- Haskell-Cafe - Haskell.org

RE: Space explosion
by Simon Marlow 06 Jan '03

06 Jan '03

> > -- Specs contains the options for the simulation; > rollBounds simply > finds the lowest and highest possible rolls > > -- type RollValue = Int > > -- type RollValueDist = Array RollValue Int > > probDist :: Specs -> [RollValue] -> RollValueDist > > probDist specs rolls = > > accumArray (+) 0 (rollBounds specs) [(r, 1) | r <- rolls] > > It should be doing an in-place array update as it evaluates the > comprehension, but apparently something's being kept in memory longer > than it has an excuse for. It does do a sequence of in-place updates, but this is another instance of the foldl space leak. The additions aren't being performed strictly, so the array is filling up with suspensions. For example: accumArray (+) 0 (1,10) [(3,1), (3,1), (3,1), ...] would produce this sequence of arrays as accumArray processed its input list: { (3,1), ... } { (3,1+1), ... } { (3,1+1+1), ... } we should really have a strict version of accumArray (the lazy version *is* useful sometimes: you can refer recursively to the final array, for example). A quick workaround in your case (GHC only, I'm afraid) is to use UArray instead, available from Data.Array.Unboxed. These arrays contain unboxed values and are therefore strict by definition; and you can use all the usual array operations including accumArray. This workaround only applies if you're using one of the types supported by UArray though (Int, Char, and other base types). Cheers, Simon

1 0

Using SGML/XML in literate code
by Peter Simons 06 Jan '03

06 Jan '03

I understand that I can mark-up code segments in a literate source module using the syntax: \begin{code} ... \end{code} But is it somehow possible to re-define this to be <haskellcode> ... </haskellcode> instead? I am asking because the latter style would enable me to write literate programs in DocBook, HTML, or any other SGML-based mark-up format. And _that_ would be very useful indeed. :-) -peter

1 0

Re: Web Application Development
by Christopher Milton 06 Jan '03

06 Jan '03

--- Dominic Steinitz <dominic.steinitz(a)blueyonder.co.uk> wrote: [snip] > The original code was in PHP and MySQL so rather than re-invent the wheel I [snip] > So my question is: what should I do to re-write this in Haskell? I haven't tried it out, but I found this project on SourceForge: http://sourceforge.net/projects/functional-php/ on to the Haskell stuff... > From the discussion on this mailing list in June and reading through the > libraries section of haskell.org, I think there are the following options: > > HTML > > 1. Use Wash/CGI but maybe somehow move to mod_haskell if the webserver > performance isn't adquate. HaXml could also be quite useful for generating HTML or XML: http://www.cs.york.ac.uk/fp/HaXml/ > SQL > > 2. Use MySQL-HS which requires HaskellDirect or use HSQL. > > I'd be very grateful for any advice and any progress as a result of the > discussion in June. Ashley Yakeley has an interface to MySQL: http://cvs.sourceforge.net/cgi-bin/viewcvs.cgi/hbase/Source/Foreign/ and I was thinking of extending the DBI model as found in Perl and the libpq binding as listed on Haskell.org: http://www.astercity.net/~khaliff/haskell/dbi/dbi.tgz Searching Freshmeat and SourceForge for Haskell turns up a few things. Actually, there's quite a bit of alpha and beta Haskell code out on the net, but we don't seem to get very far with much of it... ===== Christopher Milton cmiltonperl(a)yahoo.com __________________________________________________ Do you Yahoo!? Yahoo! Mail Plus - Powerful. Affordable. Sign up now. http://mailplus.yahoo.com

1 0

Editor Tab Expansion
by Jim Greer 03 Jan '03

03 Jan '03

Greets - [ Better late than never. ] Ran across this thread while perusing list trying to figure out whether to join or not. In the interest of sharing info with the great collective unconscious (i.e. Internet), thought I'd include part of my .vimrc so that Vim users (and others considering the same) can see how it handles the embedded tab/whitespace layout problems of various languages: set background=dark syntax on filetype on set textwidth=72 autocmd Filetype haskell set ai autocmd Filetype haskell set expandtab autocmd Filetype haskell set tabstop=8 autocmd Filetype haskell set shiftwidth=8 autocmd Filetype mail set ai autocmd Filetype mail set tabstop=4 autocmd Filetype mail set shiftwidth=4 autocmd Filetype ruby set ai autocmd Filetype ruby set tabstop=2 autocmd Filetype ruby set shiftwidth=2 A complete ('enhanced') install of Vim includes syntax recognition for a great number of file formats, including Haskell (apparently, haven't done much yet). Setting syntax on manages the syntax recognition part, so that you get colorized syntax. Setting filetype on recognizes files (by extension?), so that you can use the autocmd FileType haskell .... commands to tailor settings for particular filetypes. In this case, I'm using expandtab and setting the tab settings to 8, as mentioned previously. Cordially, Jim G p.s. http://www.vim.org/ p.p.s. I'm suprised that the *macs crowd hasn't chimed in with ways to configure their editos^Hr to set tabs differing by day of week, phase of moon, etc. -- James B. Greer <jgreer(a)midsouth.rr.com> [expires: 2004-12-27] 7F49 3D20 03C6 E859 E4F9 0735 E1F9 B259 21FA 1494

1 0

Firmalar İçin En Verimli ve Karlı TİCARET PORTALI Açıldı...
by Neslihan ÇETİN 03 Jan '03

03 Jan '03

Bu mesajın içeriğini düzgün bir şekilde göremiyorsanız, www.e-talep.com/tanitim <http://www.e-talep.com/tanitim> adresini ziyaret edebilirsiniz. <http://www.e-talep.com> _____ Neden ? E-ticaret Neden ? E-talep.com _____ Ticaretin %35'i internete taşınacak, sizde yerinizi alın !!! 2005 yılına kadar firmalar arası ticaretin %35'inin elektronik ortama taşınacağı tahmin edilmektedir. Bir firma çalışanı olarak veya firma sahibi olarak bu gelişmelerin dışında kalmayıp, sizin için tasarlanan ve hizmetinize sunulan E-talep.com gibi ücretsiz teknolojileri çalışma hayatınıza entegre etmelisiniz. E-talep.com ile Firmanız daha hızlı kar edecek Firmaların, Pazarlama ve Satınalma bölümleri için tasarlanan E-talep.com, karlı ticaret ortamı ile satışlarınızda artışa neden olacak, böylece hızlı kar etmenizi sağlayacak. Satın almada ki %15'lere varan fiyat avantajı ile girdi maliyetleriniz azalacak, böylece kar marjınız yükselecektir. E-talep.com ile rekabet gücünüzü ve verimliliğinizi artıracaksınız Tüm kamu ve firma alımlarından veya bizim tabirimizle; güncel taleplerden anında haberdar olacak, rakip firmaların bir adım önüne geçeceksiniz. Ayrıca pazarlama ve satın alımda verimliliği artırarak zaman ve para tasarrufu sağlayacaksınız. Satın alım sırasında %8 ile %15 arası kar edeceksiniz Firmanızın alımlarını e-talep.com üzerinde yayınlayarak, beklemediğiniz fiyat indirimleri ile karşılaşacak, girdi maliyetlerinizi azaltacaksınız. Alımlar sırasında ortalama %8 ila %15 arası kar sağlayacaksınız. Firmalar için zaman çok daha hızlı akıyor Firmaların artık hantal bir yapıyla büyümesi söz konusu değil, artık satacağı ürünleri kısa sürede pazarlamalı, ihtiyaç duyduğu ürünleri ise daha hızlı siparişedip satın almalı. E-talep.com yüksek teknolojisiyle, yatırım yapmanıza ve para harcamanıza gerek kalmadan bu imkanı size sunuyor. E-talep.com ailemizde sizi de görmek istiyoruz Her geçen gün ailemiz büyüyor 2 ay gibi kısa bir sürede 1000 üyeyi aştık, zamanla daha büyüyeceğimiz inancındayız. Ailemize katılarak, küçük ve orta ölçekli firmaların, kamu kurum ve kuruluşlarının oluşturduğu çok geniş bir alıcı ve satıcı kitlesine ulaşacak, yeni iş ortakları edineceksiniz. E-talep.com'un arkasında güçlü bir kadro var E-talep.com firmalar arası ticaret ve bilişim teknolojilerinde uzman olan, profesyonel bir ekip tarafından tasarlandı. Sizlerden gelen öneri ve isteklerle bu ticaret platformu daha da geliştirilerek, kolay kullanılabilir, verimli ve etkin bir ticaret ortamı oluşturulacaktır. E-talep.com Kullanımı kolay güvenli bir ticaret platformudur E-talep.com kullanımı kolay, üyelerin gizlilik kurallarını gözeten, güvenli bir ticaret platformundur. Daha fazla bilgi için; www.e-talep.com <http://www.e-talep.com> adresini ziyaret edin. _____ Görüş, öneri ve sorularınız için; t ı k l a y ı n <http://www.e-talep.com/Pages/Contact.asp> E-posta almak istemiyorsanız; t ı k l a y ı n <mailto:destek@e-talep.com?subject=E-posta almak istemiyorum>

1 0

RE: Parsing date and time specifications
by Simon Marlow 03 Jan '03

03 Jan '03

> I think it is widely agreed that the time and date structures in the > standard libraries are brok^H^H^H^Hslightly less than useful. > > I suggest you feel free to rewrite it as you see fit, and then lobby > for its inclusion in the hierarchical libraries. > > (My preju^H^Hference would be to store a date-time internally in a > posix-like manner (seconds,microsecond since the epoch).) But a ClockTime *is* implemented as (seconds,picoseconds) since the epoch. CalendarTime is just a human-readable interpretation of the ClockTime, or a way to synthesise a ClockTime from a known date/time. (BTW Peter: the weekday/yearday in a CalendarTime are ignored by the toClockTime in GHC's Time library, so you can set them to anything). I'm still not sure I understand why the Time library is considered to be broken; sure I can see that our implementation of addToClockTime is wrong (adding one minute shouldn't always be the same as adding 60 seconds, for example), but is the design fundamentally wrong? GHC's TimeExts library (package lang) is allegedly a better implementation of addToClockTime/diffClockTime, if anyone is looking for one. Cheers, Simon

5 4

Sets
by Mark T.B. Carroll 02 Jan '03

02 Jan '03

Am I right in thinking that sets of sets don't really work with GHC's Data.Set because "Set a" things aren't instances of Ord? How should I do sets of sets with it? (e.g. Set.mkSet [Set.unitSet 1] gives "No instance for (Ord (Set a))") -- Mark

3 2

Lazy streams and unsafeInterleaveIO
by Jyrinx 02 Jan '03

02 Jan '03

As an experiment for a bigger project, I cooked up a simple program: It asks for integers interactively, and after each input, it spits out the running total. The wrinkle is that the function for calculating the total should be a non-monadic stream function (that is, type [Integer] -> [Integer] so that runningTotals [1,2,3,4,5] == [1,3,6,10,15]). The task is then to write a function to return a stream of integers, grabbing them from IO-land lazily (a la getContents). My first attempts had it not displaying a running total until all input (terminated by an input of 0) had finished, at which point it spit out all the totals (i.e. it wasn't an interactive program anymore). I poked around in the docs and on the Web for a while, and found out about unsafeInterleaveIO, which solved the problem neatly (after I modified runningTotals to be less eager, as it was reading ahead by an extra integer each time). I ended up with the attached code (for GHC 5.04.2). My question is this: Is there a more elegant (i.e. non-"unsafe") way to do this? I vaguely recall from the Hudak book (which I unfortunately don't have convenient at the moment) that he used a channel for something like this (the interactive graphics stuff), but IIRC his system would be overkill for my application (including the bigger project). It doesn't seem like it should need any black magic, and concurrency (which channels need, right?) doesn't appear worth the hassle. Really, my desire comes down to a simple, safe, single-threaded way to write a function to generate a lazy stream. Is there such? Luke Maurer jyrinx_list(a)mindspring.com -- running-total -- Haskell program that takes integers as input, outputting a running total -- after each input -- Demonstrates use of lazy streams module Main where import IO import System.IO.Unsafe import Monad runningTotals :: [Integer] -> [Integer] runningTotals [] = [] runningTotals (x:xs) = rt' 0 (x:xs) where rt' tot (x:xs) = (tot+x) `seq` (tot+x):(rt' (tot+x) xs) rt' _ [] = [] -- Note that runningTotals does what appears to be a stateful calculation when -- numbers are read one at a time; however, lazy streams allow this to be a -- pure function. Haskell is cool. inputNumbers :: IO [Integer] inputNumbers = do x <- putStr "? " >> readLn if x == 0 then return [] else do xs <- (unsafeInterleaveIO inputNumbers) return (x:xs) main = do numbers <- inputNumbers mapM_ (putStrLn . (flip shows) "") (runningTotals numbers)

6 11

call china 6.2¢ www.callez.com
by promotion＠callez.com 31 Dec '02

31 Dec '02

1 0

RE: AW: slide: useful function?
by Mark Carroll 27 Dec '02

27 Dec '02

On Mon, 2 Dec 2002, David Bergman wrote: (snip) > Till then, we "Haskellers" will probably continue expressing our > patterns either directly in Haskell or using highly formal language, > with terms such as "catamorphisms". > > The virtue, and weakness, of traditional design patterns is their > vagueness and informal character, making them (1) comprehensible to the > 90% of the developer community not familiar with category theory but (2) (snip) If there are any good ways in which non-mathematicians can get to grips with these terms from category theory, they would be well worth promoting. For example, despite having a good computer science degree (in which I was at least introduced to FP, proof, etc. and even learned to draw the dual graph of hypercubes) I'm really not equipped to understand catamorphisms in terms of algebras and homomorphisms, and don't currently have time to take the math degree I fear I'd need in order to do so. Last time I was looking at category theory books I think I came to the conclusion that Lawvere and Schanuel cover things kindly but Pierce seemed to get the syllabus right, so the "right" book wasn't quite out there. My understanding of monads is already a matter of record. Does anyone know of a friendly text that might help new Haskellers to understand functors, etc. and what they mean for program design? I'm not averse to the formal language per se if it can be easily acquired; right now, I worry that I'm using Haskell suboptimally because, not only do I not know the terminology well, but I fear that I'm not even cognisant of the concepts that these terms represent. In a nutshell: if these category theory concepts indeed have an important impact in Haskell land, how to introduce them to working Haskell programmers well enough that they can use them in engineering software that's at least half as good as it could be? (I'm making the assumption here that it would be good for Haskell to be much more widely used - it shouldn't solely be for researchers.) -- Mark

3 2