September 2007 - Haskell-Cafe

Spot the difference!
by PR Stanley 20 Sep '07

20 Sep '07

Hi \_ n -> 1 + n \_ -> (\n -> 1 + n) The outcome seems to be identical. is there a substantive difference between the two definitions? The second one seems to be more expressive of the currying principle. Any thoughts? Thanks, Paul

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Call for Abstracts for 3rd SAPLING Meeting, November 12, 2007
by Manuel M T Chakravarty 20 Sep '07

20 Sep '07

Call for Abstracts for 3rd SAPLING Meeting, November 12, 2007 Sydney Area Programming Language INterest Group http://www.comp.mq.edu.au/plrg/sapling.html 10am-4:30pm, November 12, 2007 Engineering Theatre, Building 32 (Engineering) Australian National University Invited Speaker --------------- Prof William M Waite, University of Colorado, Boulder, USA About SAPLING ------------- SAPLING aims to promote and develop academic research in the Programming Languages field within the Sydney area, including nearby regional centres such as Canberra, Newcastle and Wollongong. Important Dates: ---------------- - Submission deadline: Oct 15, 2007 - Notification: Oct 19, 2007 - Workshop: November 12, 2007 SAPLING Meetings ---------------- SAPLING meetings are held twice a year to allow programming language academics, researchers and students to present and discuss their research in an informal setting. The third meeting will be held at the Australian National University. SAPLING talks are generally of 20 minutes duration with substantial periods of time available for discussion. Talks can present completed work, outline work in progress, demonstrate a system, or provide a short tutorial on a topic of general interest. Submissions for talks should be in the form of an abstract no longer than one A4 page in plain text, PostScript or PDF format. The abstract should be emailed to Tony Sloane (asloane AT ics.mq.edu.au) by close of business on October 15, 2007. As far as possible, selection of presenters is non-competitive, with all interested qualified speakers given an opportunity to talk, within the time constraints of a one day meeting. Preference will be given to topics of general interest. No proceedings will be published but the talk abstracts and links to related material will be published on the SAPLING website. There is no registration fee to attend this meeting. Participants will be responsible for their own lunch costs. Accommodation ------------- For non-Canberra residents, some accommodation suggestions are available on the web site for this meeting: http://www.comp.mq.edu.au/~asloane/pmwiki.php/SAPLING/SAPLING072 Steering Committee: ------------------- Anthony Sloane, Macquarie (Chair), asloane AT ics.mq.edu.au Manuel Chakravarty, UNSW, chak AT cse.unsw.edu.au Clem Baker-Finch, ANU, Clem.Baker-Finch AT anu.edu.au

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wxhaskell package for ubuntu feisty, amd64
by Iván Pérez Domínguez 20 Sep '07

20 Sep '07

I'm trying to install wxhaskell in ubuntu feisty, with ghc-6.6. After several days of trial and error and a few hours trying to change all types in my program to gtk2hs types, I'm tired. Does anyone have a .deb for wxhaskell that works with ghc-6.6?

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What on earth
by PR Stanley 20 Sep '07

20 Sep '07

Hi tfoldr (-) 1 [4,3] = 4-3-(-1) = 2 A similar thing happens with foldr (/) 2 [8,2] = 8.0 I thought foldr \oplus v [] = v Any ideas? Thanks, Paul

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Re: [Haskell-cafe] length defined with foldr
by PR Stanley 20 Sep '07

20 Sep '07

>>Still fighting with the botched OCR? >>I am, as a matter of fact! Is that okay with you? *smile* > > > >>length = foldr (\_ n -> 1 + n) 0 >> >>-- >>brandon s. allbery [solaris,freebsd,perl,pugs,haskell] allbery(a)kf8nh.com >>system administrator [openafs,heimdal,too many hats] allbery(a)ece.cmu.edu >>electrical and computer engineering, carnegie mellon university KF8NH

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Why isn't pattern matching lazy by default?
by Peter Verswyvelen 19 Sep '07

19 Sep '07

I'm experimenting with functional reactive programming for creating simple 2D/3D video games and interactive apps, trying to develop my own version of it from scratch, for learning Haskell. I got stuck with an endless loop when trying to split a stream into a pair of two streams (a kind of reactive if/then/else). Luckily I first read the Haskell School of Expression so I remembered that pattern matching is not lazy and this could be the cause, which it was (I had to replace (x:xs) by ~(x:xs)) I could also fix the problem by not using pattern matching at all, using head/tail calls instead. Now why isn't pattern matching lazy by default? This seems odd for a newbie since everything else is lazy by default. Thanks, Peter

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

19 Sep '07

The book is very well written. I did try to follow the wikibook thingummajig but found the English a bit trying. Cheers Paul t 07:43 19/09/2007, you wrote: >Paul, > >The Hutton book has gotten great reviews, but pouring over a faulty >OCRd version can only be counterproductive. I highly recommend Yet >Another Haskell Tutorial[1]. After that you can check out all the >other wonderful online resources (starting here [2]). At that point a >few OCR errors won't be able to stand in your way! > >Best wishes on you Haskell explorations, >Joel > >[1] http://www.cs.utah.edu/~hal/docs/daume02yaht.pdf >[2] http://haskell.org/haskellwiki/Learning_Haskell >_______________________________________________ >Haskell-Cafe mailing list >Haskell-Cafe(a)haskell.org >http://www.haskell.org/mailman/listinfo/haskell-cafe

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Re: [Haskell] Functor ((,) a)
by Ross Paterson 19 Sep '07

19 Sep '07

On Wed, Sep 19, 2007 at 10:24:50AM +0200, Janis Voigtlaender wrote: > BTW, what would have been the easiest way for me to find this out on my > own? Somehow, I would have hoped to be able to navigate to the appropriate > point from the mentioned place in the online docs, where it is stated that > the instance in question exists. Usually the instance for C (T a1 ... an) should be in either the module defining C or the one defining T (so if you import both you have it); if T is from the Prelude, then the instance should be together with C. But Control.Monad.Instances is a special case, because exists to hold instances of Haskell 98 classes for H98 types that are not defined in H98. Putting them in the proper place would break compatibility with H98.

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Missing Symbol (2)
by PR Stanley 19 Sep '07

19 Sep '07

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

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Re: [Haskell] downtime for monk ({darcs, hackage, cvs}.haskell.org) Monday from 3pm UTC
by Ian Lynagh 19 Sep '07

19 Sep '07

On Wed, Sep 19, 2007 at 09:16:56AM +0100, Bayley, Alistair wrote: > > From: haskell-bounces(a)haskell.org > > [mailto:haskell-bounces@haskell.org] On Behalf Of Ian Lynagh > > > > The machine called monk ... > > will be down from 3pm UTC on Monday 24th for an OS and RAM upgrade. > > Do you have any estimate for how long the upgrades will take? That depends on how many things go wrong. I'll send an e-mail when we believe it's all up and working again. Thanks Ian

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