM table WHERE id = ? LIMIT 1" excute stmt [id] row <- fetchRow stmt On Thu, Oct 18, 2012 at 10:51 AM, <s9gf4ult(a)gmail.com> wrote: > does hdbc have parametrized selects ? > There is execute > execute :: Statement -> [SqlValue] -> IO Integer > and some other functions which get list of parameters but return IO Integer or > IO () > and there is other couple of functions > fetchRow :: Statement -> IO (Maybe [SqlValue]) > which return values of select but do not get parameters > > How can i execute parametrized select with hdbc ? > > _______________________________________________ > Haskell-Cafe mailing list > Haskell-Cafe(a)haskell.org > http://www.haskell.org/mailman/listinfo/haskell-cafe

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