February 2009 - Haskell-Cafe

Re: [Haskell-cafe] How to create an online poll
by gregg reynolds 18 Feb '09

18 Feb '09

But what about the side effects? Rick R <rick.richardson(a)gmail.com> wrote: >I'm sure Premier Election Solutions (formerly Diebold) can provide us with >an online voting solution. >Their value-add services allows us to set the outcome beforehand, so, in >effect, the the voting process will be determinate. Which is certainly of >interest to Haskell coders. > > >On Wed, Feb 18, 2009 at 4:05 PM, Max Rabkin <max.rabkin(a)gmail.com> wrote: > >> On Wed, Feb 18, 2009 at 10:40 PM, Anton van Straaten >> <anton(a)appsolutions.com> wrote: >> > There's also the Condorcet Internet Voting Service: >> > >> > http://www.cs.cornell.edu/andru/civs.html >> >> This looks like exactly what we need! Any objections? >> >> --Max >> _______________________________________________ >> Haskell-Cafe mailing list >> Haskell-Cafe(a)haskell.org >> http://www.haskell.org/mailman/listinfo/haskell-cafe >> > > > >-- >We can't solve problems by using the same kind of thinking we used when we >created them. > - A. Einstein >_______________________________________________ >Haskell-Cafe mailing list >Haskell-Cafe(a)haskell.org >http://www.haskell.org/mailman/listinfo/haskell-cafe

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Haskell users in the Houston area??
by Galchin, Vasili 18 Feb '09

18 Feb '09

Hello, Are there Haskell users in the Houston area? Regards, Vasili

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question on types
by Daryoush Mehrtash 18 Feb '09

18 Feb '09

Is there a way to define a type with qualification on top of existing type (e.g. prime numbers)? Say for example I want to define a computation that takes a prime number and generates a string. Is there any way I can do that in Haskell? thanks, Daryoush

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How to create an online poll
by Bulat Ziganshin 18 Feb '09

18 Feb '09

Hello haskell-cafe, http://zohopolls.com/ -- Best regards, Bulat mailto:Bulat.Ziganshin@gmail.com

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ANN: The Typeclassopedia, and request for feedback
by Brent Yorgey 18 Feb '09

18 Feb '09

Hi all, If you've noticed the lack of a HWN this week, that's because I've been doggedly finishing my article entitled 'The Typeclassopedia', which I have just submitted for publication in the Monad.Reader. Here's the abstract: The standard Haskell libraries feature a number of type classes with algebraic or categorical underpinnings. Becoming a fluent Haskell hacker requires intimate familiarity with them all, yet acquiring this familiarity often involves combing through a mountain of tutorials, blog posts, mailing list archives, and IRC logs. The goal of this article is to serve as a starting point for the student of Haskell wishing to gain a firm grasp of its standard type classes. The essentials of each type class are introduced, with examples, commentary, and extensive references for further reading. My hope is that this will be a valuable resource to the Haskell community, especially those who are learning. Any feedback would be greatly appreciated, especially if it helps improve the article before publication. A draft can be found here: http://www.cis.upenn.edu/~byorgey/papers/typeclassopedia-draft-090216.pdf Also see my blog post for a bit more info: http://byorgey.wordpress.com/2009/02/16/the-typeclassopedia-request-for-fee… happy haskelling! -Brent

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what is [::]
by Daniel van den Eijkel 18 Feb '09

18 Feb '09

Dear Haskellers, please can anybody tell me what [::] means or where to read about it? A few days ago I saw this for the first time in my life, at the list of instances of the Functor class, and I don't know where to look for information. The search engines I tried didn't produce results for [::]. Thanks, Daniel

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estimating the speed of operation
by Belka 18 Feb '09

18 Feb '09

Hello, communion people! I have a little problem and ask for an advice. I'm trying to estimate the performance speed of one pure function, but get some strange results. ------------------------------------- import qualified module Data.ByteString.Lazy.Char8 as L8 import module Data.Digest.Pure.MD5 import module System.IO.Unsafe import module System.Time import module System.Random import module Data.Char clockTime2Tuple (TOD sec pic) = (sec, pic) getClockTimeTuple = getClockTime >>= (\ x -> return $ clockTime2Tuple x) subTimeTuples (s2,ps2) (s1,ps1) = let dps = ps2-ps1 in let (s,ps) = (s2-s1-(if dps<0 then 1 else 0), if dps<0 then dps+(10^12) else dps) in (s, (div) ps (10^6)) test_md5 test_input n = flip mapM test_input ( \ input_row -> do t1 <- getClockTimeTuple sequence_ (replicate n (return $ md5 input_row)) t2 <- getClockTimeTuple dt <- subTimeTuples t2 t1 return (dt) ) test_list = [ pack "Hello world!"] ++ [L8.replicate 1000000 ':'] ------------------------------------- The results are (iterations_count, microseconds): (1000, [105,105]) (+/- 10) (10000, [1000,950]) (+/- 50) (100000, [9050,9000]) (+/- 50) (1000000, [89200,89150]) (+/- 100) ------------------------------------- I suspect following problems, which make the results non-objective: 1. I cant get out of laziness 2. I don't turn off GHC internal optimizers So, perhaps, GHC evaluates the MD5 once, but cycles on something else?.. For now I can only guess. Could anybody, please clarify and maybe suggest configuration, which would allow objective speed estimation? Thanks in advance, Best regards, Belka -- View this message in context: http://www.nabble.com/estimating-the-speed-of-operation-tp22075843p22075843… Sent from the Haskell - Haskell-Cafe mailing list archive at Nabble.com.

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Bug in Cabal?
by Martin Huschenbett 18 Feb '09

18 Feb '09

Hello haskell-cafe, trying to install ghci-haskeline I got the following error message: $ cabal install ghci-haskeline Resolving dependencies... cabal.exe: dependencies conflict: ghc-6.10.1 requires process ==1.0.1.1 however process-1.0.1.1 was excluded because ghc-6.10.1 requires process ==1.0.1.0 Looks like this is a bug in Cabal or cabal-install? Regards, Martin.

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concurrent haskell debugging
by Jianzhou Zhao 18 Feb '09

18 Feb '09

Hi Folks, If I am using Control.Concurrent package, does GHC have any static or runtime tools or debuggers to detect problems, such as deadlock, data races? Cheers Jianzhou

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Fwd: [Haskell-cafe] question on types
by Alberto G. Corona 18 Feb '09

18 Feb '09

As allways, I forgot to forward the message to the list, but the Conor response makes it irrelevant: ---------- Forwarded message ---------- From: Alberto G. Corona <agocorona(a)gmail.com> Date: 2009/2/18 Subject: Re: [Haskell-cafe] question on types To: Ryan Ingram <ryani.spam(a)gmail.com> > Seriously, I love undecidable instances, but there's gotta be a way to > make type-level programming less painful. GHC team: please give us > type-level integers that don't suck! If I ever have to see S (S (S (S > Z))) again it's too soon. I´m starting to read about dependent types and it´s very promising. Maybe my suggestion makes sense: is to "compress" recursive types such are S(S(S(S Z))) into internal compiler representations S <n> Z. This would type match faster and will generate much more clear and compact compilation errors.

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