August 2008 - Haskell-Cafe

darcs weekly news #1
by Eric Kow 27 Aug '08

27 Aug '08

Hi everybody, I thought it would be useful if we got back into the habit up summarising our weekly darcs activities. This is the first entry of what I hope to be Darcs Weekly News. Note that I have also Bcc'ed the Haskell Cafe; which I will not be doing everytime, but just this once :-) News and discussions -------------------- hacking sprint (25/26 October) We are now planning three sites for the upcoming darcs hacking sprint: Brighton (moved from Cambridge), Paris and Portland. More news as we finalise the venues in the next two weeks! performance benchmarking Eric is working on integrating performance regression testing into the darcs buildbot. The progress is slow but steady! darcs 2 real world comparison Jason analyses a comparison of darcs push between 1.0.9 and 2.0.2. http://blog.codersbase.com/2008/08/21/darcs-2-real-world-push-performance-e… darcs weekly news Most of darcs weekly news is automated, but we still need human editors! To help out, darcs get http://code.haskell.org/darcs/darcs-news Issues resolved in the last two weeks (5) ----------------------------------------- * issue115 (Dmitry Kurochkin) match patches touching given files. http://bugs.darcs.net/issue115 * issue823 (Dmitry Kurochkin) do not exit on keyboard interrupt when getting patches. http://bugs.darcs.net/issue823 * issue936 (Dmitry Kurochkin) fix type witnesses configure check. http://bugs.darcs.net/issue936 * issue950 (David Roundy) fix fix_filepath to work with --repodir (and add test demonstrating this). http://bugs.darcs.net/issue950 * issue995 (Dmitry Kurochkin) changes --context : {--human-readable,--xml-output} have no effect. http://bugs.darcs.net/issue995 Patches applied in the last two weeks (69) ------------------------------------------ 2008-08-25 Jason Dagit minor refator to get_extra improve comments 2008-08-25 Eric Kow Same ChangeLog entries since 2.0.2 Some more globally ignored changes. 2008-08-24 David Roundy Simplify filepath handling, cutting lots of hardly-used code. don't bother computing path when checking prereqs (since we now can handle looking at beginning/ending working directories). resolve issue950: fix fix_filepath to work with --repodir (and add test demonstrating this). eliminate fix_flag. add new framework for ensuring that certain arguments are converted to absolute paths. make Darcs.Lock functions accept FilePathLike arguments. refactor maybeMkSubPath very slightly. refactor repoPath very slightly. make makeAbsolute behavior match comment. 2008-08-22 Dmitry Kurochkin Fix makeAbsolute to work with '../foo' paths. 2008-08-22 David Roundy move withCurrentDirectory, withTempDir and withPermDir rewrite mkAbsolutePath to be safe. 2008-08-22 Eric Kow Changelog (ignore 'Add a test entries') 2008-08-22 David Roundy resolve conflicts. 2008-08-19 Dmitry Kurochkin Resolve issue936: fix type witnesses configure check. Use forkIO in URL module as suggested by Simon Marlow. Remove HTTP.copyUrl, integrate it to URL module. More URL module refactoring. 2008-08-22 Eric Kow Canonize Nathaniel Filardo and Simon Marlow. Add test case for issue966 (from Dan Pascu's bug report) 2008-08-21 David Roundy remove trailing whitespace. 2008-08-21 Dmitry Kurochkin Documentation for match touch primitive. Resolve issue115: match patches touching given files. 2008-08-22 Eric Kow Remove unused FileSystem module. 2008-08-20 David Roundy fix type witnesses in with_selected_patch_from_repo. clean up bugs functions (eliminate darcsBug.h). 2008-08-19 Jason Dagit Fix a bug with incorrectly specified with_selecte_patch_from_repository. 2008-08-19 Dmitry Kurochkin Remove HTTP.exists, use Autoconf.have_HTTP instead. 2008-08-19 David Roundy fix improper use of bug in HTTP. 2008-08-19 Dmitry Kurochkin Do not import HTTP module in Darcs.Bug, use bug and debugFail for error reporting in HTTP module. 2008-08-19 David Roundy fix incompatibility with ghc 6.6. make scan_bundle create a lazy patch bundle. resolve conflicts with Darcs.Ordered change. 2008-08-15 Jason Dagit replace separate_middle_last_from_first and separate_last_from_first_middle with get_choices correct a bug in with_selected_patches_from_repository refine type witnesses in SelectChanges make WhatsNew work with type witnesses major refactor of SelectChanges to work with type witnesses 2008-08-16 nwf(a)cs.jhu.edu Move Darcs.Patch.Ordered to Darcs.Ordered since it isn't patchy 2008-08-19 Simon Marlow Fix use of threadWaitRead on Windows Fix Windows build 2008-08-17 Dmitry Kurochkin URL module refactoring. Do not compile curl support if libwww is enabled. URL.hs: always import debugFail, again. URL.hs: call debugFail when download fails. URL.hs: debug messages. Spacing in Darcs/Commands/Changes.lhs Rename catchInt to catchInterrupt, better message when get is interrupted. Resolve issue995: changes --context : {--human-readable,--xml-output} have no effect. 2008-08-18 Eric Kow Add test for issue1017 (as suggested by Bjorn Bringert) 2008-08-19 David Roundy don't print "Wrote patch to -" when writing patch to stdout. always send with context. 2008-08-18 Eric Kow Tidy up known failing shell tests. Tidy up failing test for issue1013. Move hidden conflicts bug to tests directory. Add failing test for issue1012 (Simon Marlow). 2008-08-15 Dmitry Kurochkin Resolve issue823: do not exit on keyboard interrupt when getting patches. 2008-08-14 David Roundy fix buggy comments in bugs/identical-patches.sh. 2008-08-13 Eric Kow Add Ian's identical-patch test case. 2008-08-13 Dmitry Kurochkin URL.hs: store only URL in waitToStart queue. 2008-08-14 Eric Kow Add (failing) test for issue944. 2008-08-13 nwf(a)cs.jhu.edu Split Cache mostly out of Darsc/Repository/Prefs into its own file (take 2) 2008-08-13 Jason Dagit remove a few unsightly functions 2008-08-13 Dmitry Kurochkin Fix URL module bug with pipelining enabled. Minor change to URL module. Enable pipelining by default, add --disable-pipelining option (issue838). -- Eric Kow <http://www.nltg.brighton.ac.uk/home/Eric.Kow> PGP Key ID: 08AC04F9

1 0

contributing to standard library
by Tim Newsham 27 Aug '08

27 Aug '08

Like everyone else who has used Haskell for a while, I'm accumulating functions which I feel should have already been in the standard libraries. What's the normal path to contributing functions for consideration in future standard libraries? Is there some experimental standard lib that we can contribute to to "try out" for the big league? Here are some functions: http://www.thenewsh.com/%7Enewsham/x/machine/Missing.hs Tim Newsham http://www.thenewsh.com/~newsham/

5 4

ANN: First Monad Tutorial of the Season
by Hans van Thiel 26 Aug '08

26 Aug '08

Hello All, I'm proud to announce the first monad tutorial of the new season. It's under the Wiki permissive licence, but the web page has some clip art, so 'The Greenhorn's Guide to becoming a Monad Cowboy' is on http://www.muitovar.com/monad/moncow.xhtml Best Regards, Hans van Thiel

6 12

unsafeInterleaveIO, lazyness and sharing
by Wolfgang Jeltsch 26 Aug '08

26 Aug '08

Hello, Haskell is non-strict but not necessarily lazy. So it’s possible that an expression is reduced to WHNF although it is not used yet. Could this “early reduction” also happen to outputs of unsafeInterleaveIO actions (which might trigger the action too early)? While I’d expect those outputs to be evaluated lazily (reduced as late as possible), I cannot find anything in the docs that guarantees this. In addition, I’d like to know whether unsafeInterleaveIO outputs are guaranteed to be evaluated at most once so that the “interleaved action” is executed at most once. Again, I suppose that this is the case while I cannot find a guarantee for it. Best wishes, Wolfgang

3 2

Re: [Haskell] Re:Fwd: Haskell job opportunity: Platform Architect at
by John Meacham 26 Aug '08

26 Aug '08

On Wed, Aug 20, 2008 at 03:17:14PM -0700, Jason Dusek wrote: > What is your company going to do? What sort of dot-com attitude is that? Your company does whatever the buzzword that the venture capitalist you are currently talking to is enthralled with. :) 'monadic B2B ultra-wideband catamorphic connection oriented infospherespace' John -- John Meacham - ⑆repetae.net⑆john⑈

2 1

String to Double conversion in Haskell
by Daryoush Mehrtash 26 Aug '08

26 Aug '08

I am trying to convert a string to a float. It seems that Data.ByteString library only supports readInt. After some googling I came accross a possibloe implementation: http://sequence.svcs.cs.pdx.edu/node/373 My questions are: a) is there a standard library implementation of string -> Double and float? b) Why is it that the ByteString only supports readInt? Is there a reason for it? Thanks, Daryoush Mehrtash

5 8

Re[2]: [Haskell] Top Level <-
by Bulat Ziganshin 26 Aug '08

26 Aug '08

Hello Derek, Tuesday, August 26, 2008, 8:14:21 PM, you wrote: >> but from my POV it's important to push this feature into haskell >> standard > Haskell should be moving -toward- a capability-like model, not away from > it. what you mean by "capability-like model"? -- Best regards, Bulat mailto:Bulat.Ziganshin@gmail.com

2 1

OpenGL's VBO with Haskell
by Twinside 26 Aug '08

26 Aug '08

Hi Haskell list, Today I'm turning to you for the use of VBO (Vertex Buffer Object) in Haskell. I seem to be able to create one without any problem using the following code : ------------------------------------------------------ vboOfList :: Int -> [Float] -> IO BufferObject vboOfList size elems = let ptrsize = toEnum $ size * 4 arrayType = ElementArrayBuffer in do [array] <- genObjectNames 1 bindBuffer arrayType $= Just array arr <- newListArray (0, size - 1) elems withStorableArray arr (\ptr -> bufferData arrayType $= (ptrsize, ptr, StaticDraw)) bindBuffer ArrayBuffer $= Nothing reportErrors return array ------------------------------------------------------ However the problem arise when I try to draw primitives using this vbo : ------------------------------------------------------ displayVbo buff size = do let stride = toEnum sizeOfVertexInfo vxDesc = VertexArrayDescriptor 3 Float stride $ offset 0 colors = VertexArrayDescriptor 4 Float stride $ offset 12 texCoo = VertexArrayDescriptor 2 Float stride $ offset (12 + 16) filt = VertexArrayDescriptor 4 Float stride $ offset (12 + 16 + 8) bindBuffer ArrayBuffer $= Just buff arrayPointer VertexArray $= vxDesc arrayPointer ColorArray $= colors arrayPointer TextureCoordArray $= texCoo arrayPointer SecondaryColorArray $= filt drawArrays Quads 0 size bindBuffer ArrayBuffer $= Nothing ------------------------------------------------------ Nothing is displayed on screen. As you can see, my VBO contain interleaved data : - 3 float for the vertex - 4 for the color - 2 for the texture coordinate - 4 for the secondary color) The 'offset' function has type Int -> Ptr Float, and is used to forge a pointer from an Int, to mimic the C way of using VBO. As far as I've checked, the values in my list for VBO generation are valid and well displayed using other techniques. So is there a workaround other method for my solution, preferably by keeping my data interleaved? Secondly, is there any sample for advanced features like VBOs in Haskell? Regards, Vincent

3 4

Haskell Speed Myth
by Thomas Davie 26 Aug '08

26 Aug '08

Lo guys, I thought you'd like to know about this result. I've been playing with the debian language shootout programs under OS X, looking at how fast Haskell code is compared to C on OS X, rather than linux. Interestingly, Haskell comes out rather better on OS X than it did on Linux. Here's my results (times in seconds): C Haskell Relative speed Inverse Binary Trees 6.842 1.228 0.179479684302835 5.57166123778502 Fannkuch 5.683 15.73 2.76790427591061 0.361284170375079 Mandelbrot 1.183 2.287 1.93322062552832 0.517271534761697 nbody 10.275 16.219 1.57849148418491 0.633516246377705 nsieve 0.167 0.253 1.51497005988024 0.660079051383399 nsieve-bits 0.471 0.713 1.51380042462845 0.660589060308555 partial sums 1.047 1.313 1.25405921680993 0.797410510281797 pidigits 1.238 1.4 1.13085621970921 0.884285714285714 recursive 1.554 3.594 2.31274131274131 0.432387312186978 spectral-norm 27.939 19.165 0.685958695729983 1.45781372293243 threadring 91.284 1.389 0.0152162481924543 65.719222462203 ------------------------------------------------------------------------- Averages 1.35333620432893 0.738914688605306 Some notes: Hardware: 2Ghz Core2Duo, enough ram to not worry about paging Some programs are not included, this is because the C code produced compile errors. The Haskell code appears to be portable in *all* cases. The average slowdown for running Haskell is only 1.3 times on OS X! That's pretty damn good. I'm sure some people will say "yeh, but you have to optimise your code pretty heavily to get that kind of result". Interestingly, the programs that have the biggest speed advantage over C here are also the most "naïvely" written ones. The thing that seems to make C slower is the implementation of malloc in OS X. This has a couple of implications, first, if apple replaced the malloc library, it would probably push the result back to the 1.7 times slower we see under Linux. Second, Fannkuch can probably be optimised differently for Haskell to look even better -- at the moment, the haskell code actually uses malloc! Finally, that threading example... WOW! 65 times faster, and the code is *really* simple. The C on the other hand is a massive mess. Bob

7 13

Valid Haskell characters
by Maurício 26 Aug '08

26 Aug '08

Hi, In Haskell reference, I see the following definitions: uniWhite -> any Unicode character defined as whitespace; uniSmall -> any Unicode lowercase letter; uniLarge -> any uppercase or titlecase Unicode letter; uniSymbol -> any Unicode symbol or punctuation. Where do I get lists for those characters? My first attempt was to check: http://unicode.org/Public/UNIDATA/UnicodeData.txt and consider large anything marked as CAPITAL and small anything marked as SMALL. I didn't know what to guess about the symbols. Am I using the right reference? How can I recognize (or get a list of) valid uppercase and lowercase unicode letters, as well as symbols and punctuation? Thanks for your help, Maurício

3 4