September 2007 - Haskell-Cafe

(win)hipe for Haskell?
by Peter Verswyvelen 19 Sep '07

19 Sep '07

During a googling session, I can across (Win)HIPE, a visualization program for the functional language HOPE. See http://dalila.sip.ucm.es/~cpareja/winhipe IMHO a similar tool would be a nice for learning/teaching Haskell; does that exist, or something else that comes close? Thanks, Peter

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Re: [Haskell-cafe] Missing Symbol (2)
by PR Stanley 19 Sep '07

19 Sep '07

It's probably \oplus then. The font size according to my trusty screen reader is 11 point which is not particularly large. Still, if anybody else finds it annoying I'll reduce it to 9pt. Paul At 13:21 19/09/2007, you wrote: >This looks like foldr, specifically: >f = foldr (.) v > >so really, there's no way of telling what the operator could be, other >than that: >(.) :: a -> b -> b >where >f :: [a] -> b >v :: b > >BTW, I find that most of your emails are in a very large font size. Do >other people notice this? It's not very nice to read. Gmail's 'Show >Original' feature tells me that the HTML version of your message >contains <font size=3> near the start. > >On 19/09/2007, PR Stanley <prstanley(a)ntlworld.com> wrote: > > Hi > > Here's another one: > > f [] = v > > f (x:xs) = x . f xs > > The "." is supposed to denote a generic operator - f [] maps to some > > value v and applied to non-empty list applies head to ? operator. > > Thanks, Paul > > > > _______________________________________________ > > Haskell-Cafe mailing list > > Haskell-Cafe(a)haskell.org > > http://www.haskell.org/mailman/listinfo/haskell-cafe > >

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transparent parallelization
by Thomas Girod 19 Sep '07

19 Sep '07

Hi there. Beeing rather new to the realm of Haskell and functional programming, I've been reading about "how is easier it is to parallelize code in a purely functional language" (am I right saying that ?). My knowledge of parallelization is also very weak, but I've been thinking about this and I have a question. Let's say we take a small piece of code, like the quicksort algorithm. > qsort [] = [] > qsort (x:xs) = qsort lesser ++ [x] ++ qsort greater > where lesser = filter (<x) xs greater = filter (>=x) xs (actually I didn't test this code, this is just for the example) Here, computing "lesser" and "greater" are two disjoint actions - we don't need the result from one to compute the other, and haskell does not allow one to alter data so that would change the behaviour of the other. So I guess those could be run in parallel. Would it be fairly simple to automatically determine parts of code that can be run in parallel, and parts that cannot (at least in non-monadic code) ? So the final question is : if it is possible to automatically define segments of code that can be run in parallel, is [insert compiler name here] compiling this code as a one thread thing, or as a multithreaded version ? I guess on single processor machines, it is more efficient to do it as a single thread - but with those "many-cores" processors that are coming, it probably won't be true anymore. Sorry if this post is blowing off open doors (I guess this doesn't mean anything in english but it sounds cool) ... Regards Thomas Girod

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Re: [Haskell] Functor ((,) a)
by Bas van Dijk 19 Sep '07

19 Sep '07

On 9/19/07, Janis Voigtlaender <voigt(a)tcs.inf.tu-dresden.de> wrote: > BTW, what would have been the easiest way for me to find this out on my > own? The following is probably not the easiest way: I keep a copy of the sources of GHC and the libraries [1] on my disk. When I want to search for something I simply do a grep. In emacs you also have a grep-find function which performs a grep in the background and shows the result in a new buffer. The results are hyperlinked so you can just click on a result and emacs will open the respected file and jump to the found string. In your case you do a 'M-x grep-find' followed by the search string: "instance Functor ((,)". This will result in: ./Control/Monad/Instances.hs:19:instance Functor ((->) r) where ./_darcs/pristine/Control/Monad/Instances.hs:19:instance Functor ((->) r) where I think you can get rid of the annoying _darcs... by following: [3]. I haven't tried that though. (Note I'm on Linux. I don't know if this works in Windows. It probably does with Cygwin.) Of course the disadvantage of this approach is that you have to know exactly what you are looking for. Then there's also Hoogle [3] with which you can search for names or types. However in your case this wouldn't have helped. regards, Bas [1] http://hackage.haskell.org/trac/ghc/wiki/Building/GettingTheSources [2] http://wiki.darcs.net/DarcsWiki/HintsAndTips#head-c189bd259a3d141796ebb4f8d… [3] http://haskell.org/hoogle

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help me ! who has vty ?
by clisper 19 Sep '07

19 Sep '07

who has vty for haskell? I can't find the right one so who can mail one to me ? thanks 2007-09-19 clisper

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Re: [Haskell] Functor ((,) a)
by Matthew Brecknell 19 Sep '07

19 Sep '07

Janis Voigtlaender: > What do I have to import to get the Functor ((,) a) instance? (redirected to haskell-cafe) Control.Monad.Instances, believe it or not.

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Re: [Haskell] Swapping parameters and type classes
by Simon Marlow 19 Sep '07

19 Sep '07

Ian Lynagh wrote: > On Tue, Sep 18, 2007 at 03:48:06PM +0100, Andrzej Jaworski wrote: >> Responding to Simon Peyton-Jones' reminder that this is a low-bandwidth list I >> was obscure and commited a blunder. >> >> This one and many other threads here are started undoubtedly by experts [sorry >> guys:-)] and coffee brake should work for them, but on numerous occasions >> threads here spawn beginner type questions. So, my thinking was that it is >> perhaps against the tide trying to stop them. >> Why not to make the list Haskell a first contact general practitioner? Then >> creating e.g. "Announcements & Challenge" or "Announcements & ask guru" list >> could take the best from "Haskell" but also would make it less front line and >> thus more elitist, which should imply the manner by itself. > > I proposed renaming > haskell@ -> haskell-announce@ > haskell-cafe@ -> haskell@ > in http://www.haskell.org/pipermail/haskell-cafe/2007-July/028719.html I suggested the same thing at the time we created haskell-cafe, but the concensus was in favour of haskell-cafe. At the time I didn't think it would work - for a long time, the number of subscribers to both lists was almost the same - but now I have to admit I think haskell-cafe is a big win for the community. The -cafe extension gives people the confidence to post any old chatter without fear of being off-topic, and I'm sure this has helped the community to grow. Those of us who grew up with Usenet (RIP) are more at home with the foo/foo-announce split, and it's certainly quite conventional for mailing-list naming too, but on the whole I don't think doing things differently has really done us any harm and it may well have been a stroke of genius :-) Cheers, Simon

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Re: [Haskell-cafe] Missing Symbol
by PR Stanley 19 Sep '07

19 Sep '07

> > Hi > > What symbol would you replace the "?" with: > > the identity function > > id x = x? > >I don't think I'd have anything where the ? symbol is. > >id x = x works just fine. Ah, that's interesting because there's a "." to the right of x in my scanned doc. Still, if no symbol is necessary, so much the better! Cheers, Paul

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Missing Symbol
by PR Stanley 19 Sep '07

19 Sep '07

Hi What symbol would you replace the "?" with: the identity function id x = x? My scanned copy of the Hutton book contains some rather interesting characters. In fact, the OCR program has placed a "." in place of most symbols - e.g. ->, <- ^, <=, \=, etc. Fortunately, I'm able to guess the correct operator in the majority of the cases. Cheers, Paul

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ANN: hstats-0.1
by Marshall Beddoe 19 Sep '07

19 Sep '07

http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hstats-0.1 I've just released hstats, a statistical computing module for the Haskell language. Current functionality includes: mean, median, mode, range, standard/average deviation, variance, iqr, kurtosis, skew, covariance, and correlation. I have plans on adding more rank correlation functions, histograms & chi square tests. darcs repo: http://www.sftank.net/code/hstats

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