November 2009 - Haskell-Cafe

hscolour + unicode
by Sean McLaughlin 30 Nov '09

30 Nov '09

Hello, Is there a way to get the source documentation from cabal haddock --hyperlink-source to show up with unicode characters preserved? Right now the unicode from my comments and source programs are being mangled. I tried the --haddock-option="--use-unicode" option, but it seems to only work on the haddock docs, not the sources that are hscoloured and linked. Thanks, Sean

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Haskell Job Openings (Pune, IN)
by Tom Hawkins 30 Nov '09

30 Nov '09

We finally got some open reqs in Eaton's engineering center in Pune, India. Could involve a little Haskell programming, or a lot, depending on what you want to do. http://jobsearch.naukri.com/job-listings-Senior-Engineer-Automotive-Embedde… I'd be happy to forward on any resumes to the hiring manager. -Tom

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Haskell Weekly News: Issue 141 - November 29, 2009
by jfredett＠gmail.com 30 Nov '09

30 Nov '09

--------------------------------------------------------------------------- Haskell Weekly News http://sequence.complete.org/hwn/20091129 Issue 141 - November 29, 2009 --------------------------------------------------------------------------- Welcome to issue 141 of HWN, a newsletter covering developments in the [1]Haskell community. Firstly, sorry for the late HWN, a turkey coma is equal parts gift and curse. This week, we have some very exciting news, a new Haskell standard -- Haskell 2010 -- was announced, including several small changes. Also, we have lots of new packages, a possible Boston-area Hackathon coming up soon, and some great discussion. I won't hold you back from skipping all that and just reading the funny quotes! Haskellers, your (belated) Haskell Weekly News! Announcements Haskell 2010. Simon Marlow [2]announced the new revision of Haskell, Haskell 2010. Part of the new, less monolithic Haskell Prime process, Haskell 2010 includes several changes to the Haskell Language, including support for nonstandard if-then-else syntax (particularly wrt `do` notation and indentation), pattern guards, and several other changes. See the post for details. Clutterhs 0.1. Matt Arsenault [3]announced Clutterhs, version 0.1. A set of bindings for Clutter, a GObject based library for creating 2.5D interfaces using OpenGL. Interesting experiences of test automation in Haskell? Automation of Software Test 2010. John Hughes [4]announced a 'heads up' for the Automation af Software Test 2010 workshop NoSlow - Microbenchmarks for array libraries. Roman Leshchinskiy [5]announced his benchmark suite for various array and list libraries. CMCS 2010: First call for papers. Alexandra Silva [6]announced a first call for papers for the Tenth International Workshop on Coalgebraic Methods in Computer Science, taking place 26-28 March 2010, in Paphos, Cyprus. GPCE'10 First Call for Papers. Bruno Oliveira [7]announced a first call for papers for the Ninth International Conference on Generative Programming and Component Engineering. GPCE 2010 October 10-13, in Eindhoven, The Netherlands. Call for Participation: TLDI'10. Andrew Kennedy [8]announced a call for participation in the 2010 ACM SIGPLAN Workshop on Types in Language Design and Implementation Deadline Extension: JSC Special Issue on Automated Specification and Verification of Web Systems. demis [9]announced an extension to the paper deadline for the JSC Special Issue on Automated Specification and Verification of Web Systems. VSTTE 2010: Verified Software -- Second Call for Papers. Gudmund Grov [10]announced the second call for papers for the Third International Conference on Verified Software: Theories, Tools, and Experiments GPipe-1.1.0 with greatly improved performance. Tobias Bexelius [11]announced a new version of the GPipe package, now with greatly improved performance. wumpus-core. Stephen T [12]announced a new version of the wumpus-core package, a library for drawing 2D vector pictures, supporting output to SVG and postscript. package-vt-0.1.3.3, Haskell Package Versioning Tool. Krzysztof Skrzetnicki [13]announced the first release of his automatic version tracking tool, package-vt. Elerea 1.1. Patai Gergely [14]announced a new version of Elerea, a simple pull-based FRP library. Elerea (and FRP in general) allow for stream oriented programming, typically done in a applicative style. mecha-0.0.4. Tom Hawkins [15]announced a new version of Mecha, a little constructive solid modeling language intended for doing 3D CAD. atom-0.1.2. Tom Hawkins [16]announced a new release of Atom, a DSL for designing hard realtime embedded software with Haskell. This release adds guarded division operations, a new scheduling constraint, and a new rule scheduling algorithm. Managing Cabal Dependencies using Nix and Hack-nix. Marc Weber [17]announced a package for dealing with Cabal dependencies on the Nix OS platform. Discussion haskell in online contests. vishnu [18]asked about using Haskell in online contests, and particularly dealing with the SPOJ tool for judging programs. Namespaces for values, types, and classes. Sebastian Fischer [19]suggested allowing a namespace separation between class-names and other language elements. I miss OO. Michael Mossey [20]lamented his desire for Object-oriented features in Haskell, this led to a interesting discussion about name punning and typeclasses. Haskell Hackathon in Boston January 29th-31st? Ravi Nanavati [21]proposed a potential Hackathon in this editor's favorite city, to be held the 29th to the 31st. Blog noise [22]Haskell news from the [23]blogosphere. Blog posts from people new to the Haskell community are marked with >>>, be sure to welcome them! * Dan Piponi (sigfpe): [24]Programming with impossible functions, or how to get along without monads.. * Neil Brown: [25]Graph Layout with Software Transactional Memory and Barriers (plus video!). * Ivan Lazar Miljenovic: [26]If wishes were tests, code would be perfect. * Adam Jones: [27]Lambda Calculus compiler, Part II: Wading in with arithmetic. * FP Lunch: [28]Implementing a Correct Type-Checker for the Simply Typed Lambda Calculus. * Manuel M T Chakravarty: [29]Haskell 2010. * Holumbus: [30]hayoo.info. * Paul Chiusano: [31]Perfect strictness analysis (Part 2). * Paul Chiusano: [32]Perfect strictness analysis (Part 1). * Paul Chiusano: [33]Optional laziness doesn't quite cut it. * Neil Brown: [34]Force-Directed Graph Layout with Barriers and Shared Channels. * Neil Mitchell: [35]Reviewing View Patterns. * JP Moresmau: [36]EclipseFP 1.109.0 is out!. * CS Design Lab, University of Kansas: [37]Special LAMBDA meeting. * Joachim Breitner: [38]arbtt now in Debian. * Neil Mitchell: [39]Haskell DLL's on Windows. * Conal Elliott: [40]Thoughts on semantics for 3D graphics. Quotes of the Week * command: lambdabot will say 'it is forever etched into my memory' and then forget the quote by tomorrow. * copumpkin: orbitz makes [##C++] especially brutal to make people appreciate #haskell more * mtnviewmark: [on the State monad] "If I had a sta-ate, I'd compute it in the morning.... I'd compute it in the evening.... All over this la-and!" * monochrom: dynamic type is poor man's dependent type, they are so poor they can't buy a theorem prover. * Veinor: just remember: you can't spell fundeps without fun. * Botje: i think it's too early to be sticking things into other things .. * Berengal: Haskell is made of sugar and spice and everything nice, plus the mysterious compound X * sproingie: sproingie enables IncoherentInstances and ends up with Sarah Palin in his living room About the Haskell Weekly News New editions are posted to [41]the Haskell mailing list as well as to [42]the Haskell Sequence and [43]Planet Haskell. [44]RSS is also available, and headlines appear on [45]haskell.org. To help create new editions of this newsletter, please see the information on [46]how to contribute. Send stories to jfredett . at . gmail . dot . com. The darcs repository is available at darcs get [47]http://patch-tag.com/r/jfredett/HWN2/pullrepo HWN2 . References 1. http://haskell.org/ 2. http://article.gmane.org/gmane.comp.lang.haskell.general/17638 3. http://article.gmane.org/gmane.comp.lang.haskell.general/17652 4. http://article.gmane.org/gmane.comp.lang.haskell.general/17649 5. http://article.gmane.org/gmane.comp.lang.haskell.general/17647 6. http://article.gmane.org/gmane.comp.lang.haskell.general/17646 7. http://article.gmane.org/gmane.comp.lang.haskell.general/17645 8. http://article.gmane.org/gmane.comp.lang.haskell.general/17644 9. http://article.gmane.org/gmane.comp.lang.haskell.general/17637 10. http://article.gmane.org/gmane.comp.lang.haskell.general/17636 11. http://article.gmane.org/gmane.comp.lang.haskell.general/17635 12. http://article.gmane.org/gmane.comp.lang.haskell.cafe/66796 13. http://article.gmane.org/gmane.comp.lang.haskell.cafe/66770 14. http://article.gmane.org/gmane.comp.lang.haskell.cafe/66751 15. http://article.gmane.org/gmane.comp.lang.haskell.cafe/66726 16. http://article.gmane.org/gmane.comp.lang.haskell.cafe/66722 17. http://article.gmane.org/gmane.comp.lang.haskell.cafe/66693 18. http://thread.gmane.org/gmane.comp.lang.haskell.cafe/66810 19. http://thread.gmane.org/gmane.comp.lang.haskell.cafe/66777 20. http://thread.gmane.org/gmane.comp.lang.haskell.cafe/66723 21. http://thread.gmane.org/gmane.comp.lang.haskell.cafe/66616 22. http://planet.haskell.org/ 23. http://haskell.org/haskellwiki/Blog_articles 24. http://blog.sigfpe.com/2009/11/programming-with-impossible-functions.html 25. http://chplib.wordpress.com/2009/11/26/graph-layout-with-software-transacti… 26. http://ivanmiljenovic.wordpress.com/2009/11/26/if-wishes-were-tests-code-wo… 27. http://blog.finiteimprobability.com/2009/11/25/lambda-calculus-compiler-par… 28. http://sneezy.cs.nott.ac.uk/fplunch/weblog/?p=291 29. http://justtesting.org/post/256283708 30. http://holumbus.fh-wedel.de/blog/?p=27 31. http://pchiusano.blogspot.com/2009/06/perfect-strictness-analysis-part-2.ht… 32. http://pchiusano.blogspot.com/2009/06/perfect-strictness-analysis-part-1.ht… 33. http://pchiusano.blogspot.com/2009/05/optional-laziness-doesnt-quite-cut-it… 34. http://chplib.wordpress.com/2009/11/24/force-directed-graph-layout-with-bar… 35. http://neilmitchell.blogspot.com/2009/11/reviewing-view-patterns.html 36. http://jpmoresmau.blogspot.com/2009/11/eclipsefp-11090-is-out.html 37. http://www.ittc.ku.edu/csdlblog/?p=20 38. https://www.joachim-breitner.de/blog/archives/352-arbtt-now-in-Debian.html 39. http://neilmitchell.blogspot.com/2009/11/haskell-dlls-on-windows.html 40. http://conal.net/blog/posts/thoughts-on-semantics-for-3d-graphics/ 41. http://www.haskell.org/mailman/listinfo/haskell 42. http://sequence.complete.org/ 43. http://planet.haskell.org/ 44. http://sequence.complete.org/node/feed 45. http://haskell.org/ 46. http://haskell.org/haskellwiki/HWN 47. http://patch-tag.com/r/jfredett/HWN2/pullrepo%20HWN2

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FAD
by Ozgur Akgun 29 Nov '09

29 Nov '09

While searching for a design tool for Haskell, I've come across the PhD thesis of Dan Russell <http://www.cs.kent.ac.uk/pubs/2001/1152/> He also mentioned the tool in cafe some time ago: http://www.haskell.org/pipermail/haskell-cafe/2003-June/004606.html Does anyone in the cafe, or himself, direct me to the download link of this tool; so that I can try it out. Cheers, -- Ozgur Akgun

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Partially applied functions
by Casey Hawthorne 29 Nov '09

29 Nov '09

You can pattern match on the right hand side of '|' in a list comprehension, since a list comprehension is just the list monad. Just changed a few things. Hopefully this answers the OP's question and any interested others. add :: Int -> Int -> Int add x y = x + y -- a list of partially applied functions adds = [add 3, add 5, add 7, add 3, add 5, add 8] -- an example usage of the list kP pred = map (\ f -> f 10 ) (addPs pred) -- Wanted to do things like this. -- add3s = filter (?) adds -- add3s = [add 3, add 3] -- addEvens = filter (?) adds --addEvens = [add 8] -- addPs num = [ x | x <- adds, x 0 == num ] -- Changed 'x' to 'f' indicating a function application. addPs pred = [ f | f <- adds, pred (f 0) ] -- Main> kP (==3) -- Main> kP even -- Regards, Casey

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ghci breakpoints
by Sean McLaughlin 29 Nov '09

29 Nov '09

Hello, I'm having trouble setting breakpoints from ghci. I load the files and I can tell things are working correctly because I can run the program and list the locations where I want to set breakpoints. E.g. Prelude> :list Focus.focus 510 > focus :: forall s m. Class s m => Neg -> m [Foci] 511 > focus f = 512 > let ats = Path.atoms f But when I try to set a breakpoint I get Prelude> :break Focus.focus No breakpoints found at that location. Does anyone have ideas about what I'm doing wrong in this case? Do I need to load with some special options to have breakpoints work? Thanks, Sean

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some help debugging ghci build on powerpc
by Brian Denheyer 29 Nov '09

29 Nov '09

I'm trying to build ghc so that ghci will be included under linux power-pc. The build dies here: ~/ghc6-6.10.4/rts$ /home/briand/ghc6-6.10.4/ghc/stage1-inplace/ghc -optc-O -optc-Wall -optc-W -optc-Wstrict-prototypes -optc-Wmissing-prototypes -optc-Wmissing-declarations -optc-Winline -optc-Waggregate-return -optc-I../includes -optc-I. -optc-Iparallel -optc-Ism -optc-DCOMPILING_RTS -optc-fomit-frame-pointer -optc-DNOSMP -optc-I../gmp/gmpbuild -optc-I../libffi/build/include -optc-fno-strict-aliasing -optc-w -H32m -O -optc-O2 -I../includes -I. -Iparallel -Ism -DCOMPILING_RTS -package-name rts -optc-DNOSMP -static -I../gmp/gmpbuild -I../libffi/build/include -I. -dcmm-lint -c StgCRun.c -o StgCRun.o /tmp/ghc21791_0/ghc21791_0.s: Assembler messages: /tmp/ghc21791_0/ghc21791_0.s:15:0: Error: junk at end of line, first unrecognized character is `@' /tmp/ghc21791_0/ghc21791_0.s:19:0: Error: junk at end of line, first unrecognized character is `@' That relates to this line(s): StgRun: .quad .StgRun,.TOC.@tocbase,0 .size StgRun,24 .globl StgReturn It _looks_ like it's grabbing the right stuff from StgCRun.c, i.e. it's really trying to compile for power pc. I was hoping that this was a bit of cruft and someone could direct me to a fix for the assembly portion so I can get a little farther along. Thanks, Brian P.S. Or somebody could also tell me if trying to have the latest ghc working on power pc is even worth working on.

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namespaces for values, types, and classes
by Sebastian Fischer 29 Nov '09

29 Nov '09

Dear Café, types and values are in separate namespaces. So, we can write data Name = Name where the first `Name` is a type and the second is a value. However, classes are in the same namespace as types. We cannot write class Name a where ... instance Name Name where ... Class contexts and types appear in different contexts just like types and values (unless I'm missing something). I googled for the reason of this design choice but found nothing. Does anyone know why types and values are in separate namespaces but classes and types are not? Cheers, Sebastian -- Underestimating the novelty of the future is a time-honored tradition. (D.G.)

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haskell in online contests
by vishnu 29 Nov '09

29 Nov '09

Ive just started learning haskell pretty recently and Ive been trying to solve some online contest problems as part of this exercise. However, Ive been having almost no success. For various reasons my answers almost always are too slow. I recently stumbled across this link which was quite useful http://www.haskell.org/haskellwiki/SPOJ. This helped me speed up some of my programs where input was slowing me down. But being a noob, to a large extent I don't even know why my programs are slow sometimes or how to tell what makes them slow. I've been attempting problems from www.codechef.com (which uses SPOJ) in actuality. Because I have an admin account I can actually compare my solution against others there (which are almost always in C/C++ or Java) to try and figure out if Im missing a trick. Recently the problem I picked up was http://www.codechef.com/problems/DDILEMMA/ and I worked through solutions that just don't seem to be fast enough. I looked at successful submissions in C++ and JAVA which seem to do mostly what I'm doing (ofcourse there are differences because those are imperative languages and I might be misunderstanding things.). I've got my program, test input that I generated, cost center analysis all up on this page. http://moonpatio.com/fastcgi/hpaste.fcgi/view?id=5120#a5137 I've been getting some significant help from the #haskell channel but unfortunately this hasn't helped me break the barrier I need to. So I was wondering if someone would be kind enough to help me understand the profiler output and help me understand how to improve performance in cases like this thanks

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Re: [Haskell-cafe] haskell in online contests
by wren ng thornton 29 Nov '09

29 Nov '09

vishnu wrote: > wow ok, I'm not even able to see why they're different in the desugared > version They're different because case is strict binding (see caveat below) whereas let is lazy binding. If we say, let foo = big ugly computation in bar Then if foo isn't used in bar, it'll never be computed. (Even if foo occurs in bar, provided it occurs somewhere that won't be evaluated.) Whereas if we say, case big ugly computation of foo -> bar Then we're forced to do the computation, regardless of whether foo is used in bar. Actually, that's not entirely true. In this example, because foo is a variable, the binding will be lazy; whereas if we replaced foo with a (non-lazy) pattern then it'd be strict. Part of the complication in explaining the exact details is because both case and let can have patterns inside of the binding so the desugaring process has to continue recursively. Also there're some details about using let for defining recursive groups, which you can't do with case. Also Haskell's syntax conflates defining functions with doing pattern matching, so there's an extra step to separate functions using pattern matching into the definition binding vs the pattern matching. In any case, once you're done compiling you end up with a strict binding operator (kind of like case) and a lazy binding operator (kind of like let). When in doubt, try playing around with different definitions to see whether they break when you pass in 'undefined'. There are also a few papers out there on how the STG works under the covers. -- Live well, ~wren

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