May 2002 - Haskell - Haskell.org

RE: Deforestration harmful?
by Simon Marlow 06 May '02

06 May '02

> An obvious thing to try was to increase the heap size. > Again we were surprised. Indeed the GC time decreased > but the running time in the profile (excluding the GC time) > increased a bit. Our guess was that it might have something > to do with the way GHC allocates new memory cells such that > larger heap results in longer allocation time. It was quite > tricky to find the best heap size at which the program > runs at maximal speed. > > Are the above guesses are plausible? Is it a known phenomena? It is entirely plausible that as you increase the heap size the mutator time increases: this is because you get fewer cache hits with a larger heap. GHC starts off with a small heap size so as to try to make the most of the cache. However, on most examples we've seen the benefits of reducing garbage collections by increasing the heap size tend to outweigh the benefits from staying in the cache. Did you try heap profiling to discover what structure was filling up the heap? Cheers, Simon

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RE: finding sublist
by Garner, Robin 06 May '02

06 May '02

See Dijkstra's 'Discipline of Programming' for an o(M + N) algorithm - naive approches are o(MN) where M and N are the length of the list and substring respectively. Essentially the algorithm calculates a sort of autocorrelation table of the substring, showing where to resume the search after a failed match. For example, if you're matching the substring [1,2,3,4], and fail on the last comparison, you already know that there's no point in advancing one element and attempting another match - you can actually start again at the element that failed. When matching the string [1,2,1,3], you can resume at the current element of the main string, and the second element of the search string. How you would do this in a functional implementation is another question - Dijkstra's example is comparing two arrays, and there may be inefficiencies translating it to a list-based implementation. Cheers -----Original Message----- From: Serge D. Mechveliani [mailto:mechvel@botik.ru] Sent: Thursday, 2 May 2002 17:37 To: haskell(a)haskell.org Subject: finding sublist Thanks to people who helped me with the task >> Import two space separated columns of integers from file. Claus Reinke <claus.reinke(a)talk21.com> recommends to exploit `lines'. Indeed, it bocomes shorter now: main = readFile "data" >>= (putStr . show . twoIntLists) where twoIntLists str = case span (not . null) $ dropWhile null $ lines str of (lns, lns') -> (readInts lns, readInts lns') readInts = map (\ str -> read str :: Integer) . dropWhile null Another question: has the Haskell Standard library a function for such a usable task as finding of occurence of a segment in a list? Say findSegmentBy (...) [2,2,3] [0,0,2,2,1,2,2,3,1,2,3] --> ([0,0,2,2,1], [2,2,3,1,2,3]) I have heard, an efficient algorithm (for large lists) for this is not so simple. ----------------- Serge Mechveliani mechvel(a)botik.ru _______________________________________________ Haskell mailing list Haskell(a)haskell.org http://www.haskell.org/mailman/listinfo/haskell

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(no subject)
by timeismonie＠btamail.net.cn 06 May '02

06 May '02

SPECIAL SITUATION ALERTS NEWSLETTER HOT PICK OF THE YEAR Environmental Remediation Holding Corp. (d.b.a. Chrome Energy Corp) (OTCBB: ERHC) RECENT PRICE: $.20 SELL TARGET: $1.25 INVESTORS: WE HAVE FOUND THE HIDDEN GEM: (OTCBB: ERHC) The IMF (International Monetary Fund) states in a worldwide published report [February 2002 IMF Country Report No. 02/30 (page 10 of 82)] that ERHC's working interest in their offshore West African oil blocks will generate $1,446,800,000 in cumulative income over the next 22 years. The IMF provides this evaluation to its 183 Member Nations while promoting international monetary exchange and fostering economic trade and growth with an arsenal of $272 Billion! Dow Jones News: ERHC enters into joint-venture license agreements with Schlumberger LTD (NYSE: SLB, $53) and Baker Hughes, INC. (NYSE: BHI, $34) for seismic data on some of the richest offshore oil blocks in West Africa, where ERHC controls a huge working interest. Investor Alert: ERHC's joint-venture with SCHLUMBERGER and BAKER HUGHES puts them in world class company with these leaders in oil exploration and reservoir imaging services. The involvement of SLB and BHI reinforces the MULTI-BILLION DOLLAR VALUE that has been placed in this offshore drilling haven. ERHC's goal is to maximize shareholder value from existing contractual rights, making them a significant player in this region. THE BIG MONEY ROLLS IN: The seismic data from this joint venture is being made available for further involvement by the LARGEST OIL COMPANIES IN THE WORLD over the next 2 weeks! Bidding wars have already developed between major oil companies such as: SHELL, CHEVRON/TEXACO, CONOCO, EXXON/MOBIL, PHILIPS, and MARATHON who are willing to pay Hundreds of Millions to drill in the oil blocks that border on ERHC's offshore zones. STOCK SET TO EXPLODE ON EARNINGS BOOM: "UPSTREAM", the International Oil and Gas Newspaper considered to be the equivalent of the "Wall Street Journal" for the Oil Industry, has stated in a number of articles that EXXON/MOBIL believes that the oil blocks "housing ERHC's working interest" contain over 8 BILLION BARRELS OF RECOVERABLE OIL TAKEOVERS RUNNING RAMPANT: Oil Companies of all sizes have been the target of significant mergers and takeovers during the past year. Many of these takeovers or buyouts have occurred due to the value of the acquired Company's offshore oil holdings in West Africa. One such example is Marathon Oil (NYSE: MRO, $28) paying $900 MILLION for the West African holdings of CMS Energy (NYSE: CMS, $23). We believe that ERHC and/or the Company's offshore oil interests could be the next target of a takeover. This is largely because of their exclusive right to participate in exploration and production along with OIL INDUSTRY GIANTS, as these oil blocks are adjacent to Billion Barrel producing regions! Global Stock Participation - On March 27, 2002--Chrome Energy Corporation ("Chrome") (OTCBB:ERHC), announced that its common stock has been approved for listing on the Berlin Stock Exchange in Germany. The Berlin Stock Exchange is the leading stock exchange in Europe for dual listings with over 6,000 American companies listed. Chrome's common stock began trading on March 28, 2002 Special Situation Alerts' Newsletter offers valuable research for serious investors with our Hot Pick Of The Year - ERHC This is a commercial email only and if you want to be removed email timeismonie(a)btamail.net.cn

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(no subject)
by mpeti laurent kabila 05 May '02

05 May '02

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C Header File Conversion
by dominic.j.steinitz＠britishairways.com 04 May '02

04 May '02

I need to use values that are kept in a C header file - see below for an extract of the header file. What I'd like to be able to say is import Word import Bits data ICMPType = EchoReply | ICMPType1 | ICMPType2 | DestUnreach | SourceQuench ... deriving Enum encode :: ICMPType -> Word8 encode x = fromIntegral (fromEnum x) Is this a sensible approach? Are there any tools that could help? C->Haskell and HaskellDirect look possibilities but I'd welcome advice before I try and install them. Many thanks, Dominic. #define ICMP_ECHOREPLY 0 /* Echo Reply */ #define ICMP_DEST_UNREACH 3 /* Destination Unreachable */ #define ICMP_SOURCE_QUENCH 4 /* Source Quench */ #define ICMP_REDIRECT 5 /* Redirect (change route) */ #define ICMP_ECHO 8 /* Echo Request */ #define ICMP_TIME_EXCEEDED 11 /* Time Exceeded */ #define ICMP_PARAMETERPROB 12 /* Parameter Problem */ #define ICMP_TIMESTAMP 13 /* Timestamp Request */ #define ICMP_TIMESTAMPREPLY 14 /* Timestamp Reply */ #define ICMP_INFO_REQUEST 15 /* Information Request */ #define ICMP_INFO_REPLY 16 /* Information Reply */ #define ICMP_ADDRESS 17 /* Address Mask Request */ #define ICMP_ADDRESSREPLY 18 /* Address Mask Reply */ #define NR_ICMP_TYPES 18

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Bug in the scaling of randoms in "Haskel: The Craft of Functional Programming"
by Dimitre Novatchev 04 May '02

04 May '02

In his excellent book Simon Thompson defines scaling of the elements of a sequence of random numbers from the interval [0, 65535] to an interval [s,t] in the following way (top of page 368): > scaleSequence :: Int -> Int -> [Int] -> [Int] > scaleSequence s t > = map scale > where > scale n = n `div` denom + s > range = t - s + 1 > denom = modulus `div` range where modulus = 65536 However, the following expression: > e4000 = (scaleSequence 1 966 ([65231] ++ [1..965]))!!0 evaluates to 974 -- clearly outside of the specified interval. I'm using the following scaling function, the correctness of which I believe can be proven: > randScale :: Float -> Float -> Int -> Int > randScale s t n = floor (rndScl ((t - s + 1)/ dintRange ) s n) > where dintRange = fromInt (modulus - 1) > rndScl :: Float -> Float -> Int -> Float > rndScl a b n = a * fromInt n + b > scaleSequence2 :: Int -> Int -> [Int] -> [Int] > scaleSequence2 s t > = map scale > where > scale n = randScale (fromInt s) (fromInt t) n Could somebody please, provide a corrected definition that still uses modulo arithmetics? Cheers, Dimitre Novatchev. __________________________________________________ Do You Yahoo!? Yahoo! Health - your guide to health and wellness http://health.yahoo.com

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(no subject)
by laurent mpeti kabila 04 May '02

04 May '02

REQUEST FOR URGENT BUSINESS ASSISTANCE -------------------------------------- I stumbled into your contact by stroke of luck after a long search for an honest and trust worthy person who could handle issue with high confidentiality. I was so dilghted when i got your contact and i decided to contact you and solicite for your kind assistance. i hope you will let this issue to remain confidential even if you are not interested because of my status. I am Laurent Mpeti Kabila (Jnr) the second son of Late President LAURENT DESIRE KABILA the immediate Past president of the DEMOCRATIC REPUBLIC OF CONGO in Africa who was murdered by his opposition through his personal bodyguards in his bedroom on Tuesday 16th January, 2001. I have the privilege of being mandated by my father,s colleagues to seek your immediate and urgent co-operation to receive into your bank account the sum of US $25m. (twenty-five million Dollars) and some thousands carats of Diamond. This money and treasures was lodged in a vault with a security firm in Europe and South-Africa. SOURCES OF DIAMONDS AND FUND In August 2000, my father as a defence minister and president has a meeting with his cabinet and armychief about the defence budget for 2000 to 2001 which was US $700m. so he directed one of his best friend. Frederic Kibasa Maliba who was a minister of mines and a political party leader known as the Union Sacree de,opposition radicale et ses allies (USORAL) to buy arms with US $200m on 5th January 2001; for him to finalize the arms deal,my father was murdered. f.K. Maliba (FKM) and I have decided to keep the money with a foreigner after which he will use it to contest for the political election. Inspite of all this we have resolved to present you or your company for the firm to pay it into your nominated account the above sum and diamonds. This transaction should be finalized within seven (7) working days and for your co-operation and partnership, we have unanimously agreed that you will be entitled to 5.5% of the money when successfully receive it in your account. The nature of your business is not relevant to the successful execution of this transaction what we require is your total co-operation and commitment to ensure 100%risk-free transaction at both ends and to protect the persons involved in this transaction strict confidence and utmost secrecy is required even after the uccessful conclusion of this transaction. If this proposal is acceptable to you, kindly provide me with your personal telephone and fax through my E-mail box for immediate commencement of the transaction. I count on your honour to keep my secret, SECRET. Looking forward for your urgent reply Thanks. Best Regards MPETI L. KABILA (Jnr)

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Re: ANNOUNCE: Haddock version 0.1, a Haskell documentation tool
by Ashley Yakeley 04 May '02

04 May '02

At 2002-05-01 04:48, Simon Marlow wrote: >I'm pleased to announce version 0.1 of Haddock, a documentation >generation tool for Haskell source code. I take it this is the "standard" Haskell documentation tool now, that implementations of the standard libraries will use? I've been waiting for something like this. -- Ashley Yakeley, Seattle WA

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duplicate instance declarations
by Hal Daume III 03 May '02

03 May '02

Why is this a duplicate instance declaration: > class C a > class D b > data T a b > instance (C (T a b), C a) => D b > instance (C (T a b), C b) => D a These are symmetric, but not duplicate, as I see it. -- Hal Daume III "Computer science is no more about computers | hdaume(a)isi.edu than astronomy is about telescopes." -Dijkstra | www.isi.edu/~hdaume

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CFP: JFP Special Issue on Functional Pearls
by Ralf Hinze 03 May '02

03 May '02

Apologies if you receive multiple copies... ============================================================================ CALL FOR PAPERS Special Issue on Functional Pearls http://www.informatik.uni-bonn.de/~ralf/necklace.html [Deadline: 31 August 2002] ============================================================================ Wer die Perle in Händen hält, fragt nicht nach der Muschel. - Peter Benary A special issue of the Journal of Functional Programming will be devoted to Functional Pearls. The submission deadline is 31 August 2002. Scope ----- Do you have a paper that is small, rounded and enjoyable to read? Please consider submitting it to the Special Issue on Functional Pearls, as we intend to string a shiny necklace. If you don't have a pearl, write one today! Papers can be on any subject connected to functional programming. A pearl is typically around 8 pages, though there is no strict page limit. The special issue also welcomes tutorial or educational papers in a broad sense. Submission details ------------------ Manuscripts should be unpublished works and not submitted elsewhere. Revised and polished versions of papers published in conference proceedings that have not appeared in archival journals are eligible for submission. All submissions will be reviewed according to the usual standards of scholarship and judged by elegance of development and clarity of expression. One of the main reviewers will be Richard Bird, the editor of JFP's regular Functional Pearls column. Deadline for submission: 31 August 2002 Notification of acceptance or rejection: 30 November 2002 Revised version due: 31 January 2003 Submissions should be sent to the Guest Editor (see address below), with a copy to Nasreen Ahmad (nasreen(a)dcs.gla.ac.uk) Submitted articles should be sent in PDF or Postscript format, preferably gzipped and uuencoded. The use of the JFP style files is strongly recommended. In addition, please send, as plain text, title, abstract (if any), and contact information. The submission deadline is 31 August 2002. Authors will be notified of acceptance or rejection by 30 November 2002. Revised versions are due on 31 January 2003. For other submission details, please consult an issue of the Journal of Functional Programming or see the Journal's web page at http://www.dcs.gla.ac.uk/jfp/. Guest Editor ------------ Ralf Hinze Institut für Informatik III Universität Bonn Römerstraße 164 53117 Bonn, Germany Telephone: +49 (2 28) 73 - 45 35 Fax: +49 (2 28) 73 - 43 82 Email: ralf(a)informatik.uni-bonn.de WWW: http://www.informatik.uni-bonn.de/~ralf/ ============================================================================

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