- Haskell-Cafe - Haskell.org

wrong GHC source files
by Hong Yang 08 Jan '16

08 Jan '16

https://www.haskell.org/ghc/download_ghc_7_10_3#sources reads Source Distribution ----------------------------------------------------------------------------- The source tarballs provide everything necessary to build the compiler, interactive system, and a minimal set of libraries. For more information on building, see the building guide. ghc-7.10.3b-windows-extra-src.tar.bz2 (92 MB) ghc-7.10.3b-windows-extra-src.tar.xz (91 MB) Shouldn't the two files be as follows? ghc-7.10.3b-src.tar.bz2 ghc-7.10.3b-src.tar.xz

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Pattern Matching for record syntax
by Jeon-Young Kang 08 Jan '16

08 Jan '16

Dear All. Hope your 2016 is off to a great start. I would like to get results from pattern matching or something. Here is the my code. data Person = Person {name :: String, age :: Int} names = ["tom", "sara"] -- list of names, String persons = [Person {name = "tom", age = 10}, Person {name="sara", age=9}, Person {name = "susan", age = 8}]. Is there any solution to get the age of "tom" and "sara"? I have no idea of pattern matching for this one. I've tried to use recursion, but I couldn't find any solution for list of records. Sincerely, Young

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LambdaConf 2016: Call for Proposals (May 26 - 29)
by John A. De Goes 08 Jan '16

08 Jan '16

Hi all, We have officially opened the call for proposals for LambdaConf 2016 <http://lambdaconf.us/>LambdaConf 2016 <http://lambdaconf.us/>! LambdaConf is the one of the largest and most respected conferences on functional programming in the world. With more than a hundred hours of high-quality content from leading practitioners and researchers, LambdaConf is designed to take attendees' skills to the next level, whether they are just beginning or are highly experienced in the art of functional programming. Last year, Haskell content truly dominated the conference, with many workshops and well more than a full track of Haskell presentations. This year, we'd like to repeat that, as well as see strong submissions from related languages such as PureScript (PureScript Conf 2016 is co-located with and will immediately precede LambdaConf). We are looking for speakers who want to share their knowledge of the Haskell language (past, present, and future), Haskell libraries, Haskell tools, real-world Haskell use cases, and theory relevant to functional programming (such as type theory, programming language theory, dependent-types, program derivation, category theory). We welcome first-time speakers, experienced presenters, and presentations at all levels. For more information or to submit your proposal, please visit the conference home page <http://lambdaconf.us/> (http://lambdaconf.us <http://lambdaconf.us/>), or the submission form <https://www.surveymonkey.com/r/lambdaconf-2016-cfp>. Please share this CFP with anyone you think might be interested! Regards, John

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Fwd: Fwd: Re: the state of Yarr?
by Dominic Steinitz 07 Jan '16

07 Jan '16

A problem with my email prevented this making it on to the mailing list. Hi Petr, I am not actively developing Yarr but I would very much like to. I keep it from bit-rotting. The problem as always is finding time. On the other hand I don't think repa is very active e.g. upgrading to vector-0.11 took a while to happen although clearly more active than me on Yarr! What I'd like is something like Python's numpy but safer and faster. If you look at the static module in the hmatrix package (https://hackage.haskell.org/package/hmatrix-0.17.0.1/docs/Numeric-LinearAlg…) you can see how type level literals can be used to prevent e.g. multiplying two inconsistent matrices together at compile time. I am sure we could do something better with either Yarr or repa (repa will currently give out of bounds errors at runtime). For reasons I don't understand (I think a bug in Haddock) the documentation does not get generated. There are examples of its use here: https://github.com/leventov/yarr/tree/master/tests. I wrote a blog using repa and Yarr here: https://idontgetoutmuch.wordpress.com/2013/08/06/planetary-simulation-with-… and compare performance. You can safely ignore the theory and need only look at "Repa Implementation", "Yarr Implementation" and "Performance". I think performance will depend on your application. I believe (but haven't confirmed) that repa will outperform Yarr on e.g grid based problems such as numerical methods for diffusions and Poisson. In the case of planets (or stars or particles) where everything is influenced by everything else then repa is a bad fit and Yarr outperforms. If your application is linear algebra, I would think that hmatrix would have what you want or could be extended to give what you want since it is LAPACK under the covers. I am very excited that you are interested in this area; it often feels very lonely. Best wishes, Dominic. On 06/01/2016 09:10, Petr Pudlák wrote: > Hi Dominic, > > what is the current state of Yarr? Is it being actively developed? Is > there some tutorial or documentation available? > > I'm deciding between repa and yarr for some linear algebra > computations. I found some references that yarr is more performant, > but I couldn't find much documentation and the hackage page [1] hasn't > indexed most modules for some reason, so there seems to be no good > place to start from. And the last commit was 9 months ago. > > [1]https://hackage.haskell.org/package/yarr > > Thank you, > Petr

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long-range performance comparisons (GHC over the years)
by Johannes Waldmann 07 Jan '16

07 Jan '16

Dear Cafe, I recently noticed a performance problem due to a fusion rule not firing for a straightforward piece of code. In fact it turned out this was already fixed in HEAD, see https://ghc.haskell.org/trac/ghc/ticket/11344 https://ghc.haskell.org/trac/ghc/ticket/9848 What worries me is that such a regression had been sitting there for over a year (and did not make it to 7.10.3) and I got to thinking: What long-range performance metering do we have? So I tried to made nofib runs for some ghc-{6,7} versions http://www.imn.htwk-leipzig.de/~waldmann/etc/nofib/comparison-k.text This is slightly broken (not all tests can be built for all compilers, and I don't known how to fix this) but there are some interesting numbers already. It seems nofib programs are self-contained (not using any libraries) so they are mainly using numbers, lists, tuples, and user-defined data. This is the heart of (traditional) Haskell, so this is supposed to work really well. The table shows that there are a lot of benchmarks where performance has been increasing. That's good. But not for all! We should certainly ignore all runtimes that are absolutely small. I think it is most interesting to look allocation numbers. A few examples from this list: * exp3_8 (allocation goes up 50 % from 6.* to 7.*) this is addition of Peano numbers. * gcd (allocation goes up 20 % from 7.8 to 7.10) using Integers, tuples (for extended Euclid), lists (for control) * tak (runtime goes up 20 % from 7.6 to 7.8) the plain Takeuchi function, just Int and recursion (it should not allocate at all?) (and I confirmed these by manually running them for more inputs, all measurements done on debian on x86_64 X5365, ghc-6.* installed from binary packages, ghc-7.* built from source) So, can this be explained? Improved? I think we should resist the temptation to change these benchmarks (using seq and ! and Int# and whatnot) Assuming nofib contains typical code, it is the task of the compiler to handle it well. In case you're wondering about my motivation - this was prompted by teaching, I wanted to show that ghc creates efficient code (by fusion) - but it's not just for the show, I generally try to believe in what I teach and I do rely on this for my real code. (Well, by definition, "real" for me might still be "academic" for others...) - Johannes.

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ideas for extending 'tensor'
by Petr Pudlák 07 Jan '16

07 Jan '16

Hi Nicola, I was very excited to see your type-safe tensor package. Are the sources available somewhere for contributing? I'd be interested in trying to extend it to use unboxed vectors, or perhaps even repa or yarr. Are there any future plans like that? Also it'd be interesting to add the distinction between covariant and contravariant indices, although this would be most likely a major change. Or perhaps it'd be possible to add it just as some kind of a wrapper. All the best, Petr

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Regarding GSoC 2016
by Abhijit Patel 06 Jan '16

06 Jan '16

I am Abhijit Patel, B.Tech second year student from Dhirubhai Ambani Institute of Information and Communication Technology (DA-IICT) . I have learnt haskell from the learnyouahaskell.com and I was informed that the tasks for GSoC .I need some guidance and someone who can give me some tasks to raise my level to start contributing to the haskell community.

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FRP : Best way to save signal history if the program needs to temporarily terminate?
by Zans Tangle 06 Jan '16

06 Jan '16

Hi guys, so I'm getting my head around FRP, and the theory is starting to make sense (just seen Conal Elliott's explanation of the original formulation and it was very illuminative). Overall I'm finding signals to be a really nice level of abstraction to reason about my code state. However I'm a little bit stuck on something: lets say I want to switch off the program, but I want it to save the signal history so that I can resume where I left off when I switch it back on. Is there a ... simple.. way to do it? Because at the moment I'm thinking of something along the lines of "build an SQL schema that matches the semantics of each FRP signal, and then build functions to translate between signal and SQL when needed". And at this precise instant I don't really feel too excited about implementing Signal-to-SQL translation from scratch (and I'm not even completely sure what sort of SQL schema would be needed to support higher-order FRP either), so I was wondering if anything like that exists already? Or even something as simple as storing the signal history in a file and just parsing it to recover it? Zans

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the state of Yarr?
by Petr Pudlák 06 Jan '16

06 Jan '16

Hi Dominic, what is the current state of Yarr? Is it being actively developed? Is there some tutorial or documentation available? I'm deciding between repa and yarr for some linear algebra computations. I found some references that yarr is more performant, but I couldn't find much documentation and the hackage page [1] hasn't indexed most modules for some reason, so there seems to be no good place to start from. And the last commit was 9 months ago. [1] https://hackage.haskell.org/package/yarr Thank you, Petr

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hscolour color set for white/light background?
by Conal Elliott 06 Jan '16

06 Jan '16

Does anyone have handy an hscolour ColourPrefs for use with a white/light background? The defaultColourPrefs <https://hackage.haskell.org/package/hscolour-1.23/docs/Language-Haskell-HsC…> look okay with a dark background but not light. Thanks, - Conal

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