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[Haskell-cafe] REMINDER - Contributions to HC&A Report (May 2004 edition)
by Arthur van Leeuwen 03 May '04

03 May '04

Dear Haskellers, we would like to remind you of the opportunity to contribute to the May 2004 edition of the Haskell Communities & Activities Report. Why not take the few minutes necessary to type up a new or updated entry and send it in? We would love to see people write on the following subject(s): - The Haskell Mailing List - The Haskell Cafe - The Haskell 98 reports - Concurrent Haskell - hierarchical libraries - HaskellDB - HXml - QuickCheck - Yale Haskell group - Parallel and Distributed Functional Languages Research Group at Heriot-Watt University Ofcourse, if you have done other interesting things with Haskell we would very much like to know about those as well! If at all possible, could you please send in your contribution by friday *this* week, i.e. May 7th 2004? We will update the topics list on http://www.haskell.org/communities/topics.html with a nice tickmark as soon as we have received your contribution, to show that you too support the Haskell Communities and Activities Report! Thanks, Arthur (interim editor, May 2004 edition) -- Haskell Communities and Activities Report (May 2004 edition) All contributions are due in by the end of next week! http://www.haskell.org/communities/

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Call for recommendation
by 无云 01 May '04

01 May '04

Hi, all I'm a newbie to Haskell and FP now, I need your help. Could anybody give me any advice on how to learn and master the Haskell language and thinking/programming in FP? I especially expect a list of some excellent books on Haskell. M.H.Fan 05/01/04 ======================================================== 是邮件你收有病毒我上！VIP邮箱全面保护！ http://vip.163.com 中国最大的免费邮箱在等你 25兆空间4兆附件！　　　　　 http://mail.163.com 点击网易泡泡惊喜无限全免费手机短信任你发!　　　　　　http://popo.163.com

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Is it possible to read existential types?
by S. Alexander Jacobson 29 Apr '04

29 Apr '04

Is is possible to read/show an existentially typed list? Would it be possible if, instead of using read/show, I defined some variant that relies on the typeof/typeable infrastructure? Is there a way to read in a typename for use in coercing a read? -Alex- _________________________________________________________________ S. Alexander Jacobson mailto:me@alexjacobson.com tel:917-770-6565 http://alexjacobson.com

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Re: sizeFM type
by Tomasz Zielonka 28 Apr '04

28 Apr '04

On Mon, Apr 26, 2004 at 08:43:44PM -0400, ajb(a)spamcop.net wrote: > > And re sizeFM, I would note that Google has more > > than 2^31 pages indexed in memory. > > I would note, in addition, that they don't have that many pages indexed > on a single machine. Almost nobody has a database with that many records > on a single machine, even those who have clusters of 64 bit machines. It seems I qualify as almost nobody, cause I've had a database with more than 2^34 records on a single IA32 machine. However, I wouldn't ever think of loading the entire database to RAM. Best regards, Tom -- .signature: Too many levels of symbolic links

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Re: [Haskell-cafe] Re: sizeFM type
by S. Alexander Jacobson 27 Apr '04

27 Apr '04

On Tue, 27 Apr 2004, Tomasz Zielonka wrote: > The data you provided is interesting. However, if I had such a machine, > my work could be much less challenging :) I would note that people today are making strenuous efforts to retain compatibility with a Haskell98 standard that it only 6 years old! If we are making choices intended to have a lifetime of e.g. 10 years (see <http://www.joelonsoftware.com/articles/fog0000000017.html>), then I would observe that the 24gb machine I specced out will, assuming Moore's law lasts, cost only $2k in 5-6 years. The Sun Fire 15k with 288GB of memory and 72 Sparcs (think GPH!), that today costs $2.6m will cost only $155k. Note, since you don't need 72 CPUs, you'll probably be able to get this machine for <$50k. So, perhaps the question here is: What is the planned lifetime of sizeFM? Do we prefer the safety of knowing our code will work at arbitrary scale or the ecstacy of having it run fast today? Put differently, would you rather cope with hardware limitations today or software limitations tomorrow? -Alex- _________________________________________________________________ S. Alexander Jacobson mailto:me@alexjacobson.com tel:917-770-6565 http://alexjacobson.com

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Re: [Haskell] Re: sizeFM type
by Ketil Malde 27 Apr '04

27 Apr '04

[Moved to -cafe at SPJ's request] "Serge D. Mechveliani" <mechvel(a)botik.ru> writes: > On Mon, Apr 26, 2004 at 10:09:18PM +0200, Ketil Malde wrote: >> "Serge D. Mechveliani" <mechvel(a)botik.ru> writes: >>> length :: [a] -> Integer >>> smallLength :: [a] -> Int >> Hmm...isn't it possible to use a class here? Perhaps even Num? > I think, for many functions, like length, it is most natural to > return Integer only. Well, perhaps Integral is a better choice. I was perhaps thinking of functions like: average xs = sum xs / length xs I'd rather have a polymorphic "length", than different versions for each possible return type. One problem could be that with average xs = sum xs / fromIntegral (length xs) the return type of length becomes ambigous? -kzm -- If I haven't seen further, it is by standing in the footprints of giants

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Data constructors
by Mark Carroll 26 Apr '04

26 Apr '04

I keep running into annoyance in having to name data constructors differently if they're for different types if they're in the same module or something. I wish that something like some Type.Constructor syntax worked in order to disambiguate. Or, better still, I have that problem with function names too (e.g. Data.List.union, Data.Set.union, IIRC) and it occurs to me that a lot of this can be resolved automatically because the types only make sense with one of the choices. I'm not really proposing any changes; more, I'm wondering what others' thinking is about this sort of thing - what annoys them, how they get around it, etc. -- Mark

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Hierarchical Library
by haskell＠alias.spaceandtime.org 24 Apr '04

24 Apr '04

Hello, Why does this fail? ========================== import System.Posix test = Temp.mkstemp ========================== Are the libraries hierarchical in name only? Thanks, James

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FiniteMap, Map, FiniteSet, Set
by haskell＠alias.spaceandtime.org 24 Apr '04

24 Apr '04

Here's a really elementary question: Why does the library have [FiniteMap and Set] instead of [FiniteMap and FiniteSet] or just [Map and Set]? Is there some reason for this inconsistency? Thanks, James

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Syntax for modifying nested product types
by Mark Carroll 23 Apr '04

23 Apr '04

I have data objects where each component is a labelled field through which I access or modify it. I have a hierarchy of these - many of the fields are themselves such data objects, so I may need to apply a few selector functions to get down to what I want (call these "deep"). For fairly flat things, the updates using field labels are okay. However, when I have a function that needs to tweak various bits of various "deep" fields, based on various conditions, then it gets really ugly, not least because of the conditions: foo { bar = baz } becomes, let old = bar foo in foo { bar = if cond then f old else old } or whatever. Do I need such a let for each component and sub-component of the object that has a child that may be modified, or will foo { bar = if cond then f (bar foo) else bar foo } be suitably optimised? (The if's inside the {} because there may be multiple fields (or children thereof) being modified based on different conditions.) -- Mark

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